Studies Related to the 

Charleston, South Carolina, 

Earthquake of 1886-

A Preliminary Report 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1028 

2 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, 

EARTHQUAKE OF 1886-A PRELIMINARY REPORT 

Studies Related to the Charleston, South Carolina, 

Earthquake of 1886-A Preliminary Report 

Edited by Douglas W. Rankin 

A. Studies Related to the Charleston, South Carolina, Earthquake of 1886-Introduction and Discussion, 

by Douglas W. Rankin 

B. Reinterpretation of the Intensitf Data for the 1886 Charleston, South Carolina, Earthquake, by G. 

A. Bollinger 

C. The Seismicity of South Carolina Prior to 1886, by G. A. Bollinger and T. R. Visvanathan 

D. Recent Seismicity Near Charleston, South Carolina, and its Relationship to the August 31, 1886, 

Earthquake, by Arthur C. Tarr 

E. Lithostratigraphy of the Deep Corehole (Clubhouse Crossroads Corehole 1) Near Charleston, South 

Carolina, by Gregory S. Gohn, Brenda B. Higgins, Charles C. Smith, and James P. Owens 

F. Biostratigraphy of the Deep Corehole (Clubhouse Crossroads Corehole 1) Near Charleston, South 

Carolina, by J. E. Hazel, L. I\L Bybell, R. A. Christopher, N. 0. Frederiksen, F. E. May, D. M. 

McLean, R. Z. Poore, C. C. Smith, N. F. Soh!, P C. Valentine, and R. J. Witmer 

G. Geochemistry of Subsurface Basalt From the Deep Corehole (Clubhouse Crossroads Corehole I) 

Near Charleston, South Carolina-Magma Type and Tectonic Implications, by David Gottfried, 

C. S. Annell, and L. J. Schwarz. 

H. Heat Flow From a Corehole Near Charleston, South Carolina, by J. H. Sass and John P. Ziagos 

I. The Nature of the Geophysical Basement Beneath the Coastal Plain of South Carolina and Northeastern Georgia, by Peter Popenoe and Isidore Zietz 

J. Magnetic Basement Near Charleston, South Carolina-A Preliminary Report, by .Jeffrey D. Phillips 

K. Bouguer Gravity Map of the Summerville-Charleston, South Carolina, Epicentral Zone and Tectonic Implications, by Leland Timothy Long and J. W. Champion, Jr. 

L. Exploring the Charleston, South Carolina, Earthquake Area With Seismic Refraction-A Preliminary Study, by Hans D. Ackermann 

M. A Preliminary Shallow Crustal Model Between Columbia and Charleston, South Carolina, Determined From Quarry Blast Monitoring and Other Geophysical Data, by Pradeep Talwani 

N. Electric and Electromagnetic Soundings Near Charleston, South Carolina-A Preliminary Report, by 

David L. Campbell 

0. Correlation of Major Eastern Earthquake Centers With Mafic/Ultramafic Basement Masses, by 

M. F. Kane. 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1 0 2 8 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1977 
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress catalog-card No. 78-600007 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 

Stock Number 024-001-03047-1 
CONTENTS 

Page 

(A) Studies related to the Charleston, South Carolina, earthquake of 1886-

introduction and discussion, by Douglas W. Rankin -------------------- 1 

(B) Reinterpretation of the intensity data for the 1886 Charleston, South 

Carolina, earthquake, by G. A. Bollinger ------------------------------ 17 

(C) The seismicity of South Carolina prior to 1886, by G. A. Bollinger and 

T. R. Visvanathan -------------------------------------------------- 33 

(D) Recent seismicity near Charleston, South Carolina, and its relationship 

to the August 31, 1886, earthquake, by Arthur C. Tarr --------------- 43 

(E) Lithostratigraphy of the deep corehole (Clubhouse Crossroads corehole 

1) near Charleston, South Carolina, by Gregory S. Gohn, Brenda B. 

Higgins, Charles C. Smith, and James P. Owens -------------------- 59 

(F) Biostratigraphy of the deep corehole (Clubhouse Crossroads corehole 1) 

near Charleston, South Carolina, by J. E. Hazel, L. M. Bybell, R. A. 

Christopher, N. 0. Frederiksen, F. E. May, D. M. McLean, R. Z. Poore, 

C. C. Smith, N. F. Sohl, P. C. Valentine, and R. J. Witmer ____________ 71 

(G) Geochemistry of subsurface basalt from the deep corehole (Clubhouse 

Crossroads corehole 1) near Charleston, South Carolina-magma type and 

tectonic implications, by David Gottfried, C. S. Annell, and L. J. Schwarz 91 

(H) Heat flow from a corehole near Charleston, South Carolina, by J. H. Sass 

and John P. Ziagos ------------------------------------------------- 115 

(I) The nature of the geophysical basement beneath the Coastal Plain of 

South Carolina and northeastern Georgia, by Peter Popenoe and Isidore 

Zietz --------------------------------------------------------------- 119 

(J) Magnetic basement near Charleston, South Carolina-a preliminary report, by Jeffrey D. Phillips ------------------------------------------- 139 

(K) Bouguer gravity map of the Summerville-Charleston, South Carolina, 

epicentral zone and tectonic implications, by Leland Timothy Long and 

J. W. Champion, Jr ------------------------------------------------- 151 

(L) Exploring the Charleston, South Carolina, earthquake area with seismic 

refraction-a preliminary study, by Hans D. Ackermann -------------- 167 

(M) A preliminary shallow crustal model between Columbia and Charleston, 

South Carolina, determined from quarry blast monitoring and other geophysical data, by Pradeep Talwani ----------------------------------- 177 

(N) Electric and electromagnetic soundings near Charleston, South Carolinaa preliminary report, by David L. Campbell -------------------------- 189 

( 0) Correlation of major eastern earthquake centers with mafic/ultramafic 

basement masses, by M. F. Kane ------------------------------------ 199 

Studies Related to the Charleston, South Carolina, 

Earthquake of 1886-Introduction and Discussion 

By DOUGLAS W. RANKIN 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1028-A 

CONTENTS 

Page 

Jlbstract ----------------------------------------------------------------- 1 

Introduction ------------------------------------------------------------- 2 

Seismicity --------------------------------------- _____ _ __ ______ ___ _______ 3 

Geologic setting: the Jltlantic Coastal Plain--------------------------------- 5 

Geology beneath Coastal Plain rocks and tectonic setting ---------------------- 9 

The source area: method of approach--------------------------------------- 10 

Studies of the meizoseismal area ------------------------------------------- 11 

Earthquake origins ------------------------------------------------------- 13 

Conclusions -------------------------------------------------------------- 13 

References cited ----------- ________________ ------------------------ _____ __ 14 

ILLUSTRATIONS 

Page 

FIGURE 1. Map showing comparison of areas of observed Modified Mercalli intensities for four major United States earthquakes _________ 4 

2. Map of the vicinity of Charleston, S.C., showing the approximate 

area of the meizoseismal area of the 1886 earthquake ________ 6 

3. Map of the southeastern United States showing location of Charleston, S.C., relative to regional features ---------------------- 7 

lll 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886-

A PRELIMINARY REPORT 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 

1886-INTRODUCTION AND DISCUSSION 

By DouGLAs W. RANKIN 

"One [Cordilleran earthquake], in 1812, destroyed a church in Los 

Angeles, California, killing a score or more people. Together with the 

Charleston earthquake [of 1886] this shock is entitled to a peculiar place 

in our history; these two shocks being the only earthquakes. which have 

caused any loss of life in the country." 

N. S. Shaler ( 1899) 

"The absence of large-ma.gnitude earthquakes in eastern North America since the Charleston, S.C., earthquake of 1886 has resulted in complacency, or perhaps unawareness on the part of the general populace of 

the existence of any earthquake threat to them." 

ABSTRACT 

The seismic history of the southeastern United States is 

dominated by the 1886 earthquake near Charleston, S.C. 

An understanding of the specific source and the uniqueness 

of the neotectonic setting of this large earthquake is essential in order to properly assess seismic hazards in the southeastern United States. Such knowledge will also contribute 

to the fundamental understanding of intraplate earthquakes 

and will aid indirectly in deciphering the evolution of Atlantic-type continental margins. The 15 chapters in this volume 

report on the first stage of an ongoing multidisciplinary 

study of the Charleston earthquake of 1886. 

The Modified Mercalli intensity for the 1886 earthquake 

was X in the meizoseismal area, an elliptical area 35 by 50 

km, the center of which was Middleton Place. Seismic activity is continuing today in the Middleton Place-Summerville 

area at a higher level than prior to 1886. The present seismicity is originating at depths of 1 to 8 km, mostly in the 

crystalline basement beneath sedimentary rocks of the 

Coastal Plain. 

The crystalline basement beneath the Charleston-Summerville area is not simply a seaward extension of crystalline 

rocks of the Appalachian orogen that are exposed in the 

Piedmont to the northwest, but has a distinctive magnetic 

signature that does not reflect Appalachian orogenic trends. 

The area underlain by this distinctive geophysical basement, 

the Charleston block, may represent a broad zone of Triassic and (or) Jurassic crustal extension formed during the 

early stages of the opening of the Atlantic Ocean. The 

Charleston block is characterized in part by prominent, 

Otto Nuttli (1973) 

roughly circular magnetic and gravity highs that are thought 

to reflect mafic or ultramafic plutons. 

A continuously cored borehole put down over the shallowest (about 1.5 km deep) of these magnetic anomalies 'On the 

edge of the meizoseismal area bottomed at 792 m in amygdaloidal basalt. Although the K-Ar ages of about 100 m.y. for 

the basalt are consistent with the Late Cretaceous (Cenomanian) age of the overlying Cape Fear Formation, this 

must be a minimum age as a result of chemical alteration. 

The interpreted magmatic composition of the basalt most 

closely resembles the high-Ti quartz-normative tholeiites of 

Late Triassic and Early Jurassic age from eastern North 

America; age of the basalt is probably similar. Various geophysical surveys suggest that Coastal Plain sedimentary 

rocks do not simply dip homoclinally to the southeast on a 

gently dipping basement surface but are disturbed by structures not yet clearly deciphered. 

The present stress regime of the Charleston-Summerville 

area appears to be one of NE.-SW. compression rather than 

of extension as it presumably was in the Mesozoic. The 

present stress regime seems similar to that of much of the 

eastern United States. Comparison of several seismic source 

areas in eastern North America shows that epicenters are 

typically near the periphery of positive gravity features 

interpreted to represent mafic or ultramafic bodies. Earthquakes may be caused by the concentration of regional stress 

around the peripheries of these inhomogeneities in an otherwise more homogeneous plate. Whether the inhomogeneities 

are more or less rigid than the surrounding material is uncertain. 

1 
2 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

INTRODUCTION 

One of the largest historic earthquakes in eastern 

North America, and by far the largest earthquake in 

southeastern United States took place about 9 :50 

p.m. on August 31, 1886, near Charleston, S.C. The 

major shock lasted less than 1 minute, but resulted 

in about 60 deaths and extensive damage to the city 

of Charleston. Because the event took place before 

seismological instrumentation, estimates of its location and size must come from observations of the 

damage and effects caused by the earthquake. Most 

of what we know of the event and the resulting damage comes from a comprehensive report by C. E. 

Dutton published in 1889. A review of Dutton's 

(1889) intensity data by Bollinger (this volume) 

confirms a Modified Mercalli intensity of X for the 

meizoseismal area (area of maximum damage) and 

of intensity IX for the city of Charleston. 

Dutton's report shows the location of craterlets 

formed of sand, but does not report any surface 

faulting. No fault, in fact, is known to be exposed at 

the surface within 100 km of the meizoseismal area. 

The cause of the Charleston earthquake has not been 

adequately explained in the 90 years since the event. 

An understanding of this large earthquake is essential in order to properly assess seismic hazards in the 

southeastern United States. The specific source of 

the earthquake and its tectonic setting must be established, both to permit evaluation of expectable 

future seismicity in the Charleston region and to 

determine whether that region differs in any tectonically S'ignificant fashion from other parts of the 

Eastern United States. 

With a few notable exceptions, the earth's seismicity is largely associated with plate boundaries or 

active volcanic areas within the plates such as 

Hawaii (see Tarr, 1974). Plate boundaries, in fact, 

were originally defined on the basis of seismicity. 

Oceanic crust is created at divergent plate boundaries and consumed at convergent plate boundaries. 

Where plate motion is parallel to the plate boundary, 

crust is neither created nor consumed. Continents 

are envisaged as being carried passively within moving oceanic crust. Because of its lower density, continental crust is probably not consumed (is not subducted) at convergent margins but becomes progreSISively deformed and crumpled, causing orogenic 

belts. 

A divergent plate boundary may originate within 

a continental mass through rifting and the subsequent formation of an oceanic ridge within the growing rift. Such a history is hypothesized for the 

growth of the Atlantic Ocean during the Mesozoic. 

Rifting within the large continental mass that included North America and Africa began in the Triassic as evidenced by the cratonal Triassic basins 

preserved in eastern North America. By the Cretaceous, a significant ocean basin had formed between the United States and Africa (Pitman and 

Talwani, 1972). As spreading from the Mid-Atlantic 

Ridge continued, the eastern margin of the North 

American continent was carried passively farther 

from the active spreading center. This continental 

margin is now commonly referred to as the type example of the seismically quiet Atlantic-type continental margin (Dewey and Bird, 1970). 

The meizoseismal area of the Charleston earthquake, although close to the Atlantic coastline, is 

well within the North American continental mass if 

one accepts the East Coast magnetic anomaly more 

than 200 km to the southeast as the continental margin (Taylor and others, 1968). The active plate 

boundary, the Mid-Atlantic Ridge, is about 3,000 km 

east-southeast of Charleston. An in-depth study of 

the Charleston area offers an opportunity to advance 

the fundamental understanding of Atlantic-type 

continental margins. Earthquakes along boundaries 

of plates, such as the San Francisco 1906 and Alaska 

1964 earthquakes, are readily understood in terms 

of relative plate motions and plate tectonics. No 

similar understanding yet exists for deformation 

and earthquakes such as Charleston which occur 

within plates. 

The Charleston earthquake shares its intraplate 

setting with the other largest historical earthquakes 

in eastern and central United States. Those took 

place in 1755 near Cape Ann, Mass., and in the winter of 1811-=-12 in the Mississippi Valley near New 

Madrid, Mo., as a series of three widely felt shocks. 

All of these large intraplate earthquakes occurred 

before instrumentation. An adequate explanation of 

any of them should aid in explaining the others (see 

Kane, this volume). 

The epicenter of the Cape Ann earthquake appears to have been offshore. It is, thus, not well located and not easy to study. The available data for 

the Mississippi Valley series, however, have been 

extensively analyzed by several seismologists (see 

particularly Nuttli, 1973 and 1976; and Evernden, 

1975 and 1976) and the epicentral area is under investigation today. 

The Mississippi Valley series included three major 

shocks: one on Dec. 16, 1811, one on Jan. 23, 1812, 

and one on Feb. 7, 1812. The February shock is considered the largest. Gupta and Nuttli (1976) recently revised upward the maximum intensity for each 
INTRODUCTION AND DISCUSSION 3 

of these events, and Nuttli is quoted by Mosaic magazine (1976) as rating the surface-wave magnitude 

(Ms) of these events in chronologie order as 8.0, 7.7, 

and 8.2, respectively. Nuttli (oral commun. 1977) 

states that this revision assumes that the surfacewave behavior of the Mississippi Valley earthquakes 

is similar to that of interplate earthquakes, such as 

those which have occurred in California. He would 

not necessarily change his published (Nuttli, 1976) 

estimates of the body-wave magnitude (mb) for 

these events of 7.2, 7.1, and 7.4, respectively. 

Bollinger (this volume) arrived at a body-wave 

magnitude (mb) estimate for the Charleston earthquake of 6.8 using the attenuation of intensity as a 

function of distance from the epicenter and Nuttli's 

(1976) intensity-particle velocity data for the central United States. As noted by Bollinger (this volume), the number of significant earthquakes in the 

central United States for which both intensity and 

particle velocity data are available is quite small because of the short period of instrumented record 

relative to the low rate of earthquake occurrence. 

Using the more abundant western United States intensity-particle velocity data, he estimates the mb 

for the Charleston ea.rthquake at 7.1. 

Seismologists disagree as to what is the most appropriate measure of earthquake size, particularly 

when comparing earthquakes in different geologic 

terranes, for example, in the eastern United States 

and the western United States (Nuttli, 1976; Evernden, 1976; and Bollinger, this volume). In a general 

way, however, the Missi,ssippi Valley earthquakes of 

1811-12 have been equated with the San Francisco 

earthquake of 1906 (these are probably the largest 

historic earthquakes in the conterminous United 

States), and the Charleston earthquake has been 

equated with the San Fernando earthquake of 1971 

which had an instrumentally determined magnitude 

ML=6.4 (Allen and others, 1973) and a mb=6.0 estimated from intensity data (Nuttli, 1976). 

The hazards which must be considered in any discussion of South Carolina seismicity include not only 

ground breakage and ground motion in the epicentral area, but significant ground motion at considerable distance from the epicenter as is common with 

all larger earthquakes. Because of the low attenuation of seismic energy in the East, the area of equivalent damage for earthquakes of the same magnitude 

is far larger for eastern and central United States 

earthquakes than for those taking place on the west 

coast (fig. 1). The Charleston ea.rthquake, for example, produced intensity V effects in Chicago (Bollinger, this volume), 1,200 km from the earthquake 

epicenter. 

Important recent work related to the seismicity of 

the Charleston earthquake includes the monitoring 

of microearthquakes in the summer of 1971 in the 

Summerville area by Bollinger, a review of seismic 

activity in South Carolina by Bollinger (1972), and 

the establishment of a 5-station reconnaissance seismographic network in March 1973 by the Seismological Investigations Group of NOAA under the 

auspices of the AEC. The Geological Survey assumed 

responsibility for the operation of this network and 

began some geophysical surveys of the area in 1973. 

In the spring of 197 4, these efforts were expanded 

into a large multidisciplinary study of the Charleston earthquake by the Geological Survey funded 

largely by the NRC, Office of Nuclear Regulatory 

Research under Agreement No. AT(49-25)-1000. 

The studies include the operation of an enlarged 

seismographic network, a wide variety of geo,physical studies, a geological program of mapping surface 

and near surface features, a deep-drilling program, 

a geochemical and paleontologic study of appropriate samples, and detailed and regional synthesis of 

the results. This research is continuing today. 

This volume is a preliminary report of these and 

some related studies. Most of the papers reflect data 

gathered before June 1976. Work in progress and 

future work undoubtedly will modify some of 

the conclusions, but should not change the data 

presented. 

In this introductory chapter, I have tried to provide a framework into, which the individual studies 

fit and to summarize the more significant findings of 

the studies. Some promising directions of continued 

research are suggested by what these studies have 

shown. I am indebted to Carl Wentworth as well as 

the members of the various Charleston projects for 

numerous lengthy discussions concerning the cause 

of the seismicity of the Charleston area. 

SEISMICITY 

A commonly held view is that the 1886 event took 

place in an area that had been essentially aseismic 

for nearly two centuries. An archival study by Bollinger and Visvanathan (this volume) reports 18 

probable earthquakes in South Carolina between 

1698 and 1886. Of these, 13 appear to have been in 

the Charleston area. The maximum intensity of the 

pre-1886 events appears to be V or possibly VI. 

Bollinger and Visvanathan (this volume) conclude 

that although South Carolina was not aseismic in the 
SAN 

FIGURE 1.-Comparison of areas of observed Modified Mercalli (MM) intensities for four major United States earthquakes. For each earthquake, the 

outer ring encloses intensities of VI to VII and the patterned inner area 

represents intensities of VII and greater. Damage areas correspond to 

intensity VII and greater. Modified from Mosaic (1976). Sources of intensity contours are as follows: Charleston, 1886, Bollinger (this volume) ; 

POPULATION DENSITY 1970 

Compiled from U.S Bureau of the Census, Population density 

by counties of the United States: 1970, GE-50, No. 38 

Washington, U.S. Govt. Print. Off., 1971 , map 1:5,000,000 

Albers Eque~l Area PrOJe<:lmn 

SCALE 1 '17, 000,000 

POPULATION 

PER SQUARE MilE 

- 250.0 or over 

- 50.0-2499 

-10.0-49.9 

D Under10.0 

U.S. average: 57.5 

New Madrid, Dec. 16, 1811, Nuttli (1973) (the closure of the intensity 

contours to the west is arbitrary because of the absence of information) ; 

San Fernando, 1971, Scott (1973); and San Francisco, 1906, Mosaic 

(1976). The base map showing population density for 1970 is from Sheet 

No. 418 of the U.S. Geological Survey National Atlas of the United States 

of America, Separate Sales Edition, 1974. 

..... 

00 

00 

0> 
INTRODUCTION AND DISCUSSION 5 

50-year period prior to 1886, the seismic activity 

does not appear to have been anomalously high relative to the surrounding States either in number of 

events or in energy levels. It should be pointed out, 

however, that their catalog lists nine events in South 

Carolina during this 50-year period, eight of which 

are approximately located in the vicinity of a specific town. Four of these were in the Charleston area. 

The 1886 earthquake was followed by a series of 

aftershocks which may still be underway today. Of 

435 or more earthquakes reported to have taken 

place in South Carolina between '1754 and 1975, more 

than 300 were aftershocks in the first 35 years following 1886 (Tarr, this volume). 

The 1886 earthquake and its aftershocks dominate 

the seismic record of the southeast. The seismotectonic map of Hadley and Devine (1974) based upon 

the record from 1800 to 1972 depicts the Charleston 

area as having the highest concentration of epicenters and the largest single event in the southeastern 

United States. Several seismic frequency contours 

close around Charleston, yet these authors show the 

area to have no known geologic control for the seismicity. On the other hand, on the basis of a 225-year 

record (1754-1970) of felt earthquakes in the southern Appalachians, Bollinger (1972) suggests a diffuse zone of seismicity trending NW. across South 

Carolina roughly perpendicular to the structural 

grain of the Appalachians. Whether the Charleston 

seismicity is part of a broad NW .-trending zone 

(Bollinger, 1972) or whether the seismicity originates in an isolated source area (Hadley and Devine, 

1974) is a question that has not been resolved. Most 

of the historical seismicity in the East, however, is 

associated spatially with the Appalachian orogen. As 

we shall see, Charleston is outside the Appalachian 

orogenic belt and is the locus of the only significant 

seismic energy release in the Coastal Plain province. 

The meizoseismal area of the 1886 earthquake has 

been variously drawn by several investigators, but 

has been most recently reinterpreted by Bollinger 

(this volume) as an elliptical area roughly 35 by 50 

km trending northeast between Charleston and Jedburg and including Summerville (fig. 2). This interpretation contrasts considerably with the dual epicentrums of Dutton ( 1889) . Middleton Place is approximately in the center of Bollinger's ellipse, about 

midway between the two epicenters shown by 

Dutton. 

The South Carolina seismographic network has 

recorded about 30 events in the South Carolina area 

between its inception in March 1973 and December 

1975 (Carver and others, 1977). It should be noted 

that the 8-month period from March through December 1973 was a reconnaissance study with 5 stations 

operating in the Charleston area. No stations operated during the period from January to May 1974, 

and 10 stations operated over a larger area in South 

Carolina between May 197 4 and December 1975. 

Thirteen of the 30 events recorded are in the 

Charleston-Summerville area, mostly between Summerville and Middleton Place. Tarr (this volume) 

now refers to this area specifically as the Middleton 

Place-Summerville seismic zone, defined by a cluster 

of epicenters trending roughly NW. The hypocenters 

are at approximate depths of 1 to 8 km. Tarr notes 

that the coordinates of the epicenters are well determined, but that because none of the seismograph stations of the 10-station network were close to the seismic activity, the depths of the hypocenters are not 

well determined. The largest event thus far recorded 

by the South Carolina seismographic network is a 

magnitude (mbLu) 3.8 event on Nov. 22, 1974 very 

close to Middleton Place at a depth of 4.1 km (Tarr, 

this volume). Analysis of first-motion of this event 

indicates NE.-SW. compression acting on planes 

striking N. 42°W. and dipping either 12° NE. or 

78° SW. Tarr (this volume, fig. 7) favors the plane 

dipping steeply to the SW. because the hypocenters 

of other events in the Middleton Place-Summerville 

seismic zone are closer to this plane. 

The historic record suggests that the CharlestonSummerville area had a continuum of low-level seismicity prior to 1886 and that a low-level of strain 

energy release continues in the same area today. 

More specifically, Middleton Place is roughly in the 

center of the meizoseismal area of the 1886 event 

and at theSE. end of a zone, perhaps 15 km long, of 

continuing microearthquake activity. These recent 

events, in the depth range of 1 to 8 km, are thought 

to be either the continuation of the aftershock series 

or events located along closely related structural 

features as the result of the modification of the 

stress environment by the 1886 earthquake. For lack 

of contrary evidence here or elsewhere, we assume 

that the 1886 earthquake originated at similar 

depths. 

GEOLOGIC SETTING: THE ATLANTIC 

COASTAL PLAIN 

The Middleton Place-Summerville seismic zone is 

near the shoreline of the emerged part of the Atlantic Coastal Plain, which consists of an essentially 

eastward-thickening wedge of very gently seaward-
6 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

+MP 

Middleton Place 

®CCC I 

Clubhouse crossroads 

corehole 1 

®CCC 2 

Clubhouse crossroads 

corehole 2 

®CCC 3 

Clubhouse crossroads 

corehole 3 

CAFB 

Charleston Air Force Base 

EXPLANATION 

0 SGS 

Seismograph station operating as of 

April 1977. Letters refer to specific 

stations (A. C. Tarr, written 

commun. , 1977) 

--200--

Magnetic contour-Interval, 100 

gammas. Patterned between 

- 200 and +400 as shown. The 

lowest closed contours are 

hachured. Data from U.S. 

Geological Survey (1975) 

--10--

Bouguer gravity anomaly 

contour-lnterval,5 milligals. The 

lowest closed contours are 

hachured. Data from Long and 

Champion (this volume) 

*-*--* 

Approximate meizoseismal area of 

the 1886 earthquake-From 

Bollinger (this volume). Dotted 

where particularly difficult to 

reconcile Dutton's base map of 

1889 with modern maps 

Earthquake epicenters, 1973-75 

FIGURE 2.-Map of the vicinity of Charleston, S.C., showing the approximate location of the meizoseismal area of the 1886 

earthquake in reference to the locations of coreholes, seismograph stations, magnetic contours, Bouguer gravity anomalies, earthquake epicenters ( 1973-75), and geographic features. 
INTRODUCTION AND DISCUSSION 7 

dipping unconsolidated and semiconsolidated sedimentary rocks. The wedge thickens from a feather 

edge against the crystalline rocks of the AppalachiTENNESSEE 

I 

I 

J' J ( GUL~L~?~~ii'Al r 

{___ I \ 

an orogenic belt along the Fall Line to thicknesses of 

more than 1 km near the coast in southeastern 

South Carolina (fig. 3). The rocks range in age from 

I I r-----, LOUISIANA ~ ----

~ ~ ' )) 

EXPLANATION 

EXPOSED ROCKS OF THE APPALACHIAN OROGEIC BELT GIVEN 

Edge of Coastal Plain 

sedimentary rocks 

Upper Triassic and (or) 

Lower Jurassic rocks 

Valley 

~ and Ridge 

g 

Blue Ridge 

~ 

~ 

Piedmont 

0 100 200 MILES ,r----.--~----~~ 

0 1 DO 200 300 KILOMETERS 

FIGURE 3.-Map of the southeastern United States showing 

location of Charleston, S.C., relative to regional features. 

The Fall Line represents the downstream extent of crystalline rock outcrops of the Piedmont and is roughly the 

same as the mapped edge of Coastal Plain rocks. Contour 

interval for submarine topography is 1,000 m. The east 

coast magnetic anomaly shown is from Schouten and 

Klitgord (1977) and Taylor and others (1968). The Blake 

Spur fracture zone is from Schouten and Klitgord (1977). 
8 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

Mesozoic to Holocene; the oldest rocks exposed at the 

surface decrease in age toward the coast. 

Most of the following description of the physiography of the Coastal Plain comes from Colquhoun 

and Johnson ( 1968). The Coastal Plain in South 

Carolina consists of three physiographic belts roughly parallel to the Atlantic coast. These are referred 

to from northwest to southeast as the Upper, Middle, 

and Lower Coastal Plains. The Upper Coastal Plain 

is a surface of fluvial or more rarely eolian erosion, 

which slopes irregularly from a maximum elevation 

of 150 to 180 m along the Fall Line to about 75 m on 

its southeastern side. It is separated from the Middle 

Coastal Plain by the Orangeburg scarp which has a 

relief of about 30 m across a distance of a few kilometers (fig. 3). The scarp is the locus of upper 

Miocene and Pliocene ( ?) shoreline deposits and coincides roughly with earlier Eocene shorelines as well 

(Colquhoun and Johnson, 1968). The Middle Coastal 

Plain consists of a surface on which fluvial erosion 

has proceeded to the point where the primary depositional topography, although present, is generally 

not obvious. 

The Charleston-Summerville area is within the 

Lower Coastal Plain. The surface of the Lower 

Coastal Plain consists mainly of primary depositional topography formed during the Pleistocene and 

Holocene. Larger landforms, such as barrier island 

chains and marsh surfaces, can be seen, particularly 

close to the present shoreline. As Colquhoun and 

Johnson (1968) point out, individual storm-beach 

ridges can be seen on aerial photographs and topographic maps. Six barrier-beach systems (old shorelines) have been recognized on the Lower Coastal 

Plain; their landward surfaces rise to approximately 

33, 21, 12, 8, 5, and 3 m. They have been named the 

Wicomico, Penholoway, Talbot, Pamlico, Princess 

Anne, and "Silver Bluff," respectively. 

The oldest rocks known to date for which there is 

paleontologic control in the Coastal Plain of South 

Carolina are of Late Cretaceous (Cenomanian) age 

(Hazel and others, this volume), although at least 

one tectonic basin containing red terrigenous sedimentary rocks (Dunbarton basin, see below) is 

buried beneath the Upper Cretaceous rocks. Most of 

our detailed knowledge of the subsurface stratigraphy in the Charleston-Summerville area comes from. 

the continuously cored drill hole (Clubhouse Crossroads corehole 1, hereafter called CCC 1) put down 

in 1974 and 1975 about 40 km west-northwest of 

Charleston as part of the Charleston studies (fig. 2). 

Results from this CO·rehole not only provide detailed 

information on the stratigraphy of the CharlestonSummerville area but modify considerably the previously held interpretations of the geologic history of 

the Coastal Plain. (see papers in this volume by 

Gohn and others, Hazel and others, and Gottfried 

and others) . 

CCC 1 penetrated 750 m of Tertiary and Upper 

Cretaceous clastic and calcareous sedimentary rocks 

with good core recovery. The hole bottomed in 42 m 

of amygdaloidal basalt with excellent core recovery; 

the total depth was 792 m ( Gohn and others, this 

volume). A general change in paleoenvironments is 

indicated from continental and marginal marine in 

the lower part of the Upper Cretaceous section to 

mostly marine in the upper Upper Cretaceous and 

younger section ( Gohn and others, this volume, and 

Hazel and others, this volume) . The change is not a 

simple transgression, however, but involves several 

transgressive-regressive cycles and four large time 

gaps. The most recent hiatus is within the Cooper 

Formation (the uppermost of the Tertiary units 

penetrated by CCC 1) composed of monotonous, bioturbated marine deposits (Gohn and others, this volume). The Cooper was deposited in an outer sublittoral (outer shelf) or deeper environment, and the 

hiatus which spans the Eocene-Oligocene boundary 

represents approximately the early Oligocene (Hazel 

and others, this volume). Work in progress suggests 

that this hiatus is useful in mapping nearsurface geology (L. M. Force, G. S. Gohn, B. B. Higgins, and 

Laurel Bybell, written and oral commun., 1976). 

One of the most significant results from the deepdrilling program has been the recovery and analysis 

of samples of lava flows of amygdaloidal basalt from 

the bottom of the corehole (CCC 1). Two flows have 

been identified. The interpretation by Gottfried and 

others (this volume) of the geochemistry of the 

basalt considerably constrains the various models 

proposed for the Mesozoic tectonic setting of 

Charleston. Analyses show that the basalt has undergone slight to extreme oxidation, hydration, and hydrothermal alteration. The effects of alteration are 

greatest near the margins of the flows, and the least 

altered rocks can be identified. Gottfried and others 

(this volume) report that the light rare earth element (REE) enriched pattern and low K/Rb indicate an origin for the basalt from an undepleted 

source area in the upper mantle. The abundances of 

the REE, Ti, Zr and Nb, and the pattern of light 

REE enrichment are most similar to those obtained 

by other workers from the high-Ti quartz-normative 

tholeiites of Mesozoic age from eastern North 

America (ENA). 
INTRODUCTION AND DISCUSSION 9 

These continental basalts were erupted during 

rifting and crustal extension in the early stages of 

continental breakup when North America separated 

from Africa. In eastern North America these basalt<; 

are of Late Triassic or Early Jurassic age (Johnson 

and McLaughlin, 1957, and Cornet and others, 1973). 

This age is consistent with the evidence from magnetic anomaly patterns and deep-sea drilling for the 

initiation of the opening of the North Atlantic Ocean 

180 m.y. ago (Pitman and Talwani, 1972; Vogt, 

1973). K-Ar ages of 94.8±4.2 m.y. and 109±4 m.y. 

were obtained for the CCC 1 basalt by Richard Marvin, U.S. Geological Survey. Although the K-Ar ages 

are consistent with a Late Cretaceous (Cenomanian) 

age of the overlying Cape Fear Formation (Hazel 

and others, this volume), such a young age for the 

corehole basalt poses problems. By the beginning of 

Late Cretaceous time, the North Atlantic Ocean was 

already a significant feature and Charleston would 

have been on the order of 1,600 km from the MidAtlantic spreading center (see Pitman and Talwani, 

1972). Gottfried and others (this volume) note that 

a magma-generating regime in the Charleston area 

100 m.y. ago would almost certainly have been different from that of 180 m.y. ago which produced 

spacially related EN A tholeiitic basalts. Because of 

the close geochemical sirhilarities of the corehole 

basalt to the ENA tholeiitic basalts, they conclude 

that these basalts are related in time as well as space. 

If that is true, a buried Triassic and (or) Jurassic 

basin may be present in the Charleston-Summerville 

area. 

Because of the documented chemical alteration of 

the corehole basalt, the K-Ar ages must be considered 

minimum ages and permissive of an original Triassic or Jurassic age of the basalt (Gottfried and 

others, this volume). The alteration and minimum 

ages may reflect postmagmatic processes associated 

with Cretaceous ( ?) tectonic activity. 

Sass and Ziagos (this volume) report on temperature measurements made in CCC 1 at 3-m intervals from the surface to the lowest depth of the hole. 

They obtain an average heat flow value of 1.3±0.12 

HFU (1 Heat-Flow-Unit (HFU) = 10- 6 cal cm- 2 

sec- 1 ). They note that this value is within the range 

of other values measured in eastern United State~ 

and that no thermal anomaly is associated with the 

Charleston-Summerville area. 

In the Upper Coastal Plain in the area of the 

Savannah River, a buried graben containing terrestrial redbeds has been documented in the subsurface 

by extensive drilling and geophysical surveys, and 

has been named the Dunbarton basin by Marine and 

Siple (1974) (fig. 3). The basin is about 10 km wide 

and 50 km long and is wholly overlain by the Tuscaloosa Formation of Late Cretaceous age. As much as 

903 m of maroon mudstone, sandstone of fluvial 

origin and fanglomerate fill the basin; no basalt 

flows were penetrated in the drilling. No fossils have 

been recovered from the basin drill holes, but by 

comparison with graben containing dated redbeds 

that are exposed elsewhere in the east, Marine and 

Siple (1974) suggest that the redbeds of the Dunbarton basin are of Triassic age. 

GEOLOGY BENEATH COASTAL PLAIN ROCKS 

AND TECTONIC SETTING 

The basement surface upon which the Coastal 

Plain sediments were deposited now dips gently seaward, on the average, but it is deformed by several 

transverse structures and contains at least one Mesozoic graben (the Dunbarton basin). The most important of these transverse structures in the southeast are the Cape Fear arch near the North CarolinaSouth Carolina border and the Peninsular arch (also 

called the Ocala arch or uplift) of Florida (fig. 3). 

These two arches are separated by the Southeast 

Georgia embayment. As summarized by Owens 

(1970), the Cape Fear arch divides the Atlantic 

Coastal Plain into two large poorly-defined sedimentary basins. Whereas glauconite-rich clastic 

rocks are dominant in the emerged Coastal Plain 

north of the arch, carbonate rocks are increasingly 

important southward and culminate in the Florida 

carbonate platform. The carbonate section is relatively thin over the Peninsula arch. A further difference in the basins is that Lower Cretaceous rocks are 

abundant in the Coastal Plain north of the Cape 

Fear arch, but, as noted in the previous section, have 

not been identified in South Carolina. 

Over the Cape Fear arch, rocks as old as Cretaceous have been planed off by marine erosion 

which took place as early as late Miocene and which 

continued into the Pliocene and Pleistocene (Colquhoun and Johnson, 1968). Recent work by Winker 

and Howard (1977) has shown that the conventional 

wisdom of correlating barrier-beach systems (old 

shorelines) by elevation above present sea level (for 

example, Colquhoun and Johnson, 1968) is not valid. 

The old shorelines have been deformed into the Pliocene and Pleistocene by persistent Cenozoic structural features such as the Cape Fear arch and the 

Peninsular arch. A study of the deformation of these 

old shorelines offers one of the most promising ap-
10 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

proaches to the elucidation of Quaternary deformation in the Charleston-Summerville area. 

The basement rocks in which the present seismicity takes place and in which the 1886 earthquake is 

presumed to have originated are not directly accessible for observation because of the Coastal Plain sedimentary cover. These basement rocks traditionally 

have been considered to be an extension of the metamorphic rocks of the Piedmont province exposed 

northwest of the feather edge of the Coastal Plain 

section (Rodgers, 1970). Aeromagnetic data suggest 

that this is not true. The basement beneath the 

Coastal Plain in the Charleston-Summerville area 

differs from the metamorphic terrane of the Piedmont in having a relatively smooth and continuous. 

low-amplitude magnetic field which Popenoe and 

Zietz (this volume) suggest represents undeformed 

tuffaceous clastic rocks intermixed with basaltic and 

rhyolitic flows and ash-fall deposits. High-amplitude, 

steep-gradient, generally circular magnetic and 

gravity positive anomalies (fig. 2) within and adjacent to this basement block are interpreted to reflect mafic or ultramafic plutons in the basement (see 

papers by Popenoe and Zietz, Phillips, Long and 

Champion, and Kane, this volume). For convenience, 

this distinctive basement terrane is hereafter called 

the Charleston block. All of the area shown on figure 

2 is thought to be within the Charleston block. 

The extent and boundaries of the Charleston block 

are not well known, but it does appear to underlie a 

sizeable area of the emerged and submerged Coastal 

Plain. The Orangeburg scarp (fig. 3) appears. to 

coincide with the northwestern boundary of the 

Charleston block and may be structurally controlled 

(Popenoe and Zietz, this volume; Higgins and others, 1976). A possible delineation of the other boundaries of the Charleston block is presented in the 

paper by Popenoe and Zietz (this volume). 

Why did the 1886 earthquake occur in the Charleston-Summerville area rather than elsewhere in the 

Charleston block? Is it reasonable, in fact, to restrict 

the probability of a recurrence of an 1886 earthquake to the Charleston block at all? Clearly, we 

need to know more about the Charleston block and 

about the nature and location of the boundaries of 

this block. 

In southwesternmost Georgia and northern Florida the mainly carbonate rocks of the Coastal Plain 

are underlain by nonfolded and nonmetamorphosed 

clastic rocks containing fossils ranging in age from 

Early Ordovician to probably Middle Devonian 

(Rodgers, 1970, and references therein). These fossiliferous Paleozoic rocks are clearly not part of the 

Appalachian orogenic belt. They have not been deformed by Appalachian or-ogenic events and they 

contain a pelecypod fauna that is closest to that of 

central Bohemia and Poland but that also has similarities to that of Nova Scotia, North Africa., and 

South America (Pojeta and others, 1976). Florida 

may thus represent a fragment of Africa (Rodgers, 

1970) that was attached to North America during 

the closing of the late Precambrian and early Paleozoic Iapetus Ocean (Odom and Brown, 1976) and 

was then left behind during the opening of the present Atlantic Ocean basin (Rodgers, 1970). The 

Charleston block separates Florida from the Appalachian orogenic belt. As suggested by Popenoe 

and Zietz (this volume) and Long and Lowell 

( 1973), the Charleston block basement may have 

formed as a zone of Mesozoic crutsal extension similar to the exposed Triassic and (or) Jurassic basins 

but much larger. This zone of extension is quite 

broad, perhaps as wide as 100 to 200 km, and is presumably related to the initial stages of the Mesozoic 

opening of the present Atlantic. The extension was 

apparently accompanied by the extrusion of continental tholeiitic lava such as that penetrated in 

CCC 1, and probably by the intrusion of large mafic 

plutons. 

Charleston probably shared this general Mesozoic 

extensional setting with New Madrid. The zone of 

extension at New Mardrid can reasonably be called 

an aulocogen or failed-arm trough (Burke and 

Dewey, 1973), the location of which may have been 

controlled by an even earlier failed-arm trough 

(Ervin and McGinnis, 1975). The zone of extension, 

if that is what it is, occupied by the Charleston block, 

is more analogous to, but much larger than, the exposed Triassic and (or) Jurassic basins in eastern 

North America. 

THE SOURCE AREA: METHOD OF APPROACH 

An adequate explanation of the Charleston earthquake of 1886 must include detailed studies of the 

source area. Earthquakes in the area are presumably caused by the sudden release of gradually accumulated strain by faulting as no active volcanoes 

are present in the' Coastal Plain. A first step in the 

study of the source area is, therefore, to identify and 

analyse faults. The histo·ry of fault movement 

through time, as well as the recency of movement 

must be determined, and this can be done only 

through study of the Coastal Plain section which 

records younger geologic events. From an understanding of the patterns of behavior of the fault 

through time as well as of changes in these patterns 
INTRODUCTION AND DISCUSSION 11 

it may be possible to place limits on the likely future 

behavior of the faults. It may be possible to establish a crude recurrence interval of movement for a 

given fault. It may be possible to establish the proba.-

bility of the length of a fault that would break in a 

single event and to predict the geometry of that 

movement. 

The modern regional stress field should be established from an analysis of the most recently formed 

structures and from in situ stress measurements. In 

unraveling these complex relations, a thorough understanding of the geologic history is necessary; the 

structure, structural history, and stress field must 

make sense in terms of the geologic history of the 

area. 

A next step in unders.tanding the source area is to 

characterize the modern seismicity including earthquake distribution and focal mechanisms. Only then, 

but not necessarily then, can one hope to relate the 

seismicity to a given fault or fault system. 

A reevaluation of the historical record shows that 

Middleton Place is roughly in the center of the 

meizoseismal area of the 1886 earthquake (Bollinger, this volume). Seismicity continues in the 

same area today (the Middleton Place-Summerville 

seismic zone), and is either a continuation of the 

aftershock series or strain-energy release along 

structural features closely related to the origins of 

the 1886 event (Tarr, this volume). Most, if not all, 

of this recent seismicity originates in the basement 

beneath the Coastal Plain sedimentary rocks. 

Observations of the basement may be made only 

by drilling and by various geophysical measurements. Drilling is extremely expensive but the information obtained is indispensible for calibrating the 

geophysical measurements as well as for the obvious 

direct geologic returns discussed earlier. Interpretation of the basement geology involves the construction of geologically reasonable models from the synthesis of the geophysical measurements, from drillhole data (including extrapolation from the petrology of the cores) and from an understanding of the 

geology of the eastern seaboard. 

Structures identified in the basement must be 

traced upward into the youngest rocks possible in 

order to determine as much as possible about the 

history and recurrence of movement and the geometry of movement. The interpretation of the deeper Coastal Plain geology involves the same process 

of constructing geologically reasonable models from 

drill-hole data and geophysics as in the interpretation of the basement geology. In addition, information on the biostratigraphy and lithostratigraphy is 

provided from the drill holes. For the shallow subsurface, a wealth of information can be obtained 

from shallow drilling. Given a mappable geophysical 

horizon and the control from shallow drilling, a de~ 

finitive map of the shallow structure should be obtainable. These studies are underway. Geologic rna~ 

ping of surface exposures will provide data on the 

Quaternary history and information to guide shallow drilling and shallow geophysical exploration and 

interpretation. Study of the raised and deformed 

barrier-beach systems are underway, and should 

contribute to the understanding of the Quaternary 

structural history. Along with this, a re,view of 

available geodetic leveling may provide information 

on any modern crustal movement. 

The seismicity monitored by the South Carolina 

Seismographic Network must be related to basement 

structures as constrained by structures in Coastal 

Plain rocks. In the long run, this may be the most 

difficult as well as the most relevant task. Finally, 

the stress axes measured in drill holes by hydrofracturing must be related to stress axes inferred from 

focal mechanisms. 

STUDIES OF THE MEIZOSEISMAL AREA 

Clubhouse Crossroads corehole 1 was drilled over 

the center of the largest of the positive magnetic 

anomalies in the meizoseismal area (fig. 2). This 

magnetic anomaly coincides with a positive Bouguer 

gravity anomaly described by Long and Champion 

(this volume). Some of the numerous findings resulting from this drilling have already been cited 

and reported in this volume in articles by Gohn and 

others, Hazel and others, and Gottfried and others. 

Unfortunately, the corehole drilling had to be abandoned in the basalt and did not reach the body causing the anomaly and (or) crystalline basement. Additional deep drilling is in progress, in part to sample 

the source of that geophysical anomaly. 1 Figure 2 

1 Additional information has been received since this report was written. 

Clubhouse Crossroads corehole 3 (CCC 3), the deepest of the drill holes, 

reached a total depth of 1,152 m (3,780 ft) before a broken drill rod on 

May 19, 1977, forced abandonment of the drilling operation (see fig, 2), 

The dri.'l penetrated basalt at 774 m (2,540 ft), passed through a thick 

section of it that contained one or two thin sedimentary rock interlayers, and entered red sandstone and shale at 1,031 m (3,384 ft) (Gohn, 

oral commun., 1977). No fossils have yet been recovered from these 

sedimentary rocks, but they do resemble rocks from exposed Triassic and 

(or) Jurassic basins. Thus, at CCC 3, 257 m of basalt are underlain by 

at least 121 m of red, probably terrestrial, clastic rocks. 

The vertical electrical sounding (VES) data which suggest that the 

basalt near CCC 1 and CCC 3 is lESS than 75 m thick (Campbell, this 

volume) is in obvious conflict with the drill- hole findings. The cause of 

this discrepancy is under investigation. Ackermann's (this volume) cal~ 

culations of basement depths were made assuming a thin basalt layer. 

These depth estimates must now also be increased, at least in the 

vicinity of CCC 3. 
12 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

shows in a simplified way the geographic relationship between many of the features discussed in the 

meizoseismal area in this and other articles. 

Phillips (this volume) presents the results of 

automated depth analysis performed on the aeromagnetic data. His work suggests that tops of most 

of the mafic plutons presumed to cause the pronounced magnetic anomalies are at a depth of 2.5 

to 3.5 km and probably extend to depths of 4.5 km. 

His analysis also suggests that the crystalline basement is at a depth of 0.6 to 1.5 km. Hence, the 

mafic plutons are within the crystalline basement. 

The mafic body causing the large anomaly at CCC 1 

appears to extend up to the top of the crystalline 

basement and is probably the only mafic pluton in 

the area which does so. The east-west magnetic low 

under Middleton Place is modeled as a nonmagnetic 

zone within the crystalline basement. Phillips suggests that this could be an altered zone along a fault, 

but also discusses the possibility that the magnetic 

pattern could be caused by reversed polarity of 

basalt lavas. The presence of reversely polarized 

basalts would also modify some other interpretations, and these complications are recognized by 

Phillips. 

Ackermann (this volume) reports on the results 

of seismic refraction studies in the meizoseismal 

area, designed for full reverse coverage from a basement horizon 600 to 1,000 m deep, and partial reverse coverage from shallower horizons. Of three 

refracting horizons discovered, the shallowest corresponds to a thin well-indurated calcarenite at the 

base of the Santee Limestone. This horizon, which 

is about 100 m deep in CCC 1, may prove useful for 

mapping structures in the shallow subsurface. The 

intermediate refracting horizon corresponds to the 

top of the basalt at a depth of 750 m in the corehole. Ackermann determined this horizon had seismic velocities which range from 5.8 km/s at the 

corehole to 4.3 km/s at Middleton Place. He suggests that the velocity decrease could be caused 

either by increased fracture porosity or by a termination of the basalt layer and notes that the lowest 

velocity coincides with the epicentral area of the 

Nov. 22, 1974, earthquake. The surface of the intermediate refracting layer shows a broad troughlike depression trending N. or NNW. (Ackermann, 

this volume, fig. 4). The trough could be more than 

50 m deep and is several kilometers west of Middleton Place. · 

Arrivals from the basalt layer, the intermediate 

refracting layer (assumed to be basalt), are 

shingled suggesting that this relatively high-velocity layer is interlayered in a lower velocity sequence. 

One interpretation of this is that the basalt is underlain by sOOimentary rock. Ackermann calculates the 

depth to the lowest refracting horizon, which he 

interprets as high-velocity crystalline basement (6.3 

to 6.5 km/s) using as a model a zone of constant 

velocity ( 4.2 km/ s) between the basalt and the basement. Under this assumption, the basalt and basement horizons appear to diverge to.ward the southeast, with crystalline basement at a depth of about 

900 m at CCC 1 but at a depth of 2,000 m some 25 

km to the ESE. (Ackermann, this volume, fig. 5). 

The basement surface, so calculated, appears to 

slope more steeply in the southeast part of the surveyed area and Ackermann suggests that this may 

be a flexure or a fault. 

Talwani (this volume) reports on the results of 

monitoring quarry blasts by portable seismographs 

in the area between Columbia and Georgetown, S.C. 

By combining data from monitoring blasts in the 

Berkeley quarry (about 35 km north of Summerville), data from seismic-refraction lines of Ackermann (this volume and unpub. data, 1977), regional 

Bouguer gravity, and densities of samples from 

CCC 1, Talwani (this volume) has calculated three 

possible crustal models between the Berkeley quarry 

and the vicinity of Middleton Place. Two of the 

seismic-refraction lines used by Talwani in constraining his model were run by Ackermann after 

he had submitted his manuscript for this volume. 

Campbell (this volume) reports on the results of 

18 audio-frequency magnetotelluric (AMT) soundings and 9 Schlumberger d.c. resistivity soundings 

(vertical electrical soundings= VES) in the meizoseismal area. The most significant results to· date 

are from the latter. In analysing the data, the resistivity of the electrical basement is assumed to be 

high with respect to that of the overlying sedimentary rocks; a value of 200 ohm-m is arbitrarily 

chosen. None of the VES showed a high-resistivity 

layer near the 750 m depth analogous to the basalt 

in CCC 1. Campbell argues that the basalt is, there~ 

fore, less than 75 m thick and is underlain by lowresistivity material. These data suggests that near 

the corehole the electrical basement is at 1,300 m 

and that the basalt is underlain by about half a kilo~ 

meter of sedimentary rock. 

Three VES soundings in the triangle between 

CCC 1, Summerville, and Middleton Place show an 

electrical basement at 900 m, significantly shallower 

than the 1,100- to 1,300-m-deep electrical basement 

elsewhere. These are soundings VES 2, 4, and 7 

shown as Campbell's figure 2. Campbell suggests 
INTRODUCTION AND DISCUSSION 13 

that this shallower highly resistive horizon (the 

deepest observed at those locations) may reflect 

thickened basalt rather than crystalline basement. If 

true, the basalt is not only thicker, but also deeper 

(down-faulted or down-bent) on the southeast side 

of a line trending northeast between CCC 1 and 

Summerville. Long and Champion (this volume) 

speculate a similar down-dropped basin (Triassic?) 

on the basis of the gravity data. 

EARTHQUAKE ORIGINS 

The present seismicity which takes place along a 

NW.-SE. zone between Summerville and Middleton 

Place, is either part of the aftershock series of the 

1886 earthquake or strain release along structures 

related to that earthquake. This seismicity is originating in the basement at depths significantly 

deeper than the basalt in CCC 1. 

The largest event so far recorded (Nov. 22, 1974) 

was at the SE. end of this zone under Middleton 

Place, also essentially the center of the meizoseismal 

area of the 1886 event. The focal mechanism for this 

event suggests compression along a NE.-SW. axis. 

One of the nodal planes determined for this event is 

consistent with nearly vertical (perhaps reverse) 

faulting on a plane striking N. 42° W. (Tarr, this 

volume). The suggested NE.-SW. compression is 

consistent with the pattern of compressive stress 

found by Sbar and Sykes ( 1973) for eastern North 

America. On the basis of this, the stress environment of Charleston appears to have changed from 

the Mesozoic stress environment which involved extension on a NE.-SW. axis. Sbar and Sykes (1973) 

further speculate that the Charleston-Summerville 

seismicity may be localized at the continental margin along the landward projection of the Blake Spur 

fracture zone (fig. 3). This hypothesis should certainly be pursued. As yet, no geologic feature has 

been recognized in the exposed crystalline rocks of 

the Piedmont that can be related to the fracture 

zone such as the train of alkalic plutons of the 

White Mountain Plutonic Series in New England 

which has been suggested as the continental projection of the Kelvin Sea Mount chain (Diment and 

others, 1972, and Sbar and Sykes, 1973) . 

Kane (this volume) notes a correlation between 

Bouguer gravity highs and seven well-defined eastern North American earthquake regions including 

Charleston, New Madrid, and Cape Ann. The gravity 

highs are interpreted as being caused by mafic or 

ultramafic plutons. He notes that the major seismic 

activity in each region does not coincide with the 

position of the gravity anomalies but is peripheral I 

to them. He suggests that the plutons may act to 

concentrate regional stress around their peripheries 

-perhaps through plastic deformation of serpentin~ 

ized rocks, a concept derived from the hole-in-plate 

problem of mechanics. A somewhat similar hypothesis of stress amplification has been proposed 

by Long (1976) for the observed relationship between mafic plutons (as deduced from the gravity 

field) and seismicity. His •concept differs from 

Kane's in that the inhomogeneities in the plate (the 

mafic plutons) are interpreted to be more rigid than 

the enclosing pla.te. 

CONCLUSIONS 

The more important concepts that are emerging 

from the work underway are as follows: 

1. Seismic activity is continuing today in the center 

of the meizoseismal area of the 1886 earthquake at a higher level than prior to 1886. 

2. The present seismic activity probably originates 

in the crystalline basement beneath the Coastal 

Plain sedimentary rocks. 

3. The crystalline basement beneath the Charleston-Summerville area is not simply a seaward 

extension of crystalline rocks exposed in the 

Piedmont. 

4. The Charleston block may represent a broad 

zone of Triassic and Jurassic crustal extension 

formed during the early stages of the opening 

of the Atlantic Ocean. 

5. The present stress regime appears to· be one of 

NE.-SW. compression rather than extension, 

and is similar to the stress regime of a large 

part of the eastern United States. 

6. The structure in the Charleston-Summerville 

area is not a simple homocline of Coastal Plain 

sedimentary rocks dipping toward the sea on 

a gently dipping basement surface. 

7. Various geophysical surveys yield interpretations that are not yet consistent. 

8. Geologic mapping is incomplete but should yield 

valuable results. 

9. Studies of one large eastern earthquake area 

may yield results that are useful to studies of 

others; for example, the association of seismicity with the margins of positive gravity 

anomalies. 

The cause of the Charleston-Summerville seismicity is still not determined. We certainly know a great 

deal more about the area than we did a few years 

ago and can begin to draw some constraints around 

some of the possibilities. The papers in this volume 
14 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

report on the first stage of an ongoing study. If the 

seismicity is to be understood, the answer will come 

from the multidisciplinary approach we are trying 

to pursue. Such detailed geologic and geophysical 

studies seeking to understand the geologic history 

and current tectonic regime of a seismic source area 

are very few and for intraplate sources areas, represent a new dimension in seismic analysis. 

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Fernando Earthquake: seismological studies and their 

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February 9, 1971: Washington, D.C., U.S. Govt. Printing 

Office, v. 3, p. 13-21. 

Bollinger, G. A., 1972, Historical and recent seismic activity 

in South Carolina: Seismol. Soc. America Bull., v. 62, 

no. 3, p. 851-864. 

Burke, Kevin, and Dewey, J. F., 1973, Plume-generated 

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433. 

Carver, David, Turner, L. M., and Tarr, A. C., 1977, South 

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U.S. Geol. Survey open-file rept. 77-429, 66 p. 

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Cornet, Bruce, Traverse, Alfred, and McDonald, N. G., 1973, 

Fossil spores, pollen, and fishes from Connecticut indicate Early Jurassic age for part of the Newark Group: 

Science, v. 186, p. 1243-1247. 

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Robertson, E. C., ed., The nature of the solid earth: 

New York, McGraw-Hill Book Co., p. 544-572. 

Dutton, C. E., 1889, The Charleston earthquake of August 

31, 1886: U.S. Geol. Survey, Ninth Ann. Rept. 1887-88, 

p. 203-528. 

Ervin, C. P., and McGinnis, L. D., 1975, Reelfoot Rift; reactivated precursor to the Mississippi Embayment: Geol. 

Soc. America Bull., v. 86, no. 9, p. 1287-1295. 

Evernden, J. F., 1975, Seismic intensities, "size" of earthquakes and related parameters: Seismol. Soc. America 

Bull., v. 65, no. 5, p. 1287-1313. 

--- 1976, A reply to "Comments on 'Seismic intensities, 

"size" of earthquakes and related parameters' by Otto 

W. Nuttli": Seismol. Soc. America Bull., v. 66, p. 339-

340. 

Gupta, I. N., and Nuttli, 0. W., 1976, Spatial attenuation of 

intensities for central U. S. earthquakes: Seismol. Soc. 

America Bull., v. 66, no. 3, p. 743-751. 

Hadley, J. B., and Devine, J. F., 1974, Seismobectonic map of 

the eastern United States: U.S. Geol. Survey Misc. 

Field Studies Map MF-620. 

Higgins, B. B., Owens, J. P., Popenoe, Peter, and Gohn, G. S., 

1976, Structures in the Coastal Plain of South Carolina: 

Geol. Soc. America Abstracts with Programs, v. 8, no. 2, 

p. 195-196. 

Johnson, M. E., and McLaughlin, D. B., 1957, Txiassic formations in the Delaware Valley: Geol. Soc. America Guidebook for field trips, Atlantic City 1957, Field Trip No. 

2, p. 31-56. 

Long, L. T., 1976, Speculations concerning southeastern 

earthquakes, mafic intrusions, gravity anomalies, and 

stress amplification: Earthquake Notes, v. 47, p. 29-35. 

Long, L. T., and Lowell, R. P., 1973, Thermal model for 

some continental margin sedimentary basins and uplift zones: Geology, v. 1, no. 2, p. 87-88. 

Marine, I. W., and Siple, G. E., 1974, Buried Triassic basin 

in the central Savannah River area, South Carolina and 

Georgia: Geol. Soc. America Bull., v. 85, no. 2, p. 311-

320. 

Mosaic, 1976, Quakes in seaTch of a theory: Mosaic, v. 7, no. 

4, p. 2-11. 

Nuttli, 0. W., 1973, The Mississippi Valley earthquakes of 

1811 and 1812; intensities, ground motion and magnitudes: Seismol. Soc. America Bull., v. 63, no. 1, p. 227-

248. 

--- 1976, Comments on "Seismic intensities, 'size' of 

earthquakes and related parameters" by Jack F. 

Evernden: Seismol. Soc. America Bull., v. 66, no. 1, p. 

331-340. 

Odom, A. L., and Brown, J. F., 1976, Was Florida a parl of 

North America in the lower Paleozoic?: Geol. Soc. 

America Abs. with Programs, v. 8, no. 2, p. 237-238. 

Owens, J. P., 1970, Post-Triassic tectonic movements in the 

central and southern Appalachians as recorded by sediments of the Atlantic Coastal Plain, in Fisher, G. W., 

and others, eds., Studies of Appalachian geology, central 

and southern: New York, Intersci. Publishers, p. 417-

427. 

Pitman, W. C., III, and Talwani, Manik, 1972, Sea-floor 

spreading in the North Atlantic: Geol. Soc. America 

Bull., v. 83, no. 3, p. 619-646. 

Pojeta, John, Jr., KHz, Jifi, and Berdan, J. M., 1976, Silurian-Devonian pelocypods and Paleozoic stratigraphy of 

subsurface rocks in Florida and Georgia and related 

Silurian pelecypods from Bolivia and Turkey: U.S. 

Geol. Survey Prof. Paper 879, 32 p. 

Rodgers, John, 1!)70, The tectonics of the Appalachians: 

New York, Intersci. Publishers, 271 p. 

Sbar, M. L., and Sykes, L. R., 1973, Contemporary compressive stress and seismicity in eastern North America: An 

example of intraplate tectonics: Geol. Soc. America 

Bull., v. 84, no. 6, p. 1861-1881. 

Schouten, Hans, and Klitgord, K. D., 1977, Mesozoic magnetic anomalies, western North Atlantic: U.S. Geol. 

Survey Misc. Field Studies Map MF-915. 

Scott, N. H., 1973, Felt area and intensity of San Fernando 

earthquake, in U.S. Natl. Oceanic and Atmospheric 

Admin., San Fernando, California, earthquake of February 9, 1971: Washington, D.C., U.S. Govt. Printing 

Office, v. 3, p. 23-48. 

Shaler, N. S., 1899, Aspects of the Earth: New York, Charles 

Scribner's Sons, 344 p. 

Tarr, A. C., comp., 1974, World seismicity map: Reston, Va., 

U. S. Geol. Survey. 
INTRODUCTION AND DISCUSSION 15 

Taylor, P. T., Zietz, Isidore, and Dennis, L. S., 1968, Geologic implications of aeromagnetic data for the eastern 

continental margin of the United States: Geophysics, v. 

33, no. 5, p. 755-780. 

U.S. Geological Survey, 1975, Aeromagnetic map of Charleston and vicinity, South Carolina: U.S. Geol. Survey 

open-file map 75-590. 

Vogt, P. R., 1973, Early ,events in the opening of the North 

Atlantic, in Tarling, D. H., and Runcom, S. K., eds., 

Implications of continental drift to the earth sciences, 

NATO Advance Study Institute, Newcastle-upon-Tyne, 

England (1972), v. 2, p. 693-712. 

Winker, C. D., and Howard, J. D., 1977, Correlation of 

tectonically deformed shorelines on the southern Atlantic Coastal Plain: Geology, v. 5, p. 123-127. 

Reinterpretation of the Intensity Data for the 

1886 Charleston, South Carolina, Earthquake 

By G. A. BOLLINGER 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, 

EARTHQUAKE OF 1886-A PRELIMINARY REPORT 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1028-B 

CONTENTS 

Page 

Abstract ----------------------------------------------------------------- 17 

Introduction ------------------------------------------------------------- 17 

Intensity effects in the epicentral region ------------------------------------ 18 

Intensity effects throughout the country ------------------------------------ 22 

Attenuation of intensity with epicentral distance ---------------------------- 27 

Magnitude estimate --------------------------------------------------- ___ 29 

Conclusions -------------------------------------------------------------- 31 

References cited ---------------------------------------------------------- 31 

ILLUSTRATIONS 

Page 

FIGURE 1. Epicentral area maps for the 1886 Charleston, S.C., earthquake ------------------------------- 20 

TABLE 

2. 

3-5. 

6. 

7, 8. 

9. 

10. 

Isoseismal map showing the State of South Carolina for the 1886 Charleston earthquake ---------- 22 

Maps of the Eastern United States showing: 

3. Distribution of intensity observations for the 1886 Charleston earthquake ----------------- 23 

4. Isoseismal map contoured to show the more localized variations in the reported intensities for 

the 1886 Charleston earthquake --------------·-------------------------------------------- 24 

5. Isoseismal map contoured to show the broad regional patterns of the reported intensities for 

the 1886 Charleston earthquake -------------·-------------------------------------------- 25 

Histogram showing distribution of intensity as a function of epicentral distance for the 1886 Charleston earthquake --------------------------------·-------------------------------------------- 28 

Graphs showing attenuation of intensity with epicentral distance for various fractiles of intensity at 

given distance intervals for the 1886 Charleston earthquake ---------------------------------- 28,29 

Histogram showing distribution of epicentral distances for given intensity levels of the 1886 Charleston earthquake --------------------------------·-------------------------------------------- 30 

Graph showing body wave magnitude estimates for the 1886 Charleston earthquake based on Nuttli's 

technique -------------------------------------·-------------------------------------------- 31 

TABLES 

Page 

1. Variation of intensity effects along the South Carolina Railroad ---------------------------------- 21 

2. Number of intensity observations as a function of epicentral distance intervals for the 1886 Charleston, S.C., earthquake ----------------------------------------------------------------------- 27 

III 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886-

A PRELIMINARY REPORT 

REINTERPRETATION OF THE INTENSITY DATA FOR THE 

1886 CHARLESTON, SOUTH CAROLINA, EARTHQUAKE 

By G. A. BoLLINGER 1 

ABSTRACT 

In 1889, C. E. Dutton published all his basic intensity 

data for the 1886 Charleston, S.C., shock but did not list 

what intensity values he assigned to each report, nor did 

he show the distribution of the locations of these data reports on his isoseismal map. The writer and two other seismologists have each independently evaluated Dutton's 1,300 

intensity reports (at least two of the three interpreters 

agreed on intensity values for 90 percent of the reports), 

and the consensus values were plotted and contoured. One 

map was prepared on which contours emphasized the broad 

regional pattern of effects (with results similar to Dutton's); 

another map was contoured to depict the more localized 

variations of intensity. As expected, the latter map shows 

considerable detail in the epicentral region as well as in the 

far-field. In particular, intensity VI (Modified Mercalli 

(MM)) effects are noted as far away as central Alabama 

and the Illinois-Kentucky-Tennessee border area. Dutton's 

"low intensity zone" in West Virginia appears on both 

isoseismal maps. 

A maximum MM intensity of X for the epicentral region 

and IX for Charleston appears to be appropriate. Epicentral 

effects included at least 80 km of railroad track seriously 

damaged and more than 1,300 km 2 of extensive cratering and 

fissuring. In Charleston, the railroad-track damage and 

cratering were virtually absent, whereas many, but not 

most, buildings on both good and poor ground were destroyed. 

The epicentral distances to some 800 intensity-observation localities were measured, and the resulting data set was 

analyzed by least-square regression procedures. The attenuation equation derived is similar to others published for different parts of the eastern half of the United States. The 

technique of using intensity-distance pairs rather than 

isoseismal maps has the advantages, however, of completely bypassing the subjective contouring step in the data 

handling and of being able to specify the partic'.llar fractile 

of the intensity data to be considered. 

When one uses intensities in the VI to X range, and their 

associated epicentral distances for this earthquake, bodywave magnitude estimates of 6.8 (Central United States intensity-velocity data published by Nuttli in 1976) and 7.1 

1 Virginia Polytechnic Institute and State University, Blacksburg, Va. 

(Western United States intensity-velocity data published 

by Trifunac and Brady in 1975) are obtained. 

INTRODUCTION 

The problems associated with the description of 

seismic ground motion in a minor seismicity area 

such as the Southeastern United States are well 

known. In that region, the largest events took place 

before instruments were available to record them, so 

that only qualitative descriptions of their effects 

exist. During the past few decades, when instruments began to be used, no event having mb>5 has 

taken place. Thus we have quantitative data only for 

small events, and we need to analyze the qualitative 

data, which are all that is available for larger events. 

The purpose of this study is to review thoroughly 

the data that do exist and to derive as much information as possible concerning regional seismio 

ground motions. Fortunately, the largest earthquake 

known to have occurred in the region, the 1886 

Charleston, S.C., earthquake, was well studied by 

Dutton (1889) and his coworkers. An excellent suite 

of intensity information is thus available for that important earthquake. Secondly, the Worldwide Standard Seismograph Network (WWSSN) stations in 

the Eastern United States provide data on the radiation from the regional earthquakes that have occurred since installation of the stations. Finally, 

intensity-particle-velocity relationships as well as 

attenuation values for various seismic phases have 

been proposed that can be utilized in an attempt to 

synthesize the above data types. 

The initial part of this paper is concerned with a 

reevaluation of the intensity data for the 1886 

Charleston earthquake, and the second part, with a 

consideration of the attenuation of intensity as distance from the epricenter increases. (The distance 

17 
18 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

from the epicenter is hereafter called epicentral distance.) The concluding section presents a magnitude 

estimate for the 1886 shock. 

This research was conducted while the author was 

on study-research leave with the U.S. Geological Survey (U.S.G.S.) in Golden, Colo. Thanks are extended 

to the members of the Survey, particularly Robin 

McGuire and David Perkins, for their many helpful 

discussions. Robin McGuire did the regression analysis presented in this paper, and Carl Stover provided a plot program for the intensity data. Thanks 

are also due to Rutlage Brazee (National Oceanographic and Atmospheric Administration, N.O.A.A.) 

and Ruth Simon (U.S.G.S.) for interpreting the 

sizable amount of intensity data involved in this 

study. 

This research was sponsored in part by the N ationa! Science Foundation under grant No. DES 75-

14691. 

INTENSITY EFFECTS IN THE EPICENTRAL 

REGION 

Dutton assigned an intensity X as the maximum 

epicentral intensity for the 1886 shock. He used the 

Rossi-Forel scale; conversion to the Modified Mercalli (MM) scale results in a X-XII value. However, 

the revised edition (through 1970) of the "Earthquake History of the United States" (U.S. Environmental Data Service, 1973) downgraded Dutton's 

value to a IX-X (MM). Because of this revision, it 

is appropriate to compare the scale differences between these two intensity levels (IX and X) with the 

meizoseismal effects as presented by Dutton. 

Ground effects, such as cracks and fissures, and 

damage to structures increase from the intensity IX 

to the intensity X level, whereas damage to rails is 

first listed in the MM scale at the X level. Taken 

literally, rail damage is indicative of at least intensity-X-level shaking. Richter (1958, p. 138) also 

listed "Rails bent slightly" for the first time at intensity X. However, he instructed (p. 136) that, 

"Each effect is named at that level of intensity at 

which it first appears frequently and characteristically. Each effect may be found less strongly, or in 

fewer instances, at the next lower grade of intensity; 

more strongly or more often at the next higher 

grade." Thus, widespread damage to rails is a firm 

indicator of intensity-X shaking. 

In discussing building damage, it is convenient to 

use Richter's (1958, p. 136-137) masonry A, B, C, D 

classification: 

Masonry A. Good workmanship, mortar, and design; reinforced, especially laterally, and bound together by using 

steel, concrete, etc.; designed to resist lateral forces. 

Masonry B. Good workmanship and mortar; reinforced, 

but not designed in detail to resist lateral forces. 

Masonry C. Ordinary workmanship and mortar; no extreme weaknesses like failing to tie in at corners, but neither 

reinforced nor designed against horizontal forces. 

Masonry D. Weak materials, such as adobe; poor mortar; 

low standards of workmanship; weak horizontally. 

At the IX level, masonry D structures are destroyed, 

masonry C structures are heavily damaged, sometimes completely collapsed, and masonry B structures are seriously damaged. Frame structures, if 

not bolted, are shifted off their foundations and have 

their frames racked at IX-level shaking, whereas at 

intensity X most such structures are destroyed. 

Nearly complete destruction of buildings up to and 

including those in the masonry B class is a characteristic of the intensity-X level. 

Only in Charleston do we have a valid sample of 

the range of structural damage caused by the 1886 

earthquake. It was the only nearby large city, and 

it contained structural classes up to the range between masonry C and masonry B. Many of the important public buildings, as well as mansions and 

churches, had thick walls of rough handmade bricks 

joined with an especially strong oyster-shell-lime 

mortar. The workmanship was described as excellent but nowhere in Dutton's (1889) account is ' . reference made to special reinforcement or design 

to resist lateral forces. Structures out:Bide the 

Charleston area (as in Summerville, seep. 21) were 

built on piers, some 1-2 m (3-6 ft) high, thereby 

making the structures inverted pendulums. Dutton's 

report for Charleston indicates that although the 

damage was indeed 'extensive (see below), most 

masonry buildings and frame structures were not 

destroyed. This fact plus Dutton's report on the 

absence of rail damage and extensive ground effects 

in the Charleston area indicates an intensity level 

of IX. 

The following quotations from Dutton's report 

(1889, p. 248-249, 253) contain detailed descriptions 

of the structural damage in Charleston caused by the 

earthquake of 1886: 

There was not a building in the city which had wholly 

escaped injury, and very few had escaped serious injury. 

The extent of the damage varied greatly, ranging from 

total demolition down to the loss of chimney tops and the 

dislodgment of more or less plastering. The number of 

buildings which were completely demolished and leveled to 

the ground was not great. But there were several hundred 

which lost a large portion of their walls. There were very 

many also which remained standing, but so badly shattered 
REINTERPRETATION OF THE INTENSITY DATA 19 

that public safety required that they should be pulled down 

altogether. There was not, so far as at present known, a 

brick or stone building which was not more or less cracked, 

and in most of them the cracks were a permanent disfigurement and a source of danger or inconvenience. A majority 

of them however were susceptible of repair by means of 

long bolts and tie-rods. But though the buildings might be 

made habitable and safe against any stresses that houses 

are liable to except fire and earthquake, the cracked walls, 

warped floors, distorted foundations, and patched plaster 

and stucco must remain as long as the buildings stand permanent eye-sores and sources of inconveniences. As soon as 

measures were taken to repair damages the amount of injury disclosed was greater than had at first appeared. Innumerable cracks which had before been unnoticed made 

their appearance. The bricks had "worked" in the embedding 

mortar and the mortar was disintegrated. The foundations 

were found to be badly shaken and their solidity was greatly impaired. Many buildings had suffered horizontal displacement; vertical supports were out of plumb; floors out 

of level; joints parted in the wood work; beams and joists 

badly wrenched and in some cases dislodged from their 

sockets. The wooden buildings in the northern part of the 

city usually exhibited externally few signs of the shaking 

they received except the loss of chimney tops. Some of them 

had been horizontally moved upon their brick foundations, 

but none were overthrown. Within these houses the injuries 

were of the same general nature as within those of brick, 

though upon the whole not quite so severe. 

The amount of injury varied much in different sections of 

the city from causes which seem to be attributable to the 

varying nature of the ground. The peninsula included between the Cooper and Ashley Rivers, upon which Charleston 

is built, was originally an irregular tract of comparatively 

high and dry land, invaded at many points of its boundary 

by inlets of low swampy ground or salt marsh. These inlets, as the city grew, were gradually filled up so as to be 

on about the same level as the higher ground. * * * As a 

general rule, though not without a considerable number of 

exceptions, the destruction was greater upon made ground 

than upon the original higher land. [p. 248-249] * * * 

In truth, there was no street in Charleston which did not 

receive injuries more or less similar to those just described. 

To mention them in detail would be wearisome and to no 

purpose. The general nature of the destruction may be 

summed up in comparatively few words. The destruction was 

not of that sweeping and unmitigated order which has befallen other cities, and in which every structure built of material other than wood has been either leveled completely 

to the earth in a chaos of broken rubble, beams, tiles, and 

planking, or left in a condition practically no better. On the 

contrary, a great majority of houses were left in a condition shattered indeed, but still susceptible of being repaired. 

Undoubtedly there were very many which, if they alone had 

suffered, would never have been repaired at all, but would 

have been torn down and new structures built in their places; 

for no man likes to occupy a place of business which suffers by contrast with those of his equals. But when a common calamity falls upon all, and by its very magnitude and 

universality renders it difficult to procure the means of reconstruction, and where thousands suffer much alike, his 

action will be different. Thus a very large number of buildings were repaired which, if the injuries to them had been 

exceptional misfortunes instead of part of a common disaster, would have been replaced by new structures. Instances 

of total demolition were not common. 

This is probably due, in some measure, to the stronger 

and more enduring character of the buildings in comparison 

with the rubble and adobe work of those cities and villages 

which are famous chiefly for the calamities which have befallen them. Still the fact remains that the violence of the 

quaking at Charleston, as indicated by the havoc wrought, 

was decidely Jess than that which has brought ruin to other 

localities. The number of houses which escaped very serious 

injuries to their walls was rather large; but few are known 

to have escaped minor damages, such as small cracks, the 

loss of plastering, and broken chimney tops. [p. 253] 

Damage to the three railroad tracks that extend 

north, northwest, and southwest from Charleston began about 6 km (3.7 mi) northwest of the city and 

was extensive (fig. 1A). More than 80 km (62 mi) 

of these tracks was affected. The effects listed were: 

lateral and vertical displacement, formation of Sshaped curves, and the longitudinal movement of 

hundreds of meters of track. A detailed listing of 

the effects along the South Carolina Railroad tracks, 

which run northwest from Charleston directly 

through the epicentral region, is given in table 1. 

Ground cracks from which mud or sand are 

ejected and in which earthquake fountains or sand 

craters are formed begin on a small scale at intensity 

VIII, become notable at IX, and are large and spectacular phenomena at X (Richter, 1958, p. 139). The 

formation of sand craterlets and the ejection of sand 

were certainly widespread in the epicentral area of 

the 1886 earthquake. Many acres of ground were 

overflowed with sand, and craterlets as much as 6.4 

m (21ft) across were formed. Dutton (1889, p. 281) 

wrote: "Indeed, the fissuring of the ground within 

certain limits may be stated to have been universal, 

while the extravasation of water was confined to certain belts. The area within which these fissures may 

be said to have been a conspicuous and almost universal phenomenon may be roughly estimated at 

nearly 600 square miles [1,550 sq. km]." By comparison, the elliptical intensity-X contour suggested 

by the present study encloses an area of approximately 1,300 km2 • 

The distribution of craterlets taken from Dutton 

( 1889, pl. 28) is also shown in figure 1A. In a few 

localities, the water from the craters probably 

spouted to heights of 4.5-6 m ( 15-20 ft), as indicated by sand and mud on the limbs and foliage of 

trees overhanging the craters. 

Other ground effects indicating the intensity-X 

level are fissures as much as a meter wide running 

parallel to canal and streambanks, and changes of 
20 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

33 

33' 

\ c . . . " i 0 5 \. (\ I J I I I I 

10 MILES 

I 

i''''l 1 f' 0 5 10 KILOMETERS 

80" 

10 15 MILES I I I I I j I I I 

5 

I 

10 

I 

I I 

EXPLANATION 

I I I I I I I I I Railroad track damaged 

1 5 KILOMETERS 

0 Craterlet area 

• Building destroyed 0 Chimney destroyed 

e Markec!"horizontal displacement 0 5 10 MILES 

J r'd 1

1

1

1 1 I 1 

MP 0 5 10 KILOMETERS 

+ Middleton Place 

FIGURE 1.-Epicentral area maps for the 1886 Charleston, S.C., earthquake. A, This study. Dashed contour encloses 

intensity-X effects. B, Dutton's map and C, Sloan's map (modified from Dutton, 1889, pls. 26 and 27, respectively) 

show contours enclosing the highest intensity zone, although neither Dutton nor Sloan labeled his contours. Base 

map modified from Dutton (1889). Rivers flowing past the Charleston peninsula are the Ashley River flowing from 

the northwest and the Cooper River flowing from the north. 

the water level in wells (Wood and Neuman, 1931). 

Dutton (1889, p. 298) reported that a series of wide 

cracks opened parallel to the Ashley River (see caption, fig. 1) and that the sliding of the bank riverward uprooted several large trees, which fell over 

into the water. His plate 23 shows a crack along the 

bank of the Ashley River about a meter wide and 

some tens of meters long across the field of view of 

the photograph. 

In a belt of craterlets (trend N. 80° E., length 

-5 km) about 10 km (6.2 mi) southeast of Summerville, Sloan reported (Dutton, 1889, p. 297) that 
REINTERPRETATION OF THE INTENSITY DATA 21 

TABLE 1.-Variation of intensity effects along the South TABLE 1.-Variation of intensity effects along the South 

Carolina Railroad Carolina Railroad-Continued 

[Based on Dutton, 1889, p. 282-287. Refer to fig. 1 for locations mentioned] 

-----·-------------------------------------- Distance from 

Charleston Effects 

(km) (mi) 

<5.8 <3.66 ----- Occasional cracks in ground; no marked disturbance of 

track or roadbed. 

5.8 ------- 3.66 ------ Rails notably bent and 

joints between rail 

opened. 

5.8-8 ----- 3.66-5 ---- Ground cracks and small 

crater lets. 

8 -------- 5 -------- Fishplates torn from fastenings by shearing of the 

bolts; joints between rails 

opened to 17.5 em (7 in.). 

9.6 6 -------- Joints opened, roadbed permanently depressed 15 em (6 in.). 

14.4 9 -------- Lateral displacements of the 

track more frequent and 

greater in amount; serious 

flexure in the track that 

caused a train to derail; more and larger craterlets. 

16 -------- 10 -------- Craterlets seemed to be 

greater in size (as much as 6.4 m (21 ft) across) 

and number; many acres overflowed with sand. 

16-17.6 ____ 10-11 _____ Maximum distortions and 

dislocations of the track; 

often displaced laterally 

and sometimes alternately 

depressed and elevated; 

occasional severe lateral 

flexures of double curva- ture and great amount; 

many hundreds of meters 

of track shoved bodily to 

the southeast; track 

parted longitudinally, 

leaving gaps of 17.5 em (7 

in.) between rail ends; 46 em (18 in.) depression or sink in roadbed over a 18-m (60-ft) length. 

17.6-24 ____ 11-15 Many lateral deflections of 

the rails. 

24-25.6 ---- 15-16 Epicentral area-a few 

wooden sheds with brick 

chimneys completely collapsed; railroad alinement 

distorted by flexures; elevations and depressions, some of considerable 

amount, also produced. 

29-80.6 ---- 18.5-19 ____ Flexures in track, one in an 8.8-m (29-ft) section of 

single rails had an S-shape 

and more than 30 em (12 

in.) of distortion. 

32 -------- =20 -------- " ... a still more complex flexure was found. Beneath 

it was a culvert which had 

been strained to the northwest and broken" (p. 286); a long stretch of the roadbed and track distorted by 

many sinuous flexures of 

small amplitude. 

Distance from 

Charleston 

(km) (mi) 

Effects 

33.9 21 -------- Tracks distorted laterally and vertically for a con- siderable distance. 

34.9 21.66 ------ At Summerville-many flexures, one of which was a sharp S-shape; broken 

culvert under tracks in a sharp double curvature. 

35.4-44.3 22-27.5 ____ Disturbance to track and 

roadbed diminishes rapidly. 

44.3 ------- 27.5 ------- At Jedburg-a severe buckling of the track. 

wells had been cracked in vertical planes from top 

to bottom, and that the wells had been almost universally disturbed, many overflowing and subsequently subsiding, others filling with sand or becoming muddy. 

In Summerville, whose population at that time was 

about 2,000, the structures were supported on wood 

posts or brick piers 1-2 m high and, though especially susceptible to horizontal motions, the great majority did not fall. Rather, the posts and piers were 

driven into the soil so that many houses settled in 

an inclined position or were displaced as much as 5 

em. Chimneys, which were constructed to be independent of the houses, generally had the part above 

the roofline dislodged and thrown to the ground. Below the roofs, many chimneys were crushed at their 

bases, both bricks and mortar being disintegrated 

and shattered, allowing the whole column to sink 

down through the floors. This absence of overturning in piered structures plus the nature of the damage to chimneys was interp·reted by Dutton as evidence for predominantly vertical ground motions. 

The preceding discussion indicates an intensity-X 

level of shaking in the epicentral area. Figure 1A 

depicts the approximate extent of this region along 

with the locations of rail damage, craterlet areas, 

building damage, and areas of marked horizontal 

displacements. Dutton and his coworkers did not 

map the regions of pronounced vertical-motion effects, but they did emphasize the importance of these 

effects in the epicentral region. Also shown in figure 

1 (B and C) is the extent of the highest intensity 

zone, as given by Dutton and by Sloan. Because of 

the sparsely settled and swampy nature of the 

region, the meizoseismal area cannot be defined 

accurately. 
22 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

INTENSITY EFFECTS THROUGHOUT THE 

COUNTRY 

Dutton ( 1889) published all his intensity reports, 

some 1,337, but he did not list the intensity values 

that he assigned to each report, nor did he show the 

location of the data points on his isoseismal map. By 

using the basic data at hand, a reevaluation was attempted to present another interpretation of the 

data (in the MM scale) and to determine whether 

additional information could be extracted concerning this important earthquake. The writer and two 

other seismologists (Rutlage Brazee, N.O.A.A., and 

Ruth Simon, U.S.G.S.) each independently evaluated 

Dutton's intensity data listing according to the MM 

scale. For the resulting 1,047 usable reports, ranging 

from MM level I to X, at least two of the three inter34° 

33' 

83' 82' 

+ 

GEORGIA 

+ 

0 I ()I ' ' I I 

0 25 

25 I [ 

I 

50 MILES 

I 

50 KILOMETERS 

l 

l. 

81° 

preters agreed on intensity values for 90 percent of 

the reports. As would be expected, most of the disagreement was found at the lower intensity levels 

(11-V). A full listing of the three independent intensity assignments for each location was made by 

Bollinger and Stover (1976). 

The consensus values, or the average intensity 

values, in the 10 percent of the reports where all 

three interpreters disagreed were plotted at two different map scales and contoured (figs. 2-5). When 

multiple reports were involved, for example, those 

from cities, the highest of the intensity values obtained was assigned as the value for that location. 

The greatest number of reports (178) for an individual State was from South Carolina. Figure 2 presents the writer's interpretation of these data. Even 

80° 79' 

+ 

'"' 8 + "' '"'-

+ 

35' 

34' 

33' 

---~ ., 

L---~~---------------~--------------~~--------------~------~-------0~----~32' 82' 81' 80' 79' 

FIGURE 2.-Isoseismal map showing the State of South Carolina for the 1886 Charleston earthquake. Intensity observations are indicated by Arabic numerals, and the contoured levels are shown by Roman numerals. 
REINTERPRETATION OF THE INTENSITY DATA 

goo 85" 

MN ) 

+ ) +· 

( .. ++ + WI 

+ .--~ 

--------------\ . .. • • , 

~----=-- . + 

lA + 

• 

80° 75" 

• 

:· ,..) ... I • ~-..--:· \ ... --.. • . :: ~~-:. . ., p: ' :. '\ ' .. • + + I • • . • • .~ + -- + .' +,+ + el \ • ~~-.:... .• \-- - ·-~-.. ___,_ ,.1 I • i • IN "•-I! • • 0!1• • •" , --r ~"~r-- .. tct• '-. ~· + !L ~~ • • • ~ • I • • / ~ •.l 

400 '\:t,- \t. +. . !+. •• •: ....... ~ + •• r-l· ( •. , __ • : : ~~·· ••• -t J4i . ~ wv:. rJ •• '-. . .. . \.-, . ·. . . ;--..--~~ . . . I . 

I

. • ' • • + } • + ,. • • • • ~ r • :. • VA • 

Ks +MO + 1 . + f.'•. ,'c_) :•• 00 .. ~ ) I • • . '- !"...:"'-' KY\ • \ • .,._;- , 

I + -~-· • • •• , • • . . • • • • •t. • • . ~ ('• • •• • . •..r: • ~--·- -~- i + --~-... • • • __ _.....-.::..---J"j -----1 • 7 • r------------·~- ••• .J N C : • 

\-

. ,_.:..__.. ~--.. ~ • ..._. •• r'-./ • • • • • •• ) .r • • .. • • • /" • • • •• • • • [_{ • rl' • TN ,r/ • '!~· -1 • ~~ • •. •• : + • .)' •• I .............-: .)#.. ·e:;lt ' 

\. • , • • • _!, __ .!. .. --r---r-- r.-~ .. c · ~~.. .. ~.: .. · + i. +- ...---~ • . • ~~ ... :-.-... . . . AR + r \ ol 1 ··~ • .. •. • o• 0 

I

. / • • • I • • • • ·. • • • • • ~ ..... I .s c. : • , + \•· • , • ..~ • 

~·"'-j + ~ J AL • ·.~: • • • • •.. : ·\. 

I ~- • • • • • • • 

r-- ---'?. M; • • • "' ~ - •• • ' '~ :l·. • • : t • GA

0 

·-~ . ~ .. +LA P + •' • 

• t • \ r .. . -----~~!t...-!'---J~ ;__ .. ----7 • • • ., • ,. 

+ ·~ ··:· •\ I 

TX 

+ 

" + G U L F 0 F MEXICO 

200 400 MILES 

I 

I I I I 

I 

I I 

200 400 KILOMETERS + 

_j_. 

95° 900 85" 

23 

40" 

CJ 

0 

+ 

3()' 

25° 

5 

FIGURE 3.-Eastem United States showing the distribution of intensity observations for the 1886 Charleston earthquake. Solid circles indicate felt reports; small crosses indicate not-felt reports. 
24 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

45' 

40' 

30' 

GULF 0 F MEXICO 

25' 

200 400 MILES 

I I I I I I I I 

I 

200 400 KILOMETERS 

.-L95' 90' .85' BO' 75' 

- FIGURE 4.-Isoseismal map of the Eastern United States contoured to show the more localized variations in the reported intensities for the 1886 Charleston earthquake. Contoured intensity levels are shown by Arabic numerals. 
90' 

+ 

G U L F 0 F 

1 '1 1

1 1 

200 

95' 

REINTERPRETATION OF THE INTENSITY DATA 

85' 

MEXICO 

200 

I I 

400 KILOMETERS 

400 MILES 

I 

80' 75' 

+ 

85 80' 

25 

45' 

40' 

<--\-

"!: 

'4 

(.) 

0 

--\-

35' 

+ (.) 

30' 

25' 

75' 

FIGURE 5.-Isoseismal map of the Eastern United States contoured to show the broad regional patterns of the reported 

intensities for the 1886 Charleston earthquake. Contoured intensity levels are shown in Roman numerals. 
26 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

in contouring the mode of the intensity values, as 

was done here, intensity effects vary considerably 

with epicentral distance within the State. In particular, two intensity-VI zones are shown that trend 

northeastward across the State and separate areas 

of intensity-VIII effects. Although some of this variation may be due to incomplete reporting and (or) 

population density, it seems more likely that the 

local ·effects of surficial geology, soils, and watertable level are being seen. Interpreted literally, a 

very complex behavior of intensity is seen in the epicentral region. 

The intensity data base and interpretive, isoseismallines throughout the Eastern United States are 

shown in figures 3-5. In figure 4, the data are contoured to emphasize local variations, whereas figure 

5 depicts the broad regional pattern of effects. Richter (1958, p. 142-145), in discussing the problem of 

how to allow for or represent the effect of ground in 

drawing isoseismal lines, suggested that two isoseismal maps might be prepared. One map would show 

the actual observed intensities; the other map would 

show intensities inferred for typical or average 

ground. The procedure followed here was to contour 

the mode of the intensity values (figs. 2 and 4) so as 

to portray the observed intensities in a manner that 

emphasizes local variations. Those isoseismal lines 

were then subjectively smoothed to produce a second 

isoseismal map showing the regional pattern of effects (fig. 5). The two maps that result from this 

procedure seem to the writer to represent reasonable 

extremes in the interpretation of intensity data. The 

subjectivity always involved in the contouring of 

intensity data is well known to workers concerned 

with such efforts. The purpose of the dual presentation here is to emphasize this subjectivity and to 

point out that, depending on the application, one 

form may be more useful than the other. Both local 

and regional contouring interpretations are to be 

found in the literature for U.S. earthquakes. 

Figures 4 and 5 show that a rather complex isoseismal pattern, including Dutton's low-intensity 

zone (epicentral distance=~::.::::550 km (341 mi)) in 

West Virginia, was present outside South Carolina. 

Intensity-VIII effects were observed at distances of 

250 km (150 mi) and intensity-VI effects were observed 1,000 km (620 mi) from Charleston. Individual reports, given below, are all paraphrased from 

Dutton (1889). They note what took place in areas 

affected by intensity VI (MM) or higher at epicentral distances greater than about 600 km ( 372 

mi). Some of these reports were ignored in the contouring shown in figure 4. 

Intensity VI-VIII in Virginia (~::.:::::600 km 

(372 mi)): 

Richmond (VIII)-Western part of the city: bricks 

shaken from houses, plaster and chimneys 

thrown down, entire population in streets, people thrown from their feet; in other parts of the 

city, earthquake not generally felt on ground 

floors, but upper floors considerably shaken. 

Charlottesville (VII)-Report that several chimneys were overthrown. 

Ashcake (VI)-Piano and beds moved 15 em (6 

in.) ; everything loose moved. 

Danville (VI)-Bricks fell from chimneys, walls 

cracked, loose objects thrown down, a chandelier swung for 8 minutes after shocks. 

Lynchburg (VI)-Bricks thrown from chimneys, 

walls cracked in several houses. 

Intensity VII in eastern Kentucky and western West 

Virginia ( ~::.:::::650 km ( 404 mi)): 

Ashland, Ky. (VIII)-Town fearfully shaken, several houses thrown down, three or four persons 

injured. 

Charleston, W. Va.-"A number of chimneys toppled over" (p. 522). 

Mouth of Pigeon, W. Va.-Chimneys toppled off to 

level of roofs, lamps broken, a house swayed 

violently. 

Intensity VI in central Alabama ( ~::.:::::700 km 

(434 mi)): 

Clanton (VII)-Water level rose in wells, some went 

dry and others flowed freely ; plastering ruined. 

Cullman-House wall cracked, lamp on table thrown 

over. 

Gadsden-People ran from houses. 

Tuscaloosa--Wails cracked, chimneys rocked, blinds 

shaken off, screaming women and children left 

houses. 

Intensity VII in central Ohio ( ~-800 km 

(496 mi)): 

Lancaster-Several chimneys toppled over, decorations shaken down, hundreds rushed to the 

streets. 

Logan-Bricks knocked from chimney to.ps, houses 

shaken and rocked. 

Intensity VI in southeastern Indiana and northern 

Kentucky ( ~::.:::::800 km ( 496 mi)): 

Rising Sun, Ind.-Plaster dislodged, ornaments 

thrown down, glass broken. 

Stanford, Ky.-Some plaster thrown down, hanging 

lamps swung 15 em ( 6 in.). 
REINTERPRETATION OF THE INTENSITY DATA 27 

Intensity VI in southern Illinois, eastern Tennessee, 

and Kentucky ( A:::::::.950 km ( 590 mi)): 

Cairo, IlL-Broken windows, "houses settled considerably" (p. 430) in one section, ceiling 

cracked in post office. 

Murphysboro, IlL-Brick walls shook, firebell rang 

for a minute, suspended objects swung. 

Milan, Tenn.-Cracked plaster, people sitting in 

chairs knocked over. 

Clinton, Ky.-Some bricks fell from chimneys. 

Intensity VI in central and western Indiana 

( A-:::::::.1 ,000 km ( 620 mi)) : 

Indianapolis-Earthquake not felt on ground floors; 

part of a cornice displaced on one hotel, people 

prevented from writing at desks, clock in court 

house tower stopped, a lamp thrown from a 

mantle. 

Terre Haute-Plaster dislodged, sleepers awakened; 

in Opera House, earthquake felt by a few on the 

ground floor, but swaying caused a panic in the 

upper galleries. 

Madison-Several walls cracked, chandeliers swung. 

Intensity VI in northern Illinois and Indiana 

( A.-:::::::.1 ,200 km (7 44 mi)) : 

Chicago, IlL-Plaster shaken from walls and ceilings in one building above the fourth floor; 

barometer at Signal Office ''stood 0.01 inches 

higher than before the shock for eight minutes" 

(p. 432) ; earthquake not felt in some parts of 

City Hall, especially noticeable in upper stories 

of tall buildings, not felt on streets and lower 

floors. 

Valparaiso, Ind.-Plaster thrown down in hotel, 

chandeliers swung, windows cracked, pictures 

thrown from walls. 

The preceding reports indicate that structural 

damage extended to epicentral distances of several 

hundred kilometers and that apparent long-period 

effects were present at distances exceeding 1,000 km 

( 620 mi). Persons also frequently repo·rted nausea at 

these greater distances. 

Dutton apparently contoured his isoseismal map 

in a generalized manner, which is an entirely valid 

procedure. The rationale in that approach is to depict not the more local variations, as was presented 

in the above discussion, but rather the regional pattern of effects from the event. Figure 5 is the writer's attempt at that type of interpretation, and the 

resulting map is very similar to Dutton's. 

ATTENUATION OF INTENSITY WITH 

EPICENTRAL DISTANCE 

The decrease of intensity with epicentral distance 

is influenced by such a multiplicity of factors that it 

is particularly difficult to measure. The initial task 

in any attenuation study is to specify the distance 

(or distance range) associated with a given intensity level. Common selections are: minimum, maximum, or average isoseismal contour distances or the 

radius of an equivalent area circle. In all these approaches, the original individual intensities are not 

considered; rather, isoseismal maps are used. Perhaps a better, but more laborious, procedure has 

been suggested by Perkins (oral commun., 1975), 

wherein the intensity distribution of observations is 

plotted for specific distance intervals. In this manner, all the basic data are presented to the reader 

without interpretation by contouring. He is then in 

a position to know exactly how the data base is 

handled and thereby to judge more effectively the 

results that follow. Once the intensity-distance data 

are cast in this format, they are then also available 

for use in different applications. 

The epicentral distances to some 800 different 

locations affected by the 1886 shock were measured 

and are listed in table 2. For these measurements, 

the center of the intensity X (fig. 1) area was assumed to be the epicenter. Figure 6 presents the 

resulting intensity distributions as functions of epicentral distance. The complexity present in the isoseismal maps (figs. 4 and 5) is now transformed to 

specific distances, and the difficulty of assigning a 

single distance or distance interval to a given intensity level is clearly shown. The approach followed 

here was to perform a regression analysis on the 

intensity-distance data set, using an equation of the 

form, 

TABLE 2.-Number of intensity observations as a function 

of epicentral distance intervals for the 1886 Charleston 

S. C., earthquake ' 

Epicentral Number 

distance IX VIII VII VI v IV II-III of 

(km) obser ... vations 

50- 99 3 4 3 3 3 16 

100- 199 2 18 18 17 18 1 74 

200- 299 9 22 25 30 5 91 

300- 399 3 16 12 31 8 70 

400- 499 2 3 10 26 19 12 72 

500- 599 1 3 11 13 19 7 54 

600- 699 1 3 3 14 33 11 65 

700- 799 3 4 22 16 22 67 

800- 899 1 2 29 20 20 72 

900- 999 3 18 17 30 68 

1,000-1,249 4 24 19 48 95 

1,250-1,499 6 6 20 32 

1,500-1,749 1 3 4 

Totals 5 38 72 94 234 164 173 780 
28 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

(16) (74) 

I I 

Number of observations 

I I (65)·~ Number of observations 

(91) (70) (72) (54) 40 20 0 

I 

- - I I I 

I I I I I I I (67) (72) 

:::!: I 

-- - I I I I I 

:::!: 

I I I I I I I I I ~ (68) (95) 

>-= !:::: I 

- - - - - I I I I I 

(/) 

I I I I I I I I I I I 

z 

w 

I- (32) 

z I 

-- - - - --- - - • 

I I I I I I I I I I I (4) 

I • • --- -- - - • I 

I I I I I I I I I (48) I I I 

I • -- ---- I 

= = = = = = = = = = = = """ J> 

= 0> ~ ~ = 0> 0> 0> ~ 0> = ~ :g: ~ "' """ ....., <D 00 0> 

I I I I I I I I I I I I I 

C> C> C> C> C> C> C> C> C> C> C> C> C> ....., C> ~ C> C> C> C> ~ C> C> C> ....., C> 

"' """ ....., <D 00 0> ~ "' ~ 

EPICENTRAL DISTANCE, IN KM 

FIGURE 6.-Distribution of intensity (Modified Mercalli, MM) as a function of epicentral distance (km) for the 

1886 Charleston earthquake. Intensity distribution is shown for specific distance intervals. 

I =Io+a+ b~+c log~. 

where a, b, c are constants, ~ is the epicentral dis~ 

tance in kilometers, Io is the epicentral intensity, 

and I is the intensity at distance ~- This equation 

form was selected because it has been found useful 

by other investigators (for example, Gupta and 

Nuttli, 1976). The resulting fit for the median, or 

50-percent fractile, was, 

I= I o + 2.87- 0 .00052~- 2.88 log ~. 

The standard deviation, uJ, between the observed 

and predicted intensities, is 1.2 intensity units for 

these data. For the 75-percent fractile, the a constant is 3.68; for the 90-percent fractile, the a constant is 4.39. The b term is very small and could 

perhaps be deleted, as it results in only half an intensity unit at 1,000 km. The minimum epicentral 

distance at which the equation is valid is probably 

10-20 km. The intensity-distance pairs extend to 

within only 50 km of the center of the epicentral 

regi001, but that region (fig. 1) has a diameter of 

approximately 20 km. 

The curves for the 50-, 75-, and 90-percent fractiles are shown in figures 7 and 8 along with other 

published intensity attenuation curves for the Central and Eastern United States. Isoseismal maps 

20 30 4050 

CENTRAL AND EASTERN U.S. 

Howell and Schultz (1975) 

100 200 300 500 1000. 

EPICENTRAL DISTANCE, IN KM 

FIGURE 7.-Attenuation of intensity (MM) with epicentral 

distance (km) for various fractiles of intensity at given 

distance intervals for the 1886 Charleston earthquake 

(heavy solid curves). Attenuation functions by Howell 

and Schultz (1975), Gupta and Nuttli (1976), and Cornell 

and Merz (1974) are shown by light dashed curves. 
REINTERPRETATION OF THE INTENSITY DATA 29 

X 

IX 

u. VIII 

a: 

~ 

~ VII 

~ 

>-' 

t:: VI (J) 

z 

w 

f-

~ v 

IV 

Ill 

10 20 30 40 50 100 200 300 500 1 000 2000 

EPICENTRAL DISTANCE, IN KM 

FIGURE B.-Attenuation of intensity (MM) with epicentral 

distance (km) for various fractiles of intensity at given 

distance intervals for the Charleston earthquake (solid 

curves). Evernden's attenuation curves (1975) (RossiForel intensity scale; L=10 km, C=25 km, k=1 and 1:1;4) 

are shown by dashed curves for lo=X. 

were utilized to develop these latter curves, and the 

general agreement between the entire suite of curves 

is remarkable. A direct comparison between curves, 

which may not be valid because of different data sets 

and different regions, would suggest that the Howell 

and Schultz (1975) curve is at about the 85-percent 

fractile, the Gupta and Nuttli (1976) curve is at the 

SO-percent fractile, and the Cornell and Merz (1974) 

curve is at the 70-percent fractile. At the intensityVI level and higher, note that there is less than one 

intensity-unit difference among the Central United 

States, Central and Eastern United States, and 

Northeastern United States curves and the 75- and 

90-percent fra.ctile curves of this study. 

Evernden's (1975) curves (fig. 8) forhisk=1 and 

k = 11;4 factors lie between the 50- and 90-percent 

fractile curves of this study. Evernden used k factors to describe the different patterns of intensity 

decay with distance in the United States. A value of 

k= 1%, was found for the Gulf and Atlantic Coastal 

Plains and the Mississippi Embayment and a k= 1 

for the remainder of the Eastern United States. 

Evernden prefers to work with the Rossi-Forel (RF) intensity scale. The difference between the R-F 

and MM scales is generally about half an intensity 

unit, and conversion to R-F values would essentially 

result in translating the fractile curves of this study 

upward by that amount. This would put the 75-

percent fractile curve in near superposition with 

Evernden's k= 1 curve. Such a result is perhaps not 

surprising because approximately two-thirds of the 

felt area from the 1886 shock is in Evernden's k= 1 

region, and isoseismal lines are often drawn to enclose most of the values at a given intensity level. 

Although differences in intensity attenuation may 

exist between various parts of the Eastern United 

States, it would appear from this study that the 

dispersion of the data ( a1 = 1.2) could preclude its 

precise definition. If, indeed, significant differences 

do exist between the various regions, then the curves 

given here would apply to large shocks in the Coastal 

Plain province of the Southeastern United States. 

The advantages of the method presented herein 

are that it allows a prior selection of the fractile of 

the intensity observations to be considered and that 

it eliminates one subjective step, the contouring inerpretation of the intensity data. Furthermore, the 

dispersion of the intensity values can be calculated. 

Neumann (1954) also presented intensity-versusdistance data in a manner similar to that described 

above. However, Neumann did not consider the intensity distribution for specific distance intervals as 

was done herein, but rather plotted the distance distribution for each intensity level. To illustrate the 

difference in the two approaches, the 1886 earthquake data were cast in Neumann's format (fig. 9). 

MAGNITUDE ESTIMATE 

Nuttli (1973), in arriving at magnitude estimates 

fo·r the major shocks in the 1811-1812 Mississippi 

Valley earthquake sequence, developed a technique 

for correlating isoseismal maps and instrumental 

ground-motion data. Later, he (1976) presented specific amplitude-period (A!T) z values for MM intensities IV through X for the 3-second Rayleigh wave. 

Basically, Nuttli's technique consists of: 

(1) Determination of a relation between (A/T). 

and intensity from instrumental data and isoseismal maps, 

(2) Use of the (A/T) z level at 10-km epicentral distance derived from the mb value for the largest well-recorded earthquake in the region. 

That level will serve as a reference level from 

which to scale other mb magnitudes, 

(3) For the historical event of interest, assign epicentral distances (6.) to each intensity level 

from the isoseismal map for the event. Convert from intensity to (A/T) z, according to 

the relationship of (1) above, then 
30 

(4) 

STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

1886 CHARLESTON, S.C., EARTHQUAKE -INTENSITY DISTRIBUTION 

X~~~------~------------~------------~----------~ 

I I Total observations 

(5) 

r H~l •• I (38) I I I 50 

0 

H HI II. (72) Percent of observations 

I II II at each intensity level ~ 

~ 

z 

>-' 

!::: 

H-i II ~ • I ~~~~~ (94) UJ 

z 

w VI f-

~ 

v I I I I • I I .. 1&1 I (234) 

I I I I I • IRIIDI I ( 164) 

11-111 ....._ ________ ......_ _____ ~ ............. I (173)~----~----------~ 10 100 1000 10,000 

EPICENTRAL DISTANCE, IN KM 

FIGURE 9.-Distribution of epicentral distances (km) for given intensity (MM) levels of the 1886 Charleston 

earthquake. 

Plot (A/T) z versus ~ and fit with a theoretical 

attenuation curve. Next, scale from (2) above 

to determine the ~mb between the historical 

shock and the reference earthquake. 

obtained a value of 6.5 when he used Dutton's isoseismal map and converted from the Rossi-Forel 

scale to the MM scale. If the Trifunac and Brady 

(1975) peak velocity versus MM intensity relationship, derived from Western United States data, is 

In the (A!T). versus intensity of (1) and the taken with the 90-percent fractile distances, then the 

curve fitting of (4), Nuttli found that surface waves mo estimate is 7.

1 (fig. 10). Because the 90-percent 

having periods of about 3 seconds (s) were implied. fractile curve is the most conservative, it results in 

He justified the use of mb (determined from waves the largest intensity estimate at a given distance. 

having periods of about 1 s) by assuming that the The magnitude estimates in this study would be 

corner periods of the source spectra of the earth- upper-bound values. 

quakes involved are no less than 3 s. This implies a My magnitude estimates, as well as those of 

constant proportion between the 1- and 3-s energy Nuttli, are based primarily on three previously menin the source spectra. Nuttli used mb rather than tioned factors: intensity-distance relations, intenM. because he felt that, for his reference earthquake, sity-particle velocity relations, and reference magnithe former parameter was the more accurately tude level (or, equivalently, the reference earthdetermined. quake, which in this instance is the November 9, 

If we apply Nuttli's technique to the 1886 earth- 1968, Illinois earthquake with mb = 5.5). In the Cenquake and use the distances associated with the 90- 1 

tral and Eastern United States, the data base for the 

percent fractile intensity-distance relationship, the I later two factors is very small. It is in this context 

resulting mb estimate is 6.8 (fig. 10) Nuttli (1976) that the magnitude estimates should be considered. 
REINTERPRETATION OF THE INTENSITY DATA 31 

150 

1.3 6 8 

mb =5.5+1.6= 7.1 

(/) 

2 --

2 

~ 100 

~ ..J 

z 

0 

1-

z 

UJ 

z 

0 

Cl. 

2 10 

0 

u 

..J 

<t X u 

;:::: 

a: 

UJ 

2:. 

0 

Q 

a: 

UJ 

Cl. 

--

UJ 

0 

:::> 

1-

:::; 

Cl. 

2 EXPLANATION 

<t • Central U.S. (Nuttli, 1976) 

X Western U.S. (Trifunac and Brady, 1975) 

0.1 

10 100 1000 

DISTANCE, IN KM 

FIGURE 10.-Body wave magnitude (mo) estimates for the 

1886 Charleston earthquake based on Nuttli's (1973, 

1976) technique. Nuttli's Central United States particle 

velocity-intensity data are indicated by solid circles. Trifunac and Brady's (1975) Western United States particle 

velocity-intensity data are indicated by X's. Distances are 

from the 90-percent fractile curve of this study. Heavy 

curve is Nuttli's (1973) theoretical attenuation for the 3-

s Rayleigh wave. Western United States data fit with a 

straight line (light curve). 

CONCLUSIONS 

The intensity data base published by Dutton 

(1889) has been studied, and the principal results 

of that effort are as follows: 

1. The maximum epicentral intensity was X (MM), 

and the intensity in the city of Charleston was 

IX (MM). 

2. The writer verified that Dutton's isoseismal map 

was contoured so as to depict the broad regional pattern of the effects from ground shaking. 

3. 

4. 

5. 

When contoured to show more localized variations, the intensity patterns show considerable 

complexity at all distances. 

The epicentral distance was measured to each 

intensity observation point and the resulting 

data set (780 pairs) was subjected to regression analysis. For the 50-percent fractile of 

that data set, the equation developed was 

I= I o + 2.87- 0.00052a- 2.88 log a 

with a standard deviation ( ur) of 1.2. For the 

90- and 75-percent fractiles, the 2.87 constant 

is replaced by 4.39 and 3.68, respectively. This 

variation of intensity with distance agrees 

rather closely with relationships obtained by 

other workers for the central, eastern, and 

northeastern parts of the United States. It 

thus appears that the broad overall attenuation 

of intensities may be very similar throughout 

the entire Central and Eastern United States. 

Using intensity-particle velocity data derived 

from Central United States earthquakes, the 

writer estimates a body-wave magnitude (mb) 

of 6.8 for the main shock of August 31, 1886. 

However, the data base upon which this estimate is made is very small; therefore, the estimated mb should be considered provisional until more data are forthcoming. Use of Western 

United States intensity-particle velocity data 

produces an mb estimate of 7.1. 

REFERENCES CITED 

Bollinger, G. A., and Stover, C. W., 1976, List of intensities 

for the 1886 Charleston, South Carolina, earthquake: 

U.S. Geol. Survey open-file rept. 76-66, 31 p. 

Cornell, C. A., and Merz, H. A., 1974, A seismic risk analysis of Boston: Am. Soc. Civil Engineers Proc., Structural Div. Jour., v. 110, no. ST 10 (Paper 11617), p. 

2027-2043. 

Dutton, C. E., 1889, The Charleston earthquake of August 

31, 1886: U.S. Geol. Survey, Ninth Ann. Rept. 1887-88, 

p. 203-528. 

Evernden, J. F., 1975, Seismic intensities, "size" of earthquakes and re-lated parameters: Seismol. Soc. America 

Bull., v. 65, no. 5, p. 1287-1313. 

Gupta, I. N., and Nuttli, 0. W., 1976, Spatial attenuation of 

intensities for Central United States earthquake: 

Seismol. Soc. America Bull., v. 66, no. 3, p. 743-751. 

Howell, B. F., Jr., and Schultz, T. R., 1975, Attenuation of 

Modified Mercalli intensity with distance from the epicenter: Seismol. Soc. America Bull., v. 65, no. 3, p. 651-

665. 

Neumann, Frank, 1954, Earthquake intensity and related 

ground motion: Seattle, Wash., Univ. Washington Press, 

77 p. 
32 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

Nuttli, 0. W., 1973, The Mississippi Valley earthquakes of 

1811 and 1812-lntensities, ground motion and magnitudes: Seismol. Soc. America Bull., v. 63, no. 1, p. 227-

248. 

--- 1976, Comments on "Seismic intensities, 'size' of 

earthquakes and related parameters," by Jack F. 

Evernden: Seismol. Soc. America Bull., v. 66, no. 1, p. 

331-338. 

Richter, C. F., 1958, Elementary seismology: San Francisco, 

Calif., W. H. Freeman Co., 768 p. 

Trifunac, M. D., and Brady, A. G., 1975, On the correlation 

of seismic intensity scales with the peaks of recorded 

strong ground motion: Seismol. Soc. America Bull., v. 

65, no. 1, p. 139-162. 

U.S. Environmental Data Service, 1973, Earthquake history 

of the United States: U.S. Environmental Data Service 

Pub. 41-1, rev. ed. (through 1970), 208 p. 

Wood, H. 0., and Neumann, Frank, 1931, Modified Mercalli 

intensity scale of 193~: Seismol. Soc. America Bull., v. 

21, no. 4, p. 277-283. 
The Seismicity of South Carolina Prior to 1886 

By G. A. BOLLINGER and T. R. VISVANATHAN 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, 

EARTHQUAKE OF 1886-A PRELIMINARY REPORT 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1028-C 

CONTENTS 

Page 

Albstract ----------------------------------------------------------------- 33 

Introduction ------------------------------------------------------------- 33 

Data set for the pre-1886 period in South Carolina ------------------------- 33 

Results ------------------------------------------------------------------ 35 

References cited ---------------------------------------------------------- 42 

FIGURE 

TABLE 

ILLUSTRATIONS 

1. Graph showing newspaper and meteorological report coverage for 

the time period 1730-1886 -------------------------------

2. Graph showing population levels in southeastern States, 1790-

1900 --------------------------------------------------- 3-6. Maps showing intensity data for the Charleston, S.C., earthquakes of: 

Page 

34 

35 

3. Alpril 11, 1799 --------------------------------------- 36 

4. January 8, 1817 -------------------------------------- 37 

5. December 19, 1857 ----------------------------------- 40 

6. January 19, 1860 ------------------------------------- 41 

7. Graph showing equivalent number of magnitude 3.0 earthquakes 

(Na) versus time (1836 to Alugust 31, 1886) for South Carolina and nearest States ---------------------------------- 42 

TABLES 

1. Newspapers and meteorological stations whose reports were used 

in this study -------------------------------------------

2. Aluxiliary newspaper references ------------------------------

3. Pre-1886 South Carolina earthquakes -------------------------

4. Felt reports for pre-1886 South Carolina earthquakes ________ _ 

5. 1886 Charleston-Summerville area earthquakes prior to Alugust 

31 ----------------------------------------------------- 6. Maximum intensities of events in South Carolina and neighborPage 

35 

36 

36 

38 

40 

ing States-1836 to Alugust 31, 1886 -------------------- 40 

III 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886-

A PRELIMINARY REPORT 

THE SEISMICITY OF SOUTH CAROLINA PRIOR TO 1886 

By G. A. BOLLINGER 1 and T. R. VISVANATHAN 2 

ABSTRACT 

Archival material on the seismicity of South Carolina 

prior to the great 1886 Charleston earthquake has been 

studied. Data sources consisted of 34 different newspapers, 

meteorological reports from 41 localities in South Carolina, 

4 historical treatises, and 6 previously published earthquake 

catalogs. Study of these data resulted in a list of 18 probable earthquakes between 1698 and 1886, and intensity maps 

for shocks in 1799, 1817, 1857, and 1860. The maximum 

Modified Mercalli intensity (MM) for the pre-1886 events 

appears to be V. 

A comparison of seismic activity in South Carolina with 

that in three neighboring States for the 50 years preceding 

1886 shows 9 events in South Carolina, 5 in Georgia, 7 in 

Tennessee, and 21 in North Carolina. For the five decades 

before the 1886 earthquake, South Carolina's seismic activity does not appear as anomalously high, either in the 

number or energy levels of seismic events. 

INTRODUCTION 

The August 31, 1886, Charleston, S.C., earthquake 

was the single large seismic event in the southeastern United States during the past three centuries. 

Its maximum intensity of X (MM, Modified Mercalli) is a full two levels higher than that of the next 

largest event. Because no comparable shocks had 

been reported since the region was settled by the 

English about 200 years prior to the event, it has 

been stated that the 1886 earthquake took place in 

an aseismic region. 

The purpose of this study is to investigate the 

seismicity of the State of South Carolina prior to 

1886. Because seismological instruments were not 

in use then, this study is necessarily archival. However, copies of newspapers and reports published 

during the rapid development that followed the very 

early settlement of Charleston may contain adequate 

information to specify, at least partially, the pre1886 seismicity. By analysing such data, perhaps we 

1 Virginia Polytechnic Institute and State University, Blacksburg, Va. 2 University of South Carolina, Union, S. C. 

can gain some insight into the nature of the Charleston area's seismic regime. 

This study was supported by State Geology, State 

Development Board of South Carolina, and by 

the National Science Foundation (Grant DES75-

14691). 

DATA SET FOR THE PRE-1886 PERIOD 

IN SOUTH CAROLINA 

The English derived their first knowledge of 

South Carolina from Sebastian Cabot who visited 

the coast in 1497, shortly after the discovery of 

America. D' Ayllon landed on St. Helena Island 

(about 40 km southwest of Charleston) in 1520, 

gave it its name, and claimed the country for Spain. 

In 1562, a settlement by 26 French Huguenots wa.s 

attempted in Port Royal (presumably at the site of 

the modern community having the same name which 

is located about 80 km southwest of Charleston), 

but they returned to France the following year, leaving the area its name, ''Caroline," after their King 

Charles IX. Charles I of England in 1629 granted 

Sir Robert Heath the area under the name, "Carolina." However, the first permanent white settlement 

in South Carolina began in Beaufort (about 75 km 

southwest of Charleston) in 1670 under a grant from 

Charles II of England. That colony moved the next 

year to the west bank of the Ashley River, and a few 

years later (about 1680) to the east bank to occupy 

the present site of Charleston (South Carolina State 

Board of Agriculture, 1883) . 

Microfilm files of early newspapers constituted 

an important data source for this study. The first 

newspaper in South Carolina, The South Carolina 

Gazette, was published in January 1732. It was the 

fifth newspaper in America and flourished for a long 

33 
34 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

time without a rival in South Carolina (South Caroline State Board of Agriculture, 1883). Thirty-four 

newspaper sources were found that contained information concerning earthquake activity. EleYen of 

these gave thorough coverage to the Charleston area 

for the entire pre-1886 period (fig. 1, table 1). The 

other 23 newspapers (table 2) were supplemental 

in that they provided data for shorter, discrete time 

frames or for individual events. 

Other important data sources were meteorological 

reports. These reports, some of which were made as 

early as 1820, were derived from voluntary observers, the hospital staff of the Surgeon General's Office, 

and the Army Signal Corps. During the earlier periods, earthquake reports Wt:. re not necessarily made 

by every observer, but from 1~70 onwards, the Signal Corps urged that particular efforts be made to 

report earthquakes. The coverage, therefore, is more 

complete after 1870. Table 1 lists the names of: the 

41 reporting localities within South Carolina. 

Lastly, four historical treatises and six previously 

published earthquake catalogs or lists were found 

that contributed data pertinent to the pre-1886 period (see "References Cited"). 

A possible relevant factor here is population density. Figure 2 presents the pre-1900 population levels 

YEAR 

1730 40 50 60 70 80 90 1800 10 20 30 40 50 60 70 80 1890 

-2 

-3 

-4 

-5 -----6 

-7 

-8 -----9 

-------------------------~· 10 ---------11 ----------12 

-13 

-14 

-15 

-16 

-17 

-18 

-19 

- -20 

------21 

-22 

--23 

-24 

-25 

-26 

-27 

-28 

-29 

--30 

-31 

-32 

-33 

-34 

-35 

-36 

-37 

-38 

-39 

-40 

-41 

-42 

-43 

-44 

- -45 

-46 

---47 

-48 

-49 

-50 

----51 

FIGURE 1.-Newspaper and meteorological report coverage for the time period 1730-1886. Length of bars indicates the time intervals investigated. Numbers at the right end of each bar are keyed to the list of references given in table 1. 
SEISMICITY OF SOUTH CAROLINA PRIOR TO 1886 35 

CJ) 

~ 2000 

<( 

CJ) 

:::> 

0 

I 

1-

z 

z 1000 

0 

1-

<( 

_J 

:::> 

a.. 

0 

a.. 

---····--- _... 

, ... ·······•· / 

/ .. ···:{_'-{. / ,."!:..····~/ 

".\...j:>..·_ ......... ~-~ ...... 

/ 

./ 

/ 

YEAR 

FIGURE 2.-Population levels in the southeastern States, 1790-1900. Data compiled from the Encyclopedia Britannica (1970, 

14th edition). 

TABLE 1.-Newspapers and meteorological stations whose 

reports were used in this study 

[Newspapers 1-10 were published in Charleston. S. C.] 

Newspaper references 

1. The South Carolina Gazette 1732-1837 

2. Gazette of the State of South Carolina 

3. South Carolina Gazette and Country Journal 

4. Charleston Gazette 

5. South Carolina Weekly Gazette 

6. South Carolina and American General Gazette 

7. Royal South Carolina Gazette 1 

8. Royal Gazette 

9. Charleston Times 

10. Charleston Courier/Charleston News and Courier; 

Charleston Daily Courier/News and Courier 

lL Camden Gazette/Camden JournaljCamden Weekly 

Journal (Camden, S. C.) 

Meteorolog.,-ic-;al,.--;sta-t07io_n_s-;i:-n-;So;-o-u~th-,;C-ai-·o70lin_a _____ _ 

12. Aiken 

13. Allendale 

14. Anderson 

15. Barratsville (Abbeville County) 

16. Batesburg 

17. Blackville 

18. Bluffton 

19. Braddock's Point (Beaufort County) 

20. Camden 

21. Charleston (and nearby points) 

22. Chester 

23. Columbia 

24. Edgefield 

25. Edisto Island 

26. Evergreen (Anderson County) 

27. Florence 

28. Fort Mill (York County) 

29. Georgetown 

30. Gowdysville (Union County) 

31. Greenville 

32. Greenwood 

33. Hacienda Saluda (Greehville County) 

34. Hardeesville 

35. Hilton Head 

TABLE I.-Newspapers and metrological stations whose 

reports were used in this study-Continued. 

Meteorological stations in South Carolina-Continued 

36. Jacksonboro 

37. Kingstree 

38. Kirkwood (Kershaw County) 

39. Limestone Springs (Spartanburg County) 

40. Morris Island (Berkeley County) 

41. Mount Pleasant 

42. Orangeburg 

43. Pacolet 

44. St. George 

45. St. Johns 

46. St. Mathews 

47. Spartanburg 

48. Stateburg 

49. Summerville 

50. Yemassee 

51. Charleston: Abstract of Daily Weather Report 

52. James Kershaw's Diary (Camden) 

for eight of the southeastern States. The population 

in South Carolina, for the most part, lagged somewhat behind that of the seven other States of the 

region. By 1900, the difference was about 30 percent. 

Even so, that disparity was probably not so great as 

to bias the historical data base for South Carolina 

seriously with respect to that for the neighboring 

States. 

RESULTS 

Examination of the above-mentioned data sources 

resulted in a list of 18 probable earthquakes that 

took place between 1698 and 1886 (table 3) and four 
36 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

TABLE 2.-Auxiliary newspaper references 

Augusta Chronicle & Gazette of the State (Augusta, Ga.) 

Augusta Herald (Augusta, Ga.) 

Carolina Spartan (Spartanburg, S. C.) 

Charleston Mercury (Charleston, S.C.) 

Charleston Tri-Weekly Courier/Triweekly Courier 

(Charleston, S.C.) 

Charlotte Bulletin (Charlotte, N.C.) 

City Gazette & Daily Advertiser/City Gazette & Commercial Advertiser (Charleston, S.C.) 

Daily Constitutionalist (August, Ga.) 

Edgefield Advertiser (Edgefield, S. C.) 

Georgetown Gazette (Georgetown, S. C.) 

Laurensville Herald (Laurens, S.C.) 

National Intelligencer (Washington, D. C.) 

Providence Gazette (Providence, R.I.) 

Savannah Georgian (Savannah, Ga.) 

Savannah Republican (Savannah, Ga.) 

South Carolina State Gazette & Timothy's Daily 

Advertiser 

Spartanburg Express (Spartanburg, S. C.) 

Sumter Watchman (Sumter, S. C.) 

The Journal (Milledgeville, Ga.) 

Wilmington Journal (Wilmington, S. C.) 

Winnsboro News & Herald (Winnsboro, S.C.) 

Winnsboro Register (Winnsboro, S. C.) 

Yorkville Enquirer (York, S. C.) 

APRIL 11, 1799 

0 50 100 KILOMETERS 

FIGURE 3.-Intensity data for the Charleston, S.C., 

earthquake of April 11, 1799. Intensities in this figure 

and the following figures are Modified Mercalli intensities. 

new intensity maps (figs. 3-6). In table 4 are excerpts from published felt reports for pre-1886 

South Carolina earthquakes. None of the data (except one report on the earthquake of May 20, 1853; 

see table 4) indicates a level of intensity greater 

than V (MM) for the pre-1886 time period. Because 

so much information has been reported for events 

of intensity V and lower levels, we think that larger 

events are unlikely to have been missed. Thus, the 

TABLE 3.-Pre-1886 South Carolina earthquakes 

Time Maximum Year .Date Locality of InteTh'!ity References occurrrenee 1 (MM scale) 

1698 February Charleston ---------- Felt ---------- McCrady (1897). 

Wallace (1961). 

1754 May 19 ---- Charleston 11:00 ---- Felt _____ , _____ South Carolina Gazette, 

1754, Taber (1914) 

1757 Feb. 07 ---- Charleston ---------- Felt Wallace (1934). 1766 Nov. 23 --- Charleston ---------- (Meu,;~?) ______ R. B. Whorton and R. Clary 

(unpub. data, 1972). 1776 November - Charleston R. B. Whorton and R. Clary 

(unpub. data. 1972). 

1799 April 11 --- Charleston, 03:20 & v ------------ Taber (1914) , this study, 

Camden. 14:55. R. B. Whorton and R. 

Clary (unpub. data 1972). 1816 Dec. 30 ---- Charleston. ---------- Felt ---------- Providence Gazette, January 

Camden ( ?) . 25 1817. 1817 Jan. 08 ---- Charleston (?) 04:00 ---- v ------------ MacCarthy (1957, 1961), this study. 1820 Sept. 03 --- Georgetown ----- 03:00- Felt ---------- Camden G"zette, Septem- 04:00. ber 24, 1820. 1843 April 11 --- Camden --------- ---------- Wallace (1934). 1853 May 20 ---- Lexington ------- AM ------ VI ------------ Camden Journal, May 31, 1853. 1857 Dec. 19 --- Charleston ------ 09:04 ---- v ------------ Coffman and von Hake (1973), Taber (1914) , this studv, R. B. Whorton and R. Clary (unpub. data, 

Charleston 1972), Woollard (1968). 1860 ----- Jan. 19 ---- 18:-19: -- v ------------ MacCarthy (1961). this study. Oct. 22 ---- Abbeville(!) ---- ---------- Felt -----~ ---- Taber (1914), R. B. Whorton and R. Clary (unpub. data, 

1972). Dec. 19 ---- Charleston ------ ---------- Felt ---------- Wallace (1934). 1869 Summer --- ----------------- ---------- Felt ---------- R. B. Whorton and R. Clary 

1876 Dec. 12 ---- Charleston (?) PM ------ (unpub. data, 1972). Felt ---------- Taber (1914), Woollard 

1879 Oct. 26 ---- Winnsboro --·---- 20:00 (1968). 

---- Felt ---------- Woollard (1968). Winnsboro 

News & Herald, October 

29, 1879. 

1 All times are in hours and minutes according to a 24-hour clock; for example, 2:55 p.m. is 14:55. For two shocks, the exact time is not reported, but we do give the hours between which each took place. 
Atlanta 

Felt • 

SEISMICITY OF SOUTH CAROLINA PRIOR TO 1886 

JANUARY 8, 1817 

Winston-Salem 

Felt • 

Washington, 

Fredericksburg e 

III 

VIRGINIA 

Richmonde 

Felt 

Raleigh 

m• 

NORTH CAROLINA 

Milledgeville 

v• 

GEORGIA 

SOUTH CAROLINA 

0 100 200 KILOMETERS 

FiGURE 4.-Intensity data for the Charleston, S.C. (?),earthquake of January 8, 1817. 

37 
38 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

TABLE 4.-Felt reports for pre-1886 South Carolina earthquakes 

Locality 

Augusta, Ga -------------------------

Camden, S. C ------------------------

Charleston, S. C ---------------------

Georgeto~, S. C --------------------

Stateburg, S. C ----------------------

Wilmington, N. C --------------------

Charleston and Camden, S. C ---------

Atlanta, Ga ------------------------- Augusta, Ga -------------------------

Baltimore, Md -----------------------

Charleston, S. C 

Charlotte, N. C ---------------------- Fredericksburg, Va -------------------

Georgeto~, S. C -------------------- Milledgeville, Ga ---------------------

Raleigh, N. C ------------------------

Richmond, Va ----------------------- Salem and New Bern, N. C -----------

Savannah, Ga -----------------------

Washington, D. C --------------------

Winstom-Salem area, N. C -----------

Georgeto~, S. C --------------------

Lexington, S. C ----------------------

Reports and source 

Earthquake of April 11, 1799 

Everyone in the house awakened and alarmed (Augusta Chronicle 

and Gazette of the State, Apr. 27, 1799). 

Windows and furniture rattled; some people left their homes; 

animals frightened; loud rattling noise (South Carolina State 

Gazette & Timothy's Daily Advertiser, Apr. 18, 1799). 

Houses shook, furniture and windows rattled, several people left 

bed (City Gazette & Daily Advertiser, Apr. 12, 1799). 

Very generally felt. Duration about 4 s. (City Gazette & Daily 

Advertiser, Apr. 17, 1799). 

Awoke and alarmed every person in the house; felt throughout 

neighborhood (City Gazette & Daily Advertiser, Apr. 17, 

1799). "* * * a great trembling of the earth"; rumbling noise; felt by 

boats in the river; duration about 30 s. (City Gazette & 

Daily Advertiser, Apr. 27, 1799). 

Earthquake of December 30, 1816 

"Two [earthquakes] are reported to have been felt in Camden, 

two in Charleston both on 30th December 1816 * * *" (Providence Gazette, Jan. 25, 1817). 

Earthquake of January 8, 1817 

Felt (MacCarthy, 1961) -------------------------------------- "A smart shock of an earthquake * * *"; some people awakened 

(Augusta Herald, Jan. 10, 1817). 

Three distinct shocks, each of about 10-s duration, separated by 

about 6 or 8 s (City Gazette & Commercial Advertiser, Jan. 

16, 1817). 

"A pretty severe shock (some say two) * * *"; rumbling noise; 

duration about 30 s (Charleston Courier, Jan. 9, 1817; City 

Gazette & Commercial Advertiser, Jan. 9, 1817). 

Felt by some (Charlotte Bulletin, no date) 

Sensibly felt; rumbling noise (City Gazette & Commercial Advertiser, Jan. 23, 1817). 

Duration about 4 s (Georgetown Gazette, Jan. 11, 1817). 

Felt; bell in state capital building struck several times (The 

Journal, Jan.14, 1817). 

Slight shock, short duration (City Gazette & Commercial Advertiser, Jan. 14, 1817). 

Felt (Providence Gazette, Jan. 25, 1817). 

Felt. "The epi<'enter appears to be quite close to Charleston, S. C." 

(MacCarthy, 1961). 

"A severe shock***"; duration about 30 s (Savannah Republican, 

Jan. 9, 1817). 

Slight but sensible earthquake felt (City Gazette & Commercial 

Advertiser, Jan. 20, 1817). 

Felt (MacCarthy, 1957) --------------------------------------

Earthquake of September 3, 1820 

"Between the hours of 3 and 4 on the morning of 3rd instance 

the shock of an earthquake was sensibly felt by several per- son in Georgetown, S. C. The shock was accompanied by a rumbling noise which was distinctly heard." (Camden Gazette, 

Sept. 24, 1820). 

Earthquake of May 20, 1853 

"An Earthquake: On Friday morning last (20th), just before sun- rise the citizens of Lexington and all the surrounding country were visited with a severe shock, the effects of an earthquake, no doubt followed by a rumbling distant thunder. Some per- sons in the vicinity had window glass broken and others had 

crockery shaken from its lodging and destroyed. The shock was so sensibly felt that many were awakened from sleep." 

(The above re·port was abstracted from the Lexington Telegraph and published by the Camden Weekly Journal, May 31, 

1853). 

intensity 

(MM) 

IV 

v 

v 

IV 

v 

IV 

Felt 

Felt 

IV 

III 

IV 

II 

III 

III 

v 

III 

Felt 

Felt 

IV 

III 

Felt 

Felt 

VI 
SEISMICITY OF SOUTH CAROLINA PRIOR TO 1886 39 

TABLE 4.-Felt Reports for pre-1886 South Carolina earthquakes-Continued 

Loca.Iity 

Augusta, Ga ------------------------- Charleston, S. C ---------------------

Columbia, S. C ----------------------- Georgetown, S. C ---------------------

Moultrieville, S. C. (near Charleston) __ 

Savannah, Ga -----------------------

Augusta, Ga -------------------------

Camden, S. C ------------------------

Charleston, S. C ---------------------

Columbia, S. C -----------------------

Edgefield, S. C -----------------------

Georgetown, S. C --------------------

Laurens, S. C ------------------------

Macon, Ga -------------------------- Savannah, Ga ----------------------- Spartanburg, S. C --------------------

Sumter, S. C ------------------------

Wilmington, N. C --------------------

Winnsboro, S. C --------------------- York, S. C --------------------------

Winnsboro, S. C ---------------------

Reports and source 

Earthquake of December 19, 1857 

Felt by a few people (Daily Constitutionalist, Dec. 20, 1857) ---- Hanging objects swung, doors rattled, felt by everyone in house; 

rumbling noise; duration 6-8 s ( Gibbes, 1859). 

Considerable alarm in some localities where occupants left building; dishes rattled; chandeliers swung; pictures moved; duration about 5 s (Charleston Mercury, Dec. 21, 1857). 

A very decided rocking or shaking of the earth (Charleston Daily 

Courier, Dec. 21, 1857). 

Felt (Carolina Spartan, Dec. 24, 1857) ------------------------ Felt (L. R. Gibbes, paper read in July 1887, pub. in Elliot Soc. 

Science and Art Charleston Proc., 1890, v. 2, p. 153). 

Deep rumbling noise; windows, doors, shutters rattled (News 

and Courier, Aug. 29, 1886). 

Most severe north t>ay; buildings so shaken that all occupants 

rushed into streets (Savannah Republican, Dec. 21, 1857). 

Earthquake of January 19, 1860 

Intensity 

(MM) 

II 

v 

v 

Felt 

Felt 

Felt 

IV 

v 

"A slight shock of an earthquake was felt * * *"; rumbling sound III 

(Daily Constitionalist, Jan. 20, 1860). 

Windows and dishes rattled; duration about a minute; roaring IV 

noise (Charleston Tri-weekly Courier, Jan. 24, 1860). 

"The shock was hard and of considerable duration." Crockery IV 

rattled (Camden Weekly Journal, Jan. 21, 1860). "* * * more violence than any felt or recorded for fifty years."; V 

furniture shaken with papers, letters, etc. thrown out; many 

people alarmed and frightened; more strongly felt in upper 

floors of buildings; in some cases not felt on ground floors or out-of-doors. Duration 20 or 30 s. (Charleston Daily Courier, 

Jan. 20, 1860). 

James Island correspondent report: House shook for a minute as V 

if struck by a locomotive going at full speed; negroes alarmed 

and ran from cabins. (Tri-Weekly Courier, Jan. 24, 1860). "* * * no section of the city seems to have been exempted * * * V 

rumbling noises were heard.'! alarm in some families; duration 

about 15 s; "No shock of equal severity was experienced since 

the shock of the earthquake in 1843 or 44.'' (Charleston Mercury, Jan. 21, 1860). 

Windows and dishes rattled; some people frightened (Spartanburg IV 

Express, Jan. 25, 1860). 

Felt by several people; rattled doors and windows (Edgefield Ad- III 

vertiser, Jan. 25, 1860). 

Duration 10 s or longer (Charleston Tri-Weekly Courier, Jan. 24, Felt 

1860). 

Rocking motions, more pronounced in brick houses; two distinct III 

vibrations separated by a short interval; oscillations east to 

west (Laurens ville Herald, Jan. 27, 1860). 

Felt by some (National lntelligencer, Jan. 21, 1860). II 

Felt by a number of persons (Savannah Georgian, Jan. 20, 1860). III 

Felt by some; perceptible shaking of houses (Spartanburg Ex- III 

press, Jan. 25, 1860). 

Buildings shook; glasses rattled; "The timbers of wooden build- IV 

ings cracked from roof to base in a similar manner as caused 

by moving."; roaring sounds some 5 or 6 s, then vibrations 

for about 10 s,; some people"* * * became momentarily some- what alarmed.'' (Sumter Watchmen, Jan. 24, 1860). 

Felt by many and most distinctly on upper floors; windows IV 

rattled (Wilmington Journal, Jan. 21, 1860). 

Felt by many (Winnsboro Register, no date). III 

"A slight earthquake was felt" (Yorkville Enquirer, Jan. 26, 1860). III 

Earthquake of October 26, 1879 

"An Earthquake: A definite shock of earthquake was felt in Winns- Felt 

boro and its vicinity about eight o'clock on Sunday evening 

(26th). In some localities it sounded like a mere thump or thud. In others, there was a rattling sound lasting several 

seconds.'' (Winnsboro News & Herald, Oct. 29, 1879). 
40 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

DECEMBER 19, 1857 

SOUTH CAROLINA 

Columbia 

Felt • 

Augusta • II 

GEORGIA 

0 

I 

50 100 KILOMETERS 

I 

FIGURE 5.-Intensity data for the Charleston, S.C., earthquake of December 19, 1857. 

TABLE 5.-1886 Charleston-Summerville area earthquakes 

prior to August 31 

Date Time of occurrence 1 Effects 

Spring -------- (PM) Knocked books off shelves at the College Library in Charleston; felt by a few 

people. 

August 27 ____ 01 :30 "Slight"; felt at Summerville 08 :30 "V ?"; felt at Summerville __ Explosive sound; a single jolt or heavy jar ; some ran from houses. A "decided" shock at Sum- merville ; felt by a few 

people in Charleston. 

August 28 ---- 05 :30 Felt at Summerville and by a few in Charleston. 

Sleepers awakened and alarmed in Summerville. 

August 29 ---------- Light tremors, some with sounds at Summerville. 

Reference 

R. B. Whorton and R. Clary (unpub. 

data, 1972). 

Taber (1914). Taber (1914). Dutton (1889). 

R. B. Whorton and R. Clary 

(unpub. data, 

1972). 

Taber (1914). R. B. Whorton and R. Clary 

(unpub. data, 

1972). 

Dutton (1889). 

Taber (1914). Dutton (1889). 

1 All times are in hours and minutes according to a 24-hour clock; for example, 5 :30 a.m. is 05 :30. 

data do not indicate any type of gradual or longterm increase in the numbers and energy levels of 

"precursory" shocks. 

TABLE 6.-Maximum intensities of events in South Carolina 

and neighboring States from 1836 to August 31, 1886 

[Events having no maximum intens:ty reported are assumed to be IV(MM) 

shocks. IV(2) indicates that two shocks of intensity IV occurred in the time interval. Dash leaders, no events reported.] 

Year South North Georgia Tennessee Carolina Carolina (East of 88"W) 

1836-37 ------------ 1938-39 ------------ 1840-41 __________ , __ 

1842-43 __________ ,_- IV IV 1844-45 ------------ IV VI 1846-47 __________ , __ 1848-49 ------------ 1850-51 ------------ IV(2) 1852-53 ------------ VI 1854-55 --·---------- 1856-57 ------------ v 1858-59 ------------ 1860-61 --------·---- V, IV(2) IV IV 1862-63 ------------ 1864-65 ------------ 1866-67 ------------ 1868-69 ------------ IV 1870-71 ------------ IV(2) 

1872-73 ------------ v 1874-75 ------------ VI III, VI IV 1876-77 ------------ IV IV IV,V 

1878-79 ------------ IV IV, V 

1880-81 ------------ IV(2) 

1882-83 ------------ JV(4) 

1884-85 ------------- V, IV(4) III, IV IV 1886 ------------ IV(5) IV 

The total number (18) of pre-1886 events is small. 

As was typical of the region, no earthquake reports 

were made during the Civil War period (1861-

1865). However, a comparison can be made between 

the seismic activity in South Carolina and that in 

the three nearest States during the 50 years preceding 1886. Such a comparison shows 9 events in South 

Carolina, 5 in Georgia, 7 in Tennessee, and 21 in 

North Carolina (Bollinger, 1975). Thus, the seismicity of South Carolina, even when the 1886 period 

prior to August 31 is considered, was not anomalously high with respect to that of its neighbors, as 

can be seen in figure 7 and tables 5 and 6. 

In summary, an extensive archival search effort 

has failed to reveal any indication of the forthcoming large event. However, inadequate knowledge of 

historic earthquakes prior to 1886 has led to the 

notion that the event of 1886 took place in a region 

that was seismically quiet for centuries. South Caro~ 

lina was not aseismic but experienced earthquakes 

on the average of one every 3 years during the 1836-

86 period. Certainly, there were additional felt 

shocks that we failed to uncover at this late date. 

However, the probability is very low that an event 

of intensity VI or higher has been missed. 
SEISMICITY OF SOUTH CAROLINA PRIOR TO 1886 41 

JANUARY 19, 1860 

York 

me 

NORTH CAROLINA 

Macon 

n• 

GEORGIA 

Laurens 

me 

Augusta e 

III 

Winnsboro 

me 

Columbia 

IVe 

SOUTH 

Camden 

.IV 

Sumter 

• IV 

0 

I 

50 

FIGURE 6.-Intensity data for the Charleston, S.C., earthquake of January 19, 1860. 

100 KILOMETERS 
42 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

... (") 

z 

;~ f 

~ -------"'·'~' J ~ · .. ·'···.,····,: .... ~ .. ,·····::' --=-TE-NN. -----..l;itJ......LJ....__ 0 J 0 

1830 40 50 60 

YEAR 

70 80 1890 

FIGURE 7.-Equivalent number of magnitude 3.0 earthquakes 

(N,) versus time (1836 to August 31, 1886) for South 

Carolina and nearest States. Two-year increments were 

plotted (wide bars), except for the year 1886 (narrow 

bar) ; data tabulated in table 6. Conversion of intensity 

(Io, maximum epicentral intensity) to magnitude (M) according to M=1+(2/3) 10 (Gutenberg and Richter, 1956). 

Conversion of M to N3 according to N,=10" 75 <><-,.o> (Allen 

and others, 1965). 

REFERENCES CITED 

Allen, C. R., St. Amand, P., Richter, C. F., and Nordquist, 

J. M., 1965, Relationship between seismicity and geologic 

structure in the southern California region: Seismol. 

Soc. America Bull., v. 55, no. 4, p. 753-797. 

Bollinger, G. A., 1975, A catalog of Southern United States 

earthquakes-1754 through 1974: Virginia Polytech. 

Inst. and State Univ. Research Div. Bull. 101, 68 p. 

Coffman, J. L., and von Hake, C. A., eds., 1973, Earthquake 

history of the United States: U.S. Dept. Commerce, 

Pub. 41-1, (Revised ed., through 1970), 208 p. 

Dutton, C. E., 1889, The Charleston earthquake of August 

31, 1886: U.S. Geol. Survey Ann. Rept. 9, 1887-88, p. 

203-528. 

Gibbes, L. R., 1859, Notice of the phenomena attending the 

shock of the earthquake of Dec. 19, 1857 [Charleston, 

S.C.]: Elliott Soc. Nat. History Charleston Proc., v. 1, 

p. 288-289 (paper read Sept. 1, 1858). 

Gutenberg, B., and Richter, C. F., 1956, Earthquake magnitude, intensity, energy, and acceleration: Seismol. Soc. 

America Bull., v. 46, no. 2, p. 105-145. 

MacCarthy, G. R., 1957, An annotated list of North Carolina earthquakes: Elisha Mitchell Sci. Soc. Jour., v. 73, 

no. 1, p. 84-100. 

---1961, North Carolina earthquakes, 1958 and 1959, with 

additions and corrections to previous lists: Elisha Mitchell Sci. Soc. Jour., v. 77, no. 1, p. 62-64. 

McCrady, Edward, 1897, The history of South Carolina 

under the proprietary government, 1670-1719: New 

York, Macmillan Co., 762 p. (see especially p. 307-308). 

South Carolina State Board of Agriculture, 1883, South 

Carolina. Resources and Population. Institutions and 

Industries: Charleston, S.C., Walker, Evans & Cogswell, 

724 p. (see especially p. 381-83, 529-534). [Reproduced 

in 1972 by The Reprint Co., Spartanburg, S.C.] 

Taber, Stephen, 1914, Seismic activity in the Atlantic Coastal 

Plain near Charleston, South Carolina: Seismol. Soc. 

Buii., v. 4, no. 3, p. 108-160. 

Wallace, D. D., 1934, The history of South Carolina: New 

York, Am. Hist. Soc., 3 v. (see especially v. 3, p. 333-

334). 

---1961, South Carolina, a short history, 1520-1948: 

Columbia, S.C., Univ. South Carolina Press, 753 p. (see 

especially p. 56). 

Woollard, G. P., 1968, A catalogue of the earthquakes in the 

United States prior to 1925; based on unpublished data 

compiled by Harry Fielding Reid and published sources 

prior to 1930: Hawaii Inst. Geophysics Data Rept. 10 

(HIG-68-9). [approx. 156 p.]. 
Recent Seismicity Near Charleston, 

South Carolina, and its Relationship to the 

August 31, 1886, Earthquake 

By ARTHUR C. TARR 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, 

EARTHQUAKE OF 1886-A PRELIMINARY REPORT 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1028-D 

CONTENTS 

Page 

Abstract ----------------------------------------------------------------- 43 

Introduction ------------------------------------------------------------- 43 

South Carolina-Georgia seismic zone ---------------------------------------- 44 

Spatial distribution of earthquakes ------------------------------------- 44 

Temporal distribution of earthquakes ----------------------------------- 45 

Recent seismicity near Charleston ------------------------------------------ 50 

Prior instrumental studies --------------------------------------------- 50 

Reconnaissance study March 1973-December 1973 ---------------------- 50 

South Carolina seismographic network---------------------------------- 52 

Seismicity May 1974-December 1975 ----------------------------------- 52 

Interpretation of results __ _ _ _ _ _ _ _ __ _ _ _ ____ _ _______ _ _____ _ ____ _ _____ __ _ _ ____ 55 

References cited ---------------------------------------------------------- 56 

ILLUSTRATIONS 

Page 

FIGURE 1-3. Maps showing: 

TABLE 

1. Seismicity of the southeastern United States, 1961-75 ___ 45 

2. Seismicity in South Carolina and adjoining States, 1754-

1975 -------------------------------------------- 46 

3. Seismicity in the Charleston, S.C., area, 1754-1972 ______ 47 

4. Graph showing the cumulative number of earthquakes in South 

Carolina versus maximum Modified Mercalli intensity, 1754-

1975 --------------------------------------------------- 49 

5. Map showing the Charleston area seismicity and seismograph stations, March 1973-December 1975 ------------------------ 51 

6. Map showing the South Carolina seismographic network, May 

1974-December 1975 ------------------------------------- 53 

7. Profile of the Middleton Place-Summerville seismic zone ________ 54 

8. Isoseismal map and focal mechanism of the November 22, 1974, 

earthquake --------------------------------------------- 55 

TABLES 

1. South Carolina earthquakes, 1754-1975 ----------------------

2. A. representative South Carolina crustal model ----------------

3. Hypocenter summary ----------------------------------------

Page 

48 

52 

52 

III 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886-

A PRELIMINARY REPORT 

RECENT SEISMICITY NEAR CHARLESTON, SOUTH CAROLINA, AND ITS 

RELATIONSHIP TO THE AUGUST 31, 1886, EARTHQUAKE 

By ARTHUR c. TARR 

ABSTRACT 

The hypocenters of recent earthquakes located in the epicentral area of the intensity-X August 31, 1886, Charleston, 

S.C., earthquake are inferred in this study to be associated 

with the probable source volume of the main shock. The 

hypocenters were determined from data recorded by a 5-

station temporary seismic network which operated near 

Summerville for 8 months in 1973 and by a 10-station permanent seismic network which began operating in May 1974. 

The temporary network revealed an iii-defined cluster of 

activity northwest of Charleston and south of Summerville. 

Earthquakes recorded from May 1974 through December 

1975 by the larger, permanent network defined a linear 

trend of hypocenters which extended northwest from Middleton Place to Summerville and to depths as great as 8 km. 

A well-constrained focal mechanism was determined for the 

largest earthquake in the zone. The strike (N. 42° W.) and 

dip ( 78 o) of one nodal plane are similar to the strike and 

dip of the seismicity. 

The historical catalog of Charleston-Summerville earthquakes shows that the area has experienced declining earthquake activity since the 1886 main shock; however, the 

seismic activity has not yet reached pre-1886 levels. The 

persistence of seismic activity during nine decades and the 

observation that the nearly vertical zone of recent seismicity 

is located near the center of the zone of highest epicentral 

intensities of the 1886 shock, suggest that the Middleton PlaceSummerville zone is closely associated with the rupture surface of the 1886 shock. The results of this study do not 

support a hypothetical connection, along a continuous northwest-trending seismic zone, of the Middleton Place-Summerville seismic activity with activity offshore to the southeast 

or with a persistent cluster of earthquakes near Bowman to 

the northwest. 

INTRODUCTION 

The most destructive earthquake in the history of 

the southeastern United States took place at 9 :51 

p.m. (local time) on August 31, 1886. The shaking 

destroyed much of Charleston, S. C., killed approximately 60 persons, and caused injury to many others 

(Dutton, 1889). Intensity-IX (Modified Mercalli 

scale) effects were observed in Charleston, and a 

maximum intensity of X was reported in the epicentral area, inferred to be near the town of Summerville, 25 km northwest of Charleston (Dutton, 

1889; Bollinger, this volume). The magnitude ( mbLu) 

has been estimated at 6.8-7.1 (Bollinger, this volume). 

The main shock was preceded by several foreshocks (Dutton, 1889; Taber, 1914) and followed 

by an extensive aftershock series (Dutton, 1889; 

Taber, 1914; Bollinger, 1975). The largest aftershock occurred about 8 minutes after the main shock 

and was of sufficiently high intensity that reference 

is made (U.S. Environmental Data Service, 1973, 

p. 25) to the "earthquakes of August 31, 1886.'' The 

catalog of earthquakes of South Carolina (Bollinger, 

1975) shows that the Charleston-Summerville area 

was quite active for at least three decades after the 

main shock. 

Most of the details contained in Dutton's (1889) 

report of the Charleston earthquake do not need to 

be reviewed. For the purposes of this study, however, several facts in the Dutton (1889) report are 

significant: 

1. Personal observations and distribution of damage indicate that the epicenter was nearer to 

Summerville than to Charleston. This fact is 

significant for interpretation of the recent 

seismicity instrumentally located near Summerville and Middleton Place. 

2. The extensive survey of earthquake effects 

showed an elongate, NNE-trending zone of 

highest intensities which, to Dutton, indicated 

the presence of two epicenters. Later, Taber 

(1914) reinterpreted the elongate zone as indicating the presence of a buried NNE-trending fault passing under Woodstock, a railroad 

stop 10 km southeast of Summerville. 

43 
44 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

3. Dutton's (1889) survey of intensities (reevaluated by Bollinger, this volume) throughout the 

Eastern United States showed that the area in 

which the earthquake was felt was very large 

and that major geological features (for example, the Appalachian Mountains) strongly 

affected the intensity pattern. 

The 1886 shock is very important for earthquake 

hazards studies (see, for example, Algermissen and 

Perkins, 1976) because it took place within an intraplate region characterized by infrequent earthquakes of relatively small and moderate magnitudes. 

In terms of damage and the size of the area in 

which it was felt, the shock ranks with the 1663 St. 

Lawrence Valley, 1755 Cape Ann, and 1811-1812 

Mississippi Valley shocks as the most significant in 

the Eastern and Central United States. The characterization of recent earthquake activity near 

Charleston and the relationship of the activity to the 

South Carolina-Georgia seismic zone are the principal topics of this chapter. Incorporated herein are 

the results of seismological studies conducted in the 

Charleston area by the U.S. Geological Survey during the period 1973 through 1975. 

Support for this study was provided by the 

Atomic Energy Commission and the Nuclear Regulatory Commission, Office of Nuclear Research, under Agreement No. AT(49-25)-1000. 

The efforts of Kenneth W. King in the design, installation, and operation of the South Carolina seismograph network and of David L. Carver in seismogram analysis and data processing activities were 

particularly important contributions to this study. 

The critical review of the manuscript in its early 

stages by Margaret Hopper, Charley Langer, and 

Frank McKeown and the continually fruitful collaboration and support of G. A. Bollinger and Pradeep Talwani are gratefully acknowledged. 

SOUTH CAR OLIN A-GEORGIA SEISMIC ZONE 

SPATIAL DISTRIBUTION OF EARTHQUAKES 

The South Carolina-Georgia seismic zone is a 

broad band of seismicity that extends southeastward from the southern Appalachian seismic zone 

across most of South Carolina and northeastern 

Georgia (fig. 1). The zone is mapped on the basis 

of information from Bollinger's (1975) earthquake 

catalog, which is a listing of hypocenter coordinates, 

intensities, and (or) magnitudes (if determined) 

of earthquakes that took place in the time period 

1754-1974. The catalog has been supplemented by 

new information on several pre-1886 shocks (Bollinger and Visvanathan, this volume) and by instrumentally recorded information on earthquakes 

which took place in 1975 (Carver and others, 1977). 

The Bollinger (1975) catalog lists both macroseismic epicenters and instrumental hypocenters for 

the southeastern United States. Macroseismic epicenters are qualitative estimates of earthquake locations inferred from one or more subjective intensity observations. Instrumental hypocenters are 

quantitatively determined from precisely timed arrivals of P- and S-waves of earthquakes recorded by 

at least four seismograph stations. 

A rectangle approximately 500 km long and 350 

km wide defines the South Carolina-Georgia seismic 

zone in this study. Its long axis (A-A') is oriented 

northwest-southeast, perpendicular to the southern 

Appalachian seismic zone (fig. 1), and the rectangle is similar in shape and orientation to Bollinger's 

(1975) definition of the zone. 

The largest South Carolina and northeast Georgia 

earthquakes, in addition to several clusters of significant seismic activity, are enclosed by the rectangle. These clusters are located in the CharlestonSummerville area, in the Orangeburg-Bowman area, 

and in the vicinity of Clark Hill Reservoir (figs. 1 

and 2). 

Previously, several workers (Woollard, 1969; Bollinger, 1973; Sbar and Sykes, 1973) noted that the 

South Carolina-Georgia seismic zone appears to 

trend northwest, perpendicular to the trend of the 

southern Appalachians in eastern Tennessee and 

western North Carolina (fig. 1). The axis (A-A') 

of the seismic zone, inferred from an alinement of 

well-determined epfcenters of earthquakes which 

took place in the period 1961-1975, is a northwesttrending line that passes near Greenville, Columbia, 

Orangeburg, and Charleston (fig. 1). The axis A-A' 

is the approximate center line of the rectangle defining the seismic zone (fig. 1) ; extension of the 

axis to the southeast and northwest connects several 

epicenters on the Continental Shelf and the epicenter of the eastern Tennessee earthquake of November 30, 1973 (Bollinger and others, 1976). 

Figure 3 is a map showing epicenters of earthquakes that took place in the Charleston area prior 

to the initiation of U.S. Geological Survey seismological studies there in 1973. The distribution of epicenters of the 1886 earthquake, of its aftershocks, 

and of subsequent activity is mapped in figure 3 

and suggests the presence of a source area northwest of Charleston and near Summerville. However, 
RECENT SEISMICITY AND ITS RELATIONSHIP TO EARTHQUAKE 45 

100 150 200 KILOMETERS rr- I I I 

: I EXPLANATION I 

• I ! Modified Mercam (MM) ELT 

-----~ intensity 1-11 Ill IV v VI 

-- J 

l I Macroseismic 0 0 0 0 ~----

FLORIDA Instrumental • • • • • 

FIGURE I.-Seismicity of the southeastern United States, 1961-75. Figure shows the relationship of the South 

Carolina-Georgia seismic zone to other seismicity in the southeastern United States. The axis A-A' is the 

approximate center line of the rectangle defining the South Carolina-Georgia seismic zone. Numbers beside 

the epicenter symbols show the number of events recorded. The macroseismic epicenters were determined 

from accounts of damage and felt reports, whereas instrumental epicenters were determined from seismographic data. 

a more precise location of the source area is virtually impossible because of the inherent inaccuracies 

in the macroseismic observations used to locate the 

historical epicenters. 

TEMPORAL DISTRIBUTION OF EARTHQUAKES 

The temporal aspects of earthquake statistics are 

conventionally represented by the Gutenberg and 

Richter (1944) relationship 

log N=a+bM (1) 

where N is the number of earthquakes recorded 

during time interval T, M is a magnitude (such as 

ML, mb, M s, or mbLu), and a and bare constants. The 

number N may be either incremental number N1 (M) 

where Nr is the number of earthquakes having magnitude in the interval 

or cumulative number Nc (M) where Nc is the number of earthquakes having magnitude greater than 

or equal to M. The functional relationship (1) is 

identical for either N1 or Nc; only the constants a 

and b are different in the equivalent representations. 

The fit of equation (1) to a plot of log N versus 

M is a straight line and yields a value for the slope 

b, a negative number that varies with the source 

region (Utsu, 1961; Karnik, 1969), the type of 

earthquake process (swarm, aftershock, or ambient 

(secular) activity) (Utsu, 1961; Page, 1968), and 

possibly, even with time itself. A relationship 

log N=A+Blo (3) 

analogous to ( 1) is used when magnitudes are not 

available but maximum intensities Io are (Karnik, 

1969; Bollinger, 1973). 

8M 8M M--L-M<M+- (2) Many difficulties exist in the use of the historical 

2 2 South Carolina earthquake catalog as a sample for 
46 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

I 

34° ~ G.2, 1974 

I . ... \ 

0 "-, 

I 0 

GEORGIA 

0 .. , 

33°L 

0 "'\ ©l ' 

r 

0 I 

I 

I 32"L - _L 

SOUTH 

0 

-

NORTH 

0 

0 

CAROLINA 

.Orangeburg 

0 Bowman° • 

80" 

I 

CAROLINA 

• 

7'!' 

0 0 

0 

I 

I 

50 100 KILOMETERS 

78" 

' 

I 

\ 

·~ 

I 

~ 

EXPLANATION 

FELT 

MM Intensity 10 I-ll Ill IV v VI VII VIII IX X 

~ Macroseismic 0 0 ooooooo ~~ ~~ 

·····-- c. 

w Instrumental • • 

Magnitude* 1 :Y:r-2 Y, 3 3% 4'/, 5 5% 61;3 7 7% 

*M=1+%/o 

FIGURE 2.-Seismicity in South Carolina and adjoining States, 1754-1975. Earthquakes are indicated by circles of varying 

sizes, which represent the maximum Modified Mercalli intensities shown in the explanation. Numbers beside the epicenter symbols show the number of events recorded. Earthquakes are from the catalog of Bollinger (1975), supplemented by earthquakes reported by Carver and others (1977) and Bollinger and Visvanathan (this volume). 

statistical treatment. Questions exist regarding (1) 

the accuracy of the values of maximum intensity 

Io for the historical shocks (Were maximum intensity effects always reported to newspapers and other 

data sources if population densities were low in the 

epicentral area?), (2) the completeness of the catalog (Could significant numbers of seismic events, especially of lower Io events, have been missed because 

of low population densities or inadequate repo·rting?), and (3) the size of the data sample (Is it 

sufficiently free from fluctuation to be characterized 

by equations (1) or (3) ?) . 

In order to determine the constants in a frequency-maximum intensity relationship of the form 
RECENT SEISMICITY AND ITS RELATIONSHIP TO EARTHQUAKE 47 

81°00' 

33°30' 

CLARENDON t' 

0 R A N G E B U R G \ '-../'~ 

• r 0 Bowman 

, e./\ I 

80°00' 

'- WILUAMSBURG / 

"'> '- / 

"\ / \.. -l GEORGETOWN 

'-"' A B E R K E L E Y '\.,. / ..... ---"' / 

\ / \ 

BAMBERG~ ~ / " < 

( \ DORCHESTER ' " '\. 

_.,....,) ' 

I 

/CHARLESTON 

33°00'1-------------+----::-::cf-C--iif'llk-~---:+++-+-----...:...'-------j~!'!'O' J 

COLLETON 

' 

\ 0 

~AMPTO~~ 

( < --~ ./ \ 1 

I BEAUFORT 

EXPLANATION 

FELT 

MM Intensity /

0 I-ll Ill IV V VI VII VIII IX X 

Macroseismic 0 0 0 

Instrumental ••• 

Magnitude* H':.-2'13 3 3% 4';3 5 5% 6';3 7 

*M=1+%/0 

/ Approximate zone of highest intensity of 

I the 1886 earthquake (from Bollinger, this volume) 

FIGURE 3.-Seismicity in the Charleston, S. C., area, 1754-1972. Data are from the same catalogs as in figure 2. The 

earthquakes shown are principally, but not exclusively, macroseismic epicenters. Numbers beside the epicenter symbols 

show the number of events recorded. 

of equation (3), several assumptions have been 

made: (1) the information in table 1 is complete in 

listing earthquakes of the highest intensities down 

to those of an intensity level where the cumulative 

number departs from the straight-line relationship 

by 10 percent or more; (2) searches of data sources, 

such as those by Bollinger (1975) and Bollinger and 

Visvanathan (this volume), have been exhaustive; 

(3) all large and moderately large events were reported to newspapers and other data sources; and 

( 4) population densities in South Carolina were sufficently high that reports were made on all events 

having intensities stronger or equal to the intensity 

where the cumulative number departs from the 

straight-line relationship by 10 percent or more. 

The Bollinger (1975) catalog is used and is supplemented by information on pre-1886 events (Bollinger and Visvanathan, this volume) and on several 

events in the instrumental catalog of Carver and 

others ( 1977) which were felt. The catalog entries 

have been separated according to incremental maximum intensity class and decade of occurrence for 
48 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

TABLE 1.-South Carolina earthquakes, 1754-1975 

[C.-S., Charleston-Summerville area; S.C., South Carolina exclusive of Charleston-Summerville area. Leaders ( ___ ) indicate no earthquake reported, Data from Bollinger (1975), Carver and others (1977), and Bollinger and Visvanathan (this volume).] 

Maximum Modified Mercalli intensity 

I- II- III- IV- V- VI- VII- VIII- IX- Felt II II III III IV IV V V VI VI VII VII VIII VIII IX IX X X Total 

1750-60: 

C.-S. 

S.C. 

1760-70: 

C.-S. 

S.C. 

1770-8\l: 

C.-S. 

S.C. 

1780-90: 

C.-S. 

S.C. 

1790-1800: 

C.-S. 

S.C. 

1800-10: 

C.-S. 

S.C. 

1810-20: 

C.-S. 

S.C. 

1820-30: 

C.-S. 

S.C. 

1830-40: 

C.-S. 

S.C. 

1840-50: 

C.-S. 

S.C. 

1850-60: 

C.-S. 

S.C. 

1860-70: 

C.-S. 

S.C. 

1870-80: 

C.-S. 

S.C. 

1880-90: 

C.-S. 

S.C. 

1890-1900: 

C.-S. 

S.C. 

1900-10: 

C.-S. 

S.C. 

1910-20: 

C.-S. 

S.C. 

1920-30: 

C.-S. 

S.C. 

1930-40: 

C.-S. 

S.C. 

1940-50: 

C.-S. 

S.C. 

1950-60: 

C.-S. 

S.C. 

1960-70: 

C.-S. 

S.C. 

1970-75: 

C.-S. 

S.C. 

Total: 

c.s. 

S.C. 

2 

1 

1 

2 

1 

1 

1 

1 

1 

3 

1 

1 

1 

155+ 

72+ 

51 

16 

1 

2 

10 

3 

12 

1 

4 

3 

4 

1 

335+ 

17 ---

1 5 

2 

1 5 2 

1 

2 

2 

6 

1 

2 

2 

12 

4 

5 

1 

2 

6 

2 

1 

1 

1 

4 

3 

1 

3 

4 

10 

1 

6 

1 

1 

2 

7 

1 

1 

1 

1 

1 

1 

1 

2 

1 

1 

1 

3 

1 

1 

7 ---

9 1 

1 

2 

1 

1 

1 

1 

4 

3 

1 1 1 

1 

1 

2 1 

1 

1 The principal aftershock of the August 31, 1886, main event is assumed to have been intensity VIII. 

2 

1 

1 

3 

2 

1 

1 

1 

1 

1 

1 

4 

1 

1 

1 

1 161+ 

72+ 

58 

28 

12 

9 

5 

13 

3 

13 

2 

6 

6 

6 

10 

3 

7 

1 382+ 

54 

Grand 

Total 

2 

1 

4 

3 

1 

2 

2 

5 

2 

161+ 

72+ 

58 

40 

14 

16 

15 

12 

16 

10 

436+ 
<:." 

c£ 

w 

Cil 

~ 

:J 

z 

w 10 > F 

~ :J 

~ 

:J 

u 

RECENT SEISMICITY AND ITS RELATIONSHIP TO EARTHQUAKE 

F.ELT 

0 

Ill IV v 

0 

VI 

EXPLANATION 

• Charleston-Summerville area 

Q South Carolina exclusive of 

Charleston-Summerville area 

Nc =1QI2.35--0.25/o) 

• 

VII VIII IX 

MAXIMUM INTENSITY, / 0 

X 

FIGURE 4.-Graph showing the cumulative number (N,) of earthquakes in South Carolina versus maximum 

Modified Mercalli intensity (/o), 1754-1975. The data, taken from table 1, are separated into two regional 

sets. Felt earthquakes are added at the intensity-11 level. Symbols in parentheses are interpolated points. 

The Charleston-Summerville data set appears to be complete down to lo=III, and the South Carolina data 

set appears to be complete down to lo=IV, if the anomalous value of N, at lo=V-VI is ignored. 

49 
50 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

two groups, Charleston-Summerville area events and 

South Carolina exclusive of Charleston-Summerville 

events (table 1). Table 1 gives the incremental numbers for the two groups and for the combined South 

Carolina total group. Events for which no intensity 

was assigned in the Bollinger (1975) catalog are 

classified as "Felt" in table 1. 

The Nc vs. Io graph (fig. 4), constructed from the 

incremental numbers of earthquakes having assigned intensities in table 1, shows relatively linear 

behavior to about intensity III for Charleston-Summerville events and to about intensity IV for other 

South Carolina shocks. These intensity values are 

assumed to be the levels at which the information in 

table 1 is complete. The paucity of events at lower 

intensities is probably caused by reduced potential 

for perception. According to figure 4, the perceptibility threshold in the more populated CharlestonSummerville area is apparently at least one intensity 

degree smaller than that in the more rural areas of 

South Carolina. 

The catalog may be complete to intensity levels 

slightly lower than the values cited above. For example, if it is assumed that all events in the "Felt" 

class of the South Carolina exclusive of CharlestonSummerville group were intensity-IV shocks, then 

that group is complete to no lower than intensity IV 

because the cumulative number of "Felt" events is 

less than the number expected from the straightline fit at higher intensities. Conversely, if it is assumed that the "Felt" events of the CharlestonSummerville group were intensity-II shocks or 

stronger, the cumulative number greatly exceeds 

the number expected from the straight-line fit at 

higher intensities. Clearly, the hundreds of aftershocks following the August 31, 1886, earthquake 

cause the slope of the Nc vs / 0 graph of the aftershock series to be steeper than that of the graph of 

ambient seismicity. 

Bollinger (1972) found a B value of -0.3 for 

South Carolina earthquakes, exclusive of CharlestonSummerville events, that took place in the period 

1886-1971. This B value is low compared to B values 

of earthquakes in other seismic zones in the East, 

and it implies a paucity of small events relative to 

large events during that 86-year period. Figure 4 

suggests that a B value of -0.44 is appropriate for 

the data set of earthquakes in South Carolina exclusive of Charleston-Summerville during 1754-

1975. 

RECENT SEISMICITY NEAR CHARLESTON 

PRIOR INSTRUMENTAL STUDIES 

Only two instrumental studies of seismicity of the 

lower Coastal Plain were conducted prior to the beginning of the seismological program described in 

this chapter. Bollinger (1972) monitored microearthquakes in the Summerville area during the 

summer of 1971 and recorded 61 events, about half 

of which were clustered in swarmlike groups. Although no epicenter locations were possible from 

these single-station recordings, a b value of 

-1.8 ± 0.5 was determined from his microearthquake data set. 

McKee (1973) monitored microearthquakes in the 

Bowman area in 1972 and 1973 and obtained a b 

value of -0.5 for seven events. McKee (1973) noted 

that this b value compares favorably with b =-0.5 

determined by Bollinger (1972) for all South Carolina earthquakes, exclusive of the 1886 aftershock 

series. 

Although these two studies demonstrated that 

small earthquakes were taking place in the Summerville and Bowman areas, they were severely 

limited in their scope. The need for additional seismological studies in South Carolina, and more specifically, the need for a seismic monitoring capability 

to locate local earthquakes provided the initial justification for a seismic program that included the design, installation, and operation of a 10-station seismograph network in South Carolina. 

RECONNAISSANCE STUDY MARCH 1973-

DECEMBER 1973 

A reconnaissance seismicity study was conducted 

during 1973 for 8 months in the Charleston-Summerville area for the purpose of gaining experience 

in the problems of operating seismograph stations 

in the environment of the lower Coastal Plain while 

procurement and fabrication of the permanent 

South Carolina network stations were underway. 

The field instruments, which included both vertical and horizontal seismometers, were deployed at 

five sites near Charleston. The data were transmitted by short radio-telemetry links to a recording site near Charleston where the seismic signals 

from different stations were recorded simultaneously with a time signal on magnetic tape and visual 

drum-type recorders. Operating magnifications were 

relatively low because of poor site conditions. 

Nevertheless, a loose cluster of eight earthquakes 

was located northwest of Charleston (fig. 5). 
RECENT SEISMICITY AND ITS RELATIONSHIP TO EARTHQUAKE 51 

81 ' 00' 80'00' 79'30' 

"Orangeburg ClARENDON (" '---..;or 

r 

0 R A N G E B U R G 

• 

' I '> WILLIAMSBURG/ ff 

\.. .c....o 

'\ / f 

' • BoMna~ /\ I 

" / ' --..!\' / 

0 

\.~ § 

'"'"'-

\ / SGS \ 

BAMBERG ~ -.J.r ~ MKC{;r 

B E R K E L E Y 

/ " ( 

\ ( \ \. DORCHESTER ' '\. 

v '---~ 

1 

COLLETON 

' \ 

HAMPTON\ '( t-~~ ./ ' l 

I 

JASPER 25 

EXPLANATION 

SEISMOGRAPH STATIONS 

{;r 1973 only (temporary) 

-.J.r 1973-1975 (permanent) * 1974-1975 (permanent) 

EARTHQUAKE EPICENTERS 

0 

(, 

50 KILOMETERS 

Mar. 1973-0ec. 1973 000000 

May 1974-0ec. 1975 ···-·· Duration magnitude ? 0 1 2 3 4 

/ 

Approximate zone of highest intensity of the 

1886 earthquake (from Bollinger, this volume) 

FIGURE 5.-Charleston area seismicity and seismograph stations, March 1973-December 1975. The earthquake at Middleton 

Place is represented by its focal mechanism. Profile B-B' is shown on figure 7. Seismograph station abbreviations, coordinates, and instrumentation are discussed by Carver and others (1977). 
52 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

TABLE 2.-A representative South Carolina crustal model 

Compressional Shear Depth to top Thickness velocity (Vp) velocity Layer of layer (km) (km) (km/sec) (V ,) (km/sec) 

1 ---------- 0.0 1.2 2.5 1.4 

2 ---------- 1.2 2.3 5.8 3.3 

3 ---------- 3.5 28.5 6.2 3.5 

Half space - 32.0 8.2 4.6 

Program HYP071 (Lee and Lahr, 1975) was 

used for hypocenter computations. A representative 

crustal model assumed three layers on a half space 

(table 2). A summary of hypocenter locations, 

depths, and times is given in table 3. 

The reconnaissance survey demonstrated, as had 

Bollinger's (1972) survey, that low-level seismic activity was indeed taking place near Summerville 

and furthermore, that the activity was located near 

the inferred location of the 1886 earthquake and 

aftershocks. However, it was not possible to discern whether the cluster represented a small source 

area or was only a segment of a longer zone of activity that extended beyond the network perimeter. 

This difficulty is due to the tendency for more 

smaller earthquakes to be detected and located near 

the center of a network (where the detection threshold is lowest) than in the area outside the network 

(where the detection threshold increases). 

SOUTH CAROLINA SEISMOGRAPHIC NETWORK 

The design of the South Carolina network and the 

objectives of the seismological program have been 

discussed by Tarr and King (1974). One of the 

principal objectives of the program was ,to monitor 

the South Carolina-Georgia seismic zone and provide, for the first time, an instrumental data base 

for earthquakes in the zone. Ten stations were installed in the Coastal Plain astride the hypothetical 

northwest-trending axis of the seismic zone. Stations were spaced 50-100 km apart at the northwestern end of the network to insure wide areal 

coverage and 30-60 km apart at the southeastern 

end where a lower detection threshold was desirable. 

A nominal three-station detection threshold of 

ML=2.5 or better was estimated for the area 

hounded roughly by the cities of Columbia, Sumter, 

Georgetown, Charleston, Beaufort, and Aiken. 

The 10-siation network became operational in 

May 1974. All data channels were radio-telemetered 

to a central site at Columbia where all the signals 

were recorded on 16-mm film and magnetic tape, 

and where three channels were recorded on visual 

drum-type recorders for monitorbg purposes. The 

network configuration was altered slightly in 1975 

to locate more accurately aftershocks of the August 

2, 1974, earthquake at Clark Hill Reservoir; however, the network that was operative during the occurrence of most of the earthquakes discussed in the 

next section is shown in figure 6. 

SEISMICITY MAY 1974-DECEMBER 1975 

Between May 1974 and December 1975, earthquakes in the South Carolina-Georgia seismic zone 

were recorded and located by the use of data from 

TABLE 3.-Hypocenter summary 

[Leaders ( ____ ), insufficient data for computation I 

Origin 

time Number 

(Universal of Coordinated RMS 1 Latitude ERY" Longitude ERX 3 Depth ERZ• Duration 5 observa- Date Time) (sec) (degrees) (km) (degrees) (km) (km) (km) magnitude tions 

1973 

March 25 04 29 31.6 0.11 32.953N. 80.080W. 0.9 4 

April 18 10 0610.7 . 56 33.044N . 80.190W. 2.5 4 

23 2132 38.2 . 38 33.012N . 80.280W. 3.3 4 

June 9 19 24 52.7 . 29 32.942N. 0.7 80.153W . 1.5 3.5 395.6 9 

12 20 45 25.0 .29 33.018N. 1.2 80.168W. 1.8 3.7 496.8 6 

August 25 09 17 30.1 .27 32.944N. .5 80.186W. .9 5.7 4.3 7 

November 13 15 10 03.0 . 05 32.945N . 80.205W. 1.3 4 

December 19 10 16 18.3 33.008N. 80.275W. 8.3 4 

1974 

May 28 05 0136.1 0.22 33.388N. 1.0 80.697W. 0.9 3.6 268.7 1.6 12 

September 2 08 54 47.0 . 33 33.053N. 79.742W . 2.6 4 

November 22 05 25 55.8 .15 32.902N. .9 80.147W. 2.0 4.1 261.0 3.8 6 

22 06 22 43.9 .35 32.874N. 1.7 80.145W. 4.4 2.2 541.8 2.6 7 

1975 

April 28 05 46 52.3 0.04 32.986N. 0.2 80.215W. 0.3 3.7 63.9 3.0 7 

1 RMS: Root-mean-square of travel time residuals 2 ERY: Standard error in latitude 3 ERX: Standard error in longitude 4 ERZ : Standard error in depth 5 Duration magnitude is an estimation of Richter magnitude M found by M=::0.87+2.00 log (T) +0.0035 l1 where T is signal duration in seconds 

and l1 is epiicentral distance in kilometers (see Lee, Bennett, and Meagher, 1972) 
RECENT SEISMICITY AND ITS RELATIONSHIP TO EARTHQUAKE 53 

82" 80" 7'!' 

I 

I 

36"84. -- 83" I n' c;;rTENNESSEE J -r ,.r ,~--._/" 

78" 

j NORTH 

35" -~~-- ---v"' __ ...J'I- ---+----_-_ --+_"~-- ~-t- ,' I 

CAROLINA 

I Greenvilie0 ~-----

, 

'"-. 

34° 

' ' 

SOUTH CAROLINA 

' ' " ' ' " ' ' 

/ 0 Sumter 

GVS / OSC •SMA 

A 0 Aiken :.:.:----

GEORGIA Orangeburg 0 ~ 

\~.PBS •sGS 

3J• f------

31"''---------_l_ 

50 100 KILOMETERS 

EXPLANATION * Central recording site 

• Vertical seismometer 

0 Horizontal seismometer 

- Radio telemetry link 

FIGURE 6.-South Carolina seismographic network, May 1974-December 1975. Seismograph station abbreviations, coordinates, 

and instrumentation are discussed by Carver and others (1977). 

the 10-station network. Although the region of uniform detection threshold is quite large, most of the 

earthquakes detected and located were concentrated near Summerville (table 3). The most important of the shocks outside the Charleston-Summerville area was the August 2, 1974, Clark Hill 

Reservoir earthquake (fig. 1). This event and its 

aftershock sequence have been described by Talwani 

and others (1975) and need not be discussed further. Another significant event took place on May 

28, 1974, and was located near Bowman (fig. 1). 

Epicenters of earthquakes taking place in the 

Charleston-Summerville area tend to cluster about 

20-25 km northwest of Charleston and about 0-10 

km south of Summerville, near Middleton Place and 

near the cluster of small earthquakes recorded by 

the five-station network in the reconnaissance study 

of 1973 (fig. 5). 

Figure 5 shows that the seismic activity of the 

3-year period is confined principally to a zone between Middleton Place and Summerville. The zone 

of epicenters seems to trend northwest, and the 

depth section shows that the activity is in the depth 

interval 1-8 km (fig. 7). Although the epicenter co-
54 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

8 8' 

0 I I I I I I I I I 2.5 km/s I 

I • 

• I 

I 1- • I -

5.8 km/s 2 

I • -- I --- • I (/) 

a: -- UJ 4 tJ 

:2: 

0 

1-

-- --.-~- - • -

...J 

i2 

~ 

~ 6 w 

0 

8 

1-

fI I I 2 4 6 

I 

I 

I 

I 

I 

I 

I 

I 

• 

I 

8 

I --- --

• -

6.2 km/s 

-

I I I I 

10 12 14 16 18 

DISTANCE, IN KILOMETERS 

EXPLANATION 

< 1.0 

• 

or ? 1.0-1 

• 

.9 2.0-2.9 

• 

3.0-3.9 • 

Duration magnitude 

FIGURE 7.-Profile of the Middleton Place-Summerville seismic zone. Hypocenters are projected onto a vertical plane passing through B-B', which is shown in figure 5. The plane B-B' is perpendicular to the 

strike of the two nodal planes (dashed lines) determined for the November 22, 1974, earthquake (fig. 8). 

The upper layers of the crustal model, used in the hypocenter computations, are shown by horizontal interfaces and compressional (P) velocities. 

ordinates are well determined, the vertical extent of 

the zone cannot be known with comparable certainty because of large errors in the estimates of depth 

(table 3). The absence of seismograph stations close 

to the seismic activity is the principal reason for the 

lack of depth control. The largest earthquake of the 

period had a magnitude ( mbLu) of 3.8 and took place 

on November 22, 1974; its focus was very near Middleton Place at a depth of about 4.1 km. Despite the 

relatively small magnitude of this earthquake, it was 

widely felt in South Carolina (fig. 8A). 

A focal-mechanism solution was determined from 

13 short-period P-wave first-motion observations 

of the November 22, 1974, event (fig. 8B). Eight of 

the first-motions of the aftershock recorded by 10 

network stations are consistent with the first motions of the main shock. One of the permissible focal-mechanism solutions, in which all observations 

are consistent, is shown in figure 8B. The B- (null-) 

axis in this solution is horizontal and parallel to the 

strike of the two planes. The strike (N. 42° W.) of 

the preferred (A) nodal plane is well-constrained 

by observations from stations both within and outside the seismic network. The dip (78°) is controlled 

by the position of the auxiliary (C) nodal plane. 

The profile B-B' in figure 7 is oriented perpendicularly to the B-axis and, hence, the two nodal planes 

are viewed end-on in the figure. Uncertainties in 

hypocenter coordinates and permissible variations 

of the crustal velocity model allow for slightly different nodal plane orientations than the ones shown 

in figure 8B. 
RECENT SEISMICITY AND ITS RELATIONSHIP TO EARTHQUAKE 55 

83° 82° 81° 

0 

0 4 

0 

Cha rlotte 0 

35° 0 0 

0 

0 0 

0 

0 CAROLINA 

34° 

0 

0 

0 

0 

0 

GEORGIA 

0 

0 

0 

0 

0 

3 0 0 

0 

EXPLANATION 

-t/ Epicenter 

4,1V MM intensity 

o Not felt 

A 

31° 

80° 79° 

N 0 R T H CARO LINA 

0 0 0 

0 

0 c 0 

0 

0 0 0 

0 

0 

0 

0 

78° 

0 

0 

0 

0 

0 

0 

0 0 

o 0 

0 

EXPLANATION 

• Compressional first-motion 

o Dilatational first-motion 

X Uncertain first-motion 

P Compression axis 

T Tension axis 

A,C Poles of nodal planes 

B Null axis 

FIGURE 8.-Isoseismal map (A) and focal mechanism (B) of the November 22, 1974, earthquake. Figure (modified from fig. 

11 of Stover and others, 1976) depicts interpretations of Modified Mercalli intensities from questionnaire canvass of 

postmasters in the area. Maximum intensity was VI. 

INTERPRETATION OF RESULTS 

The seismological studies conducted from 1973 

through 1975 have provided new information about 

the South Carolina-Georgia seismic zone near 

Charleston. Our data suggest that the small but 

persistent zone of seismic activity between Middleton Place and Summerville may be associated with 

the source volume of the 1886 Charleston earthquake. In additiO'Jl, the Middleton Place-Summerville zone appears to coincide with anomalous seismic velocities of shallow-layered structures under 

Middleton Place (Ackermann, this volume) and 

large local gravity (Long and Champion, this volume), electrical and electromagnetic (Campbell, this 
56 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

volume), and aeromagnetic (Popenoe and Zietz, 

this volume; Phillips, this volume) anomaly patterns. 

The seismological data presented in this chapter 

suggest that current seismic activity in the Middleton Place-Summerville area is taking place along a 

nearly vertical plane striking northwest and passing 

near Middleton Place (fig. 5). The largest recent 

event took place (November 22, 1974) at the southeastern end of the zone. The Middleton Place-Summerville seismic activity takes place within the zone 

of highest intensities of the 1886 shock as contoured 

by Sloan in the Dutton (1889) report and by Bollinger (this volume). Furthermore, the epicenter of 

the November 22, 197 4, shock was located midway 

between the two epicenters in Dutton's (1889) contouring of the maximum intensity zone. The preferred nodal plane determined from the focal mechanisms of the November 22, 1974, event is nearly 

vertical and suggests reverse faulting on a plane 

striking N. 42° W.; the trace of this plane at the 

surface is along the course of the Ashley River (fig. 

5). 

In prior studies, Taber (1914) and Bollinger 

(1972) suggested that the earthquakes felt in the 

Charleston-Summerville area since August 31, 1886, 

are related to, if they are not actually aftershocks 

of, the main shock. Certainly the frequency of occurrence statistics of felt earthquakes in the 

Charleston-Summerville area (table 1) shows a decline of activity typical of aftershock sequences 

(Richter, 1958) and, even in the last two decades, 

the frequency has not decreased to pre-1886 levels. 

Therefore, it may be that the current Middleton 

Place-Summerville activity is taking place within 

the rupture zone of the main shock. The current 

seismic data cannot discriminate between the alternative hypotheses that the earthquake activity 

represents either true seismic afterslip in the rupture zone or a response to the regional stress field 

in locally weak geologic structures near the 1886 

rupture zone. 

Determination of the dimensions of the Middleton Place-Summerville zone must await detection 

and location of further seismic activity and will require more precisely determined hypocenters than 

were possible for this study. Five new local seismic 

stations currently provide the seismographic network with this capability. In addition, several new 

coastal stations northeast and southwest of Charleston will expand the monitoring capability necessary to detect and locate the possible extension of 

the seismic zone onto the Continental Shelf. Because of the current configuration of the network, 

the detection and location capability fall off rapidly 

to the southeast. The seismic data from this study 

do not indicate that a seismic relationship exists between the Middleton Place-Summerville and Bowman source areas. 

The identification of the subsurface structure responsible for the current seismicity in the Middleton 

Place-Summerville zone and by inference, for the 

1886 Charleston earthquake, cannot be made at 

this time. Only one focal mechanism has been determined thus far, and many more will be required 

to determine the nature of faulting throughout the 

entire zone and to establish the relationship of the 

relatively deeper seismicity to shallow structures 

under Middleton Place. 

REFERENCES CITED 

Algermissen, S. T., and Perkins, D. M., 1976, A probabilistic 

estimate of maximum acceleration in rock in the contiguous United States: U.S. Geol. Survey open-file rept. 

76-416, 4fi p., 2 pis., 1 table. 

Bollinger, G. A., 1972, Historical and recent seismic activity 

in South Carolina: Seismol. Soc. America Bull., v. 62, p. 

p. 851-864. 

-- 1973, Seismicity of the southeastern United States: 

Seismol. Soc. America Bull., v. 63, p. 1785-1808. 

-- 1975, A catalog of southeastern United States earthquakes 1754 through 1974: Virginia Polytech. Inst. and 

State Univ., Research Div. Bull. 101, 68 p. 

Bollinger, G. A., Langer, C. J., and Harding, S. T., 1976, 

The eastern Tennessee earthquake sequence of October 

through December, 1973: Seismol. Soc. America Bull., 

v. 66,no. 2,p. 525-547. 

Carver, David, Turner, L. M., and Tarr, A. C., 1977, South 

Carolina seismological data report May 197 4-J une 1975: 

U.S. Geol. Survey open-file rept. 77-429, 66 p. 

Dutton, C. E., 1889, The Charleston earthquake of August 

31, 1886: U.S. Geol. Sm:vey 9th Ann. Rept., 1887-88, p. 

203-528. 

Gutenberg, Beno, and Richter, C. F., 1942, Earthquake magnitude, intensity, energy, and acceleration: Seismol. Soc. 

America Bull., v. 32, p. 163-191. 

--1944, Frequency of earthquakes in California: Seismol. 

Soc. America Bull., v. 34, p. 185-188. 

Karnik, Vit, 1969, Seismicity of the European area, Part I: 

Dordrecht, Holland, D. Reidel Pub. Co., 364 p. 

Lee, W. H. K., Bennett, R. E., and Meagher, K. L., 1972, A 

method of estimating magnitude of local earthquakes 

from signal duration: U.S. Geol. Survey open-file rept., 

28 p., 5 figs., 1 table. 

Lee, W. H. K., and Lahr, J. C., 1975, HYP071 (revised), A 

computer program for determining hypocenter, magnitude, and first motion pattern of local earthquakes: U.S. 

Geol. Survey open-file rept. 75-311, 59 p., 5 figs., 48 

tables. 

McKee, J. H., 1973, A geophysical study of microearthquake 

activity near Bowman, South Carolina: Atlanta, Ga., 

Georgia Inst. of Tech., unpub. Masters thesis, 75 p. 
RECENT SEISMICITY AND ITS RELATIONSHIP TO EARTHQUAKE 57 

Page, Robert, 1968, Aftershocks and microaftershocks of the 

great Alaska earthquake of 1964: Seismol. Soc. America 

Bull., v. 58, p. 1131-1168. 

Richter, C. F., 1958, Elementary seismology: San Francisco, 

Calif., W. H. Freeman, 768 p. 

Sbar, M. L., and Sykes, L. R., 1973, Contemporary compressive stress and seismicity in eastern North America; an 

example of intra-plate tectonics: Geol. Soc. America Bull., 

v.84,no. 6,p. 1861-1881. 

Stover, C. W., Simon, R. B., and Person, W. J., 1976, Earthquakes in the United States, October-December 1974: 

U.S. Geol. Survey Circ. 723-D, p. D1-D27. 

Taber, Stephen, 1914, Seismic activity in the Atlantic Coastal 

Plain near Charleston, South Carolina: Seismol. Soc. 

America Bull., v. 4, p. 108-160. 

Talwani, Pradeep, Secor, D. T., and Scheffler, P., 1975, Preliminary results of aftershock studies following the 2 

August 1974 South Carolina earthquake: Earthquake 

Notes, v. 46, no. 4, p. 21-28. 

Tarr, A. C., and King, K. W., 1974, South Carolina seismic 

program: U.S. Geol. Survey open-file rept. 7 4-58, 15 

p., 4 figs., 2 tables. 

U.S. Environmental Data Service, 1973, Earthquake history 

of the United States: U.S. Environmental Data Service 

Pub. 41-1, rev. ed. (through 1970), 208 p. 

Utsu, T., 1961, A statistical study on the occurrence of aftershocks: Geophys. Magazine, v. 30, p. 521-605. 

Woollard, G. P., 1969, Tectonic activity in North America as 

indicated by earthquakes, in Hart, P. J., ed., The eairth's 

Mon. 13, p. 125-133. 

crust and upper mantle: Am. Geophys. Union Geophys. 

Lithostratigraphy of the Deep Corehole 

(Clubhouse Crossroads Corehole 1) 

Near Charleston, South Carolina, 

By GREGORY S. GOHN, BRENDA B. HIGGINS, CHARLES C. SMITH, and 

.JAMES P. OWENS 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, 

EARTHQUAKE OF 1886-A PRELIMINARY REPORT 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1028-E 

CONTENTS 

Page 

Abstract ---------------------------------------------------------------- 59 

Introduction ------------------------------------------------------------- 59 

Core stratigraphy -------------------------------------------------------- 61 

Basalt --------------------------------------------------------------- 61 

lJpper Cretacepus Series ---------------------------------------------- 61 

Tertiary System _ __ _ __ ____ _ _ ___ _ ____ _ _ _ __ _ __ __ _ __ __ _ ____ ___ _ _ _______ _ 62 

Texture and mineralogy -------------------------------------------------- 63 

Calcium carbonate content and textural analysis ------------------------- 63 

Sand-fraction mineralogy _____ _ __ _ __ __ _ ___ _ _ __ _ __ __ __ _ _ _ __ _ __ _ _ _ __ _ __ _ 63 

Clay-fraction mineralogy ---------------------------------------------- 66 

Formation descriptions _ __ _ _ _ _ __ ___ __ _ __ _ _ _ __ __ _ ____ _ __ __ _ __ __ ___ __ ____ ___ 66 

Depositional history __________________________________________________ ---- 69 

References cited ---------------------------------------------------------- 70 

FIGURE 1. 

2. 

3. 

4. 

5. 

6. 

7. 

ILLUSTRATIONS 

Page 

Map showing location of Clubhouse Crossroads corehole 1 ____ 60 

Stratigraphic column for the Clubhouse Crossroads core ______ 62 

Graphs showing distribution of the acid-soluble fraction and 

the textural composition of the core sediments -------------- 64 

Graphs showing mineralogy of the clay-sized fraction and the 

light-mineral split of the sand-sized fraction --------------- 65 

Graph showing stratigraphic distribution of heavy minerals in 

the sand-sized fraction of the core sediments --------------- 66 

Diagram showing distribution of granitic, low-rank metamorphic, 

and high-rank metamorphic minerals in heavy-mineral suites 

of 57 core samples --------------------------------------- 67 

Diagram showing generalized paleoenvironments represented by 

Cretaceous and Tertiary sediments of the Clubhouse Crossroads 

core ------------------------------------------------------ 69 

III 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886-

A PRELIMINARY REPORT 

LITHOSTRATIGRAPHY OF THE DEEP COREHOLE (CLUBHOUSE CROSSROADS 

COREHOLE 1) NEAR CHARLESTON, SOUTH CAROLINA 

By GREGORY S. CoHN) BRENDA B. HIGGINS) CHARLES C. SMITH) and jAMES P. OwENS 

ABSTRACT 

The continuously cored Clubhouse Crossroads test hole 

is in the Cottageville 15-minute quadrangle, 40 km (25 mi) 

west-northwest of Charleston, S.C. Total depth of the hole 

is 792 m ( 2,599 ft). Seven hundred and fifty meters ( 2,462 

ft) of Cenozoic and Upper Cretaceous sediments was penetrated, and 70 percent of the core was recovered. Below 

that, 42 m (137 ft) of amygdaloidal basalt was penetrated, 

and 100 percent of this part of the core was recovered. 

The formations recognized in the core, their ages, and approximate thicknesses are: amygdaloidal basalt (K/Ar 

minimum ages: 94.8±4.2 m.y. and 109±4 m.y.), greater 

than 42 m (137 ft) ; Cape Fear Formation, Upper Cretaceous, 59 m (194 ft); Middendorf Formation, Upper Cretaceous, 124 m ( 408 ft) ; Black Creek Formation, Upper 

Cretaceous, 159 m (520 ft); Peedee Formation, Upper Cretaceous, 164m (540 ft); Beaufort(?) Formation, Paleocene, 

52 m (170 ft) ; Black Mingo Formation, Paleocene and 

Eocene, 67 m (220 ft) ; Santee Limestone, Eocene, 56 m (183 

ft); Cooper Formation, Eocene and Oligocene, 64 m (211 

ft); unconsolidated sediments, Pleistocene(?), 5 m (16 ft). 

The Cape Fear Formation contains feldspathic sand and 

interbedded clay similar to those in the overlying Middendorf Formation, but it also contains marginal marine deposits of thinly interbedded fine sand and dark clay. The 

Middendorf Formation contains fining-upward cycles of 

conglomeratic to fine-grained quartzose, feldspathic sand, 

and mottled clay deposited in continental environments. 

The Black Creek Formation is a heterogeneous sequence of 

sandy mud, well-sorted sand, shelly sand, and dark clay deposited in marine and marginal marine environments. The 

Peedee and Beaufort(?) Formations are homogeneous 

marine sequences of dark-gray silty clay and muddy sand. 

The Black Mingo Formation contains silty clay, muddy 

sand, thinly interbedded sand and clay, and shelly limestone 

deposited in marine and marginal marine environments. 

The Santee Limestone and Cooper Formation are dominantly impure glauconitic marine limestone containing varying 

amounts of silt- and sand-sized quartz. 

INTRODUCTION 

In January, February, and March 1975, a 792-m 

(2,599-ft) continuously cored test hole, the Clubhouse Crossroads corehole 1, was drilled near 

Charleston, S.C. (fig. 1). The hole was drilled in support of the Charleston Project, a multidisciplinary 

investigation by the U.S. Geological Survey, to determine the cause of seismicity in the Coastal Plain 

near Charleston, S.C. Prior to the analysis of the 

core, the lithologic character and three-dimensional 

stratigraphy of the Coastal Plain sediments in this 

area were poorly understood. Analysis of the core 

has established the stratigraphic column necessary 

for the construction of a regional stratigraphic 

framework. 

The corehole is at lat 32°53.25' N., long 80°21.41' 

W., near the center of the Cottageville 15-minute 

quadrangle, 3.5 km (2.2 mi) southwest of Clubhouse 

Crossroads and approximately 40 km (25 mi) westnorthwest of Charleston. The Clubhouse Crossroads 

hole was drilled to a total depth of 792 m (2,599 ft) 

below a surface elevation of 6 m (20 ft). Of that 

total, 244m (800 ft) of Cenozoic and 506 m (1,662 

ft) of Cretaceous sediments were penetrated, and 70 

percent of the core was recovered. The basal 42 m 

(137ft) is composed of weathered and fresh basalt; 

100 percent of this part of the core was recovered. 

Mechanical problems prevented further drilling. The 

diameter of most of the upper 225m (738ft) of the 

core is 15 em (6 in.) ; that of the lower 567 m (1,861 

ft) is 7 em (2.75 in.). The drilling was done by a 

U.S. Army Corps of Engineers team using hydraulic 

rotary drilling equipment. Eight geophysical logs 

were made by the Schlumberger Corp. (Rhodehamel, 

1975). Descriptive logs of the core were made at 

the drill site before more detailed laboratory 

investigations. 

The preliminary biostratigraphic and lithostratigraphic analyses of the core sediments and fossils 

have been completed, and the basic stratigraphic 

59 
60 

34° 

33° 

STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

81° 

Columbia 

0 

Orangeburg 

0 

Clubhouse Crossroads 

corehole 

® 

Summerville 

0 

0 

Middleton 

+ Place 

I I I I 

10 

I 

I 

20 MILES 

I I I I I I 

0 10 20 KILOMETERS 

FIGURE 1.-Location of Clubhouse Crossroads corehole 1, Charleston, S.C. 
LITHOSTRATIGRAPHY OF DEEP COREHOLE 61 

framework and sediment composition are described 

herein. The purpose of this report is to describe the 

mineralogy, texture, sedimentary structures, and 

general appearance of the core sediments and the 

nomenclature and contact relationships of the formations that have been identified. The biostratigraphic framework for the core sediments has been 

described by Hazel and others (this volume). 

This work was supported by the U.S. Nuclear 

Regulatory Commission, Office of Nuclear Research, 

AgreementNo. AT (49-25)-1000. MelodieHess, Ray 

Schneider, and Steve Perlman performed the many 

laboratory analyses of the core sediments. The potassium-argon radiometric age analyses were done by 

R. F. Marvin, U.S. Geological Survey. 

We wish to express particular appreciation to the 

Westvaco Corporation for allowing us to locate the 

drilling site on their land and for their interest and 

cooperation throughout this project. 

CORE STRATIGRAPHY 

BASALT 

The Clubhouse Crossroads corehole bottomed in 

42 m (137ft) of basalt of Cretaceous(?) age. K/ Ar 

age determinations on two basalt samples gave 

ages of 109 ± 4 m.y. (latest Early Cretaceous) and 

94.8±4.2 m.y. (earliest Late Cretaceous). These ages 

are considered to be minimum ages, however, because of observed geochemical alteration of the 

basalt (Gottfried and others, this volume). Both ages 

are consistent with the Woodbinian (Cenomanian) 

age, as determined by microfossils from sediments 

immediately overlying the basalt (see Hazel and 

others, this volume). 

The distribution of weathered, amygdaloidal, and 

massive basalts within the core indicates at least two 

distinct flow units. Seven meters (23ft) of the lower 

flow were recovered. This flow displays distinct vertical changes in lithology. The lower 1.8 m (6 ft) 

contains a network of fine fractures along which considerable alteration of the basalt has occurred. Above 

the fractured basalt the remaining 5.2 m (17 ft) 

shows an upward increase in the size and abundance 

of amygdules. The upper flow (34.7 m, 114 ft) contains a similar sequence of lithologies with 3 m (10 

ft) of fractured basalt below 22.9 m (75ft) of fresh, 

dark-gray amygdaloidal basalt. Amygdules increase 

in size and abundance upward in the fresh basalt. 

The dark-gray basalt grades upward into dark-red 

weathered basalt (4.2 m, 14ft), which grades into 

red-, yellow-, and white-mottled clay ( 4.6 m, 15 ft) 

displaying a relict amygdaloidal texture. 

UPPER CRETACEOUS SERIES 

Upper Cretaceous sediments (fig. 2) are present 

from the 750-m (2,462-ft) level to the 244-m (800-

ft) level in the core, a thickness of 507 m (1,662 ft). 

The section is provisionally divided into four formations that have been recognized previously as outcrop and subsurface units in the Carolina Coastal 

Plain (Swift and Heron, 1969). From the base to 

the top, the formations are the Cape Fear (59 m, 194 

ft), Middendorf (124 m, 408 ft), Black Creek (159 

m, 520 ft), and Peedee (164 m, 540 ft). Unlike the 

Tertiary formations, contacts between the four Cretaceous units are difficult to identify precisely because of poor core recovery in some intervals and 

similar sediment types in more than one interval. 

The base of the Cape Fear Formation (750 m, 

2,462 ft) is drawn between an upper conglomeratic 

muddy sand and the top of the basalt. The Cape 

Fear-Middendorf boundary (691 m, 2,268 ft) is 

placed at the base of the lowest 0.3 m (1 ft) or 

thicker feldspathic sand in an interbedded sand-clay 

sequence. 

Recognition of the Middendorf-Black Creek 

boundary is hampered by a lack of core recovery for 

several intervals. Core ' recovery between 575 m 

(1,787 ft) and 567 m (1,860 ft) is poor, and the 

small amount of sediment that was recovered consists of friable sand and dark clay lithologically 

similar to overlying thinly interbedded sand and 

clay. The section between 567 m (1,860 ft) and 750 

m (2,462 ft) consists mostly of interbedded 1- to 5-

m-thick (3-15-ft) yellowish-gray-, greenish-gray-, 

and red-mottled clay and coarse feldspathic sand. 

On the basis of the most pronounced lithologic 

change, the Middendorf-Black Creek contact is 

placed at 567 m (1,860 ft). Rock resistivity also decreases significantly at this point (fig. 2). 

Despite the fact that the Middendorf-Black Creek 

contact is not sharply defined, the paleontologic data 

(Hazel and others, this volume) suggest that an unconformity of considerable temporal magnitude is 

present. Fossils at about 560 m (1,837 ft) indicate a 

late Austinian age; at 586 m (1,923 ft), early Eaglefordian (late Cenomanian) fossils are present. The 

26-m (85-ft) interval between these two points is 

barren of diagnostic fossils. The data suggest that 

either the lower Austinian and middle and upper 

Eaglefordian (that is, approximately Coniacian and 

Turonian) deposits are absent, or they are represented by only 26 m (85 ft) of section. Data from 
62 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

z 

0 

~ ~ 

a: 

0 

u.. 

z wO 

wf= 

0<! 

w:;: 

~9 _ , I 

.._ 

a::Z 

oo 

Of= 

Z<! 

w:;: 

Oa:: Qo 

::;:'"-

I I 

CLUBHOUSE CROSSROADS CORE 

DORCHESTER COUNTY, SOUTH CAROLINA 

DEPTH 

50 

100 

150 

200 

250 

300 

350 

400 

450 

500 

550 

600 

650 

700 

750 

EXPLANATION 

• Glauconite 

• 

a -

~ ' 

~ 

§ . 

§3 . 

D . 

Phosphate 

Fine-grained 

limestone 

Coarse-grained 

limestone 

Sandy 

limestone 

Silty clay 

Sandy clay 

Clayey sand 

Sand 

...._....._.... Unconformity 

FIGURE 2.-Stratigraphic column for the Clubhouse Crossroads core. Spontaneous potential (S.P.) log and resistivity log are shown next to the lithologic log. 

heavy minerals, discussed below, suggest a different 

sediment provenance for the deposits above and below this barren zone. 

The Black Creek-Peedee boundary is placed at the 

contact (408 m, 1,340 ft) between an upper graygreen silty clay that has a basal phosphate pebble 

bed, and a lower calcareous, light-colored, relatively 

well-sorted quartz sand. Deposition of the sediments 

now found between 244 m (800 ft) and 567 m 

(1,860 ft) was nearly continuous (see Hazel and 

others, this volume), and similar gray-green silty 

and sandy clays are common sediment types in both 

formations. Placement of the boundary at 408 m 

(1,340 ft) confines shell-rich limestone, dark carbonaceous clay, and clean light-colored sand to the 

Black Creek Formation. In addition, the major 

change in the spontaneous potential log between 244 

m (800 ft) and 567 m (1,860 ft) takes place at 

408 m (1,340 ft). 

As defined, the Black Creek and Peedee Formations are identifiable lithologic units. Some evidence 

exists, however, for the cyclical occurrence of coarser and finer grained units in these formations. Such 

cycles would be more fundamental depositional and 

lithologic units than the two formations as presently 

defined. As a result of further study, refinement of 

changes in the lithostratigraphy of these units may 

be required. 

TERTIARY SYSTEM 

The Tertiary section (fig. 2) recovered from the 

corehole has been divided into four named formations: (1) a basal Paleocene unit tentatively identified as the Beaufort(?) Formation (52 m, 170ft); 

(2) the Black Mingo Formation, Paleocene and 

Eocene ( 67 m, 220 ft) ; ( 3) the Santee Limestone, 

Eocene (56 m, 183 ft) ; and ( 4) the Cooper Formation, Eocene and Oligocene (64 m, 211 ft). The surficial Pleistocene(?) sand and clay (5 m, 16ft) overlying the Cooper were not named. 

The name Beaufort(?) has been tentatively applied to the sequence of calcareous mud and muddy 

sand of Paleocene age that is lithologically similar 

and stratigraphically equivalent to the Beaufort Formation in North Carolina (Brown, 1958, 1959). This 

unit may also be equivalent to the "unnamed beds of 

Midway age" described by Siple ( 1975) from nearby Orangeburg County, S.C. The Black Mingo and 

the Santee have been recognized previously in the 

South Carolina Coastal Plain (Malde, 1959; Pooser, 

1965; Colquhoun and Johnson, 1968; and many 

others). Most authors have referred to the Cooper 

as the Cooper Marl. However, as noted by Pooser 
LITHOSTRATIGRAPHY OF THE DEEP COREHOLE 63 

(1965) and Malde (1959), the Cooper sediments 

contain too much quartz sand to be true marl. In this 

paper, the lithologic designation is dropped in favor 

of the name Cooper Formation. 

From their physical appearance, boundaries of 

three of the four Tertiary formations have been 

interpreted as unconformities, disco,nformities, or 

diastems. Irregular, burrowed and bored carbonatecemented mud or shelly limestone overlain and infiltrated by glauconite- and phosphate-rich sediments 

are formed at the Cretaceous-Tertiary boundary 

(244m, 800ft) at the base of the Beaufort(?) Formation, the Beaufort( ?)-Black Mingo boundary 

( 192 m, 630 ft) , and the Santee-Cooper boundary 

(69 m, 227 ft). Similar surfaces are present at the 

Paleocene-Eocene boundary (132m, 433 ft), within 

the Eocene part of the Cooper Formation (57 m, 186 

ft), and at the Eocene-Oligocene boundary (55 m, 

180 ft). The Black Mingo-Santee contact (125 m, 

410 ft) is sharp and is between an upper (Santee) 

skeletal limestone and a lower (Black Mingo) finegrained limestone (see also Hazel and others, this 

volume). 

TEXTURE AND MINERALOGY 

Sixty samples selected from representative sediment types throughout the core were subjected to 

textural and mineralogical examination. Textural 

variation, percentage of acid-soluble fraction (mostly calcium carbonate), and mineralogy of the sandand clay-sized fractions are shown in figures 3-6. 

CALCIUM CARBONATE CONTENT AND TEXTURAL 

ANALYSIS 

On the basis of the distribution of calcium carbonate (acid-soluble fraction) in the core sediments (fig. 

3), two fundamental sequences may be recognized : 

an Upper Cretaceous to lower Eocene siliciclastic sequence, and a middle Eocene to Oligocene carbonate 

sequence. Within the siliciclastic sequence, calcium 

carbonate is present primarily (from 5 to 40 percent) as shell debris and less commonly as calcitecemented nodules and layers in the Cape Fear, Black 

Creek, Peedee, Beaufort ( ?) , and Black Mingo Formations. The Middendorf Formation is noncalcareous and is the least fossiliferous of the formations. 

The amount of soluble material in the Middendorf 

averages less than 5 percent and is probably iron carbonate. In the carbonate sequence (Santee Limestone and Cooper Formation), the amount of carbonate averages 50-70 percent and is present primarily 

as macrofossil and microfossil shell debris. 

The relative percentages of clay, silt, and sand, 

including the acid-soluble fraction, are shown in 

figure 3. The low density of analyzed samples 

throughout the core has resulted in limited detail; 

however, general trends in the sediment size distribution are the bimodal size distribution of sediments below 567 m (1,860 ft) (Cape Fear, Middendorf), the heterogeneous nature of the sediments between 408 and 567 m (1,340 to 1,860 ft) (Black 

Creek) and between 125 and 192m (410 to 630ft) 

(Black Mingo), and the homogeneous size distribution between 244 and 408 m (800 to 1,340 ft) (Pee--

dee) and between 192 m and 244 m (630 to 800 ft) 

(Beaufort(?)). The abundant sand fraction of the 

calcareous sediments above 125 m ( 410 ft) is composed primarily of macrofossil and microfossil shells. 

SAND-FRACTION MINERALOGY 

Several trends in the distribution of sand-sized 

minerals are recognizable in figure 4. Cristobalite is 

abundant in most of the Beaufort(?) and the lower 

part of the Black Mingo sediments, common in most 

of the upper part of the Black Mingo sediments, rare 

in the lower part of the Santee sediments, abundant 

in most of the upper part of the Santee and lower 

part of the Cooper sediments, and rare in the upper 

part of the Cooper sediments. _This pattern matches 

the distribution of cristobalite in the clay-sized frac-

,tion of the Tertiary samples (fig. 4). Potassium feldspar is common throughout the core but is more 

abundant below 458 m (1,500 ft) and very abundant 

below 533 m (1,750 ft). Plagioclase is common only 

below about 396m ( 1,300 ft). 

On the basis of the heavy minerals in the sand 

fraction (fig. 5), the sedimentary sequence of the 

core may be divided into two parts. The transition 

zone separating the two parts is from 540 m (1,770 

ft) to 567 m ( 1,860 ft) . Below 567 m ( 1,860 ft), the 

heavy-mineral suite contains abundant zircon, tourmaline, staurolite, and monazite, and common apatite, epidote, rutile, and garnet. This suite suggests a 

source area dominated by granitic plutons or pegmatites intruded into regionally metamorphosed 

pelitic rocks. Above 540 m (1,770 ft), apatite and 

monazite are rare, and rutile is much less abundant. 

Above 567 m ( 1,860 ft), the amount of zircon and 

epidote is much decreased. Instead, chloritoid is 

abundant, and the amount of kyanite increases above 

540 m (1,770 ft). This change suggests that regionally metamorphosed pelitic rocks became the important sediment contributors and that granitic intrusions were rare or absent in the source area. 
64 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

ACID-SOLUBLE 

FRACTION, IN PERCENT 

DEPTH SEDIMENT-SIZE 

DISTRIBUTION, IN PERCENT IN IN 

0 100 FEET METERS 0 100 

100 

100 

500 

200 

1000 300 

400 

1500 

500 

600 

2000 

700 

2500 

FIGURE 3.-Distribution of the acid-soluble fraction and the textural composition of 

the core sediments. The acid-soluble fraction is included in the textural analysis. 

This fundamental change in sediment provenance 

is shown in figure 6. With two exceptions, heavymineral suites from above and below 540 m (1,770 

ft) plot in separate fields on the diagram. The transition zone, 540-567 m (1,770-1,860 ft), separating 

the two heavy-mineral suites in part overlaps the 

section of unfossiliferous sediments ( 560-586 m, 

1,837-1,923 ft) that separates fossiliferous lower 

Eaglefordian and Austinian sediments (Hazel and 

others, this volume). This overlap supports the concept, derived from the fossil evidence, that a major 

unconformity exists between 560 m (1,837 ft) and 

586 m (1,923 ft), and probably between 560 m 

(1,837 ft) and 567 m (1,860 ft). 
0 

COMPOSITION OF 

CLAY-SIZED FRACTION, 

IN PERCENT 

100 

--

= 

--

w 

!::: 

--' 0 

--' 

i= 

0.. 

0 

z 

::::; 

u 

LITHOSTRATIGRAPHY OF DEEP COREHOLE 

-

--

-

w 

1-

::::; 

<{ 

co 

0 

1-

rJl 

a: 

u 

DEPTH, 

IN IN 

FEET METERS 0 

100 

500 

200 

1000 300 

COMPOSITION OF 

SAND-SIZED FRACTION, 

IN PERCENT 

100 

65 

EXPLANATION 

[:. -:"<J Kaolinite 

[. /I Illite 

Illite/smectite 

Percent of expandable layers 

given in parentheses 

D Quartz 

D Cristobalite 

• Potassium feldspar 

Ill Plagioclase 

FIGURE 4.-Mineralogy of the clay-sized fraction and the light-mineral split of the sand-sized fraction. The feldspars are 

divided into potassium feldspar and plagioclase only below 244m (800ft). Plagioclase is rare above 244m. 
66 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

DISTRIBUTION OF HEAVY MINERALS, IN PERCENT 

w w w w 0 z w f- w 6 !:: :::; !:: -' Ui DEPTH f- -' ..: z 0 w 

~ f- w w 0 f- ..: OJ ::J !:: a: f- z f- w a: w ~ -' IN IN f- 0 z 0 0 -' ::J z a: ~ I ..: ..: z -' ~ u 0 f= ..: a: ::J :::; "- 0 FEET METERS 

"- 0 I a: a: ::J f- ..: 0 -' ~ z ..: ~ u " ;:::; w a: CJ) <C) f- Ui ..: ..: 0 0 

100 

400 

200 

BOO 

300 

1200 

400 

1600 500 

k----- 2000 600 

700 

~ ....___. ....___. ..___, .....___. ...._____. ...____. .....___. ~ .....___. .___. .....___. ....___. 

0-50 0-50 0-50 0-50 0-50 0-50 0-50 0-50 0-50 0-50 0-50 0-50 0-1 00 

FIGURE 5.-Stratigraphic distribution of heavy minerals in 

the sand-sized fraction of the core sediments. 

An interesting and significant heavy-mineral 

suite, perhaps related to the tectonic history of the 

Charleston area, is present in the upper half of the 

Black Creek Formation at 455 m (1,492 ft). This 

suite contains 95 percent andalusite. The remaining 

5 percent consists of biotite, minor cordierite, and 

trace amounts of zircon, tourmaline, garnet, amphibole, kyanite, epidote, chloritoid, and sillimanite. 

The dominant association of andalusite, biotite, and 

cordierite suggests that the source of the assemblage 

was the contact aureole of a magma body intruded 

into pelitic rocks. The unusually high concentration 

of one mineral, in this case andalusite, suggests that 

this heavy-mineral suite was deposited very close to 

its source area. 

Some credence is given to this idea by the presence 

of Cretaceous ( ?) basalt in the Clubhouse Crossroads 

core and the presence of diabase in the nearby Summerville test well (Cooke, 1936). The unroofing of 

Cretaceous or older Mesozoic shallow intrusive rocks 

and their contact zones could have provided a local 

source for the andalusite and associated minerals 

found in the younger Cretaceous sediments. 

CLAY-FRACTION MINERALOGY 

Variations in the mineralogy of the clay-sized 

fraction primarily involve small changes in the relative percentages of kaolinite, illite, and mixed-layer 

illite-smectite (fig. 4). In Cape Fear, Middendorf, 

and basal Black Creek sediments below 541 m (1,775 

ft), kaolinite and mixed-layer clay are most abundant. In Black Creek, Peedee, and basal Beaufort(?) 

sediments between 541 m (1,775 ft) and 238m (780 

ft), kaolinite, illite, and illite-smectite are present in 

nearly equal proportions. Siliciclastic and carbonate 

sediments above 238m (780 ft) contain little kaolinite and abundant illite and mixed-layer clay. 

In addition to the three clay minerals, cristobalite 

and clinoptilolite are abundant within parts of the 

Tertiary section (fig. 4). The abundance of these 

two minerals in the Tertiary sediments and their absence in the Cretaceous sediments represent a fundamental change in the origin of some of the sediments deposited in the South Carolina Coastal Plain. 

Specifically, many authors have used clinoptilolite 

and cristobalite as indicators of diagenetically altered volcanic and volcaniclastic materials in the 

Atlantic and Gulf Coastal Plains (Heron, 1969; 

Reynolds, 1970; and others). 

FORMATION DESCRIPTIONS 

Cape Fear Formation 

The Cape Fear Formation overlies the basalt and 

contains unconsolidated interbedded clay and sand. 

The lower 13 m ( 42 ft) is composed primarily of red 

or brown clay and less common feldspathic sand and 

has a basal unit of muddy conglomeratic sand. The 

clay is typically silty, noncalcareous, and unfossiliferous, and contains a trace of mica and pyrite. The 

clay has a knobby appearance and lacks primary 

sedimentary structures. Rare muddy feldspathic 

sand is interbedded with the nodular clay. The sand 

is massive, noncalcareous, and typically contains 10 

to 20 percent feldspar. 

The middle part (24 m, 80 ft) of the formation 

consists of thinly interbedded gray-olive silty clay 

and light-greenish-gray fine-grained sand. The sand 

contains abundant mica, and sparse shell fragments 

are found in both the sand and clay. The upper 22m 

(72 ft) of the Cape Fear Formation is composed of 

knobby clay similar to that in the lower part of the 

formation. The upper clay is reddish-brown to yellowish-gray, noncalcareous, and micaceous. 
LITHOSTRATIGRAPHY OF DEEP COREHOLE 67 

G 

ZIRCON A. 

TOURMALINEA ~50 MONAZITE (!) , 

RUTILE r.;-,2031\ 

EXPLANATION 

Sample below 540 m (1770 ft). Depth given in feet 

( 1 ft equals 0.3048 m) 

1872 \ APATIT~- ~ -j. 302 

• Sample above 534 m (1751 ft). Depth given in feet 

1923 ® \ 

2428 \ G 

M(L) 

Granitic minerals 

rf..\ (!)2154 --;A 

)V1934 \ 

Metamorphic minerals of 

lower pressure/temperature ·t• 2023 2409\~ '-"2360 

1863 ~ ' 

933 @2364 1:48 

M(H) Metamorphic minerals of 

higher pressure/temperature 

I 445 2304 •302 

!\ • • ®. I .. 384364 1116 

I~>~ •5o4 '-!)2181 ® 171o 27 .413 ...__ ____ ;;;:;_ __ 

529 

2241 

~54 ... 48~. (!) .135 

·1347 ..... 801 781 

~/;;13~0 .225 

;865 

I 

/k 

1

178 

1751 

.. 1607 !• 125 

1- •• 525 698 1634 .1257 \. 

I \ 1 oo3 • • 62o • \ I e 

KYANITE I \\ 

STAUROLITE 

GARNET ;\ 7 

SILLIMANITE;. \. 

AMPHIBOLE ' EPIDOTE 

ANDALUSITE 1492 \ CHLORITOID 

M(H) __!___- ___\L__ __'.L_ ___ _____y_ ··· ___ \L__ ___ _,._ ___ __y_ ____ \,1 __ ____,· "-/ -----'"---~1 M(L) 

FIGURE 6.-Distribution of granitic, low-rank metamorphic, and' high-rank metamorphic minerals in heavy-mineral suites 

of 57 core samples. Samples from above and below 540 m (1,770 ft) fall into two separate distinct fields. 

Middendorf Formation 

The Middendorf Formation is a thick sequence of 

feldspathic sand, clayey silt, and sandy and silty clay. 

The clay is typically pale red or reddish brown, or it 

may be red and gray green mottled. The fine-grained 

deposits are noncalcareous, micaceous, and lack primary sedimentary structures. The sand is poorly 

sorted, feldspathic, and noncalcareous. Typical colors for the sand are mottled combinations of red, 

reddish brown, and gray green. The sand is fine to 

coarse grained, and thin quartz-pebble-rich conglomeratic sand is common. Horizontal and inclined bedding are common in the sand. The clay, silt, sand, 

and conglomeratic sand are arranged in 1- to 5-mthick (3-15-ft) fining-upward cycles. The cycles 

tend to be better defined and more complete in the 

upper half of the formation than in the lower half. 

Black Creek Formation 

The Black Creek Formation is the most heterogeneous of the Upper Cretaceous formations in the 

core. Abundant fossiliferous silty clay, muddy sand, 

and clean sand alternate in 15- to 46-m-thick (50-

150 ft) sequences with thinly interbedded sand and 

clay and less common shelly limestone. 

The silty clay and muddy sand are typically medium-gray or gray-green, calcareous, fossiliferous 

sediments that resemble similar sediment types in 

the overlying Peedee Formation. Quartz sand and 

silt constitute as much as 50 to 60 percent of the 

coarser grained beds, and calcium carbonate content 

reaches a maximum of 40 percent. Macrofossil shells 

and shell fragments and microfossil tests vary from 

sparse to very abundant. Unusually heavy concentrations of shells are preserved in impure, shelly limestone. Minor constituents of the mud and muddy 

sand are glauconite, phosphate, mica, and pyrite. 

Physical sedimentary structures are rare in the 

muddy sediments, probably because of extensive 

bioturbation. 

Light-colored, feldspathic, quartz silt and fine sand 

are interbedded with dark-gray clay near the base 
68 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

of the Black Creek. Bedding in this basal unit is 

planar, wavy, or discontinuous on a 1-10-mm scale. 

The clay contains as much as 20 percent black carbonaceous debris. 

Well-sorted, calcareous quartz sand is found at the 

top of the Black Creek. Core recovery is poor in this 

interval, but relatively clean, poorly consolidated, 

very fine to fine-grained quartz sand was collected 

throughout the interval. 

Peedee Formation 

The Peedee Formation is a thick sequence of calcareous muddy sand and calcareous mud. The lower 

half of the formation is dominantly medium-gray to 

olive-gray fossiliferous muddy sand. The sand typically contains 50 to 60 percent fine- to mediumgrained quartz sand, 30 to 40 percent clay and silt, 

and 10 to 20 percent whole macrofossils, shell fragments, and microfossils. Trace amounts to a few percent of sand-sized glauconite, phosphate, and mica 

are also present. The acid-soluble fraction consists 

almost entirely of fossils, although calcite-cemented 

nodules and layers do exist. The upper half of the 

formation is composed of medium-gray to olive-gray, 

silty or sandy calcareous clay. These beds are dominantly silty clay but may contain as much as 20 to 

25 percent quartz sand and abundant macrofossils 

and microfossils. Glauconite, pyrite, phosphate, and 

mica are accessory constituents. Calcium carbonate 

content varies from 10 to 40 percent and represents 

both fossils and calcite cement. 

Physical sedimentary structures are rare in the 

Peedee and are restricted to thin intervals of wavy 

or disrupted laminations or thin beds. Biogenic sedimentary structures, including distinct burrows and 

bioturbated fabric, typify the poorly sorted Peedee 

sediments. 

Beaufort(?) Formation 

The Beaufort ( ?) Formation is primarily composed of medium-gray-green silty clay above a basal 

unit of nodular muddy sand. The dominant sediment 

type is a yellowish-gray to greenish-gray, moderately calcareous silty clay or locally sandy clay. Calcium 

carbonate averages 10 to 20 percent and is contained 

almost exclusively in microfossil tests. Accessory 

constituents include sand-sized glauconite, carbonized woody material, and pyrite. Physical sedimentary structures include planar, wavy, and disrupted 

laminae and thin bedding, and micrograded silt and 

fine sand. The bedding is typically disrupted or obliterated by burrows. 

The basal 11 m ( 37 ft) of the formation consists 

of gray-green to light-gray glauconitic muddy sand 

containing an abundant microfauna. If physical sedimentary structures were originally present in this 

interval, they have been obliterated by intense bioturbation. Calcite-cemented nodules averaging 60 to 

80 percent calcium carbonate are common throughout; sediment between the nodules averages 15 to 25 

percent calcium carbonate. 

Black Mingo Formation 

The Black Mingo is the most heterogeneous of the 

Tertiary formations recovered in the core. Much of 

the middle and lower part of the formation is graygreen bioturbated silty clay and muddy sand similar 

to those of the underlying Beaufort(?) and Peedee 

Formations. The uppermost 7 m (22 ft) of the formation is light-colored, fine-grained, impure limestone similar to the limestone in the upper part of 

the overlying Santee Limestone. 

Other sediment types in the Black Mingo are thinly interbedded sand and clay and less common 

quartzose shelly limestone. The interbedded sand 

and clay form a regularly alternating sequence of 

olive-gray silty clay that often contains abundant 

wood fragments, and light-colored, fine-grained, 

slightly calcareous quartz sand or shelly limestone. 

Stratification is typically in the form of flaser and 

lenticular beds that are disrupted by vertical and 

horizontal burrows. The shelly limestone is 0.3-1 m 

(1-3 ft) thick, and is typically composed of oyster 

and other pelecypod valves and fine- to mediumgrained quartz sand. 

Santee Limestone 

The Santee Limestone is herein divided into three 

informal lithologic units: a lower bryozoan-pelecypod sand, 11 m (35 ft) thick; a middle shelly limestone, 7 m (23 ft) thick; and an upper fine-grained 

limestone, 38 m (125 ft) thick. The basal part of 

the Santee consists of porous bryozoan-pelecypod 

sand. Calcium carbonate averages 60 to 80 percent; 

the remainder of the unit is composed of quartz and 

sand-sized glauconite and phosphate. Sedimentary 

structures are restricted to inclined bedding, probably representing crossbedding, and to local concentrations of the noncarbonate fraction that may 

represent burrows. 

The middle part of the formation is composed of 

yellowish-gray glauconitic, quartzose fossiliferous 

limestone. These rocks average 60 to 70 percent calcium carbonate. Whole shells and valves of pelecy-
LITHOSTRATIGRAPHY OF DEEP COREHOLE 69 

pods plus foraminifers and ostracode shells dominate the fauna. 

The upper unit resembles similar sediments in the 

overlying Cooper Formation but is a pale yellowish 

gray rather than the more greenish gray of the 

Cooper ·Sediments. This unit is composed primarily 

of microfossil tests and fine quartz sand, with minor 

glauconite and clay minerals. Calcium carbonate 

averages 40 to 60 percent. Hard cemented nodules 

and occasional burrows are present in the finegrained limestone. 

Cooper Formation 

The Cooper Formation is a monotonous sequence 

of impure limestone. The amount of calcium carbonate ranges from 60 to 75 percent. Minor lithologic components include quartz sand (5-25 percent), 

glauconite (1-10 percent), phosphatic sand and pebbles (1-5 percent), bone material (1-5 percent), 

pelecypod shell hash (1-5 percent), mica (1 percent), and clay minerals (10-30 percent). Subtle 

differences in the abundance of these components 

result in the variability observed in the Cooper sediments. Colors of the sediment vary from moderate 

or pale greenish or yellowish gray to olive brown 

and pale olive. Grain-size analysis indicates that 

most of the Cooper is made up of samd-sized foraminiferal tests ( 40-70 percent). 

Physical sedimentary structures are rare in the 

Cooper and are restricted to thin wavy laminae. The 

Cooper sediments are either thoroughly bioturbated 

or contain distinct burrows. 

DEPOSITIONAL HISTORY 

From the preliminary study of the core sediments, 

generalized depositional paleoenvironments may be 

assigned to the formations in the core (fig. 7). In 

figure 7, the terms "continental," "marginal marine," "inner shelf," and "middle to outer shelf" are 

each used to represent a spectrum of specific related 

paleoenvironments. The term "continental" potentially represents both fluvial sediments and residual 

materials. Marginal marine sediments accumulated 

in estuarine, lagoonal, tidal-flat, or barrier-system 

environments. Inner- and middle- to outer-shelf 

sediments were deposited on the marine shelf at 

various distances from the shoreline and under various energy regimes. 

Unfossiliferous reddish clay and coarse-grained 

feldspathic sand in the Cape Fear and Middendorf 

Formations are assigned to the continental environment. Rare fossiliferous clay in the Middendorf and 

FORMATION 

COOPER 

SANTEE 

LIMESTONE 

BLACK MINGO 

BEAUFORT(?) 

PEEDEE 

BLACK CREEK 

MIDDENDORF 

CAPE FEAR 

--' 

~ z 

LU 

z 

f= 

z 

0 

u 

I 

--' 

<(LU 

zz 

<:iii: a:<( 

<(:2; 

:2; 

I.L. 

--' LU 

:I: 

CfJ 

a: 

LU 

z 

z :2;::::> 0 

I 

~ 

ffl 

1 

J 

FIGURE 7.-Generalized paleoenvironments represented by Cretaceous and Tertiary sediments of 

the Clubhouse Crossroads core. 

fossiliferous thinly interbedded sand and dark clay 

in the Cape Fear indicate ~ marginal marine setting 

for those specific beds. The heterogeneous Black 

Creek Formation represents a cyclic alternation of 

poorly sorted marine deposits and marginal marine 

beds including shelly or well-sorted sand and dark 

clay. The more homogeneous Peedee Formation contains sandy and silty marine clay that may also be 

present in cyclic units. 

The large-scale sequence of paleoenvironments 

f~mnd in the Upper Cretaceous sediments of the 

Clubhouse Crossroads co·re is superficially similar to 

that described . by Swift, Heron, and Dill (Swift and 

Heron, 1969; Swift, Heron, and Dill, 1969) for sediments in the Cretaceous outcrop belt of North and 

South Carolina. These authors described a vertical 

sequence composed of thin basal estuarine? sediments (Cape Fear), then fluvial sediments (Middendorf), estuarine sediments (Black Creek), and 

neritic sediments (Peedee). In general, a large-scale 

transgressive sequence (Middendorf, Black Creek, 

Peedee) is indicated. 

The temporal distribution of sediments in the 

Clubhouse Crossroads core does not readily support 

the model of Swift, Heron, and Dill (1969). In the 

Clubhouse Crossroads core, most or all of the fluvial 

facies (Middendorf) is restricted to the Woodbinian 
70 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

and lower Eaglefordian and is separated by a considerable period of time from the upper Austinian 

and younger estuarine and neritic facies (Black 

Creek and Peedee) . Time transgression of facies is 

implicit in a transgressive sedimentary sequence. 

However, large time gaps should not exist in a vertical sedimentary sequence produced by transgressing lithosomes of a single horizontal facies 

sequence. 

The repetition of coarse- and fine-grained units 

in the Black Creek and Peedee Formations on a 

scale of 15-46 m (50-150 ft) is similar to that 

shown by cyclic units in the Cretaceous section of 

New Jersey described by Owens and Sohl ( 1969). 

Such transgressive-regressive cycles are on a smaller 

scale than the single transgression described by 

Swift, Heron, and Dill (1969) and would require 

more frequent shifts of the shoreline and of paleoenvironments. These two concepts may possibly be 

reconciled, at least for the Black Creek and Peedee, 

if the smaller cycles are considered second-order 

features superimposed on a generally transgressive 

upper Austinian to N avarroan sequence. In such a 

setting, environmental shifts within each of the 

smaller cycles may have been only of limited magnitude. Environmental shifts within Black Creek 

cycles would have involved marginal marine and 

marine lithotopes, whereas Peedee cycles would have 

involved only marine deposits of the outer, middle, 

and inner shelf. 

The fine-grained microfossiliferous Beaufort(?) 

Formation represents an open marine environment, 

whereas cyclic deposits in the Black Mingo Formation include mari~e and marginal marine beds and 

represent a large-scale Tertiary regressive sequence. 

Fine-grained limestones of the Santee Limestone and 

Cooper Formation are monotonous bioturbated marine deposits. Skeletal limestone in the Santee does 

not appear to be a part of a peritidal facies mosaic 

and is also assigned a marine (subtidal) origin. 

Pooser (1965), Colquhoun and Johnson (1968), 

Inden and Zupan ( 1976), and others have assigned 

Tertiary sediments in South Carolina to a wide 

range of marine and nonmarine environments. Their 

studies are based primarily upon surface and subsurface data from the updip outcrop belt. Predictably, the more downdip location of the Clubhouse 

Crossroads core is reflected in the dominantly marine nature of the Tertiary sediments in the, core. 

REFERENCES CITED 

Brown, P. M., 1958, Well logs from the Coastal Plain of 

North Carolina: North Carolina Div. Mineral Resources 

Bull. 72, 68 p. 

--- 1959, Geology and ground-water resources in the 

Greenville area, North Carolina: North Carolina Div. 

Mineral Resources Bull. 73, 87 p. 

Colquhoun, D. J., and Johnson, H. S., Jr., 1968, Tertiary sealevel fluctuations in South Carolina, in Tanner, W. 

F., ed., Tertiary sea-level fluctuations: Paleogeography, 

Paleoclimatology, Paleoecology, v. 5, no. 1, p. 105-126. 

Cooke, C. W., 1936, Geology of the Coastal Plain of South 

Carolina: U.S. Geol. Survey Bull. 867, 196 p. 

Heron, S. D., Jr., 1969, Mineralogy of the Black Mingo mudrocks: South Carolina Div. Geology, Geol. Notes, v. 13, 

no. 1, p. 27-41. 

Inden, R. F., and Zupan, Alan-Jon W., 1976, Facies and 

facies equivalents of the Santee Limestone (Lower Tertiary) in South Carolina: Geol. Soc. America Abs. with 

Programs, v. 8, no. 2, p. 204-205. 

Malde, H. E., 1959, Geology of the Charleston phosphate 

area, South Carolina: U.S. Geol. Survey Bull. 1079, 

105 p. 

Owens, J. P., and Sohl, N. F., 1969, Shelf and deltaic paleoenvironments in the Cretaceous-Tertiary formations of 

the New Jersey Coastal Plain, in Subitzky, Seymour, 

ed., Geology of selected areas in New Jersey and eastern Pennsylvania and guidebook of excursions: New 

Brunswick, N.J., Rutgers Univ. Press, p. 235-278. 

Pooser, W. K., 1965, Biostratigraphy of Cenozoic ostracoda 

from South Carolina: Kansas Univ. Paleont. Contr., 

Arthropoda, art. 8, p. 1-80. 

Reynolds, W. R., 1970, Mineralogy and stratigraphy of 

Lower Tertiary clays and claystones of Alabama, in 

Symposium on environmental aspects of clay minerals: 

Jour. Sed. Petrology, v. 40, no. 3, p. 829-838. 

Rhodehamel, E. C., 1975, Geophysical logs from a geologic 

test hole near Charleston, South Carolina: U.S. Geol. 

Survey open-file report 75-247, 1 p. 

Siple, G. E., 1975, Ground-water resources of Orangeburg 

County, South Carolina: South Carolina Div. Geology 

Bull. 36, 59 p. 

Swift, D. J. P., and Heron, S. D., Jr., 1969, Stratigraphy of 

the Carolina Cretaceous: Southeastern Geology, v. 10, 

no. 4, p. 201-245. 

Swift, D. J. P., Heron, S. D., Jr., and Dill, C. E., Jr., 1969, 

The Carolina Cretaceous-Petrogr.aphic reconnaissance 

of a graded shelf: Jour. Sed. Petrology, v. 39, no. 1, p. 

18-33. 
Biostratigraphy of the Deep Corehole 

(Clubhouse Crossroads Corehole 1) 

Near Charleston, South Carolina, 

By .J. E. HAZEL, L. M. BYBELL, R. A. CHRISTOPHER, N. 0. FREDERIKSEN, 

F. E. MAY, D. M. McLEAN, R. Z. POORE, C. C. SMITH, N. F. SOHL, 

P. C. VALENTINE, and R. J. WITMER 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, 

EARTHQUAKE OF 1886-A PRELIMINARY REPORT 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1028-F 

CONTENTS 

Page 

Abstract -----------------------------------------

Introduction --------------------------------------

71 

71 

73 

73 

75 

75 

75 

78 

Fauna and flora ----------------------------------

Ostracodes ----------------------------------- Cretaceous larger invertebrates ----------------

Tertiary calcareous nannofossils ---------------

Biostratigraphy _________________________________ _ 

Stage placement ____________________________ _ 

Correlation ---------------------------------- Foraminifers ________________________________ _ 

Paleoenvironment ____________________________ _ Spores and pollen ------------------------------ Trangressions and regressions ________________ _ Dinoflagellates ____ -- _____ - -- _____ ---- _ -------

Rates of sedimentation _______________________ _ References cited ----------------------------------

FIGURE 

TABLE 

ILLUSTRATIONS 

1. Generalized geologic map of South Carolina showing location 

of the Clubhouse Crossroads corehole 1 --------------------

2. Stratigraphic column and spontaneous potential and resistivity 

Page 

72 

logs for the Clubhouse Crossroads core -------------------- 73 

3. Generalized correlation chart for the Upper Cretaceous and lower 

Tertiary of the Atlantic and Gulf Coastal Plains ____________ 76 

4. Diagram showing generalized transgressive and regressive cycles 

in the Gulf and Atlantic Coastal Plains --------------------- 78 

TABLES 

1. The thickness, duration, and calculated sedimentation rate for 

each provincial stage represented in the Clubhouse Crossroads 

Page 

core ------------------------------------------------------ 79 

2. The thickness, duration, and calculated sedimentation rate for 

each European stage represented in the Clubhouse Crossroads 

core ----------------------------------------------------- 79 

III 

Page 

80 

80 

81 

82 

83 

85 

86 

88 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886-

A PRELIMINARY REPORT 

BIOSTRATIGRAPHY OF THE DEEP COREHOLE 

(CLUBHOUSE CROSSROADS COREHOLE 1) 

NEAR CHARLESTON, SOUTH CAROLINA 

By J. E. HAZEL, L. M. BYBELL, R. A CHRisTOPHER, N. 0. FREDERICKsEN, F. E. MAY, D. M. McLEAN, 

R. Z. PooRE, C. C. SMITH, N. F. SOHL, P. C. VALENTINE, and R. J. WITMER 

ABSTRACT 

Microfossils (calcareous nannoplankton, dinoflagellates, 

foraminifers, ostracodes, and sporomorphs) and mollusks 

have been used to date the sedimentary part of a 792-m 

(2,599-ft) core from a test hole (Clubhouse Crossroads 

corehole 1) drilled 40 km (25 mi) west-northwest of Charleston, S.C. The sedimentary section is 750 m (2,462 ft) thick 

and is of Late Cretaceous and (except for a few meters of 

probable Pleistocene) early Tertiary age. The drillhole bottomed in amygdaloidal basalt of Cretaceous ( ?) age. 

The Cretaceous section is composed almost entirely of 

clastic sediments. The oldest Cretaceous sedimentary unit is 

the Cape Fear Formation which contains Cenomanian 

(Woodbinian) fossils. The Middendorf Formation overlies 

the Cape Fear. Rare fossils in the Middendorf indicate 

a Cenomanian (lower Eaglefordian) placement. No fossils 

suggestive of a Turonian or Coniacian Age (middle Eaglefordian to early Austinian) were found. The overlying 

Black Creek Formation is of probable late Santonian and 

early Campanian Age (late Austinian and early Tayloran). 

The youngest Cretaceous unit is the Peedee Formation. 

The Peedee contains assemblages indicative of a late Campanian to middle Maestrichtian Age (late Tayloran and 

Navarroan). The Cretaceous-Tertiary boundary is at 244 m 

(800ft). 

The oldest Tertiary unit is the Beaufort (?) Formation, 

the clays and sands of which contain early Paleocene assemblages (Danian; early and middle Midwayan). Overlying the Beaufort ( ?) are clayey sands and sandy clays assigned to the Black Mingo Formation. This unit is of Paleocene and early Eocene age (Thanetian and Ypresian; late 

Midwayan and Sabinian). The overlying Santee Limestone 

is of middle and late Eocene age (late Lutetian and Bartonian; late Claibornian and Jacksonian). The youngest 

Tertiary formation present is the Cooper Formation. The 

lower part of the Cooper is late Eocene (Bartonian; Jacksonian). The upper part, however, is of late Oligocene age 

( Chattian; Chickasawhayan). Both the Cooper and the 

Santee are dominantly carbonate. 

The biostratigraphy is summarized as follows: 

Formation 

CooPer --------------------

Santee -------------------- Black Mingo -------------- Beaufort(?) --------------

Peedee -------------------- Black Creek --------------- Middendorf ---------------

Cape Fear ----------------

Thickness 

(m) 

6 

64 

56 

67 

52 

164 

159 

124 

59 

Age 

Pleistocene(?). 

Chattian and Bartonian. Bartonian and Lutetian. 

Ypresian and Thanetian. 

Danian. 

Maestrichtian and Campanian. 

Campanian and Santonian(?). Cenomanian. 

Cenomanian. 

Palynomorphs, foraminifers, and ostracodes were studied 

from both the Cretaceous and Tertiary parts of the core. 

Mollusks have been examined from only the Cretaceous 

part, and calcareous nannofossils from only the Tertiary. 

INTRODUCTION 

The sedimentary rocks of a 792-m (2,599-ft) core 

from the Clubhouse Crossroads corehole 1 (CCC 1) 

in Dorchester County, S.C., (fig. 1) have been examined for micro- aod macrofossils. Most of the 

core is 15 em ( 6 in.) in diameter for approximately 

the upper 225 m (738 ft) and 7 em (2.75 in.) in 

diameter for the remaining 567 m (1,861 ft). The 

following groups have been studied in some detail : 

calcareous nannofossils (by Bybell), dinoflagellates 

(by May, McLean, and Witmer), mollusks (by 

Sohl), ostracodes (by Hazel and Valentine), planktic 

foraminifers (by Poore and Smith), and sporomorphs (by Christopher and Frederiksen). Other 

calcareous forms are rare or absent, and no siliceous 

microfossils were observed. 

In this paper, the lithostratigraphic units delineated in the core are dated paleontologically, assigned 

to commonly used provincial and international 

stages, and correla..ted with other lithostratigraphic 

units in the Atlantic and Gulf Coastal Province. In71 
72 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

EXPLANATION 

[2J Quaternary 

1:;:>:1 Miocene and Pliocene 

Eocene and Oligocene 

• Upper Upper Cretaceous 

0 50 100 MILES 

~ Lower Upper Cretaceous 

0 50 100 KILOMETERS 

FIGURE !.-Generalized geologic map of South Carolina showing location of the Clubhouse 

Crossroads corehole 1. The exact site is in tpe Cottageville, 1943, 15' quadrangle, at lat 

32•53.25' N., long 80•21.4' W., 3.5 km (2.2 mi) southwest of Clubhouse Crossroads and 

40 km (25 mi) west-northwest of Charleston, S.C. Geology modified from Cooke (1936). 

terpretations as to environment of deposition are 

also presented. Most of the studies are still incomplete at this writing, and investigations are continuing. We are confident of the age assignments of most 

of the beds seen in the core, but some assignments 

are tentative, and examination of additional samples 

in some intervals will be needed to document more 

precisely both zone and stage boundaries. At present, paleoenvironmental conclusions are very generalized and quite tentative. 

This paper is divided into two parts-in the first 

part, our interpretations are presented on biostratigraphy and paleoenvironment of the core; in the second part are short discussions on the occurrence, 

value, and degree of study of the six biologic groups 

used. 

Without the excellent technical support of many 

persons, this report could not have been prepared 

in the time allotted. Ellen E. Compton, Diane V. McNeave, W. A. Bryant, and Patricia B. Swain of the 

U.S. Geological Survey deserve special mention for 

their efforts. 

This study was funded in part by the U.S. Nuclear 

Regulatory Commission, Office of Nuclear Regulatory Research, under agreement number AT (49-

25)-1000. 
BIOSTRATIGRAPHY OF THE DEEP COREHOLE 73 

BIOSTRATIGRAPHY 

STAGE PLACEMENT 

Figure 2 is a generalized lithologic log of the core 

showing the spontaneous potential and resistivity 

curves and the formations recognized. The lithologies 

present are discussed in some detail by Gohn and 

others in this volume. Except for the upper 5 m (16 

ft) of unconsolidated Pleistocene(?) sediments, the 

core is entirely of Paleogene and Late Cretaceous 

age. Below the Pleistocene ( ?) to a depth of 137 m 

( 449 ft), the deposits are dominantly carbonate. 

The lowermost sedimentary rocks, present in the 

core above 13 m (43 ft) of mottled red clay which 

perhaps represents weathering of the underlying 

basalt, extend from 750 m (2,462 ft) to about 691 m 

(2,268 ft) and are assigned to the Cape Fear Formation. Rare late Cenomanian planktic foraminifers 

are present in the Cape Fear, and pollen in the unit 

suggests a W oodbinian assignment. The W oodbinian 

is placed in the middle Cenomanian by Pessagno 

(1969). 

Beds assigned to the Middendorf Formation are 

present between about 691 m (2,268 ft) and 567 m 

(1,860 ft). These beds are largely unfossiliferous; 

however, planktic foraminifers of the Rotalipora 

cushmani-R. greenhornensis Subzone of late Cenomanian Age (early Eaglefordian) are present at 

586 m (1,923 ft). This indicates that the unfossiliferous interval between 586 and 560 m (1,923-1,837 

ft), including whatever disconformities that may be 

present, represents the Turonian and Coniacian 

Stages, or in provincial terms, the middle and upper 

Eaglefordian and most, if not all, of the lower Austinian. According to the time scale of van Hinte 

( 1976), this interval would approximate 11 million 

years. An erosional disconformity probably is present in this 26-m (85-ft) interval, although the paleontological data do not indicate definitely whether 

this presumed disconformity is between the Middendorf and Black Creek Formations or within the 

Middendorf. Heavy-mineral data (Gohn and others, 

this volume) suggest that it is at the base of the 

Black Creek Formation. 

The sands and clays between 567 and 408 m 

(1,860-1,340 ft) are assigned to the Black Creek 

Formation. The fauna and flora of the Black Creek 

in the core indicate that the unit is of questionable 

Santoniam to Campanian Age and is referable to 

the upper part of the Austinian and lower part of 

the Tayloran Provincial Stages. No diagnostic fossils have been found in the lower 7 m (23 ft) of the 

Black Creek. The interval from about 560 to 533 m 

z UJO 

UJi= 

0<{ 

ttj::;; 

"'a: 0 

u,_ 

r6z i 

UJQ I 

5~ I 

""::;; ( Ua: 

<>:o 

cr:u.-

' 

I r _: ~ 

u,_ 

a:Z 

oo 

Oi= 

Z<l: 

UJ::;; 

Oa: 

Qo 

::;;"-

CLUBHOUSE CROSSROADS CORE 

DORCHESTER COUNTY, SOUTH CAROLINA 

>- I- DEPTH 

> (f) t= "I- cr: (f) zw Ui zw 

-W _I- w u.. w cr: :2 

EXPLANATION 

... Glauconite 

• Phosphate 

~ Fine-grained 

limestone 

~ Coarse-grained 

limestone 

~ Sandy . limestone 

200 

~ Silty clay 

250 

§ . Sandy clay 

300 § Clayey sand . 

350 D Sand . 

~ Unconformity 

400 

450 

500 

550 

600 

650 

700 

750 

FIGURE 2.-Stratigraphic column for the Clubhouse Crossroads core. Spontaneous potential (S.P.) and resistivity 

logs are also shown. 
74 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

(1,837-1,749 ft) contains mollusks, ostracodes, and 

pollen of early late Austinian Age, which may be 

Santonian (Pessagno, 1969) or early Campanian 

(Young, 1963) in age. The Austinian-Tayloran 

boundary in the core is between 522 and 473 m 

(1,713-1,552 ft). Foraminifer data suggest that 

this provincial stage boundary should be placed in 

the lower part of this interval, between 522 and 487 

m (1,713-1,598 ft). Ostracode data, on the other 

hand, suggest that the stage boundary is at about 

480 m (1,575 ft). For the purposes of this paper, 

the last depth is tentatively accepted, with the realization that the Austinian-Tayloran boundary may 

ultimately be revised downward in the core (but almost certainly not upward). 

The uppermost Cretaceous lithostratigraphic unit 

recognized in the core is the Peedee Forma.tion; it 

is represented by sandy clays and clayey sands 

within the interval between 408 and 244 m ( 1,340-

800 ft) . The lower beds of the Peedee from between 

408 and 335 m (1,340-1,100 ft) are Tayloran on 

the basis of both benthic macrofaunas and benthic 

and planktic microfaunas. The mollusks, foraminifers, ostracodes, dinoflagellates, and sporomorphs 

of the 335- to 244-m (1,100- to 800-ft) interval indicate that these beds are N avarroan. The Campanian-Maestrichtian boundary is at about 335 m 

(1,100 ft). According to Pessagno (1969), the 

Campanian-Maestrichtian and provincial TayloranNavarroan Stage boundaries are coincident. This 

assignment is followed herein, although this practice is not accepted by many workers, and more research on the problem is called for. The more argillaceous upper part of the formation from between 

296 and 281 m (971-922 ft) to 244 m (800 ft) is 

of middle Maestrichtian age as determined by planktic foraminifers, and is assignable to the Globotruncana gansseri Subzone of Pessagno (1969). 

Overlying the Peedee is a silty- to sandy-claystone 

unit not known from outcrops in the area of the 

Clubhouse Crossroads core. Beds of the same age 

do crop out to the northeast on the Black River near 

Georgetown, S.C. The unit is at least biostratigraphically equivalent in part to and is here questionably referred to the Beaufort Formation of North 

Carolina (see Gohn and others, this volume). The 

stratigraphic interval between 244 and 192m (800-

630 ft) is of Danian Age. The upper part, from 

about 213 m (700 ft) to 192 m (630 ft), is in the 

P 2 planktic foraminifer zone, and the lower part 

is in the P 1 zone. 

The Black Mingo Formation overlies the Beaufort ( ?) Formation and is present from 192 to 125 

m (630-410 ft). The unit consists mostly of clayey 

sands and sandy clays; sandy limestone beds are in 

the middle and at the top of the formation. The base 

of the Sabinian Stage is at 180 m (590 ft) ; thus, 

the lower 12m (40ft) of the Black Mingo, as identified in the core, is of Midwayan Age. Above this, 

from 180m to about 132m (590-433 ft), the Black 

Mingo is late Paleocene in age (Thanetian). The 

upper beds of the Black Mingo, at least from 132 to 

125 m ( 433-410 ft), are lower Eocene (Ypresian 

and upper Sabinian). The upper bed of the Black 

Mingo can be placed in the NP 12 nannoplankton 

zone, which is the middle zone of the Ypresian 

(Berggren, 1972). An unconformity between the 

Black Mingo and the Santee Limestone seems to 

represent the upper Ypresian and the lower Lutetian. 

The Santee Limestone is present from 125 to 69 m 

( 410-227 ft) in the core. The lower part of the 

Santee, from 125 to 102 m ( 410-336 ft), is of late 

Lutetian Age (NP 16-17) and is correlative with 

upper Claibornian formations in the Gulf Coast 

(Bybell, 1975). Nannofossils suggest that the middle Eocene-late Eocene boundary (Lutetian-Bartonian) is between 104 and 101 m (341-331 ft) in 

the core. This age assignment is consistent with ostracode data that suggest that the ClaibornianJacksonian boundary is between 110 and 95 m (361-

312 ft). The boundary is placed at 102 m (336 ft) 

in the core, at a point where the resistivity incre,ases 

markedly. The interval between 104 and 82 m (341-

269 ft) can be placed in the upper Eocene nannofossil zones NP 18 or NP 19, which are approximately 

equivalent to P 15 and P 16 in the planktic foraminifer zonation of Blow (1969) (see Berggren, 1972, 

p. 203). 

The contact between the lower part of the Cooper 

Formation and the underlying Santee Limestone is 

quite sharp. The upper beds of the Santee are extensively bored, and the borings are filled by 

glauconitic calcareous sediment of the lower part of 

the Cooper. Phosphate pebbles are concentrated near 

the boundary; some pebbles are as much as 3 em 

(1.2 in) in diameter. The beds above and below this 

contact are upper Eocene (Bartonian and Jacksonian), however, and both are placed in nannofossil zone NP 20. 

The Cooper Formation, as that term has been used 

in South Carolina (for example, Pooser, 1965; 

Sanders, 1974), is present from 69 to 5 m (227-16 

ft) and contains beds of late Eocene and Oligocene 

age. At least in the area of the Clubhouse Crossroads 

core, the contact between the Eocene and Oligocene 
BIOSTRATIGRAPHY OF THE DEEP COREHOLE 75 

parts of the Cooper is an unconformity representing 

the lower Oligocene (Lattorfian and Rupelian 

Stages), a duration of approximately 5 million to 6 

million years (Berggren, 1972). This indicates that 

the lower part of the Cooper is part of a separate 

depositional cycle, even though the lithologies of the 

upper and lower parts perhaps cannot be consistently 

differentiated in the field without fossil control. 

The Cooper Formation present between 69 and 55 

m (227-180 ft) is of late Eocene age on the basis 

of its planktic flora and fauna. Ostracodes suggest 

assignment to the Jacksonian Provincial Stage. The 

upper 50 m (164ft) of the Cooper from a depth of 

55 to 5 m ( 180-16 ft) is of Oligocene age. Ostracodes, particularly, suggest the presence of at least 

upper Vicksburgian sediments, and the Vicksburgian-Chickasawhayan boundary is placed at about 

35 m (115 ft) depth. However, calcareous nannoplankton zones NP 21, 22, and 23 (see Martini, 

1971) are seemingly absent; all of the Cooper above 

55 m (180 ft) is referable to NP 24, therefore, 

suggesting that the entire upper part of the Cooper 

is Chickasawhayan and upper Chattian. However, 

foraminifers questionably indicating planktic foraminifer zone P 20 are present at 52 m (171 ft), 

and P 20 is conside,red indicative of the lower Chattian and equates with the upper part of nannoplankton zone NP 23 according to Berggren (1972). Thus, 

the nannoplankton, ostracode, and planktic foraminifer data are not compatible, although the apparent 

age disagreement is comparatively slight. The problem probably is in the correlation of the ostracode 

range zones with the nannoplankton (NP) and 

planktic foraminifer (P) zones. Data from all three 

groups do indicate that most, if not all, of the lower 

Oligocene is missing. 

For the purposes of this paper, the upper part of 

the Cooper Formation (above 55 m; 180 ft) is considered to be late Vicksburgian and Chickasawhayan 

in age, and foraminifer zone P 20 is placed in the 

lower Chattian (and upper Vicksburgian), which 

was suggestied as a possibility by Berggren ( 1972, 

fig. 3). Thus, the entire Oligocene part of the Cooper 

is considered to be Chattian. 

CORRELATION 

Figure 3 is a generalized chart showing our conclusions as to correlation of the units of the Clubhouse Crossroads core with outcropping lithostratigraphic units in the Atlantic and Gulf Coastal 

Plains. The figure is self-explanatory, but some 

comments are appropriate. Note that several of the 

lithostratigraphic units of the Carolinas approach 

stage magnitude in temporal extent. Note also the 

significant segments of time that are not represented 

by sediments in the core or in the North Carolina 

outcrop. 

PALEOENVIRONMENT 

Incomplete studies of the fauna and flora of the 

Clubhouse Crossroads core lead to the following conclusions. The Cape Fear Formation represents inner 

sublittoral to brackish-water conditions of deposition (also see Swift and Heron, 1969). The Middendorf Formation was deposited under fluvial to 

marginal marine conditions. The lower pa.rt (Santonian?) of the Black Creek contains a nearshore 

possibly brackish-water assemblage, whereas the 

upper part was deposited at inner to middle sublittoral depths. The Peedee Formation was generally 

deposited in middle to outer sublittoral environments. 

The lower part of the Beaufort ( ?) Formation was 

deposited at middle to outer sublittoral depths; the 

upper part was deposited in the inner to middle sublittoral zone. The lower part of the Black Mingo was 

deposited in the middle to inner sublittoral zone 

with considerable oscillation in the depth of deposition, but the upper part of the formation seems to 

represent outer sublittoral deposition. The lower 

part of the Santee Limestone probably represents 

middle to outer sublittoral depths. The upper part 

of the Santee and both the lower and upper parts of 

the Cooper Formation were deposited at outer sublittoral (outer shelf) or even greater depths. 

TRANSGRESSIONS AND REGRESSIONS 

Figure 4 is a generaJized comparison of transgressive and regressive cycles in the northeast Texas and 

Mississippi emba.yments with those in the core and 

with those in other areas in the Atlantic Coastal 

Plain. The Clubhouse Crossroads core contains more 

maj(}r hiatuses, which represent regressions or periods of nondeposition. Otherwise, the curves for the 

Gulf Coast are generally similar to the curve for 

the core, except (1) in late Eaglefordian time, when 

there was regression in the eastern Gulf Coastal region and Atlantic Coastal region and transgression 

in the western Gulf Coastal region; and (2) in late 

Oligocene time, when apparently there was major 

transgression in the southern Atlantic Coastal region but minor regression in the Gulf Coastal region. 

The Jacksonian and Chickasawhayan transgressions of the core did not take place in the Salisbury 

embayment of the Virginia-Maryland-Delaware re-
76 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

"' European Provincial North Clubhouse LJ.J 

a: New Jersey Stage Stage Carolina Crossroads core LJ.J 

"' 

Chickasawhayan Trent Marl Upper part of 

(part) Cooper LJ.J Chattian z Formation LJ.J 

'--' 0 ? 

I 

(.!:) 

:::; 

! 

0 

Rupelian Vicksburgian I 

Lattorfian 

? 

Lower part of 

Cooper Formation 

Bartonian Jacksonian 

Castle flayne 

Limestone Santee 

LJ.J Limestone 

z 

LJ.J 

'--' 0 ? Lutetian Claibornian LJ.J Shark River 

Formation 

Ypresian Manasquan 

Sabinian Formation 

I I Black Mingo 

Vincentown Formation LJ.J Thanetian z Formation LJ.J 

'--' 0 

LJ.J 

--' Midwayan Hornerstown Sand Beaufort (?) ·~ Beaufort Danian 

?I Formation Formation 

Red Bank Sand 

Maestrichtian Navarroan Navesink 

Formation Pee dee 

Formation Pee dee _ l'1ount Laure~ar1CI__ __ Formation 

Wenonah Fm. 

Marshalltown Fm. 

Tayloran Englishtown Fm. f--.--------

Campanian Woodbury Clay Black Creek 

"' Merchantville Formation Black Creek :::J 

0 Formation LJ.J Formation '--' 

~ 

Santonian Magothy Fm. t:u Austinian ? a: 

'--' ? a: Coniacian LJ.J 

Q_ 

Q_ 

:::J 

Turonian 

Eaglefordian 

? ? 

Raritan Middendorf Fm. Middendorf Fm. 

Formation ? 

Cenomanian Cape Fear Fm. Cape Fear Fm. 

Woodbinian 

1 l 

The Sabmetown, Rockdale, and Segum Formations of the Wilcox Group of Plummer (1933) are herein adopted for U.S. Geological Survey useage. 2

The Bergstrom and Sprinkle Formations of Young (1965) are herein adopted for U.S. Geological Survey useage. 

FIGURE 3.-Generalized correlation chart for the Upper 

Cretaceous and lower Tertiary of the Atlantic and Gulf 

Coastal Plains. The interpreted stratigraphic position of 

the formations of the Clubhouse Crossroads core is shown. 

The Cape Fear Formation at Clubhouse Crossroads is underlain by basalt which has yielded K-Ar whole-rock ages 

of 94.8 m.y. and 109 m.y. Gottfried and others (this 

volume) present arguments that these are probably minimum ages and that the basalt is most likely of Late 

Triassic or Early Jurassic age. 
BIOSTRATIGRAPHY OF THE DEEP COREHOLE 77 

Clubhouse Chattahoochee C/) 

Western Texas ~ 

Crossroads core River area Alabama a: 

u.J 

C/) 

Paynes Hammock Catahoula Sandstone 

Sand I part) Upper part of ? Cooper Chickasawhay u.J 

Formation Formation z 

u.J 

u 

0 

Byram (.9 

::::; 

Formation 0 

Marianna Limestone 

Red Bluff Clay 

Lower part of Whitsett Fm. 

Cooper Formation Ocala 

Yazoo Clay MannirlJl Fm. 

Limestone Wellborn Sandstone 

f---------- Caddell Fm. 

Santee Moodys Branch Moodys Branch Moodys Branch 

Limestone Formation Formation Formation 

? Gosport Sand Yegua Fm. u.J 

Lisbon z 

Lisbon u.J 

Formation Cook Mountain Fm. u 

0 Formation Sparta Sand u.J 

Tallahatta Fm. Tallahatta Fm. Weches Fm. 

Queen City Sand 

1"'- Reklaw Fm 

Hatchetigbee Hatchetigbee Carrizo Sand Formation Formation 

Black Mingo Sabinetown Fm.l 

Formation T uscahoma Fm. T uscahoma Fm. Rockdale Fm.l 

Nanafalia Fm. Nanafalia Fm. Seguin Fm.l u.J 

~ Naheola Fm. z 

u.J 

u 

Wills Point Fm. 0 

Porters Creek Clay u.J 

Beaufort I? I Clayton --' <( 

Formation Formation a_ 

Clayton Fm. Kincaid Fm. 

I I I I I I I I I I 

Providence Sand Prairie Bluff Chalk Corsicana Marl 

Pee dee Ripley Fm. Ripley Fm. Nacatoch Sand 

Formation Neylandville Marl 

Cussetta Demopolis Bergstrom Fm.2 

Sand Member Chalk 

------- __reca_n__lll!l !,)]l!!K 

Wolfe City Sand 

Blufftown Mooreville Sprinkle Fm.2 Black Creek Formation Chalk C/) 

::J 

Formation 0 Burditt Marl u.J 

u 

Eutaw Fm. Dessau Fm. u.J 

~ 

a: ? Eutaw Fm. u Lower Austin Group a: 

u.J 

a_ 

11111111 

a_ 

South Bosque Formation ::J 

? rrrt:rrr111 

Middendorf Fm. Gordo Fm. Lake Waco Fm. 

Tuscaloosa 

? Formation Cape Fear Fm. Coker Fm. 

7 

.I Ill Ill/ Pepper Shale Member 

of Woodbine Formation 

FIGURE 3.-Continued. 
78 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

(/) 

European Provincial Northeast Texas Mississippi !,!! 

cr: MYBP Embayment UJ Stage Stage Embayment (Mann and Thomas, 1968) (/) 

22 j Chattian Chickasawhayan UJ 

z 

UJ 

u 

0 

(!) 

Rupelian ::::; 

0 Vicksburgian 

Lattorfian 

~ 37 

Bartonian Jacksonian 

>-

cr: 

<{ 

>= UJ cr: 

f--

UJ 

u 

0 

z 

UJ 

UJ 

Lutetian Claibornian 

~ 

~ 

Ypresian 

57 

Sabinian 

~ 

u 

0 

UJ 

z 

UJ Thanetian ~ / UJ 

<( Danian Midwayan c... 65 <------ Maestrichtian Navarroan 

70 

Campanian Tayloran 

(/) 

:::> 

0 

UJ 

u 79 ;:! 

UJ Santonian Austinian cr: 

u 83 

cr: Coniacian UJ J c... 86 

{~ c... 

:::> 

Turonian Eaglefordian 

~ 92 

Cenomanian 

Woodbinian \ - Regression 

Transgression +-

FIGURE 4.-Generalized transgressive and regressive cycles in the Gulf and Atlantic Coastal Plains. 

gion or in the Raritan embayment of New Jersey. 

Published (Brown and others, 1972, plates 24, 27) 

and unpublished data indicate, however, that sediments deposited during the Chickasawhayan transgression are present as far north as the Richmond, 

Va., area. 

RATES OF SEDIMENTATION 

By use of the time scales recently published by 

Berggren (1972), Obradovich and Cobban (1975), 

and van Hinte (1976), the duration in millions of 

years (m.y.) for the provincial and European stages 

recognized in the study of the Clubhouse Crossroads 

core has been calculated. From these data, the rate 

of sedimentation per million years for each stage 

also can be calculated. However, because differences 

in compaction rates of the lithologies present have 

not been taken into consideration, the values can 

only be considered rough approximations. Table 1 

lists the thickness, duration, and calculated sedimentation rate for each provincial stage, and table 2 

gives the same data for each European stage. Missing section is taken into consideration. For example, 

the fossils suggest that only the upper Claibornian 

(upper Lutetian) is present; thus the sedimentation 

rate given, 7.7 m/m.y. (25 ft/m.y.), is based on 3.0 

m.y. rather than on the 6.0-m.y. estimated duration 

of the Claibornian Stage (Berggren, 1972). Where 

significant parts of stages are represented by disconformities, the stages are divided into parts. 
Clubhouse 

Crossroads core 

BIOSTRATIGRAPHY OF THE DEEP COREHOLE 

Salisbury 

Embayment 

(Brown and others, 1972) 

~ Regression 

Transgression -

FIGURE 4.-Continued. 

Raritan Embayment 

(Owens and Sohl. 1969) 

(Petters, 1976) 

C/) 

~ 

a: 

L.I.J 

C/) 

>-

a: 

<( 

>= a: 

L.I.J 

1-

C/) 

::> 

0 

L.I.J 

u 

<( 

t::u 

a: 

u 

a: 

L.I.J 

a... 

a... 

::> 

79 

TABLE 1.-The thickness, duration, and calculated sedimentation rate for each provincial stage represented in the 

Clubhouse Crossroads core 

TABLE 2.-The thickness, duration, and calculated sedimentation rate for each European stage represented in the 

Clubhouse Crossroads core 

Stage Time represented 

(m.y.) 

Chickasawhayan ________________ _ 

Upper Vicksburgian -------------- Lower Vieksburgian ------------- Jacksonian ______________________ _ 

Upper Claibornian ---------------

Lower Claibornian ---------------- Sabinian ____ ----- __________ ------

Midwayan ___ --------------------- Navarroan ________ -------- ______ _ 

Tayloran ________ ---------·--------

Upper Austinian -----------------

Lower Austinian ----------------- Middle and Upper Eaglefordian __ _ 

Lower Eag]efordian -------------- Woodbinian _________ -------------

6.0 

2.0 

0 

5.5 

3.0 

0 

7.0 

6.0 

3.0 

6.0 

7.0 

0 

0 

2.7 

2.7 

Thickness (m) 

30 

20 

0 

47 

23 

0 

55 

64 

91 

145 

87 

0 

0 

124 

59 

Rate (m/m.y.) 

5.0 

10.0 

8.5 

7.7 

7.9 

10.7 

30.3 

24.2 

12.4 

45.9 

21.9 

Stage 

Chattian _______________ ----------

Rupelian ___________ --------------

Lattorfian ___ -------------------- Bartonian ______ ------------------

Upper Lutetian ------------------

Lower Lutetian ------------------ Ypresian ___ --------------------- _ Thanetian ______________ ----------

Danian ____ ---------------------- _ Upper Maestrichtian -------------

Lower and Middle Maestrichtian __ 

Campanian ___ ------------------ __ 

~:~~~~l:~ ( ~~- ===================== Turonian ------------------------ Middle and Upper Cenomanian ___ _ 

Time represented 

(m.y.) 

8.0 

0 

0 

5.5 

3.0 

0 

2.5 

6.5 

4.0 

0 

3.0 

8.0 

5.0 

0 

0 

5.4 

Thickness (m) 

50 

() 

0 

47 

23 

0 

12 

55 

52 

0 

91 

198 

34 

0 

0 

183 

Rate (m/m.y.) 

6.3 

8.5 

7.7 

4.8 

8.5 

13.0 

30.3 

24.8 

6.8 

33.9 
80 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

(lower, middle, or upper) to reflect this in the tables. 

The biostratigraphic assignment of the lithostratigraphic units of the core suggests that a rapid rate 

of clastic sedimentation during the Woodbinian and 

early Eaglefordian (middle and late Cenomanian) 

was followed by a regression resulting in the absence of middle and upper Eaglefordian and lower 

Austinian deposits (Turonian and Coniacian). After 

this event, the rate of clastic deposition increased 

throughout the remainder of the Cretaceous. The 

end of this period of marine deposition is marked 

by the unconformity at the Cretaceous-Tertiary 

boundary. 

Rates of sedimentation were generally lower in 

the Tertiary. The sedimentation rate decreased during the Paleocene and early Eocene, culminating in 

an unconformity seemingly equivalent to the upper 

part of the Sabinian and the lower part of the Claibornian. The Paleocene and lower Eocene sediments, 

like the Cretaceous, are dominantly clastic. The remainder of the Tertiary was characterized by two 

episodes of carbonate deposition apparently separated by a regressive phase as evidenced by an unconformity representing the lower Oligocene. 

FAUNA AND FLORA 

As stated in the "Introduction," six fossil groups 

were studied-calcareous nannofossils, dinoflagellates, mollusks, ostracodes, planktic foraminifers, 

and sporomorphs. However, not all groups were 

found or studied throughout the core. To date, mollusks have been studied only in the Cretaceous, and 

calcareous nannofossils only in the Tertiary. 

OSTRACODES 

Ostracodes are absent below 538 m (1,765 ft) except for a small assemblage in the Cape Fear 

Formation at 721 m (2,365 ft). The presence of 

Fossocytheridea lenoirensis Swain and Brown, 1964, 

at 721 m (2,365 ft) suggests placement in the brackish water facies of Unit F of Brown and others 

(1972). 

At 538 m (1,765 ft) Asciocythere macropunctata 

(Swain, 1952) occurs with "Cythereis" canteriolata 

Crane, 1965, and other species. This sample is probably correlative in part with Unit C of Brown and 

others (1972). Assemblages of probable late Austinian Age are present from a depth of about 538 m 

(1,765 ft) to about 481 m (1,578 ft). An assemblage 

at 481 m (1,578 ft) includes Haplocytheridea? 

nanifaba Crane, 1965, Cythereis dallasensis Alexander, 1929, Brachycythere pyriforma Hazel and 

Paulson, 1964, and "Phacorhabdotus" pokornyi 

Hazel and Paulson, 1964 (late form). This assemblage suggests correlation with the Burditt Marl or 

lowermost beds of the Sprinkle Formation of Texas. 

Assemblages suggesting uppermost Austinian to, 

perhaps, lower Tayloran are present from between 

481 and 473 m (1,578-1,552 ft) up to 408 m (1,340 

ft). 

The early to middle Tayloran species "Cythereis" 

plummeri Alexander, 1929, is present at 408 m 

(1,340 ft) and at 398m (1,306 ft). Haplocytheridea 

insolita (Alexander and Alexander, 1933), "Veenia" 

gapensis (Alexander, 1929), and Brachycythere 

porosa Crane, 1965, also occur in the deeper sample. 

At 385 m (1,263 ft), the Tayloran markers Haplocytheridea insolita and "Veenia" gapensis again 

occur. From between 385 and 366 m (1,263-1,201 

ft) to just below 322m (1,056 ft), the ostracode assemblage consists of species that occur in both the 

Navarroan and the Tayloran. The Peedee Formation 

above 322 m (1,056 ft) contains a typical Navarroan assemblage including such species as Haplocytheridea renfroensis Crane, 1965, "Cythereis" 

pidgeoni Berry, 1925, Brachycythere ovata Berry, 

1925, "Cythereis" huntensis (Alexander, 1929), and 

Haplocytheridea everetti (Berry, 1925). 

A diverse assemblage indicative of an early Midwayan Age is present in -the lower part of the Beaufort(?) Formation. Occurring in the lower part of 

the Beaufort(?), among others, are Phractocytheridea ruginosa Alexander, 1934, Loxoconcha atlantica (Alexander, 1934), Hermanites gibsoni Hazel, 

1968, H. midwayensis (Alexander, 1934), Phacorhabdotus sculptilis (Alexander, 1934), Acanthocythereis washingtonensis Hazel, 1968, Brachycythere 

plena Alexander, 1934, and Opimocythere browni 

Hazel, 1968. Ostracode assemblages. of late Midwayan Age are not well known in the Gulf and Atlantic Coastal Plains. Therefore, although ostracodes 

occur in the lower part of the Black Mingo Formation and upper part of the Beaufort(?) Formation 

in the core, they have not been as biostratigraphically definitive as the other fossil groups studied in 

this interval. 

Ostracode assemblages suggesting a Sabinian 

Age are present in the core from about 150 m ( 492 

ft) to at least 125m (410ft). Ouachitaia broussardi 

(Howe and Garrett, 1934), Haplocytheridea leei 

(Howe and Garrett, 1934), Acanthocythereis hilgardi (Howe and Garrett, 1934), Buntonia alabamensis (Howe and Garrett, 1934), Phractocytheridea moodyi (Howe and Garrett, 1934), "Cythereis" 

dictyolobus of Pooser (1965), H ermanites bassleri 
BIOSTRATIGRAPHY OF THE DEEP COREHOLE 81 

(Ulrich, 1901), and Opimocythere cf. 0. nanafaliana 

(Howe and Garrett, 1934), occur in this interval. 

The Claibornian indicators Opimocythere martini 

(Murray and Hussey, 1942) and Actinocythereis 

gosportensis (Blake, 1950) occur at about 110 m 

(361 ft). Ostracodes are fairly common in that part 

of the Cooper assigned to the Jacksonian, 69-55 m 

(227-180 ft). Cytheretta jacksonensis (Meyer, 

1887), Acanthocythereis spinomural?:s Howe and 

Howe, 1973, Echinocythereis jaclcsonensis (Howe 

and Chambers, 1935), Acanthocythereis fiorienensis 

(Howe and Chambers, 1935), and several others 

are typical Jacksonian species that are present in 

this interval. 

Several Vicksburgian guide species occur in the 

core between 55 and 35 m (180-115 ft). These include Actinocythereis dacyi (Howe and Law, 1936), 

A. thomsoni (Howe and Law, 1936), Buntonia sulcata Butler, 1963, and Buntonia huneri Howe and 

Law, 1936. The Chickasawhayan upper part of the 

Cooper Formation contains a diverse ostracode assemblage of about 40 species. Actinocythereis waynensis Butler, 1963, and Leguminocythereis 

scarabaeus of Brown (1958) and Pooser (1965), 

are two of the diagnostic species that occur in this 

interval. In the uppermost part of the Cooper, above 

about the 10-m (33-ft) depth in the core, species 

common in lower Miocene sediments, for example 

Echinocythereis clarlcana (Ulrich and Bassler, 

1904), make their first appearance. 

CRETACEOUS LARGER INVERTEBRATES 

Macrofossils are common at many Upper Cretaceous levels in the core between 537 and 245 m 

(1,763-804 ft). Although the shelled larger invertebrate groups of worms, sponges, bryozoans, scaphopods, and cephalopods are all represented, the 

assemblages are dominated by bivalves and gastropods. No single sample contains more than 20 species 

of mollusks, but this is only because of the limited 

nature of the core samples. Samples equivalent in 

volume to outcrop collections would undoubtedly 

yield greater diversity, including many of the larger 

forms not recoverable in cores. 

Below 537 m (1,763 ft) only one sample, at 721 m 

(2,365 ft), contained fossil mollusks; these are 

poorly preserved and nondiagnostic. 

The species Ostrea cretacea Morton, 1834, was 

found from 537 to 535 m (1,763-1,754 ft). This 

species is common to the upper part of the Eutaw 

Formation of the Chattahoochee River region of 

Alabama and Georgia, and to the Tombigbee Sand 

Member of the Eutaw of central and western Alabama; it has been reported from the uppermost part 

of the Magothy Formation at Cliffwood, N.J. In 

addition, it has been encountered in wells in North 

and South Carolina at a similar stratigraphic level. 

In outcrop, the Tombigbee Sand Member contains 

ammonites of the upper Austinian which Young 

( 1963) has assigned to the early Campanian. 

Up to 444 m (1,456 ft) the association of 

abundant Lucina glebula Conrad, 1875, Veniella 

mullenensis Stephenson, 1923, Camptonectes perlamellosa Whitfield, 1885, and others is similar to 

assemblages that occur through the middle and 

lower parts of the Blufftown Formation of the Chattahoochee River region and in the Woodbury Clay 

of New Jersey. The occurrence of a large Trigonarca 

and Aphrodina of the A. regia Conrad, 1875, type 

and several other mollusks in the assemblages at 411 

and 410 m (1,347 and 1,345 ft) suggests a correlation with the type section of the Snow Hill Member 

of the Black Creek Formation of North Carolina 

and the basal part of the Cusseta Sand Member of 

the Ripley Formation of Georgia and eastern Alabama. The lowest depth in the core at which Exogyra 

ponderosa Roemer, 1849, is found is 354 m (1,162 

ft). This species ranges through the upper Austinian 

into the Tayloran and forms the basis for a stratigraphically broad but well-recognized zone throughout the Gulf and Atlantic Coastal Plains. 

Navarroan molluscan assemblages are present 

from a depth of at least 332m (1,090 ft) to 245m 

(804 ft). Specimens of Exogyra assignable to E. 

costata Say, 1820, occur sporadically throughout 

this interval; the varietal form spinifera is common. 

In outcrop, the Exogyra costata zone has been considered coordinate in range with the Navarroan. 

Flemingostrea subspatulata (Forbes, 1845), occurs 

commonly in samples at depths between 325 and 314 

m (1,066-1,030 ft). This species ranges through the 

lower and middle N avarroan, but the specimens 

from the core material represent the form common 

to the lower part of the range zone that on the outcrop is associated with Exogyra cancellata Stephenson, 1914. The Exogyra cancellata zone is considered 

lower N avarroan. Thus, the interval from about 335 

to about 314 m (1,100-1,030 ft) appears to be assignable to the E. cancellata zone. This early form 

of Flemingostrea subspatulata occurs in the uppermost part of the Wenonah Formation of New Jersey, 

the basal part of the Peedee Formation in North 

Carolina, and in the upper part of the Cusseta Sand 

Member of the Ripley Formation of Georgia and 

eastern Alabama. 
82 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

TERTIARY CALCAREOUS NANNOFOSSILS 

Calcareous nannofossils are present throughout 

the Paleogene part of the core except for a 6-m (20-

ft) interval at the Paleocene-Eocene boundary. 

Coccolith abundance and diversity are less than normally observed in Gulf Coast Paleogene material, 

but coccoliths are present in sufficient numbers to be 

one of the more biostratigraphically useful groups 

in the Clubhouse Crossroads core. 

Martini's (1971) standard calcareous nannoplankton zonation contains 25 NP zones in the Paleocene 

through Oligocene. Because many calcareous nannofossil marker species are absent from the core, and 

because several unconformities are present, only 

eight of these zones can be confidently recognized. 

The Beaufort ( ?) Formation from 244 to 192 m 

(800-630 ft) is entirely within the lower Paleocene 

NP 3 zone (Danian). Some of the lowest nannofossil diversities are in the Paleocene part of the core; 

however, the first appearances of Chiasmolithus 

danicus (Brotzen, 1959) and Coccolithus pelagicus 

(Wallich, 1877) within this interval indicate zone 

NP 3. Other typical Paleocene species are Coccolithus cribellum (Bramlette and Sullivan, 1961), 

Cruciplacolithus tenuis (Stradner, 1961), N eococcolithes protenus (Bramlette and Sullivan, 1961), 

and Zygolithus sigmoides (Bramlette and Sullivan, 

1961). 

The Black Mingo Formation from 192 to 125 m 

(630-410 ft) is divided among three zones-NP 4, 

NP 5-9, and NP 12. The first late Paleocene 

(Thanetian) species appear within this formation. 

Chiasmolithus bidens (Bramlette and Sullivan, 

1961) and Toweius craticulus Hay and Mohler, 1967, 

occur in the assemblage and indicate the presence of 

zone NP 4. 

From 177 to 138m (581-454 ft), the Black Mingo 

Formation covers zones NP 5 through NP 9 (upper 

Paleocene). Because of low species. diversity, individual zones within this interval could not be recognized. Ellipsolithus distichus (Bramlette and 

Sullivan, 1961) and Fasciculithus typmpaniformis 

Hay and Mohler, 1967, have their first occurrences 

within the NP 5 zone, and Discoaster multiradiatus 

Bramlette and Riedel, 1954, has its extinction at the 

top of zone NP 9. 

Between 138 and 136 m (451 and 445 ft), the 

Black Mingo Formation is barren of calcareous nannofossils, and this interval may include an unconformity encompassing zones NP 10-11. From 131 

to 125 m ( 431 to 410 ft), the Black Mingo Formation is within the lower Eocene (Ypresian) NP 12 

zone. Here the first Discoaster barbadiensis (Tan 

Sin Hok, 1927) Sphenolithus moriformis Bronnimann and Stradner, 1960), and several discolith 

species, among them Pontosphaera duocava (Bramlette and Sullivan, 1961), P. pulchra (Deflandre, 

1954), P. ocellata (Bramlette and Sullivan, 1961), 

and P. vesca (Sullivam, 1965), are found. Some late 

Paleocene species have been reworked into these 

sediments. 

The contact of the Black Mingo Formation with 

the overlying Santee Limestone represents an unconformity covering zones NP 13-16. The lower 

part of the Santee Limestone from 125 to 104 m 

(410-341 ft) is in zones NP 16-17 (middle Eocene, 

Lutetian) . Typical middle Eocene species first occurring within this interval include Blackites spinosus (Deflandre and Fert, 1954), Cyclococcolithus 

formo,sus Kamptner, 1963, Cyclococcolithus reticulatus Gartner and Smith, 1967, Helicopontosphaera 

compacta (Bramlette and Wilcoxon, 1967), Pontosphaera pulcheroides (Sullivan, 1956), Reticulafenestra umbilica (Levin, 1965), and Zygrhablithus 

bijugatus (Deflandre, 1954). 

The calcareous nannofossil species diversity increases from 16 species in the Paleocene part of the 

core to 54 species in the upper Eocene. Part of this 

increase is due to a normally increasing diversity of 

calcareous nannofossils in the Paleocene and Eocene, 

but in the Clubhouse Crossroads core, it is also due 

to either more favorable living conditions in the 

water column or better preservation of upper 

Eocene sediments. Several species, normally common throughout the middle and upper Eocene, are 

present only in upper Eocene sediments in the core. 

The Santee Limestone interval between 101 and 

83 m (331-271 ft) represents zones NP 18-19 (upper Eocene, Bartonian). H elicopontosphaera bramletti Muller, 1970, H. euphratis (Haq, 1966), and 

Sphenolithus obtusus Bukry, 1971, first appear here, 

and many other typical middle and late Eocene 

species are also found. Pentaliths are especially 

abundant within this interval. 

The uppermost part of the Santee Limestone and 

lowermost part of the Cooper Formation, 81-55 m 

(266-180 ft) can be placed in the upper Eocene NP 

20 zone. Sphenolithus pseudoradians Bramlette and 

Wilcoxon, 1967, and Helicopontosphaera intermedia 

(Martini, 1965) first occur in this zone, whereas 

species with their last occurrences here include Discoaster barbadiensis (Tan Sin Hok, 1927), D. 

saipanensis Bramlette and Riedel, 1954, and Micmntholithus procerus Bukry and Bramlette, 1969. 

An unconformity occurs within the Cooper Formation at 55 m (180 ft) and represents zones NP 
BIOSTRATIGRAPHY OF THE DEEP COREHOLE 83 

21-23. From 55 to 5 m (180-16 ft) the Cooper Formation is in zone NP 24 (upper Oligocene, Chattian), which is marked by the first occurrence of 

H elicopontosphaera recta ( Haq, 1966) and Pontosphaera clathrata (Roth and Hay, 1967). Heliocopontosphaera compacta Bramlette and Wilcoxon, 

1967, and Sphenolithus predistentus Bramlette and 

Wilcoxon, 1967, which become extinct within zone 

NP 24, are found throughout this intervaL Considerable reworking of late Eocene species into the 

lower half of this zone has taken place. 

FORAMINIFERS 

Late Cretaceous planktic foraminifers are common to abundant throughout much of the Cretaceous 

strata penetrated in the Clubhouse Crossroads core; 

they are particularly abundant in the Campanian 

and Maestrichtian parts of the Peedee and Black 

Creek Formations. Samples from these units have 

yielded superbly preserved faunas, many having a 

species diversity nearly identical to the rich faunas 

documented from the Upper Cretaceous of the western Gulf Coastal Plain area (Pessagno, 1967; Smith 

and Pessagno, 1973). Within the Campanian-Mae~ 

strichtian interval, however, is strong faunal and 

floral evidence, supported by lithologic data, of rapid 

and in some instances rather extensive changes in 

paleoenvironmental depositional settings. Within 

these more shallow neritic intervals, diversity of the 

planktic foraminifers is quite low (although preservation remains excellent) and is acc.ompanied by 

the appearance of or increase in abundance of typical shallow-water benthic foraminifers. The more 

shallow neritic parts of the Campanian and Maestrichtian sections, as well as the majority of preCampanian samples that were studied, are 

characterized by low species diversity and the absence of many key species normally present in more 

open marine paleoenvironments. This has resulted 

in questionable biostratigraphic assignments for 

several samples. In instances such as these, the zonal 

assignment of the sample is questioned or, where 

practicable, referred to an interval of two or more 

biostratigraphic zones. The biostratigraphic zonal 

assignment and chronostratigraphic correlation of 

these samples closely follows that utilized by Pessagno (1967, 1969) in his studies of the western 

Gulf Coast. 

Both the Middendorf and the Cape Fe,ar Formations, from the total depth of available samples, 741-

579 m (2,430-1,900 ft), contain a restricted shallowwater foraminiferal fauna, many samples being 

barren of planktic foraminifers. However, this 

interval contains rare individuals of H eterohelix 

moremani (Cushman), H edbergella brittonensis 

Loeblich and Tappan, Globigerinelloides cf. G. caseyi 

(Bolli, Loeblich, and Tappan), and very abundant 

and excellently preserved Guembelitria harrisi Tappan, which are referable to the Rotalipora cushmanigreenhornensis Subzone of late Cenomanian Age. 

This subzone is also present within the upper parts 

of the Woodbine Formation and about the lower 

half of the Eagle Ford Group of Texas (Pessagno, 

1967; 1969). 

In the interval from 579 to 522 m (1,900-1,713 

ft), all samples that were studied were barren or 

contained no biostratigraphically important planktic 

foraminiferal faunas. In the lower part of the Black 

Creek Formation, a sample at 522 m (1,713 ft) contained M arginotruncana angusticarenata ( Gandolfi), as well as several species of the genus 

Archaeoglobigerina. The concurrent range of these 

species is indicative of the Marginotruncana concavata Subzone of Santonian Age. 

The Black Creek section between 518 and about 

494 m (1,700-1,620 ft) contains a sparse and poorly 

preserved foraminiferal fauna lacking the key 

species that would permit a precise biostratigraphic 

zonal assignment. Tentatively these faunas can be 

referred to the lower and middle Campanian Globotruncana fornicata and Archaeoglobigerina blowi 

Subzones. According to Pessagno (1969), these 

subzone.s are representative of the upper part of the 

Austinian and the lower part of the Tayloran Provincial Stages. A sample at 487 m (1,599 ft), in 

the middle part of the Black Creek Formation, contains a moderately diverse planktic foraminiferal 

fauna that can be assigned to the Archaeoglobigerina 

blowi Subzone of middle Campanian Age. 

Samples from the upper part of the Black Creek 

Formation and the lower part of the Peedee Forma~ 

tion, from about 480 to 375 m (1,575-1,230 ft), are 

assignable to the Campanian Globotruncana elevata 

Subzone. Planktic foraminifers within this interval 

are very abundant, moderately diverse, and generally well preserved. Characteristic of this interval 

is the overlap between the ranges of Globigerinelloides multispina (Lalicker) and Globotruncana 

linneiana ( d'Orbigny) and those of V entilabrella 

glabrata (Cushman), Rugoglobigerina tradinghousensis Pessagno, and Globotruncana elevata 

(Brotzen). Units normally placed in the middle and 

upper parts of the Tayloran Provincial Stage contain an assemblage characteristic of this subzone 

(see Pessagno, 1967, 1969; Olsson, 1975; Petters, 

1976). Lower and middle parts of the Peedee strata 
84 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

within the interval between about 375 and 312 m 

(1,230-1,025 ft) are predominantly shallow marine; they contain nondiagnostic planktic foraminifers but probably are equivalent to either the 

upper Campanian Globotruncana elevata Subzone 

or to the lower Maestrichtian Rugotruncana subcircumnodifer Subzone. 

Samples from the Peedee within the interval between about 312 and 290 m (1,025-950 ft) are assignable to the lower Maestrichtian Rugotruncana 

subcircumnodifer Subzone. Although the planktic 

foraminiferal faunas within this interval are less 

diverse than those from overlying strata, the presence of Globigerinelloides yaucoensis (Pessagno), 

Archaeoglobigerina blowi Pessagno, Globotruncana 

bulloides (Vogler), and G. fornicata Plumm,er, is 

indicative of an early Maestrichtian Age and indicates placement of the interval in the lower part of 

the N avarroan Provincial Stage. 

The upper part of the Peedee Formation within ' the interval between 290 and 244m (950-800 ft), is 

assignable to the middle Maestrichtian Globotruncana gansseri Subzone. Samples within this section 

have yielded an excellently preserved and diverse 

planktic formaminiferal assemblage including abundant individuals of Guembelitria cretacea Cushman 

Heterohelix glabrans (Cushman), Planoglobulind 

carseyae (Plummer), Pseudotextularia deformis 

(Kikoine), Globotruncana aegyptiaca Nakkady, G. 

duwi Nakkady, G. gansseri Bolli, G. trinidadensis 

Gandolfi, Rugoglobigerina hexacamerata Bronnimann, R. reicheli Bronnimann, and Globotruncanella 

monmouthensis (Olsson). None of these species 

have been documented from strata older than middle Maestrichtian in age (Smith and Pessagno, 

1973). 

Planktic foraminiferal faunas assignable to 

the uppermost Maestrichtian Abathomplalus mayaroensis Subzone were not found during this investigation. Because an obvious erosional unconformity 

exists between the Maestrichtian Peedee Formation 

and the overlying Danian Beaufort(?) Formation, 

and because both lithologic units are richly microfossiliferous, it seems reasonable to presume that 

strata assignable to the A. mayaroensis Subzone 

were removed (rather than never deposited) during 

latest Maestrichtian and (or) Danian time. 

Examination of the rather poorly preserved 

planktic foraminifers from the Cenozoic parts of 

the Clubhouse Crossroads core has resulted in the 

following biostratigraphic zonal assignments and 

age determinations. The lower part of the Beaufort ( ?) strata from its unconformable contact with 

the underlying Peedee Formation at 244 m (800 

ft) to approximately 215 m (705 ft) contains Globoconusa daubjergensis (Bronnimann) and other 

species diagnostic of the G. daubjergensis Zone 

(zone P 1) of early Paleocene (early Danian) age. 

Beaufort(?) strata in the interval from between 

about 215 and 201 m (705 and 659 ft) are questionably assigned to the Morozovella uncinatu-M. 

angulata Zone (P 2) of late early Paleocene (late 

Danian) age. 

The uppermost 8-15 m (25-50 ft) of the Beaufort ( ?) Formation and the basal few feet of the 

Black Mingo Formation contain Morozovella angulata (Bolli), Subbotina trilocu,linoides (Plummer), 

S. pseudobulloides Plummer, Planorotalites compressa (Plummer), and P. ehrenbergi (Bolli). This 

assemblage is typical of the early part of the late 

Paleocene (early Thanetian) and is assignable to 

the Morozovella pusilla pusilla-M. angulata Zone (P 

3). 

A sample at 170 m (557 ft) from the middle of 

the Black Mingo Formation contains a fauna that 

includes Morozovella angulata (Bolli), M. pusilla 

(Bolli), Planorotalites imitata (Subbotina), P. 

ehrenbergi (Bolli), P. cf. P. pseudomenardii 

(Bolli), P. compressa (Plummer), and Truncorotaloides esnaensis (LeRoy). This assemblage is referable to the Planorotaloiaes pseudomenardii Zone 

(zone P 4) of late (although not latest) Paleocene 

age. The upper part of the Black Mingo Formation 

contains a distinctive early Eocene planktic foraminiferal assemblage, although because of the lack of 

diagnostic species, the Paleocene-Eocene boundary 

(between zones P 6a and P 6b, Berggren, 1972) can 

be defined no more precisely than somewhere within 

the interval between 169 to 133 m (555-435 ft). 

' Most of the Santee Limestone strata within the 

interval between about 120 and 77 m (393-254 ft), 

contain poorly preserved and generally nondiagnostic planktic foraminiferal assemblages assignable 

to zones P 11 through P 14 of middle Eocene (Claibornian) age. 

The lower part of the Cooper Formation contains 

a rare and generally poorly preserved fauna, although species such as Cassigerinella eocaena Cordey, Chiloguembelina cubensis (Palmer), C. martini 

(Pijpers), Pseudohastigerina barbadoensis Blow, 

Globigerina ouachitaensis Howe and Wallace, G. 

angiporoides Hornibrook, G. praebttlloides Blow, 

Hantlcenina primitiva Cushman and Jarvis, Globigetinathelca mexicana (Cushman), and Globorotalia 

cerroazulensis (Cole) are present and indicate a 

late Eocene age assignment (zones P 15-17 of Blow, 

1969). 
BIOSTRATIGRAPHY OF THE DEEP COREHOLE 85 

A sample from the Cooper Formation at 57 m 

(188 ft) is questionably referred to the Globigerina 

tapuriensis Zone (P 18) of early Oligocene age; 

however, a late Eocene age assignment is also quite 

possible. If the sample at 57 m (188ft) is Oligocene, 

then the Eocene-Oligocene boundary is between 59 

m (193ft) and 57 m (188ft). If the sample at 57 m 

(188 ft) is of late Eocene age, then the EoceneOligocene boundary is somewhat higher, between 57 

and 55 m ( 188-179 ft). From about 55 to 25 m 

( 179-83 ft), the presence of forms related to Globigerina angulisuturalis Bolli suggests assignment to 

the upper part of the Globigerina ampliapertura 

Zone (zone P 20 of Blow). Foraminifers recove·red 

between about 25 and 10 m (83-32 ft) are referable 

to zone P 21. 

Samples from the upper part of the Cooper Formation, from a depth of 10-5m (32-16 ft), contain 

Cassigerinella chipolensis (Cushman and Ponton), 

Globigerina angulisuturalis Bolli, G. anguliojficinalis Blow, G. angustiumbilicata Bolli, G. ciperoensis 

Bolli, and Globoquadrina cf. G. globularis Bermudez, among others, which suggest correlation 

with the Globigerina angulisuturalis-Globo1'otalia 

opima Zone or the Globigerina angulisuturalis Zone 

(zones P 21-22 of Blow, 1969) of late Oligocene 

age. 

SPORES AND POLLEN 

Very little has been published on spores and pollen from the Tertiary of the Atlantic Coast; therefore, study of the Clubhouse Crossroads core has 

provided an opportunity to gather the first detailed 

information on the stratigraphic distribution of 

spores and pollen in· the Paleogene rocks of the 

southern Atlantic Coastal Plain. No spore~pollen 

zonation of the Paleogene rocks of the Gulf Coast 

has been proposed in the literature, but the ranges 

of many Gulf Coast species are fairly well known 

from the Midwayan to the lower Vicksburgian and 

can be compared with the ranges of the species d~ 

termined in the South Carolina material. 

All samples below 733 m (2,404 ft) were barren 

of palynomorphs. Spor~pollen assemblages from 

the Cretaceous System of the core were correlated 

with the informal palynological zones established 

by Brenner (1963), Doyle (1969), Sirkin (1974), 

and Wolfe (1976) for the Middle Atlantic States. 

From 733 to 714 m (2,404-2,342 ft), the assemblage is considered equivalent to Doyle.'s (1969) 

Zone IV, on the basis of samples from the Woodbridge Clay Member of the Raritan Formation of 

New Jersey. At 714 m (2,342 ft), this assemblage 

includes only the Normapolles genera Atlantopollis 

and Complexiopollis, along with Tricolpites crassimurus (Groot and Penny, 1960) Singh, 1971, "Retitricolpites" georgensis Brenner, 1963, and "R." 

geranioides (Couper, 1958) Brenne·r, 1963. 

All samples examined between 714 and 580 m 

(2,342-1,902 ft) in the core were barren of palynomorphs. Between the 580- and 550-m (1,902- and 

1,804-ft) depths in the core, units equivalent to the 

South Amboy Fire Clay Member of the Raritan Formation were identified on the basis of the presence 

of Porocolpopollenites spp., Labrapollis sp., Triatriopollenites spp., Complexiopollis spp., Santalacites 

spp., and Pseudoplicapollis spp. 

A comparison of samples from the Clubhouse 

Crossroads core with outcropping units from New 

Jersey indicates that the biostratigraphic equivalents of the Magothy Formation extend from 550 to 

520 m (1,804-1,706 ft) in the core. Within this interval occur the N ormapolles Praecursipollis sp., 

Santalacites spp., Complexiopollis funiculus 

Tschudy, 1973, C. abditus Tschudy, 1973, Pseudoplicapollis spp., Plicapollis rusticus Tschudy, 1975, 

and Trudopollis spp., along with an abundance of 

oblate triangular foveoreticulate tricolporates. 

In the Middle Atlantic States, Wolfe's (1976) 

Zone CA-2 encompasses the entire Merchantville 

Formation of the Raritan embayment and the lower 

part of the Merchantville Formation of the Salisbury embayment. In the core this zone is recognized 

between 520 and 490 m (1,706-1,607 ft) ; it is characterized by an assemblage that includes H olkopollenites sp. A (CP3D-1), Plicapollis rusticus 

Tschudy, 1975 (NE-1), Propylipollis sp. B (PR-1), 

Complexiopollis abditus Tschudy, 1973 (NB-1), 

Santalacites sp. (NB-2), and Osculapollis cf. 0. perspectus Tschudy, 1975 (N0-4). (Note: the alphanumeric code following each binomen refers to 

Wolfe's, 1976, species designation.) 

Zone CA-3 of Wolfe (1976), established for the 

Woodbury Clay of the Raritan embayment and the 

upper part of the Merchantville Formation of the 

Salisbury embayment, extends from 490 to 430 m 

(1,607-1,410 ft) in the core. Within this interval 

the following species occur: Brevicolporites sp. A 

(CP3F-1), Tricolporites sp. C (C3C-2), and Holkopollenites sp. B (CP3D-2). 

In the core, the biostratigraphic equivalent of the 

Englishtown Formation of the Middle Atlantic 

States (Wolfe's, 1976, Zone CA-4) was difficult to 

delineate. However, the assemblage that character~ 

izes this unit in both the Salisbury and Raritan embayments and in what is interpreted to be Englishtown equivalent in the core includes Santalacites sp. 
86 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

(NB-2), ?Plicapolli~ sp. A (ND-1), Plicapo~lis 

rusticus Tschudy, 1975 (NE-1), and Holkopollenites sp. B (CP3D-2). The unit extends from the 

430- to 420-m (1,410- to 1,378-ft) depths in the 

core. 

Wolfe's (1976) Subzone CA-5, characteristic of 

the Marshalltown Formation of the Raritan and 

Salisbury embayments, is between 420 and 360 m 

(1,378-1,181 ft) in the core. The concurrent ranges 

of Complexiopollis abditus Tschudy, 1973 (NB-1), 

Pseudoculapollis admirabilis Tschudy, 1975 (NR1), ?Plicapollis sp. B (ND-2), Holkopollenites cf. 

H. chemardensis Fairchild in Stover, Elsik, and 

Fairchild, 1966 ( CP3D-3), and Plicapollis retusus 

Tschudy, 1975 (NE-3), among others, were used 

to identify this biostratigraphic unit. 

Beds correlative with the Mt. Laurel Sand and 

Wenonah Formation of the Middle Atlantic States 

(Subzone CA-5 B of Wolfe, 1976) exist between the 

360- and 290-m (1,181- and 951-ft) depths in the 

core. The occurrence of Pseudoplicapollis endocuspis 

Tschudy, 1975 (NC-2), Osculapollis aequalis Tschudy, 1975 (N0-1), Triatriopollenites sp. (NP-2), 

Labrapollis sp. (NV -1), and Pseudovacuopollis involutus Tschudy, 1975 (NT-1), help to correlate this 

interval. 

Biostratigraphic equivalents of the Navesink Formation and Red Bank Sand of the Raritan embayment and of the Monmouth Group of the Salisbury 

embayment (Wolfe's, 1976, Zone CA-6/MA-1) were 

identified between the 290- and 244-m (951- and 

800-ft) depths in the core. The lower boundary of 

this interval is marked by the last occurrence of 

Pseudoplicapollis endocuspis Tschudy, 1975 (NC2), and ?Plicapollis sp. C (ND-3) and by the first 

appearance of Plicatopollis sp. (NN-2) and Momipites sp. (NK-3). 

The Cretaceous-Tertiary boundary in the Clubhouse Crossroads core is marked by the first appearances of Momipites coryloides Wodehouse, 1933, 

Momipites cf. M. inaequalis Anderson, 1960, and 

Favitricolporites baculoferus (Pflug in Thomson 

and Pflug, 1953) Srivastava, 1972. Whether these 

three species also have first occurrences at this 

horizon in the Gulf Coast is not known. 

The middle Midwayan is characterized by the 

first occurrences of Trudopollis plena Tschudy, 1975, 

and probably also Triporopollenites n. sp. A (thinwalled) of Tschudy, 1973. The last occurrence of 

Pseudoplicapollis serena Tschudy, 1975, is within the 

upper Midwayan in both the Gulf Coast and the core 

and is one orf the most important spore-pollen extinction events of the Paleogene. The first occurrence of 

Aesculiidites circumstriatus (Fairchild in Stover 

and others, 1966) Elsik, 1968, is at about the Midwayan-Sabinian boundary in both regions. In the 

middle Sabinian of the Gulf Coast and in the core, 

the best datum is provided by the last occurrences 

of Momipites dilatus (Fairchild in Stover and others, 

1966) Nichols, 1973, and Momipites spp. of the 

Tenuipolus Group. The upper Sabinian (lower Eocene) both of the Gulf Coast and of the core from 

137 to about 125m (450-410 ft) is distinguished by 

the concurrence of Thomsonipollis magnifica (Pflug 

in Thomson and Pflug, 1953) Krutzsch, 1960, and 

Nuxpollenites spp. and especially by the rather high 

relative abundance of Platycarya spp. and Platycaryapollenites spp. 

In the Gulf Coastal Plain and in the Clubhouse 

Crossroads core, the Jacksonian and the uppermost 

Claibornian contain similar spore-pollen assemblages. Important marker species present for this 

part of the Paleogene are Qu.ercoidites microhenricii 

(Potonie, 1931) Potonie, 1960, and Pollenites ventosus Potonie, 1931. Nuxpollenites spp. is regularly 

present in the Claibornian but is extremely rare in 

the Jacksonian. The Chickasawhayan and late Vicksburgian, 55- to 5-m (180- to 16-ft), spore-pollen 

assemblages of the Clubhouse Crossroads core are 

dominated by Cupressacites spp., Quercus spp., and 

a new species of Momipites that is mostl simila~ 

morphologically and stratigraphically to Triatriopollenites coryphaeus s. str. (Potonie, 1931) Thomson and Pflug, 1953. Many species found in the lower 

Vicksburgian of the Gulf Coast are lacking from the 

upper Vicksburgian and Chickasawhayan of South 

Carolina, including Momipites coryloides Wadehouse, 1933, and M; microfoveolatus (Stanley, 1965) 

Nichols, 1973. 

DINOFLAGELLATES 

Phytoplankton, primarily dinoflagellates, are present in many of the stratigraphic intervals of the 

Clubhouse Crossroads core. Dinoflagellates are rare 

in the deepest interval sampled, 734-714 m (2,404-

2,342 ft). No phytoplankton were observed in samples from an interval between 704 and 580 m (2,309-

1,902 ft), and diversity is very low between 559 and 

543 m (1,835-1,781 ft). Dinoflagellates are present 

in moderate abundance and diversity from between 

543 and 518 m (1,781-1,700 ft) to 244 m (800 ft). 

From 244 to 198m (800-649 ft), dinoflagellates are 

abundant, but diversity is generally low. In the interval from 190 to 124 m (623-407 ft), dinoflagellates are virtually absent. Between 120 and 5 m 
BIOSTRATIGRAPHY OF THE DEEP COREHOLE 87 

(394-16 ft) dinoflagellates are generally abundant 

and diversicy is variable. 

Only three species of dinoflagellates were observed 

in the core below 559 m ( 1,835 ft) . Odontochitina 

costata Alberti, 1961, Florentinia lasciniata Davey 

and Verdier, 1975, and Oligosphaeridium pulcherri~ 

mum (Deflandre and Cookson) Davey and Williams, 

1966, occur between 733 and 714 m (2,404-2,342 ft). 

The concurrent ranges of these species suggest a 

Cenomanian Age for the interval. 

Because of low species diversity, the sampled interval between 559 and 543 m (1,835-1,781 ft) could 

not be dated precisely. The concurrence of the ranges 

of Defiandrea granulifera Manum, 1963, and Palaeohystrichophora infusorioides Deflandre, 1935, suggests an age not older than Santonian. 

On the basis of the concurrent ranges of Horologinella apiculata Cookson and Eisenack, 1962, Defiandrea sverdrupiana Manum, 1963, and Palaeostomacystis laevigata Drugg, 1967, it is suggested that 

the 518- to 383-m (1,700- to 1,257-ft) interval is of 

Campanian Age. Other species present in this interval are Dinogymnium undulosum Cookson and 

Eisenack, 1970, Dinogymnium euclaensis Cookson 

and Eisenack, 1970, Dinogymnium digitus (Deflandre) Evitt and others, 1967, Dinogymnium denticulatum (Alberti) Evitt and others, 1967, and Defiandrea echinoidea Cookson and Eisenack, 1960. 

The assemblages in the 366- to 305-m ( 1200- to 

1000-ft interval of the core are distinctly different 

from those of the Maestrichtian units above. The 

most characteristic feature is the presence of species 

that appear to be restricted to the Marshalltown and 

Wenonah Formations of New Jersey. Included in the 

flora are Defiandrea victoriensis Cookson and Manum, 1964, Defiandrea cf. D. armata Cookson and 

Eisenack, 1970, Palaeocystodinium sp., Dinogymnium sp., and Amphidinium mitratum Vozzhennikova, 

1967. The apparent correlation of this interval with 

the Marshalltown and Wenonah Formations of New 

Jersey is also supported by the occurrence of the following species: Odontochitina costata Alberti, 1961, 

Defiandrea n. sp., and Trigonopyxidia ginella (Cookson and Eisenack) Downie and Sarjeant, 1964, 

Palaeohystrichophora infusorioides Deflandre, 1935, 

and Phoberocysta ceratioides Deflandre, 1937. The 

age of this interval is late Campanian. 

The interval from 296 to 270m (970-885 ft) contains an assemblage that, in terms of the outcrop section, is a mixture of species restricted to either the 

Mount Laurel Sand and older units of the northern 

Atlantic Plain or to the Navesink and Red Bank 

interval. These forms are Defiandrea pannucea 

Stanley, 1965, Gonyaulacysta sp., Achomosphaera 

ramuli/era (Deflandre) Evitt, 1963, Ophiobolus lapidaris Wetzel, 1933, Samlandia angustivela (Deflandre and Cookson) Eisenack, 1963, Palaeohystrichophora infusorioides Deflandre, 1935, Systematophora 

n. sp., and Phoberocysta ceratioides Deflandre, 1937. 

This assemblage is what one might expect in rocks 

equivalent to the disconformity between the Mount 

Laurel Sand and the Navesink Formation of northern New Jersey. The suggested age is late Campanian or early Maes,trichtian. 

Between 267 and 244 m (875-800 ft), dinoflagellate-acritarch assemblages are similar to those of 

the Navesink Formation-Red Bank Sand sequence 

of northern New Jersey. Species restricted to both 

this intervalin the core and the Navesink-Red Bank 

interval are Palaeocystodinium australinum (Cookson) Lentin and Williams, 1976, Gonyaulacysta sp., 

Defiandrea speciosa Alberti, 1961, Drugg, 1967, and 

Dinogymnium westralium (Cookson and Eisenack) 

Evitt and others, 1967. Between 267 and 259m (875 

and 850 ft) , the assemblage also contains three undescribed species that are known to occur elsewhere 

only in the Navesink Formation of New Jersey. 

These are new species of Dinogymnium, Hystrichokolpoma, and Trithyrodinium. The above occurrences suggest that the 267- to 244-m (875- to 

800-ft) interval is Navesink equivalent (lower 

Maestrichtian). 

The presence of at least three species of the Cretaceous genus Dinogymnium at 245 m (804 ft) and 

244 m (800 ft) suggests that the Cretaceous-Tertiary boundary is at about 244m (800ft). 

Between 244 and 198 m (800-649 ft) an assemblage is present that suggests an early Paleocene age 

and correlation, at least in part, with the Brightseat Formation of Maryland. Present in this interval are Defiandrea n. sp., which is known only from 

the Brightsea,t Formation; Defiandrea magnifica; 

Stanley, 1965; Defiandrea obscura Drugg, 1967; Defiandrea dilwynensis Cookson and Eisenack, 1965 ; 

Spiniferites buccina (Davey and Williams) Sarjeant, 1970; Spiniferites septatus (Cookson and 

Eisenack) McLean, 1971; and Spinidinium densipinatum Stanley, 1965. 

In the interval from 190 to 124 m ( 623-407 ft), 

dinoflagellates are too rarely represented to be of 

biostratigraphic value. The interval from 120 to 55 

m (394-179 ft) is tentatively considered to be of middle and late Eocene age. The difficulty of separating 

the middle from the late Eocene in this core by 

means of dinoflagellates was also experienced by 

Gradstein and Williams (1976) on the Labrador 
88 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

Shelf. Species that characterize the middle and late 

Eocene assemblages in both areas include Cyclonophelium ordinatum Williams and Downie, 1966, 

W etzeliella articulata Eisenack, 1938, W. coleothrypta Williams and Downie, 1966, W. tenuivirgula 

Williams and Downie, 1966, and Diphyes colligerum 

(Deflandre and Cookson) Cookson, 1965. The first 

appearance of Pentadinium laticinctum Gerlach, 

1961, and Achilleodinium biformoides (Eisenack) 

Eaton, 1976, at 69 m (225ft) suggests a late Eocene 

age because P. laticinctum Gerlach, 1961, was found 

in the upper Eocene of wells on the Grand Banks, 

Newfoundland (Gradstein and Williams, 1976). 

Also, Achilleodinium biformoides (Eisenack) Eaton, 1976, has been found only in upper Eocene sediments from other areas. Some of the other more 

common species recovered from this interval include 

De[landrea heterophlycta Deflandre and Cookson, 

1955, Hystrichokolpoma rigaudae Deflandre and 

Cookson, 1955, Homotryblium ( = Cordosphaeridium) fioripes Eisenack, 1963, Pentadinium laticinctum subsp. granulatum Gocht, 1969, Spiniferites 

pseudofurcatus (Klumpp) Sarjeant, 1970, Tectadodinium spp., Systematophora placacantha (Deflandre 

and Cookson) Davey and others, 1969, Gonyaulacysta giuseppei (Morgenroth) Sarjeant, 1969, and 

a new species of Leptodinium. 

The assemblage of the interval 53-12 m (175-

41 ft) contains Chiropteridium lobospinosum Gocht, 

1960, and suggests an Oligocene age. Other species. 

present in this interval include Hystrichokolpoma 

rigaudae Deflandre and Cookson, 1955, Pentadinium 

laticinctum subsp. granulatum Gocht, 1969, W etzeliella articulata Eisenack, 1938, Homokyblium 

( = Cordosphaeridium) fioripes Eisenack, 1963, Cordosphaeridium funiculatum Morgenroth, 1966, 

Gonyaulacysta cantharellum (Brosius) Gocht, 1969, 

Lingulodinium machaerophorum (Deflandre and 

Cookson) Wall, 1967, Defiandrea heterophlycta Deflandre and Cookson, 1955, Thalassiphora pelagica 

Eisenack and Gocht, 1960, Gonyaulacysta giuseppei 

(Morgenroth) Sarjeant, 1969, Chiropeteridium 

aspinatum (Gerlach) Brosius, 1963, and Spiniferites 

spp. The interval from 11 to 5 m (37-16 ft) in the 

upper part of the Cooper Formation contains, 

among other forms, Tuberculodinium vancampoae 

(Rossignol) Wall, 1967, which in other areas is 

used as a marker for the Miocene. 

REFERENCES CITED 

Berggren, W. A., 1972, A Cenozoic time-scale-some implications for regional geology and paleobiogeography: 

Lethaia, v. 5, no. 2, p. 195-215. 

Blow, W. H., 1969, Late middle Eocene to Recent planktonic 

foraminiferal biostratigraphy, in Bronnimann, P., and 

Renz, H. H., eds., International Conference on Planktonic 

Microfossils, 1st, Geneva, 1967, Proceedings: Leiden, 

Netherlands, E. J. Brill, v. 1, p. 199-422, 54 pis. 

Brenner, G. J., 1963, The spores and pollen of the Potomac 

Group of Maryland: Maryland Dept. Geology, Mines and 

Water Resources Bull. 27, 215 p. 

Brown, P. M., 1958, Well logs from the Coastal Plain of 

North Carolina: North Carolina Div. Mineral Resources 

Bull. 72, 68 p. 

Brown, P. M., Miller, J. A., and Swain, F. M., 1972, Structural and stratigraphic framework, and spatial distribution of permeability of the Atlantic Coastal Plain, North 

Carolina to New York: U.S. Geol. Survey Prof. Paper 

796, 79 p. 

Bybell, L. M., 1975, Middle Eocene calcareous nannofossils 

at Little Stave Creek, Alabama: Tulane Studies Geology 

and Paleontology, v. 11, no. 4, p. 178-252. 

Cooke, C. W., 1936, Geology of the Coastal Plain of South 

Carolina: U.S. Geol. Survey Bull. 867, 196 p. 

Doyle, J. A., 1969, Angiosperm pollen evolution and biostratigraphy of the basal Cretaceous formations of 

Maryland, Delaware, and New Jersey [abs.]: Geol. Soc. 

America Abs. with Programs, [v. 1], pt. 7, p. 51. 

Gradstein, F. M., and Williams, G. L., 1976, Biostratigraphy 

of the Labrador Shelf, Part I: Canada Geol. Survey, 

open file 349, 39 p. 

Mann, C. J., and Thomas, W. A., 1968, The ancient Mississippi River: Gulf Coast Assoc. Geol. Socs. Trans., v. 

18, p. 187-204. 

Martini, Erlend, 1971, Standard Tertiary and Quaternary 

calcareous nannoplankton zonation, in Farinacci, Anna, 

and Matteucci, R., eds., Proceedings of the II Planktonic 

Conference, Roma, 1970: Rome, Edizioni Tecnoscienza, 

v. 2, p. 739-785. 

Obradovich, J. D., and Cobban, W. A., 1975, A time-scale 

for the late Cretaceous of the Western Interior of North 

America: Geol. Assoc. Canada Spec. Paper 13, p. 31-54. 

Olsson, R. K., 1975, Upper Cretaceous and lower Tertiary 

,stratigraphy of New Jersey coastal plain: Petroleum 

Exploration Soc. New York, Second Ann. Field Trip 

Guidebook, May 3, 1975, 49 p. 

Owens, J. P., and Soh!, N. F., 1969, Shelf and deltaic paleoenvironments in the Cretaceous-Tertiary formations of 

the New Jersey Coastal Plain, in Subitzky, Seymour, 

ed., Geology of selected areas in New Jersey and eastern 

Pennsylvania and guidebook of excursions: New Brunswick, N. J., Rutgers Univ. Press, p. 235-278. 

Pessagno, E. A., Jr., 1967, Upper Cretaceous planktonic 

Foraminifera from the western Gulf Coastal Plain: 

Paleontographica Americana, v. 5, no. 37, p. 245-445, 

pl. 48-101, fig. 1-63. 

--- 1969, Upper Cretaceous stratigraphy of the western 

Gulf Coast area of Mexico, Texas, and Arkansas: Geol. 

Soc. America Mem. 111, 139 p., 60 pis. 

Petters, S. W., 1976, Upper Cretaceous subsurface stratigraphy of Atlantic Coastal Plain of New Jersey: Am. 

Assoc. Petroleum Geologists Bull., v. 60, no. 1, p. 87-

107, fig. 1-7. 
BIOSTRATIGRAPHY OF THE DEEP COREHOLE 89 

Plummer, F. B., 1933, The geology of Texas, part 3, Cenozoic 

systems in Texas: Texas Univ. Bull. 3232, p. 519-818. 

Pooser, W. K., 1965, Biostratigraphy of Cenozoic Ostracoda 

from South Carolina: Kansas Univ. Paleont. Contr. 

[38], Arthropoda, art. 8, 80 p. 

Sanders, A. E., 1974, A paleontological survey of the Cooper 

Marl and Santee Limestone near Harleyville, South 

Carolina-preliminary report: Columbia, South Carolina 

Div. Geology Geol. Notes, v. 18, no. 1, p. 4-12. 

Sirkin, L. A., 1974, Palynology and stratigraphy of Cretaceous strata in Long Island, New York, and Block 

Island, Rhode Island: U.S. Geol. Survey Jour. Research, 

v. 2, no. 4, p. 431-440. 

Smith, C. C., and Pessagno, E. A., Jr., 1973, Planktonic 

foraminifera and stratigraphy of the Corsicana Formation (Maestrichtian) north-central Texas: Cushman 

Found. Foram. Research Spec. Pub. 12, p. 1-68, pl. 1-27, 

fig. 1-24. 

Swift, D. J. P., and Heron, S. D., Jr., 1969, Stratigraphy of 

the Carolina Cretaceous: Southeastern Geology, v. 10, 

no. 4, p. 201-245. 

Tschudy, R. H., 1973, Stratigraphic distribution of significant Eocene palynomorphs of the Mississippi embayment: U.S. Geol. Survey Prof. Paper 743-B, p, B1-B24. 

van Hinte, J. E., 1976, A Cretaceous time scale: Am. Assoc. 

Petroleum Geologists Bull., v. 60, no. 4, p. 498-516. 

Wolfe, J. A., 1976, Stratigraphic distribution of some pollen 

types from the Campanian and lower Maestrichtian 

rocks (Upper Cretaceous) of the Middle Atlantic States: 

U.S. Geol. Survey Prof. Paper 977, 18 p. 

Young, Keith, 1963, Upper Cretaceous ammonites from the 

Gulf Coast of the United States: Texas Univ. Pub. 6304, 

373 p. 

--- 1965, A revision of Taylor nomenclature, Upper 

Cretaceous, central Texas: Texas Univ. Bur. Econ. 

Geology Geol. Circ. 65-3, 10 p. 

Geochemistry of Subsurface Basalt From the 

Deep Corehole (Clubhouse Crossroads Core hole 1) 

Near Charleston, South CarolinaMagma Type and Tectonic Implications 

By DAVID GOTTFRIED, C: S. ANNELL, and L. J. SCHWARZ 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, 

EARTHQUAKE OF 1886-A PRELIMINARY REPORT 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1028-G 

CONTENTS 

Abstract 

Introduction -------------------------------------------------------------

Description of basalt -----------------------------------------------------

Analytical methods ___________________________________________ ------------

Analytical results ____________________________ ------------------ ____ ------

]dajor elements ------------------------------------------------------- Normative composition _______________________________________________ _ 

Trace elements -------------------------------------------------------

Large cations ---------------------------------------------------- Rare-earth elements ________________ ------------- _____ ------------

High-valence cations ___________________________ -------------------

Ferromagnesian elements ______________________________ ---------- _ 

Alteration effects ---------------------------------------------------------

Age ---------------------------------------------------------------------

Comparison with basalts of other provinces ---------------------------------

]daj or elements 

Page 

91 

91 

92 

92 

93 

93 

95 

95 

96 

97 

97 

98 

99 

100 

102 

102 

Trace elements ____________________________________________ ---------- 103 

Tectonic setting ---------------------------------------------------------- 105 

Summary and conclusions ------------------------------------------------- 109 

References cited ---------------------------------------------------------- 110 

FIGURE 

ILLUSTRATIONS 

1. Normative mineralogy of Clubhouse Crossroads corehole 1 basalts 

plotted on diopside-hyper::;thene-olivine-nepheline-quartz diaPage 

gram -------------------------------------------------- 95 

2-5. Graphs showing2. Average abundances of rare-earth elements (REE) in basalts from the corehole normalized to chondrites____ 98 

3. Comparison of alteration effects for selected elements in 

altered marginal samples relative to less altered interior samples of corehole basalt flows _____________ 100 

4. Variations of large cations and smaller high-valence 

cations with depth in corehole basalts ______________ 101 

5. Average abundances of REE of tholeiitic diabases and basalts normalized to chondrites -------------------- 104 

6. Samples of corehole basalts and some tholeiitic basalts and diabases from continental provinces plotted on discrimination 

diagrams of Pearce and Cann (1973) --------------------- 106 

7. Graph showing comparison of REE patterns of corehole basalts 

with chilled margins of diabase from three continental provinces --------------------------------------------------- 108 

III 
IV CONTENTS 

TABLES 

TABLE 1. Major-oxide and normative mineral compositions, in weight percent, 

of basalt from Clubhouse Crossroads corehole 1 near Charleston, 

Page 

s.c ------------------------------------------------------- 94 

2. Trac,e-element abundances, in parts per million, in basalt from Clubhouse Crossroads corehole 1 near Charleston, S.C ____________ 96 

3. K-Ar ages and analytical data of basalts from Clubhouse Crossroads 

corehole 1, 32'53.2' N., 80'21.5' W., Dorchester County, S.C ____ 101 

4. Geochemical comparison of basalt from the Clubhouse Crossroads 

corehole 1 (CCC 1) near Charleston, S.C., with basaltic rocks 

from other provinces --------------------------------------- 102 

5. Rank ordering of chemical similarities between basalts from the Clubhouse Crossroads corehole 1 near Charleston, S.C., and selected 

comparison basaltic rocks ---------------------------------- 103 
STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886-

A PRELIMINARY REPORT 

GEOCHEMISTRY OF SUBSURFACE BASALT FROM THE DEEP COREHOLE 

(CLUBHOUSE CROSSROADS COREHOLE 1) NEAR CHARLESTON, SOUTH CAROLINAMAGMA TYPE AND TECTONIC IMPLICATIONS 

By DAviD GoTTFRIED) C. S. ANNELLJ and L. J. ScHWARZ 

ABSTRACT 

Geophysical studies indicate that mafic volcanic and associated plutonic rocks may be important components,of the 

basement beneath the Coastal Plain of the southeastern 

United States. A drill hole, 40 km northwest of Charleston, 

S.C., over a magnetic and gravity high penetrated 750 m of 

Coastal Plain sediments and bottomed in 42 m of basalt. 

Petrographic and major element data on 11 samples of 

basalt selected from the drill core, representing at least 2 

lava flows, indicate that the basalts have undergone slight 

to extreme oxidation, hydration, and hydrothermal alteration. Effects of alteration are greatest in the marginal zones 

and least in the interior parts of the flows. The upper parts 

of the flows have abundant amygdules which contain laumontite, calcite, and chlorite. Petrochemical data olt the least 

altered samples indicate that the basalts are of the quartznormative tholeiitic magma type and closely resemble the 

Mesozoic high-Ti quartz-normative chilled diabase of eastern 

North America. 

Eight samples were analyzed for 27 trace elements, including rare-earth elements (REE), Rb, Ba, Sr, Th, Zr, Hf, 

Nb, Ta, Ni, Co, Cr, and Cu, by neutron activation, emission 

spectrography, and spectrophotometry. Concentrations of K, 

Rb, Ba, and Sr are highly variable in the marginal zones 

and reflect the mobility of these elements during postmagmatic processes. K;Rb ratios of the least altered samples 

are in the range 300-400. The abundances of REE, P, Ti, 

Zr, Nb, and Th show little ( <20 percent) or no variation 

regardless of the degree of alteration and indicate that the 

two flows were originally of the same chemical composition. 

The contents of minor and trace elements of the covehole 

basalts are compared with those of rocks of tholeiitic composition which occur on Atlantic-type passive continental 

margins (eastern North America, Tasmania, Antarctica, 

South Africa: all of Mesozoic age) and with basalts from 

island arc and oceanic-ridge settings. The low abundances 

of REE, Ti, Zr, and Nb in the corehole basalt and in quartznormative tholeiites from eastern North America and Tasmania are more similar to those of island arc and oceanicridge basalts than to those of "average" continental basalts. 

However, the pattern of enrichment in light REE and the 

low ratio, K;Rb, for the corehole basalt indicate that it 

originated from an undepleted source area in the upper 

mantle. The abundances of REE, Ti, Zr, and Nb and the 

light-REE enrichment patterns are strikingly similar to 

those of the high-Ti quartz-normative tholeiitic diabases of 

eastern North America. K-Ar analyses of a relatively fresh 

sample and an altered sample yield ages of 94.8 m.y. and 

109 m.y., respectively. These are considered minimum ages 

and may be significantly younger than the time of volcanism. 

The characteristic geochemical features of the corehole basalts suggest that they have a temporal as well as spatial 

relationship with the Late Triassic and Early Jurassic t'holeiitic province of eastern North America which formed 

during an extensional tectonic regime. The subsurface basalts may be associated with structural features produced 

by tensional faulting and suggest the possible presence of a 

buried Triassic basin beneath the Charleston area. 

INTRODUCTION 

Recent geophysical surveys of the Charleston area 

show pronounced posith:e magnetic and gravity 

anomalies which are interpreted as mafic or ultramafic plutons associated with mafic volcanic rocks 

(Popenoe and Zietz, this volume; Long and Champion, this volume; Kane, this volume; Phillips, this 

volume). Contrasting models based largely on the 

magnetic and gravity patterns have been proposed 

for the tectonic setting of the crust beneath the 

Coastal Plain: Zietz and others (1976) proposed an 

ocean-floor or island arc tectonic setting, and Pope-

:n'oe and Zietz (this volume) propose a z;one of continental extension. A deep hole was drilled over a 

magnetic and gravity high about 40 km west-northwest of Charleston as part of the program to investigate the seismicity of the Charleston-Summerville 

area (see fig. 3 of Rankin, this volume). The drill 

hole, called Clubhouse Crossroads corehole 1 (CCC 

1), penetrated 750 m of Coas,t•al Plain sediments and 

bottomed in 42 m of basaltic lavas which may be 

genetically related to the bodies causing the magnetic and gravity highs. The basalt is overlain by 

fossiliferous sediments of early Late Cretaceous 

(Cenomanian) age (Hazel and others, this volume; 

Gohn and others, this volume). A geochemical study 

of the basaltic rocks recovered from the corehole 

should provide direct evidence for constraining mod91 
92 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

els of the regional tectonic setting that have been 1 

inferred from the geophysical and geological data. 

The purpose of the present study is to present new 

data on major elements and trace elements for the 

corehole basalts and to discuss the implications of 

the data with regard to tectonic setting. The first 

stage of the study is to determine the composition of 

the parental magma of the basalts. This, by necessity, includes an assessment of the degree of alteration of the basalts. The second stage is to infer the 

tectonic setting of the basalts from a comparison of 

geochemical features of the corehole basalts with 

those of basalts of known tectonic setting. The third 

stage is to apply this information to an interpretation of the tectonic setting of the Charleston area at 

the time of extrusion of the basalts; therefore, 

knowledge of the age of the basalts is essential. In 

reading the detailed discussion that follows, the 

reader should keep in mind that one of our major 

conclusions is that no single group or pair of geochemically associated elements can be used alone for 

distinguishing magma type and tectonic setting. 

We have benefited greatly from many helpful discussions with D. W. Rankin, Peter Popenoe, J. P. 

Owens, B. B. Higgins, R. L. Smith, and S. L. Russell. 

J.D. Fletcher provided preliminary semiquantitative 

spectrographic analyses which later expedited quantitative spectrographic determinations. M. E. Mrose 

and E. J. Dwornik provided important mineralogical 

data by X-ray diffraction and scanning electron 

microscopy. We are grateful to Michael Fleischer, 

G. T. Faust, L. P. Greenland, and J. G. Arth for 

critical reviews of this paper and for their suggestions for its improvement. Part of the work was supported by the U.S. Nuclear Regulatory Commission, 

Office of Nuclear Regulatory Research, Agreement 

No. AT (49-25)-1000. 

DESCRIPTION OF BASALT 

The basalt can be divided into two flows on the 

basis of criteria described by Nichols (1936) for 

distinguishing successive flows. The following criteria have been used in the present study: distribution of vesicles (now amygdules), grain size, and 

petrography. The upper flow is 35 m thick. The top 

of the flow (5 m) is highly oxidized, is reddish 

brown, and contains abundant amygdules. This zone 

grades downward into relatively fresh dark gray 

basalt containing fewer amygdules. The basal zone 

of the flow (3 m) is essentially aphyric and greenish ; fractures are greenish black. Only 7 m of the 

lower flow were penetrated before drilling was terminated. The top of the lower flow is amygdaloidal, 

but less oxidized than the top of the upper flow, and 

grades downward into less altered gray fractured 

basalt. 

Limited mineralogical studies have been carried 

out to date because the basalts are altered and the 

matrix is fine grained. Petrographic data obtained 

on least altered samples from the upper flow show 

that the basalt is composed mainly of clinopyroxene,. 

plagioclase (An6o), and Fe-Ti oxides. Preliminary 

studies by scanning electron microscope and X-ray 

diffraction techniques have thus far identified the 

following secondary minerals: laumontite, calcite, 

chlorite (all in large amygdules), and stilbite. 

ANALYTICAL METHODS 

Major-element oxide, water, and C02 contents 

were determined by the rapid rock-analysis methods 

described by Shapiro ( 1975). Abundances of 10 

major constituents were determined from a single 

solution obtained by a nitric acid dissolution of a 

sample fused with lithium metaborate-lithium tetra .. 

borate. CaO, MgO, N azO, and K20 contents were 

determined by atomic absorption spectrometry; 

SiOz, Al20:1, Fe203, Ti02, P205 , and MnO contents 

were determined spectrophotometrically. Separate 

sample portions were used to determine FeO, H20 

( + and - ) , and C02 contents. 

Minor- and trace-element abundances were determined by means of chemical, emission spectrographic, and instrumental neutron-activation analyses. Niobium content was determined by a spectrophotometric method (Greenland and Campbell, 

1974). After decomposition by hydrofluoric acid and 

evaporation to volatilize silica, the samples were 

fused with pyrosulfate and dissolved in hydrochloric 

acid-tartaric acid. After separation by a thiocyanate 

extraction with amyl alcohol and back-extraction 

with dilute hydrofluoric acid, the niobium was reacted with 4- (2-pyridylazo) -resorcinol. Analytical 

error, calculated on the basis of replicate analyses of 

eight U.S.G.S. (U.S. Geological Survey) s.tandard 

rocks, ranges from 2.9 to 6.4 percent in the concentration range from 10 to 27 ppm (parts per million). 

Three modifications of d.c. (direct-current) arc 

emission spectroscopy were used to determine the 

concentrations of 17 minor and trace elements. 

1. A 15-ampere arc in air was used to determine 

Ba, Co, Cr, Cu, Ga, Mn, Ni, Sc, Sn, Sr, V, Y, 

and Zr concentrations; this method has a co-
GEOCHEMISTRY OF SUBSURFACE BASALT FROM DEEP COREHOLE 93 

efficient of variation of approximately 15 percent (Bastron and others, 1960). 

2. A 25-ampere arc in an argon atmosphere was 

used to determine Pb and Zn concentrations by 

fractional volatilization of a sample buffered 

by a N a2C03 admixture. This method has a 

coefficient of variation of approximately 10 

percent at the concentrations reported by Annell (1967). 

3. A 15-ampere arc in air and a sample buffered 

with KzC03 were used to determine Rb and Li 

concentrations. A coeffieient of variation of 10 

percent is realized by this technique (Annell, 

1964). 

Synthetic standards and U.S.G.S. standards, 

BCR-1, W-1, and AGV-1 (Flanagan, 1973), were 

used to establish analytical curves for the element 

concentrations determined spectrographically. 

Instrumental neutron activation was used to determine La, Ce, Sm, Eu, Tb, Yb, Lu, Hf, Ta, and Th 

concentrations. Three 0.15-g replicate samples 

packed in polyethylene vials were irradiated for 2 

hours at a flux of 5 X 1013 neutrons cm-2 sec-1 at the 

National Bureau of Standards reactor, Gaithersburg, Md. A standard was synthesized from an 

analyzed obsidian doped with solutions of selected 

trace elements, dried, reground, and calibrated relative to seven U.S.G.S. standard rocks: BCR-1, G-2, 

AGV-1, GSP-1, PCC-1, DTS-1, and W-1 (.F'lanagan, 1973). The samples and standards were counted 

on a Ge(Li) detector 1 week and 6 weeks after irradiation. The tantalum content was determined by 

counting on a low-energy photon detector 5 months 

following irradiation. The spectral data were processed on an IBM 370 1 computer by means of the 

program SPECTRA (Baedecker, 1976). 

ANALYTICAL RESULTS 

MAJOR ELEMENTS 

Major-element a-nalyses were made on 11 corehole 

samples that represent the different zones of the 

two flow units as characterized by texture and grain 

size and that show to varying degrees the effect of 

posteruptive processes. The major-oxide compositions and the normative mineral compositions of the 

basalts are presented in table 1, where the data are 

arranged in order of increasing depth of the s~amples 

in the corehole. The contact between the upper and 

lower flow units is between samples B-5A and B-6. 

Chemical evidence of variable alteration in the suite 

1 Any trade names in this publication are used for descriptive purposes 

only and do not constitute endorsement by the U.S. Geological Survey. 

of samples is clearly indicated by the relatively high 

and variable contents of H20 and C02 • As expected 

from megascopic observation, sample B-1, which is 

reddish brown, amygdaloidal, and extensively zeo~ 

litized, and which is taken from the top of the uppe'r 

flow, has the highest H20 content and FezOa/FeO 

ratio; it also has the lowest MgO content. Some important petrogenetic elements have been remobilized, 

and possibly others have been introduced along the 

contact between the upper and lower flow units. The 

lowest K20 and NazO contents (0.02 and 0.48 percent, respectively) are in the top of the lower flow 

(sample B-6), which resembles the top of the upper 

flow (B-1) in texture and zeolite content and has 

the third highest content of H20, second highest content of Fe20:1, and next lowest MgO content. This 

sample also has an exceptionally high Si02 content 

and is strongly depleted in Al20:1. The highest contents of K20 (1.3-1.4 percent) and NazO (3.4 percent) are found in samples (B-5, B-5A) of massive 

aphanitic rock in which amygdules are virtually absent. The basal zone showing potassium enrichment 

extends approximately 1 m above the contact between the flows. The presence of an analogous zone 

of potassium enrichment extending downward for 

approximately 3 m from the contact is indicated by 

the relatively high potassium content in B-7. The 

approximate symmetry of alteration indicates that 

in addition to weathering, oxidation, and hydration 

processes, which have affected the tops of the two 

flows to a greater degree than the interior parts, hydrothermal activity has affected the contact zone 

between the two flows. 

An important feature of the chemistry of the samples is the uniformity of concentrations of two minor 

constituents, phosphorus and titanium. P205 concentrations are virtually the same (range, 0.12 to 0.15 

percent) within the limits of error of the analytical 

method; titanium is nearly as uniform in its distribution except for the two most altered samples, 

B-1 and B-6, which show a depletion of about 1~ 

percent in Ti02 content (range, 0.82-0.87 percent) 

relative to that of the other samples (range, 0.95-

1.1 percent). Although the introduction of water 

has strongly influenced the variations in the oxidation state of the rocks, the total iron concentrations 

are relatively unaffected. The distribution pattern 

for the values of total iron is approximately parallel 

to the pattern for the values of titanium. Prior 

studies (Cann, 1970; Pearce and Cann, 1971, 1973; 

Pearce and others, 1975; Floyd and Winchester, 

1975; Winchester a.nd Floyd, 1976) have shown that 

Ti and P concentrations have remained stable in 
94 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

TABLE 1.-Major oxide and normative mineral compositions, in weight percent, of basalt from Clubhouse Crossroads core hole 1, near Charleston, S.C. 

[Analyses by F. W. Brown, S. D. Botts, and Leonard Shapiro, using methods described by Shapiro (1975)] 

Sample No. ------------- Depth below surface 

(meters) --------------

B-1 

756 

B-2 

764 

B-·3 

771 

B-3A 

774 

B-4 

779 

B-4A 

782 

Major-oxide composition 

B-5 

784.6 

B-5A 

785 

B-6 

785.4 

B-7 

789 

B-8 

791 

SiO, --------------- 49.5 51.3 52.6 54.4 52.8 53.5 50.5 52.1 64.2 50.7 51.1 

Al,O" -------------- 14.4 13.3 13.4 14.0 13.5 14.2 13.4 14.4 6.8 12.8 13.6 

Fe203 -------------- 8.2 2.9 2.7 3.6 2.4 3.0 3.1 3.2 4.1 3.9 3.2 

FeO --------------- .68 7.5 8.4 8.0 8.7 8.5 8.2 8.1 5.5 7.4 8.0 

MgO --------------- 2.2 5.6 5.7 5.7 5.9 6.0 6.0 6.2 4.5 6.4 5.9 

CaO --------------- 6.7 7.7 9.2 9.0 9.0 9.0 7.8 7.5 7.0 6.6 8.7 

Na20 -------------- 2.7 3.1 2.4 2.3 2.4 2.2 3.4 3.4 .48 3.3 2.7 

K,O --------------- .70 .73 .50 .53 .62 .48 1.3 1.4 .02 .98 .48 

H,O+ ------------- 8.6 4.4 1.7 1.4 2.0 2.0 2.6 2.1 4.3 3.6 3.4 

H20- ------------- 4.0 1.2 .66 1.1 .61 .93 1.2 1.5 1.2 1.6 .88 

TiO, --------------- .75 .89 .96 .98 .96 1.1 .99 1.0 .77 .93 .91 

P,O, --------------- .13 .12 .14 .12 .14 .13 .14 .13 .12 .13 .13 

MnO -------------- .12 .19 .21 .24 .22 .26 .24 .26 .18 .22 .21 

C02 ---------------- .08 .03 .04 .05 .02 .07 .01 .03 .62 .07 .01 

Total ________ --~99~----9~9~--~9~9----~1~01~----9~9~--~1~01~~--9~9----~1~0~1~--~10~0~~~9=9~--~99~ 

Major-oxide composition recalculated volatile-free 

SiO, --------------- 57.5 55.0 54.7 55.0 54.6 54.4 53.1 53.3 68.5 54.3 53.8 

Ab03 -------------- 16.7 14.3 13.9 14.2 14.0 14.4 14.1 14.7 7.3 13.7 14.3 

Fe,03 -------------- 9.5 3.1 2.8 3.6 2.5 3.1 3.3 3.3 4.4 4.2 3.4 

FeO --------------- .79 8.0 8.7 8.1 9.0 8.6 8.6 8.3 5.9 7.9 8.4 

MgO -------------- 2.6 6.0 5.9 5.8 6.1 6.1 6.3 6.4 4.8 6.9 6.2 

CaO --------------- 7.8 8.3 9.6 9.1 9.3 9.2 8.2 7.7 7.5 7.1 9.2 

Na,O -------------- 3.1 3.3 2.5 2.3 2.5 2.2 3.6 3.5 .51 3.5 2.8 

K,O --------------- .81 .78 .52 .54 .64 .49 1.4 1.4 .02 1.1 .51 

TiO, --------------- .87 .95 1.0 .99 .99 1.1 1.0 1.0 .82 1.0 .96 

P20, --------------- .15 .13 .15 .12 .14 .13 .15 .13 .13 .14 .14 

MnO-~;i~======--~1~00~·~ -~1~00~·~Z_0 __ 10~0~·~~-~10~0~·~24-~l0~0~ ~~1~0~0~ -~l~0~0~ -~l~0~0- -~1~00~· 1~00~·~ -~1~00~·-~ 

Normative mineral composition' 

Q --------------- 12.49 3.86 7.08 8.80 6.68 8.16 41.51 

.13 

4.32 

17.39 

6.22 

11.93 

12.92 

1.14 

6.22 

29.97 

18.48 

6.55 

4.14 

2.99 

24.12 

24.88 

8.40 

OR ---------------- 4.84 4.63 3.08 3.17 3.80 2.88 8.09 8.48 

AB ---------------- 26.75 28.15 21.13 19.71 21.03 18.93 30.31 29.47 

AN ---------------- 29.40 21.70 25.30 26.64 25.10 27.91 18.40 20.38 

wo --------------- 3.45 7.80 8.96 7.23 8.52 6.67 9.03 6.88 

EN ---------------- 6.42 14.97 14.77 14.37 15.22 15.19 12.19 13.97 17.11 

15.46 

15.51 

FS ---------------- 12.24 14.24 14.80 15.01 14.79 14.85 11.79 13.08 15.17 

FO ---------------- 2.49 1.30 

FA ---------------- 2.65 1.34 

MT ---------------- 2.28 2.62 2.72 2.75 2.72 2.75 2.80 2.72 2.36 2.83 2.78 

IL ---------------- 1.67 1.81 1.90 1.88 1.89 2.12 1.98 1.95 1.56 1.90 1.82 

AP ---------------- .31 .28 .34 .28 .34 .31 .34 .31 .28 .31 .28 

cc ---------------- .21 .07 .10 .12 .05 .16 .02 .07 1.50 .17 .02 

Total ________ --c:l-::-ooc;------:-cl o""o;-----...,1,-;;0:-:oo-----:-1-=-oo-:-----::-:1 o;;;o:------:o-1~oo::-----:1::-:o""o,-----=1-:::-0~o --71 o:c-:o::------:1;-;o""o---=1""0-;;-0-

1 Based on analyses recalculated to 100 percent water-free oxides; Fe:?03/Ft:O+Fe2 0:J ratio assumed to be 0.15. 

mafic rocks that have undergone weathering, deuteric alteration, and greenschist facies metamorphism; these studies have used concentrations of Ti 

and P in various oombinations with concentrations 

of other stable trace elements, such as Zr, Y, and 

Nb, to characterize magma types and tectonic 

environments. 

These stable elements are indicators of the stage 

of fractional crystallizatiion during the early and 

middle stages of differentiation of tholeiitic magmas 

(Anderson and Greenland, 1969). Their contrasting 

patterns of variation, such as progressive enrichment in tholeiitic differentiates and depletion as contents of KzO and Si02 increase in calc-alkaline lavas, 

are also useful as indicators of petrologic province 

and hence geologic setting (Anderson and Gottfried, 

1971; Miyashiro, 197 4; Miyashiro and Shido, 1975; 

Martin and Piwinskii, 1972). 

The results of the present study provide further 

confirmation that P and Ti are relatively insensitive 

to processes of chemical alteration. Thus, we interpret the uniform distribution of these elements plus 

that of total iron ( 1) as a primary feature of the 

flows, (2) as an indication that the random variations of the other petrogenetic elements within and 

between the flows are a reflection of secondary alter-
GEOCHEMISTRY OF SUBSURFACE BASALT FROM DEEP COREHOLE 95 

ation processes, and (3) as evidence that all 

the rocks were originally of the same chemical 

composition. 

NORMATIVE COMPOSITION 

Plots of the normative compositions of the corehole samples in the normative diopside-hyperstheneolivine-nepheline-quartz dia.gram are shown in figure 

1. Because hydration and attendant oxidation affect 

the position of the points in the diagram, the normative calculations were made on water-free oxides, 

and the FezO,/ ( FeO + Fez03 ) ratio was assumed to 

be 0.15. On the basis of their normative mineralogy, 

two of the basalt samples are olivine-normative tholeiites, but the other nine are quartz-normative tholeiites according to the classifica,tion scheme of 

Yoder and Tilley (1962). The olivine-normative tholeiites (samples B-5, B-5A) and the strongly 

quartz-normative tholeiite (sample B-6), which together represent the opposite extremes in composition of the compositions plotted on the diagram, reflect the introduction of potassium and silica, respectively, during alteration of the marginal zones 

of the flows. The next most altered samples (B-7, 

B-1) plot on the diagram in positions intermediate 

between the extremely altered and the least altered 

I 

I 

I 

~ I Ne 1 

I 

I 

I 

I 

ALKALI OLIVINE BASALTS 

Di 

samples. Inasmuch as the effects of secondary processes appear to be gradational, any distinction based 

on the degree of alteration is arbitrary. Analyses 

representing the interior parts of the flows, (samples 

B-2, B-3, B-4, B-8) cluster closeJy together in the 

quartz-tholeiite field. Petrographic and chemical evidence indicate that these are the least altered samples. This suggests that their composition best 

approximates the composition of the liquids from 

which they were formed. The average major-element 

composition of these samples is also assumed to be 

close to the original composition of the two lava 

flows. This will be discussed further when comparisons are made between basalts from CCCI and mafic 

rocks representative of a variety of magma types 

and tectonic settings. 

TRACE ELEMENTS 

The results of analyses for 27 trace elements in 

individual samples are given in table 2. The data are 

subdivided according to the scheme recommended by 

Taylor (1965) and Taylor and White (1966) wherein elements are grouped mainly on the basis of their 

geochemical associations and within each group are 

listed according to their ionic radius and charge. As 

noted above, the nature of the variations o.f the 

major elements indicates a complicated history of 

QUARTZ THOLEIITES 

3 

• .4 3A 

8 • 

.5 \2 e4A 

e5A 7 

• 

\ 

.1 

\ 

\ 

\ ;:'( \ Qz 

\ 

\ 

.6 \ 

\ 

\ 

OLIVINE THOLEIITES 

01 Hy 

FIGURE !.-Normative mineralogy of Clubhouse Crossroads corehole 1 basalts from table 1 (prefix B is omitted here) 

plotted on a diopside (Di)-hypersthene (Hy)-olivine (01)-nepheline (Ne)-quartz (Qz) diagram. 
96 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

TABLE 2.-Trace-element abundances, in parts per million, in basalt from Clubhouse Crossroads corehole 1 near Charleston, S.C. 

Sample No. ------- B-1 B-2 B-3 B-3A B-4 B-4A B-5 B-5A B-6 B-7 B-8 

Large cations 

Rb+ ---------- 2 26 14 16 19 10 43 52 0.7 34 19 Ba•+ __________ 155 230 120 140 135 140 360 330 20 235 110 

K• 

Sr"+ ----------- 6,700 6,500 4,300 4,500 5,300 4,100 11,600 11,600 200 9,100 4,200 

---------- 140 190 200 160 200 220 160 160 40 250 160 ca•+ ---------- 56,000 59,000 69,000 65,000 66,000 66,000 59,000 55,000 54,000 51,000 66,000 Pb2+ ---------- 5.4 5.0 5.0 3.9 4.6 4.6 4.5 4.6 4.7 3.9 4.2 

K;Rb -------- 3,400 250 310 280 280 410 270 230 285 270 220 

Ba;Rb -------- 78 8.8 8.6 8.8 7.1 14 8.4 6.3 29 6.9 5.8 

K;Ba --------- 43 28 36 32 39 29 32 35 10 39 38 

High-valence cations 

Th4+ ---------- 1.7 1.9 2.0 2.2 2.1 1.7 2.0 2.0 

Zr<+ ---------- 65 74 82 77 70 71 71 73 

Hf<+ ---------- 1.6 1.8 2.1 2.1 2.0 1.7 1.7 2.0 

Nb'+ ---------- 7.0 7.0 7.4 6.8 7.4 7.5 7.2 7.7 

Ta'+ ---- .33 .28 .32 .26 .33 .18 .32 .30 

Zr 

Hf 41 41 39 37 37 ----------- 35 42 42 

NbX100 .13 .13 .13 .12 .13 .16 .13 .14 Ti 

Nb 21 25 23 26 22 42 22 26 

Ta -----------

Ferromagnesian elements 

Co2+ ---------- 35 49 47 40 46 52 42 44 42 45 43 

cu•+ ---------- 8 28 34 25 20 28 26 24 38 19 16 

Li+ ----------- 16 6 7 5 14 10 16 16 36 25 11 

NP• ---------- 24 19 20 19 17 16 16 14 15 11 14 

Zn2+ ---------- 55 80 90 84 82 96 80 82 95 78 88 

Cr"+ ---------- 39 38 36 35 34 28 32 31 30 37 32 

Ga'+ ---------- 26 14 15 15 15 18 14 12 16 16 15 

Sc'+ ---------- 40 54 50 52 56 52 54 52 48 48 46 

V'+ ----------- 210 310 310 310 320 400 400 330 310 280 250 

Ni;Co -------- .69 .39 .43 .48 .37 .31 .38 .32 .36 .24 .33 

Rare earth elements 

La ----------- 10 10 11 

Ce ----------- 17 18 19 

Nd ----------- <28 <36 <36 

Sm ----------- 2.9 2.7 3.1 

Eu ----------- .99 .90 1.02 

Tb ----------- .62 .61 .73 

Yb ----------- 1.9 1.8 2.1 

Lu ----------- .38 .42 .47 

y ------------ 28 34 33 

alteration for the lava flows; therefore it is important to evaluate the effects of alteration on the 

suites of trace elements before they can be used for 

characterization of magmatic and tectonic affinities. 

LARGE CATIONS 

The elements in the group of large cations that 

have the largest ionic radii, Rb, Ba, and K, cannot 

conveniently fit into the crystal structures of the 

major minerals (pyroxenes, plagioclase, olivine) of 

basaltic rocks. These elements are probably highly 

concentrated in interstitial material, and thus, they 

may be more susceptible to leaching and remobilization by geologic processes during and after crystallization. The concentrations of these elements vary the 

most in the altered zone (extending from sample B11 11 10 11 9 

19 19 17 18 18 

10 10 <36 <37 <37 

3.0 3.0 2.6 3.5 3.0 

.95 .96 .75 .99 .99 

.68 .70 .59 .66 .68 

2.3 2.4 1.8 2.1 2.1 

.44 .44 .38 .47 .44 

34 32 34 31 28 

5 to B-7) that straddles the contact between the 

upper and low flows. The patterns of abundance 

variations for Rb and Ba are similar to those for K. 

In samples from the altered zone in which the K 

content is relatively high, the contents of Rb (34-

52 ppm) and Ba (235-360 ppm) are relatively high; 

in sample B-6, in which the K content is low, Rb 

(0.7 ppm) and Ba (20 ppm) contents are also low. 

An extreme depletion of Rb relative to Ba and K is 

found in the strongly hydrated amd oxidized sample 

(B-1) from the top of the upper flow, although K, 

and to a lesser extent Ba, a.re somewhat enriched in 

this sample with respect to the least altered samples 

of the .suite. Sample B-2, which in figure 1 is shown 

to be similar in normative composition to the least 

altered basalts, has distinctly higher Rb (26 ppm) 
GEOCHEMISTRY OF SUBSURFACE BASALT FROM DEEP COREHOLE 97 

and Ba (230 ppm) contents than B-1 (2 ppm Rb 

and 155 ppm Ba), though both have essentially the 

same K contents. Rubidium appears to be the most 

sensitive indicator of alteration and is particularly 

useful for subdividing the heterogeneously altered 

flows into alteration domains. The wide variations 

for Rb, between adjacent samples (B-1 and B-2) 

from the top of the upper flow (thirteenfold) and 

between the top of the lo,wer flo,w and adjacent samples (approximately fiftyfold), out:tine the extent of 

the alteration zones developed at the margins of the 

flows. In the least altered zone, the Rb variation is 

less than twofold (10-19 ppm). Except for the 

anomalously high value for the K/Rb ratio (3,400) 

in sample B-1, the K/Rb ratios range from 220 to, 

410. Because of the lack of any appreciable difference between the K/Rb ratios of the relatively unaltered samples and those of the strongly altered 

samples, it might be argued that the K/Rb ratio of 

the least altered samples does not reflect the original 

K/Rb ratio of the rocks. However, the original K/Rb 

ratio may have been modified to a limited extent because of the close geochemical coherence of these 

two elements in hydrothermal as weU as magmatic 

processes. Inasmuch as the magnitude of the change 

is unknown, the K/Rb ratio would have to be used 

with caution in distinguishing between ma,gma 

types. 

The range of variation of Sr concentration is less 

than that of Rb, Ba, and K concentrations. The maximum change (fivefold) is in the lower alteration 

zone where Sr is strongly depleted in B-6 (40 ppm) 

relative to adjacent samples B-5A and B-7 (160 and 

250 ppm, respectively). In this zone, the variation of 

Sr concentration is similar to that of the alkali 

metals. However, in the least altered zone and in the 

upper alteration zone (upper flow) the concentration 

pattern for Sr is nearly the same as that observed 

for Ca. Possible explanations for the diverse behavior of Sr are (1) Sr is in part locat~d in site's 

similar to those occupied by the alkali metals; (2) 

Sr is incorporated to some extent in plagioclase, pyroxene, and zeolites; and ( 3) the nature and (or) 

degree of the alteration may vary in different parts 

of the basalt flows. 

The uniformity in Pb contents (3.9 to 5.4 ppm) in 

the suite of samples is somewhat surprising. Lead is 

generally considered a K-related element in igneous 

rocks, and we would have expected somewhat: analogous variations. 

RARE-EARTH ELEMENTS 

The rare-earth elements (REE) are probably the 

most important single group of geochemically coherent trace elements that have been used in studies 

on modes of origin, petrologic evolution, and tectonic setting of basaltic rocks (Frey and others, 

1968; Kay and others, 1970; Schilling and Winchester, 1967; Jakes and Gill, 1970). Moreover, prior 

studies have shown that the processes of weathering, 

low-grade metamorphism (greenschist facies), and 

spilitization do not change or alter the primary REE 

pattern (Frey and others, 1968; Kay and Senechal, 

1976; Herrmann and others, 1974). It is, therefore, 

important to extend such studies to include the corehole basalts. The abundances of eight REE and Y 

were determined (by neutron-activation analysis 

and emission spectrography, respectively) in eight 

samples. The data given in table 2 indicate that the 

abundances are virtually the same in each of the 

samples, regardless of the degree of alteration. The 

REE data also support our previous interpretation 

based on the uniformity of Ti and P concentrations, 

that all samples were of the same composition prior 

to alteration. The normalized REE pattern of the 

basalts is shown in figure 2, in which the ratios of 

the average concentration for each REE in the eight 

samples to the average concentration of the same 

REE in chondrites are plotted on a logarithmic ordinate against a linear scale of the REE atomic number along the absdssa. For normalization purposes, 

the average concentrations of the individual REE in 

20 ordinary chondritic meteorites (table 8 in Haskin and others, 1966) were used. The REE pattern 

of the corehole basalts shows enrichment of the light 

REE (La-Sm) relative to the heavy REE (Gd-Lu). 

A comparison of this REE pattern with those of 

basalts of known tectonic setting and magma type is 

made in a later section. 

HIGH-VALENCE CATIONS 

The contents of Th, Zr, Hf, Nb, and Ta are remarkably uniform in this suite of samples, except 

for Ta depletion in highly altered sample B-6. Their 

uniformity leaves little doubt about the immobility 

of these elements during alteration. These elements 

generally show threefold to fivefold increases in 

abundances in the course of differentiation of continental tholeiitic magmas (Gottfried and others, 

1968; Eales and Robey, 1976). The cons,tancy of 

these elements in the two flows again suggests the 

absence of amy differentiation trends in the two 

flows. The stability of the high-valence cations is an 

important feature because in thi;s study we use Zr 
98 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

w 

1--

a: 

0 

z 

0 

:c 

u 

~ 20 u 

0 

a: 

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 

ELEMENTS 

FIGURE 2.-Average abundances of rare-earth elements (REE) in basalts from the Clubhouse Crossroads corehole 1 near 

Charleston, S.C., normalized to average REE abundances in 20 chondrites (Haskin and others, 1966). Each vertical 

bar indicates the range of normalized values of eight samples. 

in conjunction with other immobile minor and trace 

elements, in particular Ti, Y, and Nb, in our attempt 

to identify the tectonic setting of the volcanic rocks 

according to the classification scheme of Pearce and 

Cann (1973). Discrimination diagrams, such as TiZr, Ti-Zr-Y, and Ti-Zr-Sr, have been widely utilized 

by many workers to investigate past environments 

of a wide variety of mafic rocks (Pearce, 1975; 

Seidel, 1974; Bickle and Nisbet, 1972; Pearce and 

Cann, 1971; Smewing, Simonian, and Gass, 1975; 

Kay and Senechal, 1976; Perfit, 1977). 

FERROMAGNESIAN ELEMENTS 

Features of petrologic interest in the group of 

ferromagnesian elements are the low abundance levels of Ni, Co, Cr, and especially Cu as compared to 

the average abundances given by Prinz (1967) of 

these elements in quartz-normative tholeiites. Although Cu is a chalcophile element, it is included 

here for convenience. Variations in the abundances 

of these elements between the least altered and 

strongly altered samples of the corehole basalts are 

generally less than twofold to threefold. The effect 

of alteration is readily apparent for Cu which is 

depleted (8 ppm) in the strongly oxidized sample 

(B-1) from the top of the upper flow and .somewhat 

enriched (38 ppm) in the intensely altered sample 

(B-6) from the top of the lower flow relative to the 

least altered samples (16-34 ppm). Mobility of Cu 

during weathering and alteration of tholeiitic diabase from Pennsylvania has been noted by Smith and 

others (1975). 

Copper is generally enriched in the residual liquids 

during tholeiitic differentiation until a copper-rich 

sulfide appears. This is clearly shown in the wellstudied Palisades sill (Walker, 1969) and in differentiated diabase intrusions of the Tasmanian 

tholeiitic province (Greenland and Lovering, 1966). 

In the latter province, crystallization of chalcopyrite 

during the middle stage of differentiation resulted in 

strong depletion of Cu in the later differentiates 

(McDougall and Lovering, 1963; and McDougall, 

1964). The low copper contents of the corehole basalt 

might reflect prior crystallization of sulfides. Sample 

B-1 is also depleted in cobalt, zinc, scandium, and 

vanadium. Chromium and scandium contents are 

uniform and do not appear to have been affected by 

alteration. Bloxam and Lewis (1972) previously 

noted that chromium is fairly stable during alteration. The Ni/Co ratios of the corehole basalts (0.24-

0.48) are significantly lower than the Ni/Co ratios 

commonly found in nonorogenic tholeiitic basalts 

( 2-3) . Variation of this ratio in several tholeiitic 

diabase-granophyre suites has been reviewed by 

Fleischer (1968) who showed that the Ni/Co ratio 

decreases systematically during differentiation ( ,_,3 
GEOCHEMISTRY OF SUBSURFACE BASALT FROM DEEP COREHOLE 99 

to < 1) and is useful as an index of fractionation. 

Thus the low Ni/Co ratios and also the low Cr contents (28-39 ppm) could be accounted for if the 

corehole basalts represent residual liquids derived 

from a more primitive magma that has undergone 

extensive fractionation prior to eruption. However, 

low Ni and Co contents and low Ni/Co ratios are 

considered chara.cteristic features of some calc-alkalic basalts and andesites of island arcs and active 

continental margins. The petrogenetic significance 

of these elements has been extensively discussed by 

Taylor (1969), Taylor and others (1969, 1971), 

Hedge ( 1971), and Marsh ( 1976). Taylor and others 

(1969, 1971) suggested that neither fractional crystallization of basalt nor partial melting of undifferentiated mantle can account for the relative abundances of these elements in orogenic magmas; they 

postulated a two-stage model to explain the low Ni, 

Co, and Cr contents and low Ni/Co ratios. Therefore, 

caution is required in using contents of these elements by themselves to identify magma type and 

tectonic setting because similar abundance relations 

may occur in mafic volcanic rocks of contrasting 

magma types (calc-alkalic and tholeiitic) and, hence, 

tectonic settings (orogenic and non-orogenic). 

ALTERATION EFFECTS 

In this study, our efforts were directed mainly at 

"seeing through" the effects of alteration by an empirical approach. Detailed studies of the zeoJit.es and 

other secondary minerals dispersed through parts of 

the flow are clearly needed before we can achieve an 

adequate understanding of the mechanism or the 

nature of the alteration processes. Petrographic, 

mineralogic, and chemical data indicate that alteration is greatest in the marginal zones and least in 

the interior parts of the flows. A gross correlation 

exists among the degrees of alteration indicated by 

(1) trace-element composition, (2) megascopic examination, for example, of color variation ( Gohn and 

others, this volume), and (3) H 2 0 and Fe20:l contents. By analogy with alteration studies of sea-floor 

basalts, in which altered rims are compared with 

less altered interior parts of pillow fragments (Hart, 

1969, 1971; Hart and others, 197 4; Phil potts and 

others, 1969), we have compared chemical variations 

between margin and interior samples. 

Various aspects of the effects of alteration of the 

major and minor elements have been discussed in 

preceding sections. Some of the results are summarized in figure 3, where selected major-, minor-, 

and trace-element concentrations in six samples from 

altered marginal zones are compared with the average concentration of the least altered samples from 

the interiors of the flows. The elements selected are 

those that have been used for identification of magma type or tectonic setting. They are plotted in figure 

3 in order of decreasing ionic radii. In a general way, 

this also is their order of relative susceptibility of 

alteration; the larger ions are most easily altered 

(Rb>K::::,.Ba>Sr>Ca), and the REE and highly 

charged cations (Zr, Nb, Ti, and P) are the least 

easily altered. The large alkali trace elements are the 

most sensitive indicators of alteration, and they enhance the recognition of the existence and extent of 

subtle alteration effects in the flows. 

Figures 3 and 4 show that the magnitude and direction of the chemical changes resulting from alteration in B-1 and B-2 (top of upper flow) are different from those of the chemical changes in B-6 

(top of lower flow). The two contrasting alteration 

trends may be the effects of different degrees or 

types of alteration. The trends for B-1 and B-2 suggest a stage of alteration during which the alkali 

metals were added to these samples. However, continued alteration, or some later process, resulted in 

preferential loss of Rb relative to K and hence the 

anomalously high K/Rb ratio (3,400). Except for 

Rb loss in B-1, this alteration trend for the largesized ions is similar to tliose observed in slightly 

weathered margins of submarine basalt fragments 

(Hart, 1971). The alteration trend for B-6 suggests 

that the top of the lower flow may have undergone 

alteration of a different type. Alkali metals in this 

sample are depleted by more than an order of magnitude relative to the least altered samples. The fractionation of Ta from Nb, as indicated by the high 

Nb/Ta ratio ( 42), is also an important feature of 

this sample. Samples immediately above (B-5, B5A) and below (B-7) have alteration patterns 

showing relatively strong enrichment of the alkali 

elements and seem qualitatively to have a complementary relationship to that of sample B-6. These 

abrupt chemical changes along the contact zone may 

reflect the effects of a hydrothermal event which 

took place after extrusion of the upper flow. 

Weathering (hydration and oxidation), hydrothermal activity, and possibly low-grade metamorphism (zeolite facies) have contributed in varying 

degrees to the complex chemical and mineralogical 

changes that much of the lava flows have undergone. 

However it is extremely difficult, if at all possible, 

in some samples from the lava flows, to determine 

the sequence in which some of these processes occurred or to assign them correctly. 
100 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

4 r-------------------------------------------------------------------------~ 

CfJ 

w 

--' 

3 

~ 0.8 

<( 

CfJ CfJ 0.6 w 0 

![~ :2w 

<( 1'- Cfl <1. 0.4 

01-

WCJJ 

ffi ;;5 ~--' <( z z - 0.2 - z 

z 0 0 F F <( 

~ ;: I- z z w 0.1 w u u z 

z 0 0 u u w 

(C) 

<( 

0:: 

w 

> <( 

0.08 

0.06 

0.04 

0.02 

0 0 

• 

• 

Rb Ba 

0 

6. 

·~ 

K Pb 

ELEMENTS 

EXPLANATION 

Altered marginal samples: 

• B-1 

~ B-2 

A B-6 

0 B-5 and 5A 

6 B-7 

-Average concentration of 

least altered samples 

(B-3, B-3A, B-4, B-4A, and B-8) 

FIGURE 3.-Comparison of alteration effects on concentrations of selected elements in altered marginal samples relative 

to the average concentration of the less altered interior samples of the basalt flows penetrated in the Clubhouse Crossroads corehole 1 near Charleston, S.C. 

AGE 

Knowledge of the time of volcanism and associated tectonic activity is essential to understanding 

the pre-Late Cretaceous structural evolution of the 

Charleston area. Potassium-argon (K-Ar) wholerock ages were determined on a fine-grained sample (B--3) from the least altered zone and an altered aphyric sample (B-5A) from the base of the 

upper flow. The K-Ar ages and analytical data are 

given in table 3. The similarity in age between the 

least altered sample (94.8 m.y.) and a more altered 

K-rich sample (109 m.y.) indicates that these are 

minimum ages, probably dating some posteruptive 

processes that have affected the volcanic rocks. 

These apparent ages are not in stratigraphic confiict with the Cenomanian Age (Hazel and others, 

this volume) of the overlying sedimentary rocks. 

Currently assigned estimates of the time interval of 

the Cenomanian Stage are 90 m.y. to 94 m.y. 

(Obradovich and Cobban, 1975). Prior to the detailed analysis of the geochemistry of the basalts 

and because of the similarity in ages of the basalts 

and the overlying rocks there was little reason to 

question the K-Ar ages. However, the possibility 

cannot be precluded that this similarity is fortuitous and that the basalts are significantly older than 

the K-Ar ages indicate. 

Several investigators have evaluated the effects of 

alteration on K-Ar ages of basaltic rocks whose ages 

were well established by geologic evidence or by in-
GEOCHEMISTRY OF SUBSURFACE BASALT FROM DEEP COREHOLE 101 

0 

B-1 

<f) 

a: 

w 

fw 

:2 10 

~ ~ 

0 

~ "" :;; -' <! c. B-3 <f) c. 

<! :::J 

m B-3A 

u.. 20 0 

"- 0 B-4 f-

:2 B-4A 0 

u.. 

a: ~11>:::-=-=--=-=-=---~ 30 B-6 I 

f- ~ "-w 0 B-7 "" 0 :;; B-6 ~ 0 

-' 

40 

FIGURE 4.-Variations of large cations and smaller high-valence cations in samples from different depths in the two basalt 

flows penetrated in the Clubhouse Crossroads corehole 1 near Charleston, S.C. 

TABLE 3.-K-Ar ages and analytical data of basalts from Clubhouse Crossroads corehole 1, 32° 53.2' N., 80° 21.5' W., 

Dorchester County, S.C. 

[Analysts: R. F. Marvin, H. H. Mehnert, and Violet Merritt, U.S. Geological Survey] 

B-3 

Sample 

No. 

B-5A ---------------------

1 Radiogenic argon. 2 Constants: K"/\,= 0.585 X 10-lOjyr. 

/\p=4.72X-lojyr. 

Depth below surface (meters) 

770 

785 

K40 = 1.19 X 10-4 atomic abundance. 

K,O 

( wt. percent) 

0.63, 0.62 

.625 avg. 

1.37, 1.43 

1.40 avg. 

dependent radiometric methods. Kaneoka (1972) 

found that rocks containing more than 1 percent 

HzO ( +) generally show much younger ages than 

fresh rocks as a result of radiogenic '

0

Ar loss due 

to hydration. Mankinen and Dalrymple (1972) 

showed that significant amounts of radiogenic '

0 Ar 

have been lost from basaltic rocks in which K is 

concentrated in interstitial glass and which show 

no evidence of chemical alteration. They suggested 

that only holocrystalline rocks, in which K is bound 

in primary minerals, are suitable for age work. Low 

and variable K-Ar ages of Mesozoic tholeiitic basalts 

from Antarctica were ascribed to significant loss 

of radiogenic 40 Ar which varies inversely with 

amount of devitrified matrix in the samples (Fleck 

and others, 1977). Fleck and others (1977) found 

no chemical or petrographic evidence for loss or 

gain of K in the samples and postulated that argon 

loss occurred only during the devitrification process. 

Armstrong and Besancon (1970) discussed in some 

IAr"o (10-10 moles/g) 

0.8968 

2.309 

1Ar40 

(wt. percent) 

83 

85 

Calculated age (m.y.) 2 

±20 

94.8±4.2 

109±4 

detail the problems encountered in interpreting the 

geologic significance of K-Ar ages for the Upper 

Triassic tholeiitic hypabyssal and extrusive rocks of 

eastern North America. They believed that, regardless of the close grouping of most of the ages between 180 m.y. and 200 m.y., the ages do not record 

the time of igneous activity but are probably the result of zeolite facies regional metamorphism which 

has affected all of the sedimentary and volcanic 

rocks. Taking into consideration the alteration history of the corehole basalts and the chemical and 

(or) petrographic criteria suggested by various geochronologists for selection of samples for age determination, we think that all of the corehole basalts 

and, for that matter, most of the older basalts are 

unsuitable for yielding reliable K-Ar ages. The age 

of the lavas can only be considered as pre-Late 

Cretaceous until additional detailed geochronological studies, such as, 40 Ar / 39 Ar experiments, are carried out. 
102 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

COMPARISON WITH BASALTS OF OTHER 

PROVINCES 

A comparison of the major-element and selected 

trace-element abundances in the corehole basalts, 

with mean compositions of several types of basalts 

representative of diverse magma types and tectonic 

settings is shown in table 4. The composition given 

for the corehole basalts is the average of five samples (B-3, B-3A, B-4, B-4A, and B-8), which on 

the basis of petrographic and chemical criteria are 

the least altered. Data for basalts chosen for comparative study are taken from compilations by other 

authors. (See references in table 4.) Because of 

their proximity to the study area, compositions of 

the main tholeiitic magma types represented by 

eastern North America (ENA) chilled diabases 

were selected to represent continental tholeiites. 

Data from the well-studied continental tholeiitic 

province from Tasmania are also given for comparison. 

MAJOR ELEMENTS 

Misleading comparisons can be made using the 

major-element chemistry of the corehole basalts especially with regard to the alkali elements. However, 

some important petrochemical features appear to 

have been retained that are important for characterization of magma type. For example, except for the 

TABLE 4.-Geochemical comparison of basalt from the Clubhouse Crossroads corehole 1 (CCC 1) near Charleston, S.C., with 

basaltic rocks from other provinces 

Island arc series 

Eastern North America tholeiitic diabases Tasmania Oceanic- CCC 1 Mesozoic High-A! ridge basalt High-Ti High-Fe Low-Ti Olivin~ tholeiitic Calc-Alk. Tholeiitic tholeiitic Qtz.-Norm. Qtz.-Norm. Qtz.-Norm. Norm. diabase basalt basalt basalt 

Major oxides (weight percent) 

SiO, --------------- 54.0 52.1 52.7 51.7 47.9 53.4 50.59 51.57 49.9 

Al,03 -------------- 14.0 14.2 14.2 15.0 15.3 16.4 16.29 15.91 17.3 

Fe,O" -------------- 3.08 '11.6 1 13.9 1 11.8 '12.1 .52 3.66 2.74 2.01 

FeO --------------- 8.56 8.32 5.08 7.04 6.9 

MgO -------------- 6.01 7.41 5.53 7.44 10.5 6.72 8.96 6.73 7.3 

CaO --------------- 8.99 10.66 9.86 10.8 10.7 11.49 9.50 11.74 11.9 

Na,O -------------- 2.75 2.12 2.51 2.23 2.0 1.60 2.89 2.41 2.8 

K,O --------------- .54 .66 .64 .48 .29 .91 1.07 .44 .16 

TiO, --------------- .97 1.12 1.14 .76 .59 .59 1.05 .80 1.5 

Trace elements (parts per million) 

Rb ---------------- 16 21 22 15 8 33 10 5 1 

Ba ---------------- 130 160 115 100 115 75 10 

Sr ----------------- 190 186 180 186 115 130 375 200 135 

Zr ----------------- 77 92 90 60 44 55 100 52 95 

Hf ---------------- 2.0 2.5 1.5 1.1 .8 2.6 1.0 2.9 

Nb ---------------- 7.2 9.5 8.0 5 3 5 2.5 2 5 

Th ---------------- 2.0 2.4 .4 3.2 1.1 .5 .18 

Ni ---------------- 18 81 34 48 308 67 25 12 97 

Co ----------------- 46 49 52 53 65 42 40 34 32 

K/Rb -------------- 310 280 240 285 300 200 340 900 1,060 

Nbx100;Ti -------- .12 .13 .12 .11 .14 .13 .05 .03 .06 

Zr/Hf ------------- 39 37 40 40 69 38 52 33 

Ni;Co ------------- .39 1.7 .65 .91 4.7 1.3 .63 .4 3.0 

Sources of data 

Major elements ____ CCC 1 basalt ___________________________ this paper, table 1, average of least altered samples (B-3, 

B-3A, B-4, B-4A, and B-8). 

Eastern North America tholeiitic diabases_ Weigand and Ragland, 1970. 

Tasmania Mesozoic tholeiitic diabase ______ Edwards, 1942. 

Island arc series _______________________ Jakes and White, 1972a, b. 

Ocean-ridge tholeiitic basalt _____________ Engel and others, 1965. 

Trace elements ____ CCC 1 basalt ___________________________ this paper, table 2, averag-e of least altered samples (B-3, 

1 Total Fe as Fez03. 

B-3A, B-4, B-4A, and B-8). 

Eastern North America tholeiitic diabases_ Weigand and Ragland, 1970; Ragland and others, 1968; 

Smith and others, 1975; David Gottfried, unpub. data. 

Tasmania Mesozoic tholeiitic diabase ______ Heier and others, 1965; Compston and others, 1968; Gottfried and others, 1968. 

Island arc series _______________________ Jakes and White. 1970, 1972a, b; Pearce and Cann, 1973; 

Taylor, 1969; Gill, 1970. 

Oceanic-ridge tholeiitic basalt ___________ Engel and others, 1965; Tatsumoto and others, 1965; Hart, 

1971; Pearce and Cann, 1973; David Gottfried, unpub. 

data. 
GEOCHEMISTRY OF SUBSURFACE BASALT FROM DEEP COREHOLE · 103 

most altered samples, the magnitude of the effects 

of alteration for total Fe, Mg, and AI is small compared with the variations of these elements between 

the corehole basalts and some other groups of basalt. 

The contents of Fe, Mg, and AI, thus, are still useful for comparative purposes. 

To explore the relationship between magma type 

and tectonic setting a rank ordering of chemical 

similarities between the corehole basalts and the 

comparison basalts was obtained, following the procedure of Ragland and others (1968). The following statistics were calculated : 

1. The sum, for all oxides of the quantity 

)%x- ;7aChj 

%Ch 

2. The sum, for all oxides of the quantity 

(%s- ;7oCh) 2 

where %xis the oxide abundance in the compa.rison 

basalt and %Ch is the oxide abundance in the corehole basalt. The two comparison numbers obtained 

permit a rank ordering of the comparison basalts 

compared to the corehole basalts; the smaller values 

indicate closer similarity between the comparison 

basalts and the corehole basalts. Results of the comparison are given in table 5 in which the comparison 

basalts are listed according to this rank-ordering. 

This rank-ordering shows that the corehole basalts 

are most similar to the Mesozoic continental highFe-Ti quartz-normative tholeiitic diabases from 

eastern North America. 

TABLE 5.-Rank ordering of chemical similarities between 

basalts from the Clubhouse Crossroads corehole 1 near 

Charleston, S.C., and selected comparison basaltic rocks 

'C'"'I %x-%Ch I~ i%x-%Ch) 2 

Comparison basalts L.J o/oCh 6 %Ch I 

Value Rank Value Rank 

EN A 2 High-Fe, quartz-normative tholeiitic diabase ------ 0.76 

ENA' High-Ti, quartz-norma- tive tholeiitic diabase ______ 1.15 

ENA2 Low-Ti, quartz-normative tholeiitic diabase 1.15 

Island arc, tholeiitic basalt 1.26 

Island arc, high-A!, calc-alk. 

basalt -------------------- 2.13 Tasmania Mesozoic tholeiitic 

diabase -------------------- 2.26 ENA 2 olivine-no'rmative 

tholeiitic diabase ----------- 2.32 

Oceanic-ridge tholeiitic basalts_ 2.32 

1 

2 

2 

3 

4 

5 

6 

6 

0.58 1 

.97 2 

1.19 3 

1.68 4 

3.41 6 

2.59 5 

5.14 8 

3.46 7 

' Data from table 4, Fe as FeO, and analyses recalculated water-free. 2 EN A= Eastern North America. 

TRACE ELEMENTS 

For the most part, variations in trace elements in 

these basaltic provinces can be related to (1) the 

composition and mineralogy of the source region 

and (2) the degree of partial melting and subsequent fractional crystallization during ascent of 

magma in the mantle and in the crust. Other factors that may play a role are "wall rock reaction," 

which is discussed in detail by Green and Ringwood 

(1967), and contamination resulting from interaction of basaltic magma with rocks of the continental crust (Faure and others, 1974). Although 

these processes affect the major-element chemistry 

to some extent, the trace-element concentrations are 

affected much more and, more importantly, can provide clues to the history and origin of basalts that 

are not readily observed from the relations among 

the major elements. 

Comparison of the trace-element data in table 4 

indicates that the corehole basalts show the greatest similarity to the ENA quartz-normative diabases, in particular to the high-Fe and high-Ti types. 

Wiegand and Ragland (1970) and Ragland, Brunfelt, and Weigand (1971) regarded the ENA highFe type as a subgroup of the ENA high-Ti group 

with which it shares similarities (REE, Ti, Rb, Sr, 

Zr, Co) but from which it is different in having a 

lower Ni content and hence a lower Ni/Co ratio. 

The corehole basalts are closer in composition to the 

high Fe-type than to the high-Ti type. A close similarity exists between the corehole basalts and the 

high-Fe type in abundances of stable minor and 

trace elements (Ti, Zr, Hf, Nb) and of mobile elements (K, Rb), as well as in the unusually low Nil 

Co ratios. This similarity can be extended to include Cu which, as noted previously (table 2), is 

unusually low in the corehole basalts ( -25 ppm). In 

high-Fe types, Cu decreases as the Ni/Co ratio decreases to values as low as 37-44 ppm (Weigand 

and Ragland, 1970). 

A comparison of the REE pattern of the corehole 

basalts (from fig. 2) with average REE patterns 

for the ENA high-Ti quartz-normative diabase (an 

average which includes the high-Fe type), ENA 

olivine-normative diabase, and oceanic-ridge tholeiitic basalts is shown in figure 5. The abundances 

and REE pattern for the corehole basalts and for 

the ENA high-Ti type are virtually the same. The 

REE pattern for the ENA olivine-normative type 

is similar to that for the high-Ti type but is distinctly lower in absolute abundance. Light-REE enriched patterns intermediate between those of the 
104 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

EXPLANATION 

... OCEANIC-RIDGE THOLEIITIC BASALT 

• EASTERN NORTH AMERICA OLIVINE-NORMATIVE DIABASE 

• EASTERN NORTH AMERICA HIGH-T! QUARTZ-NORMATIVE DIABASE 

+ BASALTS FROM CLUBHOUSE CROSSROADS COREHOLE 1 

NEAR CHARLESTON, S. C. 

UJ 

1-

a: 

Cl • 0 

z .._-r- • :I: --r- u ,... ~ u • 

¥4 0 

a: =r 

:<--._ • 

10 

• • • • 

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 

FIGURE 5.-Average abundances of rare-earth elements (REE) in tholeiitic diabases and basalts normalized to average 

REE abundances in 20 chondrites (Haskins and others, 1966). Data sources: oceanic-ridge tholeiitic basalt (Schilling, 

1971); eastern North America olivine-normative diabase and eastern North America high-Ti quartz-normative diabase 

(Ragland, Brunfelt, and Weigand, 1971); and basalts from Clubhouse Crossroads corehole 1 near Charleston, S.C., 

table 2 (this paper). 

high-Ti and olivine-normative types characterize 

the low-Ti type (fig. 4 in Ragland, Brunfelt, and 

Weigand, 1971; Ragland, Weigand, and Brunfelt, 

1971). The light-REE depleted patterns of oceanicridge tholeiitic basalt (fig. 5) are in sharp contrast 

to the light-REE enriched patterns of the corehole 

basalts and ENA high-Ti and olivine-normative 

tholeiitic types. Other trace-element contents and 

interelement ratios that clearly distinguish the corehole basalts and the EN A tholeiitic diabases from 

oceanic-ridge tholeiitic basalts are higher Rb, Ba, 

and Th contents, higher Nb/Ti ratios, and lower 

K/Rb ratios. However, the abundance levels for Nb, 

Zr, and heavy REE (Sm-Lu) are either similar or 

even lower in the ENA low-Ti type, ENA olivinenormative type, and Tasmanian tholeiitic diabase 

than in the average oceanic- ridge tholeiitic basalt. 

Depletion of trace elements of large ionic radii such 

as Cs, Rb, Ba, Th, and U and the high K/Rb, K/Ba, 

and K/Cs ratios have led to the interpretation that 

the oceanic-ridge tholeiitic basalt was derived from 

a source in the mantle that had previously undergone one or more periods of partial melting (Tatsumoto and others, 1965; Gast, 1968; Hart, 1969, 

1971; Hart and others, 1970). These geochemical 

features once considered unique to the worldwide 

oceanic-ridge system have also been recognized in 

volcanic suites, designated by Jakes and Gill (1970) 

as the island arc tholeiitic series. The REE patterns 

of these rocks are indistinguishable from those of 

the oceanic-ridge tholeiitic basalt (Jake~ and Gill, 

1970), as are several other geochemical features 

shown in table 4. 

Thus far, it can clearly be shown that the corehole basalt is neither an ocean-floor basalt that 

originated from the mid-Atlantic ridge system nor a 

basaltic rock with affinities to the island arc tholeiite series. The corehole basalt, and for that matter, the ENA quartz-normative types, have many 

features in common with basalt, or basaltic andesite, 

of the calc-alkalic series of island arcs. These include 

the low Ti, Ni, Co, and Cr contents, which, as previously mentioned, are considered distinctive of the 

calc-alkalic basalts (table 4) and andesites. They 
GEOCHEMISTRY OF SUBSURFACE BASALT FROM DEEP COREHOLE 105 

also have similar K/Rb ratios (Jake~ and White, 

1970) and light-REE enrichment patterns (Jakes 

and Gill, 1970). However, important differences that 

can be observed are the generally higher K20, Al203 , 

and Sr abundances in the calc-alkalic basaltic rocks, 

than in the ENA high-Ti and high-Fe quartz-normative diabases. These differences may be' related to 

differences in water pressure and oxygen fugacity 

of the magmas from which they formed. The higher 

water content in calc-alkalic magmas favors crystallization of large amounts of plagioclase (Yoder, 

1969) which results in the higher AI and Sr contents. The presence of low Ni, Co, Cr, and Cu in the 

continental ENA high-Ti quartz-normative diabase 

cannot be explained by the two-stage model of 

Taylor (1969) which involves partial melting of 

oceanic crust carried down the Benioff Zone in an 

island arc environment. The geochemical data indicate that the EN A and corehole basalt magmas 

were derived from a mantle undepleted with regard 

to the lithophilic elements. We suggest that prior 

to extrusion, olivine and copper-bearing minerals 

may have crystallized and depleted the Ni, Co, Cr, 

and Cu of the magma. Studies of immiscible sulfide 

melts and polymineralic sulfide minerals from 

Hawaiian tholeiitic basalts (Skinner and Peck, 

1969; Desborough and others, 1968) indicate that 

crystallization of chalcopyrite and Cu- and Ni-rich 

pyrrhotite solid solutions has taken place. These 

studies, and those referred to earlier, show that 

these features are the result of late-stage fractionation processes of basaltic magma. 

The (Nbx 100) /Ti ratio (0.05) in high-Al basalts 

(from data in Pearce and Cann, 1973) is lower than 

that in the corehole basalts (0.12) and continental 

tholeiites ( 0.11 to 0.14). This ratio may serve as a 

useful discriminant because it remains relatively 

constant during the early and middle stages of differentiation of tholeiitic magmas (Gottfried and 

others, 1968). Variation of Zr/Hf in the comparison suites, with the exception of suites of the Tasmanian province, has not yet been adequately documented and at this stage provides no more information than Zr alone. 

The preceding discussions of the implications of 

the geochemical data with regard to magma type 

can be summarized as follows: (1) the corehole 

basalts can be classified as quartz-normative tholeiites and were derived from an undepleted source 

area, presumably the upper mantle; (2) striking 

similarities between major-element, trace-element, 

and REE compositions of the corehole basalts and 

those from the Mesozoic ENA tholeiitic province indicate that the corehole basalts are continental tholeiitic basalts. 

TECTONIC SETTING 

In recent years, extensive geochemical studies have 

shown that young mafic volcanic rocks in a given 

geographic or geologic setting have consistent or 

characteristic geochemical features that characterize 

their tectonic setting. These studies have led to the 

recognition of several trace elements that were 

shown to be relatively insensitive to alteration 

processes and that were characteristic of magma 

type and tectonic setting. Subsequently, the abundance patterns of these trace elements were used to 

construct binary or ternary discrimination diagrams which allowed comparisons to be made between trace-element abundances in an unknown rock 

and those in volcanic rocks of known tectonic setting. The volcanic rocks are generally classified 

according to a scheme that combines tectonic setting and chemical characteristics (Pearce and 

Cann, 1973). Tectonic setting is based on the relative motions of lithospheric plates. Thus mafic volcanic rocks are designated as ( 1) ocean-floor basalts 

(diverging plate margins), (2) low-K tholeiites and 

calc-alkalic basalt of the island arc series ( converging plate margins), and (3) oceanic island and continental basalts (intraplate oceanic crust and intraplate continental crust). Elements generally used 

are Ti, Zr, Y, Nb, P and, also, K and Sr in situations where the rocks are considered unaltered 

(Pearce and Cann, 1973; Floyd and Winchester, 

1975; Winchester and Floyd, 1976; Pearce and 

others, 1975). The most widely applied discrimination diagrams are the Ti-Zr, Ti-Zr-Y, and Ti-Zr-Sr 

diagrams of Pearce and Cann (1973). 

The results of plotting the abundances of these 

elements in the corehole basalts and in some comparison continental basalt samples on these three 

diagrams are presented in figure 6. The comparison 

samples include basalts or chilled diabases from the 

eastern North America, Tasmania, Antarctica, and 

Karroo tholeiitic provinces. The Ti and Zr values 

for the corehole basalts and ENA high-Ti types plot 

in fields B and C on the Ti-Zr diagram (fig. 6A) 

which would indicate the samples are calc-alkalic 

basalts of the island-arc series. The other continental tholeiitic diabases show affinities to island 

arc tholeiitic basalt or ocean-floor basalt. Figure 

6B (Ti-Zr-Y) shows that the corehole basalts are 

in the field of ocean-floor basalts; the diabase from 
106 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

12,000 --

10,000 -

D 

2' 8000 

"-

"-

~ 

i= 

6000 8 X 

+ 0 c s 

4000 A s X 

~ 

2000 

0L·--------2~0---------4L0--------~60 _________ 8L0--------1~0-0--------1L20 ________ 1_4L0 ________ 16L0 ________ 1~8-0------~ 

Zr, IN PPM 

EXPLANATION 

FIELDS Eastern North America 

A. A-B Low-potassium tholeiitic basalt of island arc series 

B-C Calc-alkalic basalt of island arc series 

0 High-Ti quartz-normative diabase + Low-Ti quartz-normative diabase 

B-D Ocean-floor basalt S Olivine-normative diabase 

BASALTS AND DIABASES OF EASTERN NORTH AMERICA 

Corehole basalts, Charleston, S. C. 

DIABASES OF OTHER CONTINENTS 

• Tasmanian diabase 

0 B-1, 2, 5, 6, 7 (most altered) 

e B-3, 4, 8 (least altered) 

FIGURE 6.-Samples of corehole basalts and some tholeiitic 

basalts and diabases from continental provinces plotted 

on discrimination diagrams of Pearce and Cann (1973). 

A, Samples plotted on the Ti-Zr discrimination diagram. 

Data sources: basalts from Clubhouse Crossroads corehole 1 near Charleston, S.C., tables 1 and 2 (this paper); 

eastern North America (ENA), table 3 of Ragland, 

Brunfelt, and Weigand (1971); Great Lake sheet, Tasmania, McDougall (1964), Gottfried ond others (1968); 

the Palisades sill is in the field of calc-alkalic 

basalts. In figure 6C (Ti-Zr-Sr), the samples cluster 

at or near the junctions of the fields: ocean-floor 

basalt, island arc tholeiitic basalt, and calc-alkalic 

basalts of the island-arc series. It is thus clear that 

these diagrams are inappropriate for identification 

of tectonic setting and magma type of these types 

of continental tholeiites. 

X Ferrar diabase, Antarctica 

.& Karroo diabase, South Africa 

Ferrar diabase, Gunn (1966); Karroo basalts of southern province, South Africa, table 3 of Cox and others 

(1967). B, Plot of corehole basalts and chilled diabase 

of Palisades sill on Zr-Ti-Y discrimination diagram. 

Note that the corehole basalts and chilled margin of the 

Palisades sill (Walker, 1969) plot in fields B and C, 

respectively. C, Samples of corehole basalts and diabases 

from eastern North America plotted on Zr-Ti-Sr diagram. 

Each of the continental tholeiitic magma types 

that we used for comparison occurs on Atlantic-type 

passive continental margins and represents the 

early cycles of magmatism that preceded or coincided with rifting, continental drift, and sea-floor 

spreading. A comparison between the chondritenormalized REE abundance pattern for the corehole basalts and the chondrite-normalized REE 
GEOCHEMISTRY OF SUBSURFACE BASALT FROM DEEP COREHOLE 

A-B 

B 

B-e 

D 

EXPLANATION Ti/100 

Low FIELDS potassium tholeiitic basalt of island arc series I 

Ocean-floor basalt -+ 

Calc-alkalic basalt of island arc series 

Intraplate basalt: oceanic island or continental basalt 

BASALTS AND DIABASES OF EASTERN NORTH AMERICA /1 

Corehole basalts, Charleston, S.C. I 

0 B-1, 2, 5, 6, 7 (most altered) _ 

• B-3, 4, 8 (least altered) 

D Palisades sill, New Jersey, 

A 

B 

c 

0 

• 

X 

+ 

[] 

oh;ll,d m.,g;" /' 

I I 

/ 

B. I 

EXPLANATION Ti/100 

FIELDS /\ 

Low-potassium tholeiitic basalt of island arc series I 

Calc-alkalic basalt of island arc series 

Ocean-floor basalt 1 BASALTS AND DIABASES OF EASTERN NORTH AMERICA r 

Corehole basalts, Charleston, S. C. 1 

B-1, 2, 5, 6, 7 (most altered) ~~/ B-3, 4, 8 (least altered) . 

Eastern North America 

High-Ti quartz-normative diabase 

Olivine-normative diabase 

Palisades sill, New Jersey, average diabase 

c. 

\! \! Sr/2 

107 

abundances for the Karroo, Ferrar, and Red Hill 

diabases (Philpotts and Schnetzler, 1968) is shown 

in figure 7. Plots of the REE data for each of these 

suites are on a single variation curve and show that 

the suites are indistinguishable from each other on 

the basis of their REE variation patterns. 

Other important geochemical features shared by 

the corehole basalts, rocks of the EN A tholeiitic 
108 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

EXPLANATION 

40 • KARROO 

• FERRAR 

,& RED HILL 

I w • t: 

a: 

0 

z 20 

0 

I 

u 

~ 

u 

0 

a: 

10 

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 

ELEMENTS 

FIGURE 7.-Comparison of chondrite-normalized rare-earth element (REE) abundance patterns in basalts from Clubhouse 

Crossroads corehole 1 near Charleston, S.C. (see fig. 2, this paper), with average REE abundances of chilled margins 

of Karroo diabase, South Africa; Ferrar diabase, Antarctica; and Red Hill diabase, Tasmania (Phil potts and Schnetzler, 1968). 

province, and the Tasmanian-Antarctic and Karroo 

tholeiitic rocks are their unusually low abundances 

of Ti, Nb, and Zr. Schilling (1971) suggested that 

the relatively low abundances of REE in the chilled 

diabases of these provinces might be related to differences between 'extrusive and intrusive crystallization regimes. This difference in regime appears not 

to be the reason for different REE patterns because 

the REE patterns and absolute abundances are essentially the same in the Palisades diabase (Philpotts and Schnetzler, 1968) and in the Watchung 

Basalt flow (Donnelly and others, 1973). Furthermore, Smith, Rose, and Lanning (1975) found that 

flows, sills, and dikes of the high-Ti quartz-normative magma type in Pennsylvania are nearly identical in chemical composition. For comparisons with 

the corehole basalts, we selected samples or suites 

of continental rocks of similar composition to minimize effects of fractional crystallization or other differentiation processes on the abundance variations. 

The petrogenetic implications of the similar or lower 

abundance levels of lithophilic elements of small 

ionic radii (Ti, Zr, Hf, Nb, Ta) in a Tasmanian 

diabase-granophyre suite as compared to those in 

oceanic-ridge tholeiitic basalt were discussed previously (Gottfried and others, 1968). Ragland, Brunfelt, and Weigand (1971) showed that the olivinenormative tholeiitic dikes from North Carolina have 

half the absolute REE concentrations of oceanicridge tholeiitic basalt. Smith and others (1975) 

pointed out similarities between the low-Ti quartznormative diabase and island arc tholeiitic basalt. 

The rocks selected by Pearce and Cann (1973) 

for establishing the field of continental basalts on 

their discrimination diagrams are from the African 

Rift Valley, Karroo, and Deccan provinces. Their 

mean contents in parts per million for Ti (15,150) ; 

Zr (215), and Nb (20) are at least twice those of 

the abundances found in the corehole basalts, in the 

chilled margins of the sills and dikes of the EN A 

province, and in the Tasmanian province. In the 

Red Sea region, which is considered the modern 

analog of early Mesozoic rifting and continental 

drift, magma associated with rifting and crustal 

extension was dominantly of the alkalic basalt type, 

and magma in the median trough of the Red Sea 

was tholeiitic (Gass, 1970; Mohr, 1972). The REE 

patterns of the tholeiites from the Red Sea trough 

are similar to those of basalts from the oceanicridge system (Schilling, 1969; 1973). Both the 
GEOCHEMISTRY OF SUBSURFACE BASALT FROM DEEP COREHOLE 109 

Karroo and Deccan provinces contain a wide range 

of tholeiitic basalts as well as intermediate, felsic, 

and undersaturated alkalic rocks (Ghose, 1976; Cox, 

1970). Clearly, the basalts (containing 328 ppm 

Zr and 27 ppm Nb) of the Karroo province selected 

by Pearce and Cann (1973) are more strongly fractionated than the Karroo samples we selected for 

comparison. A similar situation may 'exist with regard to REE abundances in the Deccan basalts. The 

REE pattern for the Deccan basalt given by Frey 

and others (1968) was considered "typical" of continental basalts but shows light REE absolute 

abundances two to three times those shown by the 

comparison suites shown in figure 7 and is more 

similar to that of alkalic basalts. The REE pattern of the average Deccan plateau basalt given by 

Nakamura and Masuda (1971) is believed to be 

more representative of the province and shows REE 

abundances similar to those of our comparison 

quartz-normative tholeiites. The examples noted 

above indicate that part of the data used for characterizing continental basalt provinces seems to have 

given misleading impressions about the representative geochemical features for some continental 

tholeiitic provinces. 

The preceding discussion noted that most of the 

suites of samples selected for construction of the 

discrimination diagrams discussed previously represented magmas of alkalic affinity or highly evolved 

tholeiitic magmas. By way of contrast, the tholeiitic 

magmas of Mesozoic age in eastern North America 

represent perhaps the most primitive end of the 

spectrum of tholeiitic magma types erupted into continental crust. This is particularly true for the olivine-normative type (Ragland and others, 1972; 

Ragland, Weigand, and Brunfelt, 1971; Gottfried 

and Greenland, 1972). By virtue of the striking 

similarities of geochemical features of the corehole 

basalts with those of the quartz-normative tholeiitic 

magmas of this province, it is reasonable to assume 

a similar mode of origin and tectonic environment 

at the time of extrusion. The similarity of K-Ar ages 

of the corehole basalt and the age of the overlying 

sediments presents a knotty problem. Although we 

considered the K-Ar age (-100 m.y.) as a mini-. 

mum age because of posteruption alteration effects, 

it could be argued that alteration occurred shortly 

after extrusion and that the basalt is of Cretaceous 

age. However, on the basis of their characteristic 

geochemical features, we suggest that the corehole 

basalts are related to the tholeiitic province of eastern North America in time as well as space. The age 

of the quartz-normative tholeiites in the northern 

part of the province is Late Triassic or Early Jurassic on the basis of geologic and paleontologic evidence (Johnson and McLaughlin, 1957; Cornet and 

others, 1973). In general, it is believed that the 

magmas representing these tholeiitic flows, sills, and 

dikes were intruded at the onset of rifting and separation of North America from North Africa (Faust, 

1975). Evidence from deep drilling and magnetic 

anomaly patterns indicate that continental drift began 180 m.y. ago (Pitman and Talwani, 1972; Vogt, 

1973). Magmatism, rifting, and an extensional tectonic regime were associated with upwelling of the 

mantle and a steep geothermal gradient. A rather 

high degree of partial melting of the upper mantle 

in this area of high heat flow could account for the 

"primitive" nature of the ENA tholeiitic magmas 

and their intrinsic geochemical features. If the corehole basalt is approximately 100 m.y. old, then volcanism took place after the continental margin 

moved progressively further from the spreading 

axis. It is reasonable to assume that the petrochemical features of later formed magma types 

would be different because of differences in the 

thermal regimes that prevailed at the time of their 

formation. 

SUMMARY AND CONCLUSIONS 

The results of our geochemical study of 11 corehole samples can be summarized as follows: 

1. Major- and minor-element and petrographic 

data indicate that the basalts have undergone 

slight to extreme oxidation, hydration, and 

hydrothermal alteration. Effects of these processes are strongest on the marginal zones of 

the flows and are reflected mineralogically by 

the presence of zeolites, calcite, and chlorite, 

and chemically by high abundances of H20, 

Fe20a, and C02 and by remobilization of K, Ba, 

Rb, and Sr. Rubidium is the most sensitive indicator of alteration and is useful for assessing the degree and extent of alteration in the 

flows. The minor elements P and Ti and the 

trace elements Zr, Nb, Hf, Th, and REE are 

essentially uniform in the two flows and indicate the absence of any in situ differentiation 

trends. Normative compositions of the least 

altered samples indicate that the basalts are of 

the quartz-normative tholeiitic magma type. 

2. The major-element and trace-element composition of the corehole basalts is compared with 

available data on rocks of theoleiitic composition from Atlantic-type, passive continental 
110 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

margins (eastern North America, Tasmania, 

Antarctica, South Africa) and on basalts from 

island arc (calc-alkalic basalt, low-potassium 

tholeiitic basalt) and mid-oceanic ridge settings. The light REE enrichment pattern and 

low K/Rb ratio ( -300) of the corehole basalts 

contrast markedly with corresponding data on 

island arc tholeiitic basalt and oceanic-ridge 

basalt which characteristically are depleted in 

light REE and have high K/Rb ratios ( -950-

1050). These data indicate that the corehole 

tholeiitic magma was derived from an undepleted source area in the upper mantle. Some 

geochemical features believed to be characteristic of orogenic high-A! basalts and andesites 

are shared by both the corehole basalts and 

the high-Fe quartz-normative tholeiitic dia~ 

base of the eastern North America province. 

These include low Ti, Cr, Cu, Ni, and Co contents and low Ni/Co ratios. We attribute some 

of these features to low-pressure fractional 

crystallization processes involving separation 

of olivine and Cu- and Ni-hearing sulfides during magmatic ascent. On the basis of the REE 

pattern, as well as absolute abundances, the 

corehole basalts are virtually indistinguishable 

from the quartz-normative tholeiitic rocks 

from eastern North America, Karroo (South 

Africa), Ferrar (Antarctica), and Red Hill 

(Tasmania) . 

3. The low abundances of ions of relatively small 

ionic radii, (Ti, Zr, Hf, Nb, and Ta) in the 

corehole basalts and in our comparison suites 

of continental tholeiites are more similar to 

those found in island arc and oceanic-ridge 

basalts than to "average" abundances in continental basalts. As a result of these primitive 

features, Mesozoic continental tholeiitic diabases from eastern North America, Tasmania, 

and Antarctica would be erroneously classified as oceanic-ridge and (or) island arc tholeiites on the basis of their Ti-Zr-Nb abundance relations. In the present study, no single 

group or pair of geochemically associated elements could be used alone for distinguishing 

magma type and tectonic setting of the corehole basalts from basalts of all of the contrasting tectonic environments considered. 

This emphasizes the importance of using trace 

elements of widely different chemical properties and sizes for discrimination purposes. 

4. K-Ar analyses of two whole-rock samples yield 

ages of 94.8 m.y. for the least altered sample, 

and 109 m.y. for an altered K-rich sample. 

These dates are considered minimum ages 

which may be significantly younger than the 

time of volcanism. 

Geochemical data on the corehole basalts constitute a substantial body of information which has 

placed certain constraints on proposed models of 

the regional tectonic setting. The geochemical features of the basalts suggest to us that they are related in space and time to the tholeiitic province of 

eastern North America and have features in common with quartz-normative tholeiitic suites found 

on other rifted continental margins. The tectonic 

regime associated with magmatic activity during 

early rifting is dominated by extensional tectonics. Flows, dikes, and sills of the eastern North 

America province are closely associated with Triassic-Early Jurassic rift valleys and deep-seated 

grabens. Geophysical studies and limited chemical 

and radiometric age data indicate that mafic flows 

and dikes are found in similar structural settings 

which underlie the Coastal Plain of the southeastern 

United States (Barnett, 1975; Milton and Hurst, 

1965; Milton, 1972; Marine and Siple, 1974) and the 

Gulf of Maine (Ballard and Uchupi, 1975). The 

primary geochemical features of the corehole basalts may be taken as an indication of the presence 

of a buried Triassic-Jurassic basin beneath the 

Charleston area. The secondary features (hydrothermal alteration effects and minimum ages) may 

reflect postmagmatic processes associated with later 

tectonic activity. 

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abundances in andesites: Bull. Volcano!., v. 29, p. 177-

194. 

Taylor, S. R., White, A. J. R., Ewart, A., and Duncan, A. R., 

1971, Nickel in high-alumina basalts; A reply: Geochim. 

et Cosmochim. Acta, v. 35, no. 5, p. 525-528. 

Vogt, P. R., 1973, Early events in the opening of the North 

Atlantic, in Tarling, D. H., and Runcorn, S. K., eds., 

Implications of continental drift to the earth sciences 

New York, Academic Press, v. 2, p. 693-712. 

Walker, K. R., 1969, The Palisades sill, New Jersey; a reinvestigation: Geol. Soc. America Spec. Paper 111, 178 p. 

Weigand, P. W., and Ragland, P. C., 1970, Geochemistry of 

Mesozoic dolerite dikes from eastern North America: 

Contr. Mineralogy and Petrology, v. 29, no. 3, p. 195-214. 

Winchester, J. A., and Floyd, P. A., 1976, Geochemical magma 

type discrimination; Application to altered and metamorphosed basic igneous rocks: Earth and Planetary 

Sci. Letters, v. 28, no. 3, p. 459-469. 

"Xoder, H. S., Jr., 1969, Calcalkalic andesites-experimental 

data bearing on the origin of their assumed characteristics, in McBirney, A. R., ed., Proceedings of the Andesite Conference, Eugene and Bend, Oreg., July 1-6, 

1968: Oregon Dept. Geology and Mineral Industries Bull. 

65, p. 77-89. 

Yoder, H. S., Jr., and Tilley, C. E., 1962, Origin of basalt 

magmas; an experimental study of natural and synthetic rock systems: Jour. Petrology, v. 3, no. 3, p. 

342-529. 

Zietz, Isidore, Popenoe, Peter, and Higgins, B. B., 1976, 

Regional structure of the southeastern United States 

as interpreted from new aeromagnetic maps of part of 

the Coastal Plain of North Carolina, South Carolina, 

Georgia, and Alabama [abs.]: Geol. Soc. America, Abs. 

with Programs, v. 8, no. 2, p. 307. 

Heat Flow From a Corehole Near 

Charleston, South Carolina, 

By J. H. SASS and JOHN P. ZIAGOS 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, 

EARTHQUAKE OF 1886-A PRELIMINARY REPORT 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1028-H 

CONTENTS 

Page 

Albstract ---------------------------------------------------------------- 115 

Introduction ------------------------------------------------------------- 115 

IIeat-fiovv data ----------------------------------------------------------- 115 

Regional significance ------------------------------------------------------ 116 References cited ___ _____ _ _____ ____ _____ _ ____ ______ _____ __ __ _ _____ ____ __ _ _ 116 

ILLUSTRATIONS 

Page 

FIGURE 1. Graph shovving temperature versus depth in Clubhouse Crossroads corehole 1 ----------------------------------------- 116 

TABLE 

Page 

TABLE 1. Temperature gradient, harmonic mean thermal conductivity, and 

heat fiovv for nearly linear segments of the temperature profile 116 

III 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886-

A PRELIMINARY REPORT 

HEAT FLOW FROM A COREHOLE NEAR CHARLESTON, SOUTH CAROLINA 

By J. H. SAss and JoHN P. ZrAGos 

ABSTRACT 

Temperature measurements were made at 3-m intervals 

from the surface to total depth (790 m) in Clubhouse Crossroads corehole 1 located near the epicenter of the 1886 

Charleston earthquake. The temperature profile is irregular, 

reflecting the observed variability of thermal conductivity 

with depth. With the exception of one 150-m-thick interval 

within the Middendorf Formation (Upper Cretaceous), 

temperature gradient varies inversely with thermal conductivity over individual stratigraphic units, resulting in 

internally consistent component values of heat flow averaging 1.3±0.12 hfu (1 heat flow unit, hfu,=lo-o cal em-' 

s-'=41.8 m W m-2 ). This value is within the range of other 

values measured in the region; thus, no thermal anomaly is 

associated with the observed seismicity in the area. 

INTRODUCTION 

As an adjunct to the geological, geophysical, andl 

seismological investigations related to the 1886 

Charleston earthquake, thermal studies were made 

in the Clubhouse Crossroads corehole 1 (CCC 1), 

located about 40 km west-northwest of Charleston 

(fig. 2, Rankin, this volume). The thermal studies 

were undertaken primarily to obtain a well-documented value of regional heat flux but incidentally 

to discover if any thermal anomalies were associated with the observed seismicity (Bollinge'r and 

Visvanathan, this volume; Tarr, this volume) of the 

area. In general, thermal anomalies would be expected only in regions of strong and recent tectonic 

strain, such as plate margins (Lachenbruch and 

Sass, 1973) or where igneous activity has occurred 

during the last few million years over areas having 

horizontal dimensions on the order of a crustal 

thickness (Lachenbruch and others, 1976; Lachenbruch and Sass, 1977) .. Thermal anomalies might 

also be expected in regions. of large-scale convective 

water movement (see, for example, Lachenbruch 

and Sass, 1977). This report summarizes the thermal studies in CCC 1 and their relation to regional 

heat flux and the tectonic setting. The thermal measurements are discussed in detail by Ziagos, Sass, and 

Munroe (1976). 

HEAT-FLOW DATA 

Temperatures were measured at 3-m intervals 

over the entire length of the hole (fig. 1). Irregularities in the temperature profile, which indicate 

abrupt changes in thermal conductivity, reflect the 

stratification of the sedimentary section. 

Ninety measurements of thermal conductivity on 

water-saturated sections of core showed a stratification that corresponded closely to the variations in 

thermal gradient with depth. The lowest thermal 

conductivities (2-4 cal cm-l s-1 oc-1 were measured 

in the Cooper Formation in the uppermost 60 m of 

the hole and in shale and clay-rich units. Basalt 

had a small range of conductivities ( 4.2-4.6 cal 

cm-1 s-1 oc-1)' and gravelly and sandy sections and 

well-indurated sandy and silty limestone and sandstone had the highest conductivities (5-8 cal cm-1 

s-1 oc-1). 

With the exception of the depth interval 555-

698 m (mostly within the Middendorf Formation 

(Upper Cretaceous) ; Gohn and others, this volume), 

component heat flows range from 1.1 to 1.5 hfu (1 

hfu, heat flow unit, = 10-" cal cm-2 s-1 = 41.8 m W 

m-2 ) (table 1). The mean of these seven values, 

weighted according to the thickness of the intervals, is 1.30±0.12 hfu. The value of 0.71 hfu within the Middendorf Formation is significantly lower 

than the mean for the other intervals. This formation contains layers of coarse sand and pebbles, and 

we attribute the low heat flow mainly to the convective transfer of heat across the formation by 

moving ground water. 

Ziagos, Sass, and Munroe (1976) used a number 

of methods for reducing the data, and, in all in115 
116 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

(/) 

a: 

w 

f--

w 

::?! 

z 

:i 

t 

w 

0 

(/) 

:J 

0 

a: 

~ u 

a: 

w 

c.. 

c.. 

:J 

PEE DEE 

FORMATION 

26.0 30.0 

MIDDENDORF 

FORMATION 

34.0 38.0 

TEMPERATURE, IN DEGREES CELSIUS 

FIGURE I.-Temperature versus depth in Clubhouse Crossroads corehole 1. Temperatures were measured at 3-m intervals. Lithologic column based on figure 2 of Gohn and others, this volume. 

TABLE I.-Temperature gradient, harmonic mean thermal 

conductivity, and heat flow for nearly linear segments of 

the temperature profile (fig. 1) in Clubhouse Crossroads 

corehole 1 

Depth Temperature Number Thermal Heat 

interval gradient, of conductivity flow 

(m) ('C km-1) samples ( 1()•3 cal cm-1 (10-<' cal g-loC-1) cm-2 s-1) 

274-399 _________ 21.0 11 5.99±0.29 1.26 

405-442 _________ 23.0 5 6.38± .83 1.47 

442-469 _________ 40.1 5 3.39± .16 1.36 

469-515 _________ 25.3 6 5.28± .55 1.34 

509-555 ---------30.1 4 3.76± .82 1.13 

555-698 _________ 18.4 15 3.88± .32 0.71 

713-738 _________ 42.2 5 3.43± .11 1.45 

754-789 _________ 30.4 16 4.23± .13 1.28 

stances, the heat flow calculated was within the 

limits of 1.3 ± 0.2 hfu. 

REGIONAL SIGNIFICANCE 

The heat flow of 1.3 hfu is within the range of 

values commonly found in the Coastal Plains physiographic province and adjoining parts of the Appalachian province of Fenneman (1946) (see fig. 

1 of Ziagos and others, 1976, fig. 2 of Sass and 

others, 1976, or fig. 1 of Lachenbruch and Sass, 

1977, for the most recent maps). From a thermal 

standpoint, the Charleston area seems to be indistinguishable from the rest of the United States east 

of the Great Plains. It thus appears that steadystate frictional heating within the upper crust does 

not contribute significantly to the observed heat 

flux in this region of relatively high seismicity. In 

contrast, in the San Andreas fault zone north of 

the Transverse Ranges in California, Lachenbruch 

and Sass (1973) estimated that as much as 0.8 hfu 

might be produced by shear-strain heating associated with relative movement between the Pacific 

and American plates (Atwater, 1970) over a band 

about 100 km wide, roughly coincident with the fault 

zone. 

REFERENCES CITED 

Atwater, Tanya, 1970, Implications of plate tectonics for 

the Cenozoic tectonic evolution of western North 

America: Geol. Soc. America Bull., v. 81, no. 12, p. 

3513-3535. 

Fenneman, N. M., 1946, Physical divisions of the United 

States: Map prepared in cooperation with the Physiographic Committee, U.S. Geological Survey, U.S. De-
HEAT FLOW FROM A COREHOLE 117 

partment of the Interior, Washington, D. C. scale 

1: 7,500,000. 

Lachenbruch, A. H., and Sass, J. H., 1973, Thermo-mechanical aspects of the San Andreas Fault system, in Proceedings of the conference on tectonic problems of the 

San Andreas fault system: Standford Univ. Pubs. Geol. 

Sci., v. 13, p. 192-205. 

Lachenbruch, A. H., and Sass, J. H., 1977, Heat flow in the 

United States and the thermal regime of the crust: 

Am. Geophys. Union Geophys. Mon. 20, in press. 

Lachenbruch, A. H., Sass, J. H., Munroe, R. J., and Moses, 

T. H., Jr., 1976, Geothermal setting and simple heat 

conduction models for the Long Valley caldera: Jour. 

Geophys. Research, v. 81, no. 5, p. 769-784. 

Sass, J. H., Diment, W. H., Lachenbruch, A. H., Marshall, 

B. V., Munroe, R. J., Moses, T. H., Jr., and Urban, T. C., 

1976, A new heat-flow contour map of the conterminous 

United States: U.S. Geol. Survey open-file rept. 76-'756, 

24 p. 

Ziagos, J. P., Sass, J. H., and Munroe, R. J., 1976, Heat flow 

near Charleston, South Carolina: U.S. Geol. Survey 

open-file rept. 76-148, 21 p. 

The Nature of the Geophysical Basement 

Beneath the Coastal Plain of 

South Carolina and Northeastern Georgia 

By PETER POPENOE and ISIDORE ZIETZ 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, 

EARTHQUAKE OF 1886-A PRELIMINARY REPORT 

GEOLOGICAL SURVEY PROFESSIOl\AL PAPER 1028-1 

CONTENTS 

Page 

Abstract ----------------------------------------------------------------- 119 

Introduction ------------------------------------------------------------- 119 ~egional setting _ __ _ __ _ _ __ _ ___ __ _____ _ _____ _ ______ _ _______ _ _ __ __ __ _ _______ 120 

Aeromagnetic and gravity surveys ------------------------------------------ 125 

Interpretation of the aeromagnetic and gravity fields ------------------------- 128 

Conclusions -------------------------------------------------------------- 135 

References cited ---------------------------------------------------------- 136 

ILLUSTRATIONS 

FIGURE 1-7 Maps: 

1. Index map showing the location of the area discussed in 

this report and boundaries of the individual aeromagPage 

netic surveys ------------------------------------ 120 

2. Structure-contour map of the surface of the geophysical 

basement in parts of North Carolina, South Carolina, 

Georgia, Florida, and Alabama -------------------- 124 

3. Generalized aeromagnetic map of southeastern South 

Carolina and eastern Georgia ---------------------- 126 

4. Simple Bouguer anomaly map of the South Carolina and 

Georgia Coastal Plain in the area of aeromagnetic 

coverage ______ ------------- ______ _ ____ _ __________ 127 

5. Interpretive map showing the major geophysical and geologic basement units underlying the Coastal Plain 

of South Carolina and eastern Georgia ------------- 129 

6. Location map showing major geophysical basement units 

and localities discussed in text -------------------- 130 

7. Interpretive map showing the larger diabase dikes of assumed Triassic or Jurassic age present be.neath the 

Coastal Plain of South Carolina and eastern Georgia _ 131 

TABLE 

Page 

TABLE 1. Data on wells penetrating basement rocks in South Carolina and 

northeastern Georgia _ ___ _ __ ___ __ _ __ _ _ ____ ____ _ _ __ _ _________ 121 

III 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886-

A PRELIMINARY REPORT 

THE NATURE OF THE GEOPHYSICAL BASEMENT BENEATH THE COASTAL PLAIN 

OF SOUTH CAROLINA AND NORTHEASTERN GEORGIA 

By PETER PoPENOE and IsmoRE ZIETZ 

ABSTRACT 

Geophysical data delineate two distinctive crust~! provinces beneath the Coastal Plain of Georgia and South Carolina. The province adjacent to and east of the Fall Line is 

a continuation of the Piedmont, composed chiefly of schist 

and gneiss units, which geologically and geophysically reflect the fabric of the Appalachian orogen. In structure and 

composition, the basement rocks are similar to those of the 

Carolina slate belt and the Charlotte belt immediately west 

of the Fall Line. At least two small Triassic basins are 

present within the province and are clearly delineated by the 

magnetic data. 

The second basement provice that underlies southeastern 

South Carolina and east-central Georgia has no counterpart 

in the exposed southern Appalachians. This basement is composed of undeformed tuffaceous clastic rocks intermixed with 

basaltic and rhyolitic flows and ash-fall deposits, which are 

associated with a relatively smooth, low-amplitude magnetic 

and gravity field. Emplaced within and directly adjacent to 

this sequence of rocks are a number of mafic plutons, which 

produce high-amplitude, steep-gradient, circular aeromagnetic and gravity positives. These positives occur within 

broad areas of higher magnetic level, which may reflect 

extensive basaltic flows, but also appear to be related to 

deeper mafic crustal sources. The association of the mafic 

plutons with basaltic flows at the basement surface suggests 

that the two are genetically related. 

The boundary between the region of northeast-trending 

aeromagnetic anomalies and the smooth magnetic field consists of a number of long, straight segments. This boundary 

probably reflects a series of major faults, which juxtapose a 

metamorphic and nonmetamorphic terrane. The association 

of mafic plutons with the boundary suggests a deep crustal 

break. 

The smooth gravity and magnetic fields associated with 

basement in southeastern South Carolina and east-central 

Georgia are similar to those associated with Triassic basins, 

suggesting that a large area of the basement is underlain 

by a deep structural basin filled with Triassic ( ? ) clastic and 

volcanic material, and intruded by a number of Triassic ( ?) 

or later mafic plutons. 

INTRODUCTION 

S. C., geographically belongs to the Coastal Plain 

physiographic province, analyses of the depth of 

focus of present seismicity (Tarr, this volume; 

Bollinger, 1972) and the depth estimation of the 

1886 earthquake (Dutton, 1889) indicate that 

these earthquakes occurred within the basement 

underlying the Coastal Plain sedimentary section. 

This "basement" is traditionally believed to be the 

buried eastward extension of the Appalachian Piedmont province which, where exposed, consists of 

highly to moderately deformed metamorphic rocks 

and intrusive igneous rocks of Precambrian and 

Paleozoic age, overprinted in places by a system of 

downfaulted basins containing clastic rocks and a 

system of northwest-trending mafic dikes, both of 

Triassic ( ?) age. Because the crystalline rocks in 

eastern South Carolina and eastern Georgia are 

covered by up to 2 km of Coastal Plain sedimentary 

rocks and cannot be mapped directly, geophysical 

methods must be employed to aid in understanding 

the composition and structure of these rocks, the socalled geophysical basement. 

The geophysical basement is defined as the top of 

a moderate-to high-velocity layer identified by seismic refraction surveys. Velocities of this layer range 

generally from 4.3 to 6.8 km/ s, and are characteristic of well-indurated sedimentary rocks, volcanic 

flows or sills, or crystalline basement. The surface 

of this layer is the lower limit of the poorly-indurated Coastal Plain sedimentary rocks, with velocities typically less than 3.0 km/ s. 

Within the last several years, detailed gravity 

and magnetic surveys covering the Coastal Plain 

area of southeastern South Carolina and eastern 

Georgia have been obtained. These data document 

that two very different basement provinces are present beneath the Coastal Plain of South Carolina and 

Although the area of the 1886 earthquake and Georgia, one with a geophysical expression that is 

that of present earthquake activity near Charleston, , typical of rocks of the Appalachian orogen and one 

119 
120 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

8 w 36o r--7"--~6:.:_ o __ _!8~5:___~~4~-~8,'l~:r-<:,.---8~:_o __ _J81_1_'1~-____!!!80~---7~9":__ _ _}_7~8o __ _}_:77~o-;::;:;;~'"j~r-~ 

TENNESSEE 

_r , ,...,--..._/' 

_j' 

r-_j 1 NORTH CAROLIN('< 

350 -----------..------- ---l ________ __ r __ ../ __ _,.__ __ ~---- -- ~- \ 

\ 1,' oGreenville r 

34° 

33° 

32" 

: "-, SOUTH 

\ -,_\ CAROLfNA 

1 \ c~ ', ._ N\~ 

\ 'l~O J ' 0 Atlanta :<\ ~ 

\ ~0~ \ GEORGIA ~\~Q 

ALABAMA \ ~\!>-~ 

\ ~p..G 

!>-~~\)' 

/ / .. 

'! 

f 

31° -- ---- -- -----~. 

l ____ _ ____ _J 

FLORIDA 

I 

I 

0 50 100 150 200 KILOMETERS -

EXPLANATION 

Patterns show directions of flight lines. 

Component surveys are: 

1 U.S. Geological Survey, 1970 

2 U.S. Geological Survey, 1975 

3 U.S. Geological Survey, 1976a 

4 Daniels, 1974 

5 U.S. Geological Survey, 1976b 

6 U.S. Geological Survey, 1976b 

TT Orangeburg or Citronelle escarpment 

Approximate location of Fall Line 

FIGURE L-Index map showing the location of the area discussed in this report and boundaries of the individual aeromagnetic surveys. 

that appears to have no counterpart in the exposed 

Appalachian system. Geophysical differences between these two provinces and probable sources are 

discussed. 

REGIONAL SETTING 

The area of aeromagnetic data coverage (fig. 1) 

lies in parts of two physiographic provinces: the 

Appalachian Piedmont province underlain chiefly 

by highly deformed and metamorphosed sedimentary and igneous rocks of Precambrian and Paleozoic age, and the Atlantic Coastal Plain physiographic province underlain chiefly by consolidated 

and unconsolidated younger sedimentary rocks of 

Cretaceous to Holocene age. The line dividing the 

two provinces is known as the Fall Line. At this 

line, the ancient crystalline rock surface, which 

slopes gently toward the coast, becomes covered by 

the younger sedimentary rocks of the Atlantic 

Coastal Plain. 

For a general discussion and summary of the 

geology of the exposed Piedmont within the area 

covered by the aeromagnetic survey, see Overstreet 

and Bell (1965a, b); Bell and others (1974); 

Georgia Geological Survey (1976a, b) ; Crickmay 

(1952) ; Hurst (1970) ; and Snoke, Secor, and 

Metzgar (1977) . The rocks of the Piedmont are generally discussed in terms of geologic "belts" that 

have distinctive lthologies or metamorphic grades. 

In many places, these belts are distinct tectonic 

units bounded by faults. The northwest edge of the 

Survey area is within the Carolina slate belt of 

South Carolina and the similar Bel Air belt of 

Georgia, which consist of low-grade, mildly deformed metasedimentary and metavolcanic rocks. 

Locally, adjacent to the Fall Line is the Kiokee belt, 

which consists of various granitoid gneisses, biotite muscovite gneiss, and hornblende gneiss. The 

major difference between the two belts has been interpreted to be not their original composition, but 

metamorphic grade and type of deformation. The 

Carolina slate belt-Bel Air belt rocks are low-grade 

greenschist facies/ rocks, which have been only mildly deformed and folded along northeast-trending, 

subhorizontal axes, whereas the Kiokee belt rocks 

are highly deformed and injected albite-epidoteamphibolite to amphibolite facies/ rocks. 

The relati<mship of the two metamorphic and tectonic styles exhibited by these two belts is poorly 
GEOPHYSICAL BASEMENT BENEATH COASTAL PLAIN 121 

understood. In places, the contact between the belts 

is clearly along major fault systems. 

The rocks of both the Carolina slate belt-Bel Air 

belt and the Kiokee belt are cut by granodioritic to 

quartz-monzonitic plutons whose crosscutting relationships and lack of strong foliation clearly show 

that these plutons were emplaced after the main 

metamorphic event of the Appalachian orogen. The 

two main bodies of these porphyritic granites exposed in the survey area are the Liberty Hill and 

Pageland plutons of South Carolina (Bell and 

Popenoe, 1976), which intrude Carolina slate belt 

rocks. On the basis of their unmetamorphosed character and because they are intruded by mafic dikes 

believed to be of Triassic age, these intrusive bodies 

have been considered late Paleozoic or Carboniferous in age. Rubidium-strontium whole rock isochron 

ages of the granites range from 249 to 332 m.y. 

(Fullagar, 1971; Butler and Fullager, 1975). 

Although no large structural basins containing 

Triassic age rocks are exposed in the area covered 

by the survey, the area is just south of the Wadesboro-Deep River Triassic basin of North Carolina, 

and structural basins of similar-appearing clastic 

rocks of presumed Triassic age are known to exist 

beneath the Coastal Plain of both South Carolina 

and Georgia (Marine and Siple, 1974). The Triassic 

basins of the east coast characteristically are northeast-trending, deep trough-shaped grabens, filled 

with coarse- to fine-grained continental clastic rocks, 

representing both high and lower energy deposits. 

The structures probably formed during the initial 

stages of continental rifting that accompanied the 

formation of the present Atlantic Ocean. Basaltic 

volcanism and intrusion of mafic rock accompanied 

or closely followed this rifting. Massive diabase 

stocks, dikes, and sills were emplaced both within 

the Triassic and in the surrounding older rocks. The 

dikes were emplaced in a remarkably systematic 

regional pattern, trending consistently northwest in 

the southern Appalachians, north-northeast in the 

central Appalachians, and northeast in the northern 

Appalachians (King, 1971). 

The structure and composition of the basement 

rocks underlying the Coastal Plain of South Carolina and Georgia are not well known. Some drill 

holes have penetrated basement in widely scattered 

areas of the Coastal Plain. Published descriptions 

of basement samples within the survey area are 

listed in table 1. 

TABLE 1.-Data on wells penetrating basement rocks in South Carolina and northeastern Georgia 

Altitude of basement Well No. Name and location Type of basement rock (meters) Source 

1 ---- Town of Hartsville water Pre-Cretaceous schist -80 Maher, 1971 (granite) 

well, Darlington County, (granite). Woollard, Bonini, and 

S.C. Meyer, 1957 (preCretaceous schist) . 2 Town of Dillon water well, Rhyolite breccia ----------- -147 Maher, 1971. 

Dillon County, S.C. 

3 Town of Florence water Triassic olivine diabase -173 Maher, 1971. 

well, Florence County, 

S.C. 

4 Town of Marion water well, Pre-Cretaceous schist ------ -193 Maher, 1971. 

Marion County, S.C. 

5 Palmetto Drilling Allsbrook ''Pre-Cretaceous'' ---------- -318 Maher, 1971. 

No. 1, 1.6 km N of Allsbrook, Horry County, S.C. 

6 Pioneer Oil, Smart No. 1, 19 ''Pre-Cretaceous'' ---------- -417 Maher, 1971. 

km SW of Conway, Horry 

County, S.C. 

7 Myrtle Beach, Horry 

County, S.C. 

Chlorite schist _____________ -433 Zupan and Abbot, 1976. 

8 Calabash, Brunswick Chlorite schist ------------- -395 Zupan and Abbot, 1976. 

County, N.C. 

9 Town of Sumter water Pre-Cretaceous granite _____ -189 Maher, 1971. 

well, Sumter COunty, 

S.C. 

10 Oil test between Perry and 

Wagner, Aiken County, 

S.C. 

Pre-Cretaceous granite _____ -59 Maher, 1971. 

11 Town of Aiken water well, Pre-Cretaceous granite _____ -12 Maher, 1971; Daniels, 1974. 

226, 1.6 km S of center 

of Aiken, Aiken County, 

S.C. 

12 ---- Survey Drilling oil test, 8 Pre-Cretaceous granite _____ -41 Maher, 1971. 

km SW of Aiken County, 

S.C. 
122 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

TABLE 1.-Data on wells penetr·ating basement rocks in South Carolina and northeastern Georgia-Continued 

Well No. 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31 

32 ----

33 ----

34 ----

36 ----

37 ----

38 ----

39 ----

40 ----

41 

42 ----

Name and location 

Aiken County, S.C. _______ _ Aiken County, S.C. _______ _ Aiken County, S.C. _______ _ Aiken County, S.C. _______ _ 

Aiken County, S.C. _______ _ Aiken County, S.C. _______ _ Aiken County, S.C. _______ _ 

Aiken County, S.C. --------

Barnwell County, S.C. ____ _ Barnwell County, S.C. ____ _ 

Sumerville --------------- USGS Clubhouse Crossroads corehole 1, Dorchester County, S.C. 

Seabrook Island, Charleston 

County, S.C. 

Richmond County, Ga. ___ _ 

Aliens Station, 14.5 km S 

of Augusta, Richmond 

County, Ga. 

Burke County, Ga. _______ _ 

Middle Georgia Oil and Gas, 

19 km NW of Sandersville, Washington County, 

Ga. 

Town of Sandersville, 

Washington County, Ga. 

Layne-Atlantic NSC water 

well, 3.2 km SW of Tennile, Washington County, 

Ga. 

A. F. Lucas and Georgia 

Petroleum oil well, 5.6 

km SW of Louisville, 

Jefferson County, Ga. 

Grace McCain No.1, 0.8 km 

S of Minter, Laurens 

County, Ga. 

Barnwell No. 1, Jim Gillis, 

4.8 km S of Soperton, 

Treutlen County, Ga. 

McCain and Nicholson H. 

Gillis No. 1, 11 km E of 

Soperton, Treutlen 

County, Ga. 

Pryor No. 1, 6.5 km NE of 

Newington, Screven 

County, Ga. 

J. E. Weatherford-Lonnie 

Wilkes No. 1, .8 km S of 

Higgston. Montgomery 

County, Ga. 

Tropic Oil Co., Gibson No. 

1, 11 km SE of Vidalia, 

Toombs County, Ga. 

S. J. Felsenthal No.1, 11 

km W of Baxley, Appling 

County, Ga. 

J. E. Weatherford, S. J. 

Felsenthal, W. E. Bradley, 

No. 1, 1.6 km W of 

Baxley, Appling County, 

Ga. 

Jelks-Rogers No.1, LaRue 

and others. S of Retreat, 

Liberty County, Ga. 

Union Bag & Paper Co. No. 

1, 11 km N of Gardi, 

Wayne County, Ga. 

Type of basement rock 

Chlorite schist ------------- Hornblende chlorite _______ _ 

Epidote chlorite schist _____ _ Hornblende chlorite schist __ 

Chlorite schist ------------- Quartz-feldspar gneiss ____ _ 

Hornblende chloride schist __ Mica quartzite and chloritebiotite schist. 

Triassic ( ?) fanglome.rate __ Triassic ( ? ) siltstone _____ - _ 

Diabase ------------------- Amygdaloidal basalt ______ _ 

Fine-grained quartzitic 

sandstone (basement?). 

Talcose schist ------------- Talcose schist -------------

Chlorite-sericite schist _____ _ Crystalline rock __________ _ 

Quartzite, biotite gneiss 

and schist. 

Granite -------------------

Crystalline rock ------------

Diabase -------------------

"Paleo" (metaquartzite) ___ _ 

"Basement" (biotite gneiss)_ 

"Granite" (no bedrock sam- ple recovered). 

Diabase -------------------

Conglomeratic arkose ______ _ 

"Quartzite" (sandstone probably indurated by intrusive 

diabase). 

Amygdaloidal basalt ______ _ 

Quartz rhyolite porphyry __ _ 

Volcanic ash --------------

Altitude of basement 

(meters) 

-108 

-210 

-196 

-198 

-178 

-187 

-192, 

-205 

-309 

-740 

-744 

-814 

-58 

-6 

-144 

+27 

-691 

-879 

-865 

-777 

-943 

-1062 

-1180 (apptr.) 

-1182 

-1289 

-1372 

Source 

Daniels, 1974. 

Daniels, 1974. 

Daniels, 197 4. 

Daniels, 1974. 

Daniels, 197 4. 

Daniels, 197 4. 

Daniels, 1974. 

Daniels, 1974. 

Daniels, 1974. 

Daniels, 197 4. 

Cooke, 1936. 

Gottfried, this volume. 

Charles Speier, drillers log. 

Daniels, 197 4. 

Milton and Hurst, 1965; 

Daniels, 1974, 

Daniels, 1974. 

Milton and Hurst, 1965. 

Maher, 1971. 

Milton and Hurst, 1965. 

Milton and Hurst, 1965. 

Milton and Hurst, 1965. 

Milton and Hurst, 1965. 

Milton and Hurst, 1965. 

Milton and Hurst, 1965; 

Pickering (oral com- mun.) 1976. 

Milton and Hurst, 1965. 

Milton and Hurst, 1965. 

Milton and Hurst, 1965. 

Milton and Hurst, 1965. 

Milton and Hurst, 1965. 

Milton and Hurst, 1965. 
GEOPHYSICAL BASEMENT BENEATH COASTAL PLAIN 123 

TABLE 1.-Data on wells penetrating basement rocks in South Carolina and northeastern Georgia-Continued 

Altitude of baaement Well No. Name and location Type of basement rock (meters) Source 

43 ---- Brunswick Peninsular No. 

1, 2.9 km E of McKinnon, 

Wayne County, Ga. 

Tuffaceous arkose _________ -1386 Milton and Hurst, 1965. 

44 ---- California Co., Brunswick 

Peninsula Corp. No. 1, 

Wayne County, Ga. 

Gray and pink arkosic quartz- -1375 

ite and diabase. 

Applin and Applin, 1964. 

45 ---- Humble Oil Co., W. C. Granite ------------------- -1436 Maher, 1971. 

McDonald No. 1, Ga. Military District 1499, SW of 

Brunswick, Glynn County, 

Ga. 

The basement descriptions (Milton and Hurst, 

1965; Maher, 1971; Siple, 1967; Cooke, 1.936; 

Daniels, 1974) show that a heterogeneous basement 

underlies the Coastal Plain. Many of the basement 

rocks appear similar in composition to rocks of the 

Piedmont, particularly near the Fall Line; however, 

in other areas, only fine-grained igneous rocks, such 

as basalt and diabase, have been found. A few holes 

have bottomed in clastic rocks resembling those in 

exposed Triassic basins. 

Of particular interest to this study are a series 

of fine-grained igneous rocks and clastic rocks 

(Milton and Hurst, 1965) known to underlie a large 

area of the Coastal Plain of Georgia. These rocks 

show little or no deformation, and include volcanic 

flows of both basaltic and rhyolitic composition, ashfall deposits, and tuffaceous arkose (Milton and 

Hurst, 1965). 

The surface of the basement is an erosional surface, which slopes gently eastward beneath the 

Coastal Plain sediments. During the Early Cretaceous, this surface apparently occupied a regional 

topographic high, which was not fully inundated 

until late in the Cretaceous Period. Figure 2 is a 

regional structure-contour map of the surface of the 

geophysical basement which is in part this erosion 

surface. The map is based chiefly on published 

depths of drill holes that have reached basement or 

near basement, and the seismic refraction studies of 

Ackerman (this volume) ; Bonini (1957) ; Bonini 

and Woollard (1960); Meyer (1956); Pooley 

(1960); Hersey and others (1959); and unpublished 

seismic reflection data of the U.S. Geological Survey. 

Only broad, regional structures are shown on the 

map because of the wide data spacing. The most 

prominent of these structures in northeastern South 

Carolina is the Cape Fear arch, which trends northwest and brings the basement to within 400 m of 

the surface near the coast at the North CarolinaSouth Carolina State boundary. A thick section of 

Lower Cretaceous rocks are present north of the 

arch, but these rocks are absent over the arch and 

to the south. This, plus a vertical displacement of 

strand lines at the surface attest to a long tectonic 

history. The second most prominent feature is the 

southeast Georgia embayment, which is recessed 

into the coast roughly between the Georgia-South 

Carolina and the Georgia-Florida State boundaries. 

The embayment is believed to be primarily a tectonically passive feature (Maher, 1971), and the 

uplift probably occurred on the Peninsular arch of 

Florida and Cape Fear arch, rather than downwarp 

in the embayment. 

In addition to the broader regional structures, a 

basement feature known as the Yamacraw Ridge 

lies parallel to the coast in eastern Georgia. The 

Yamacraw Ridge, a ridge of about 350 m relief, 

was defined on the basement surface by seismic refraction studies (Meyer, 1956; Pooley, 1960). Drilling in Georgia in the area of the ridge indicates that 

it apparently is not reflected in the overlying beds 

(Maher, 1971). Basement contours and the apparent 

lack of deformation of the overlying sediments suggest that the ridge may be topography on the basement erosional surface. 

In South Carolina, the Beaufort or Burton High 

are along the strike of the Yamacraw Ridge. These 

features and a trough to the west named "Ridgeland trough" were defined by structure contours on 

different elevations of Tertiary horizons (Siple, 

1969; Heron and Johnson, 1966). The expression of 

these features within the Tertiary rocks suggests a 

basement structural control, but our structure-contour map indicates that these are only minor features on the basement in the area in which they 

were defined. We have used the name Ridgeland 

trough for the basement depression west of the 

Yamacraw Ridge in Georgia. 

The refraction work of Ackerman (this volume) 

and the electrical work of Campbell (this volume) 
124 

33' 

32' 

STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

TENNESSf:E NORTH cPlROLINA 

-----~----------~-- ----- ---,...,. __.. __ .,.,.. ___ T _______ l'":_ __ 

AlABAMA 

\ 

\ 

\ 

i, 

\ 

i 

I 

I 

S~UTHEASt GEORGIA I ·• -E BA¥MENf 

100 200 300 KILOMETERS 

EXPLANATION 

• Well to basement or to near basement 

"' Site of depth to basement or highvelocity refractor from seismic 

refraction or reflection survey 

• Beaufort-Burton High 

24'~----L_ ____ L_ ____ L_ ____ l_ ____ l_ ____ l_ ____ l_ ____ j_ ____ ~ ____ J_ ____ J---~ 

FIGURE 2.-Structure-contour map of the surface of the geophysical basement in parts of North Carolina, South Carolina, 

Georgia, Florida, and Alabama. Elevations are in meters below sea leveL Basement is defined as the top of the 

crystalline rocks, top of the Triassic rocks or Jurassic volcanic rocks, or top of the high-velocity refractor in South 

Carolina and Georgia. 
GEOPHYSICAL BASEMENT BENEATH COASTAL PLAIN 125 

have defined a trough-shaped depression on the 

surface of the amygdaloidal basalt horizon (basement?) in the seismically active area west of 

Charleston, S. C. The significance of this feature is 

still under study. 

A discussion of the geology of the Coastal Plain 

rocks is given by Gohn and others (this volume) and 

Rankin (this volume), and will not be 'repeated here. 

The only important physiographic feature relating 

to this study is the Orangeburg or Citronelle escarpment (see fig. 1). This escarpment produces a 15 to 

60 m change in the general topographic level along 

a 965-km line, extending from Florida to Washington, D. C. (Doering, 1960), and its maximum development is in South Carolina. At its northern end, 

it follows the Fall Line, but in South Carolina, it 

divides the upper from the middle Coastal Plain 

with its toe at about 60 m and its crest at about 110 

m elevation. The Orangeburg scarp in South Carolina is believed to be composite in origin ( Colquhoun, 1965), formed by a late Miocene and perhaps 

Oligocene sea level transgression. 

AEROMAGNETIC AND GRAVITY SURVEYS 

Figure 3 presents a composite aeromagnetic map 

of southeastern South Carolina and eastern Georgia, 

compiled from the six smaller surveys shown in 

figure 1. These surveys were conducted by the U.S. 

Geological Survey in cooperation with the U.S. Nuclear Regulatory Commission, the Coastal Plains 

Regional Commission of the U.S. Department of 

Commerce, and the former U.S. Atomic Energy 

Commission. The map has a contour interval of 100 

gammas and is a simplification of the more detailed 

individual maps, which have contour intervals of 

10 to 50 gammas. Data in all areas were obtained 

at a nominal flight elevation of 152.4 m above mean 

terrain, and have been reduced to remove the international geomagnetic reference field (Fabiano and 

Peddie, 1969), which permits a comparison of magnetic levels over widely separated areas. Flight line 

spacing was 1.6 km for all data but area 1, where 

it was 0.8 km. 

The patterns shown on the magnetic map reflect 

structure and lithology in crystalline and metamorphic rocks. The crystalline and metamorphic 

rocks are the basement rocks or in thin intrusive 

rocks or volcanic flows within the sedimentary section. The magnetic contribution of sedimentary 

rocks, such as those of the Coastal Plain, is negligible. The only significant effect of the sedimentary 

rocks is to increase the distance between the anomaly-producing rocks of the basement and the airborne magnetometer. The effect of this increased 

distance causes both a smoothing and merging of 

anomalies from deeper sources and a lowering in 

their amplitude and gradient. 

The magnetic properties of crystalline and metamorphic rocks are generally related to magnetite 

content, but similar rocks may vary widely in 

magnetization because of such factors as magnetic 

size domain and remanent and induced components. 

Generally, mafic rocks are more magnetic than felsic 

varieties, but this is not always true. Daniels (1974) 

measured the magnetic susceptibility of exposed 

rocks in the central Savannah River area and found 

that only a small fraction of Carolina slate belt 

rocks are significantly magnetic (10- 1 to 10-2 cgs/ 

em 3 ), whereas a large fraction of felsic gneisses 

from a small area of the Kiokee belt fall in this 

magnetic range. Amphibolitic schists (chloriteepidote-hornblende schist) from basement cores in 

the Savannah River Plant area are also fairly high 

in susceptibility (:::::::::2.1 X 10- 3 cgs,/cm3 ). The difference in this measured susceptibility appears to be 

related to metamorphic grade rather than to composition. The concept that metamorphic grade affects 

magnetic susceptibility was outlined by Reed, 

Owens, and Stockard (1968), who suggested that 

medium-grade metamorphic rocks (epidote-amphibolite facies) are enhanced in magnetite relative to 

those of either higher or lower grade. 

Figure 4 is a simple Bouguer gravity map of the 

area of the magnetic survey. The map is based on 

the simple Bouguer anomaly map of South Carolina and Georgia by Long, Bridges, and Dorman 

(1972) and Long, Talwani, and Bridges (1976), as 

well as on unpublished data from H. L. Krivoy. 

Contour intervals are 5 and 10 mGals based on a 

station spacing of 4 to 6 km. 

The patterns on gravity maps reflect density 

variations associated with lithologic changes in the 

Earth's crust. These changes are of both regional 

and local extent and derive from both near-surface 

and deep sources. In figure 4, most of the anomalies 

are believed to be produced by intra-basement 

sources because of the limited thickness and lateral 

homogeneity of the Coastal Plain rocks in this area. 

An established practice in interpreting gravity 

and magnetic maps is to observe the anomalylithology relations in areas of exposed or known 

geology and to use these observations as principal 

guidelines in interpreting anomalies in covered 

areas. This is the method that we have used in the 

following interpretation. Insight into the anomaly 

source is provided by shape, amplitude, and the cor-
126 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

80" 

SOUTH CAROLINA 

·"' 

GEORGIA 

82° 

FIGURE 3.-Generalized aeromagnetic map of southeastern South Carolina and eastern Georgia. See figure 1 for location 

of area and sources of data. Contour interval is 100 gammas, and values are relative to a datum of 53,715.02 gammas. The data have been reduced to remove the international geomagnetic reference field (Fabiano and Peddie, 1969). 

relation or lack of correlation of the gravity and 

magnetic fields. As examples, granitic plutons of the 

Piedmont generally produce gravity lows, and mafic 

plutons produce gravity highs. Usually felsic plutons 

produce aeromagnetic lows, but many produce aeromagnetic highs. Magnetic aureoles in the country 
GEOPHYSICAL BASEMENT BENEATH COASTAL PLAIN 127 

84" 

"r-------7 ~· 

I 1/ I ~ I 

"-..,,, I 

'I"\ I 

\ 

34"1- ----'---

/ 

I 

GEORGIA 

33° ~ 

32" -

31 " 

82" 

SOUTH CAROLINA 

80" 7'!' 

T 

CAROLINA 

150 KILOMETERS 

EXPLANATION 

45• Well penetrating basement, number keyed to 

table 1 

78" 

FIGURE 4.-Simple Bouguer anomaly map of the South Carolina and Georgia Coastal Plain in the area of aeromagnetic 

coverage. Contour intervals are 5 and 10 milligals; hachures indicate areas of lower gravity. See text fOil' sources of data. 

rock and magnetic border phases or compositional 

layering of the younger plutons are reflected in the 

magnetics. Linear aeromagnetic high anomalies, particularly those associated with corresponding gravity high anomalies, are often caused by bedded 

sources. Other linear high magnetic anomalies may 

reflect cataclastic zones or compositional layering in 

plutonic rocks. The least ambiguous of all geophysical fields is the association of steep gradient, high 

amplitude, circular or elongate gravity and aeromagnetic highs with mafic or ultramafic plutons. 

Aeromagnetic and gravity maps also provide information not only on lithology, but also on the 

structural deformation of the rocks of an area. For 

example, when rocks are subjected to a horizontal 

compressive stress exceeding their elastic limit, 

they fold, elongate, buckle, and shear, and at sufficiently high temperatures become injected along 

axes perpendicular to the direction of applied force. 

Even large bodies of solid granite, if subjected to 

sufficient stress and heat, flow through plastic deformation to reflect the direction of applied stress. 
128 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

The stress direction is imprinted in their geologic 

fabric, which, in turn, is reflected in the magnetic 

grain. 

Such a grain is strongly developed in the geologic 

and aeromagnetic patterns of rocks of the Appalachian system. The rocks involved in the Appalachian 

orogen have a common geologic fabric and a corresponding geomagnetic pattern of anomalies that 

are elongated in the northeast direction. Regardless 

of the causative rocks or structures, this pattern of 

anomalies may be observed on aeromagnetic maps 

from diverse parts of the Appalachian system, including rocks beneath the Atlantic Coastal Plain. 

The pattern reflects lithologic changes associated 

with bedding repeated through folding, tilting, or 

faulting, and shear structures along the geologic 

grain. Later intrusive rocks can generally be differentiated from rocks involved in the orogen because 

they crosscut this geologic grain or do not show the 

above fabric. 

INTERPRETATION OF THE AEROMAGNETIC 

AND GRAVITY FIELDS 

We have divided the magnetic map shown on figure 3 into a number of areas of similar geophysical 

signature. Figure 5 shows these subdivisions, in addition to drill hole locations keyed to numbers on 

table 1. 

To aid in locating the units with respect to cultural or political boundaries, we have also plotted 

these major units on a location map (fig. 6). 

Magnetic zones 1n, 1s, and 2a all lie west of the 

Fall Line (fig. 1) where sources are generally exposed. Areas 1n and ls are underlain by bedded, 

tuffaceous metavolc-anic rocks of the Carolina slate 

belt and area 2a by the higher grade gneissic granite, granitic gneiss, hornblende gneiss, and quartzmicrocline gneiss of the Kiokee belt. The most 

prominent trend in the magnetics over both belts is 

northeast, reflecting the geologic grain of the Appalachian orogen. 

In the Carolina slate belt, the magnetic anomalies 

are sharp, and wavelengths are about 1 km, and 

amplitudes generally less than 200 gammas. Many 

are continuous for distances up to 50 km, suggesting 

a continuity of the causative units. Most of the field, 

however, is smooth. The anomaly pattern is known 

to reflect dipping bedding within the volcanic and 

depositional units of the belt. The tectonic style of 

the belt is one of broad regional folding along subhorizontal axes. The beds are tilted gently to the 

east in area 1n (Bell and Popenoe, 1976), and gently folded in area 1s. 

The Kiokee belt in area 2a is characterized by a 

more complex flat to moderately convoluted magnetic field of slightly higher amplitude and generally more discontinuous sharp linear northeast-trending anomalies. These linear anomalies occur over 

both granitic gneiss ll!nd gneissic granite units. 

The linear zone dividing magnetic zone 1 from 

magnetic zone 2 is labeled F1 and reflects a major 

fault system that can be traced from North Carolina into Georgia by its magnetic pattern (Hatcher 

and others, 1977 ; Daniels, 197 4; Bell and others, 

1974; Bell and Popenoe, 1976). The fault system not 

only separates areas of differing geophysical character, but is marked by short wavelength, linear 

magnetic highs characteristic of cataclastic zones 

of major faults of the Piedmont. Similar aeromagnetic highs have been noted associated with the 

Alexander City, Brevard, Towaliga, Bartletts 

Ferry, and Goat Rock fault systems (Neathery and 

others, 1976). 

The general gravity field of the Carolina slate belt 

is flat, and has an average Bouguer value of + 5 

mGals (fig. 4). This is high, relative to the more 

felsic rocks of the Kiokee belt. 

Magnetic highs and deep gravity lows of 10 to 15 

mGals amplitude are associated with granitic to 

quartz-monzonitic plutons underlying areas 1a 

(Pageland pluton) and 1b (Liberty Hill plurun) (fig. 

6). These plutons exhibit a strong discontinuous: 

magnetic aureole. Both plutons exhibit some internal 

compositional differences evident in the aeromagnetic signature. Their crosscutting relationships 

identify that the plutons were emplaced after the 

last regional metamorphic event (Bell and Popenoe, 

1976). This is evident from their magnetic signature. 

A second prominent magnetic trend is evident in 

area 1n and in extensive areas over the Coastal 

Plain. These are northwest-trending linear aeromagnetic highs which correlate with diabase dikes 

of assumed Triassic or Jurassic age (King, 1961, 

1971; Bell and Popenoe, 1976). Figure 7 shows our 

interpretation of the distribution of these dikes in 

the survey area. Where deeply buried, only the 

largest are traceable, and no doubt other dikes exist 

that are not shown on figure 7. The dikes can be 

recognized most easily where they cut low-susceptibility material, or in areas of aeromagnetic lows, 

but some are evident in areas of aeromagnetic highs. 

In addition to the northwest-trending set of dikes, 

a north-trending dike set is evident over the Coastal 

Plain near long 79°30' W. Dikes of this trend and 

longitudinal position are exposed in the Deep River 
GEOPHYSICAL BASEMENT BENEATH COASTAL PLAIN 

GEORGIA 0 37 

.,39 

()'10 

SOUTH CAROLINA 

3b Geophysical area or feature discussed in text 

~?;'~ Mafic intrusive pluton 

-- Geologic boundary or contact 

--- Fault interpreted from geophysical data 

0 

0 50 100 150 KILOMETERS 

EXPLANATION 

Composition of basement determined from 

drill hole descriptions. Numbers are 

keyed to table 1. 

43e Shale, sandstone, quartzite, or arkose 

40o Diabase or basalt 

424 Granophyre, rhyolite, or rhyolitic ash 

36 7 Pre-Cretaceous rocks 

45e Granite 

35e Gneiss or schist 

129 

FIGURE 5.-Interpretive map showing the major geophysical and geologic basement units underlying the Coastal Plain of 

South Carolina and eastern Georgia. 

Triassic basin of North Carolina, where they were 

mapped discontinuously by Reinemund (1955). Although Reinemund did not recognize the northtrending dikes as CO'lltinuous at the surface, new magnetic data (U.S. Geol. Survey, 1974) indicate 

that this dike set is continuous at depth in that area. 
130 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

78° 

200 KILOMETERS 

EXPLANATION 

3b Geophysical area or feature discussed 

in text 

0 Mafic intrusive pluton 

Geologic boundary or contact 

Fault interpreted from geophysical data 

~ County or location mentioned in text 

Boundary of survey area 

FIGURE G.-Location map showing major geophysical basement units and localities discussed in text. 

If the two widely separated areas are connected by 

continuous dikes, which they appear to be, the length 

of this swarm is thus greater than 275 km. 

Anomalies characteristic of the Kiokee belt and 

Carolina slate belt are extensive in a broad area 

under the Coastal Plain, and drill data confirm that 

similar sources cause the anomalies. We have labeled 

this area 2b on figure 5. In addition, several subareas labeled 2c and 2d have been delineated. The 

magnetic signature of area 2c was correlated by 

Daniels (1974) with exposures of low-grade rocks 

near Augusta, Ga. (Bel Air belt of Crickmay, 1952), 

and we have extended Daniels' correlation to the 

south. The highly convoluted and distinctive magnetic unit 2d appears to correlate with low-grade 

rocks exposed in river valleys north of Columbia, 

S.C. (lower metasiltstone unit of Daniels). We have 

extended this unit to the northeast of Columbia on 

the magnetic signature. 

The central area of zone 2b is characterized by a 

large, closed gravity low with a minimum value of 

-45 mGals and an average Bouguer value on the 
GEOPHYSICAL BASEMENT BENEATH COASTAL PLAIN 131 

35'r-----~--------------~a~r ______________ ~B~1' ______________ ~a~~--------------~7~~--------------~7~ 

SOUTH CAROLINA 

+ 

33' 

GEORGIA 

+ 

150 KILOMETERS 

31' 

FIGURE 7.-Interpretive map showing the larger diabase dikes of assumed Triassic or Jurassic age present beneath the 

Coastal Plain of South Carolina and eastern Georgia. 

order of -25 mGals. Basement samples (holes 9-

12, fig. 5) and magnetic and gravity data indicate 

that a large proportion of this area is underlain by 

low-density gneissic granite. The proportion of 

granite to the rock it intrudes seems to be directly 

related to the Bouguer value. The granite appears 

to be the predominant basement lithology south and 

east of Columbia, S. C., but is probably subordinate 

to metavolcanic rocks near the North Carolina State 

boundary, where longer, more continuous linear 

magnetic and gravity highs and lows predominate, 

indicating probable bedded sources. Areas underlain by this foliated granite have a northeast-trending linear magnetic grain similar to areas underlain 

by bedded sources. This grain probably reflects 

compositional layering. 

We could find no aeromagnetic anomalies characteristic of the large bodies of nonfoliated porphyritic granites such as the Pageland and Liberty 

Hill plutons in the area of 2b beneath the Coastal 
132 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

Plain. Gravity anomalies that suggest circular plutons are present south of drill hole 10 and at drill 

hole 9; however, the magnetic highs characteristic 

of the exposed plutons are not associated with these 

gravity lows. The linear aeromagnetic highs over 

the gravity minima indicate that the source of these 

gravity lows is probably foliated granite. 

A number of long, moderate amplitude aeromagnetic highs crossing areas 2a, 2b, and 2c are not associated with gravity highs. Their anastomosing pattern suggests that they may reflect cataclastic zones 

associated with Piedmont faults. We have labeled 

one particularly prominent break, which is probably, a fault, Fz. Daniels (1974) showed that amphibolitic rocks (hornblende-chlorite schist) are probably the cause of the long, linear highs north of 

area 2e. 

Area 2h has two pronounced 10+ mGal gravity 

highs associated with aeromagnetic highs and area 

2f lies on a 15 mGal high. If the source of these 

anomalies derive from the contrast of amphibolitic 

gneiss (2.8-2.9 gs/cm 3) with more felsic rocks 

(2.7-2.8 gs/cm 3), the source would have a minimum 

depth extent of 1.2 and 1.8 km, respectively. If they 

derive from the contrast of diabase or gabbro (2.9-

3.0 gs/cm 3 ) with felsic volcanic rocks, their minimum depth extent would be 0.8 and 1.2 km. In both 

areas we favor intrusive gabbros as the source of 

the gravity highs. 

The Dunbarton Triassic ( ?) basin, described by 

Marine and Siple (1974), underlies area 2e. This 

basin is the cause of a deep, smooth, northeasttrending aeromagnetic low due to a considerable 

depth of nonmagnetic rock. Marine and Siple (1974) 

have shown front drill data and geophysical analysis 

that the basin is 50 km long, 10 km wide, and contains more than 900 m of fanglomerate, mudstone, 

and sandstone. No volcanic flows or sills are present 

in the sequence. 

Areas 2f and 2g are underlain by smooth, northeast-trending aeromagnetic lows, although the lows 

are not well developed, as in area 2e. Area 2f is 

also underlain at basement depth by a Triassic ( ?) 

structural basin, as a deep well at Florence, S. C., 

penetrated 221.6 m of Triassic-appearing sediment 

below basement depth before bottoming in "trap 

rock" (Darton, 1896, p. 218), and seismic refraction velocities (Bonini and Woollard, 1960, station 

43) are compatible with Triassic sediments at the 

basement (3.9 km/s). The identification of "trap 

rock" suggests that some of the linear aeromagnetic 

highs surrounding area 2f could reflect diabase sills 

or flows of Triassic age, as suggested by Bonini 

and Woollard ( 1960) from seismic velocity data; 

however, the 15 mGal gravity anomaly is more compatible with a body of greater depth extent than a 

sill (previously discussed) and suggests that either 

an intrusive body or a dense lithologic unit underlies the basin. The seismic refraction velocity in area 

2g (Bonini and Woollard, 1960, station 44) of 6.8 

km indicates that this magnetic low probably does 

not reflect a sediment-filled Triassic basin unless it 

is overlain by a diabase sill or flow. 

The geophysical fields discussed thus far are all 

typical of those produced by rocks of the Appalachian orogen. The anomalies of the older crystalline 

rocks have a northeast grain; the Triassic ( ?) 

basins cause smoth, northeast-trending aeromagnetic lows of limited width and length. The geophysical fields of the southern part of the area discussed in the subsequent section are quite different 

in character, suggesting profound differences in the 

crustal composition, structure, and (or) metamorphic history of these areas. 

The straight boundaries in segments between 

B1-B2, B2-Ba, B3-B. and the profound change in 

basement character across the boundaries strongly 

suggest a series of faults juxtaposing high density 

magnetic rocks on the northwest and lower density 

nonmagnetic to mildly magnetic rocks on the southeast. The abruptness of the gravity and magnetic 

breaks also suggests faulting. The postulated fault 

between B2 and B3 is continuous with B3-A., which 

together closely follow the base of the Orangeburg 

or Citronelle escarpment at the surface of the 

Coastal Plain for a distance of more than 150 km. 

The coincidence almost certainly reflects a structural 

control for the scarp, a conclusion reached on geologic evidence by Doering (1960), who believed the 

scarp marked a hinge line, but refuted by Colquhoun (1965) on the basis of heavy-mineral assemblages in the upper beds of the Coastal Plain. 

South of line AcA2-A3-A.-Ao (fig. 5) and north 

of BcB2-B3-B, (fig. 5), the crust is highly mafic, 

causing high-amplitude gravity and magnetic anomalies, except for area 3c, the large gravity low centered around Georgetown, S.C. The magnetic field 

south of BcB2-B3-B, does not have the grain of the 

Appalachian orogen and is composed of a smooth 

southward decreasing field of low amplitude, random to east-trending anomalies, and several areas of 

higher magnetic level that enclose sharp, steepgradient, high-amplitude circular anomalies. The 

Bouguer gravity field of this southern area is smooth 

and can be viewed as a broad regional low, averaging 
GEOPHYSICAL BASEMENT BENEATH COASTAL PLAIN 133 

-10 mGals, on which are superimposed sharp, steepgradient gravity positives. 

Part of the smoothing of the regional field south of 

line B1-B, can be accounted for by an increased 

section of Coastal Plain rocks in the southeast 

Georgia embayment. Figure 2 indicates that this 

thickening is not rapid, however, but gradual, and 

magnetic anomalies from northwest-trending dike 

sources are not significantly diminished. Therefore, 

the low-amplitude field south of the line indicates 

weakly magnetic rocks beneath the Coastal Plain 

sediments, caused by a major change in basement 

composition, metamorphic grade, tectonic style, or a 

combination of ail three. The smooth field contains 

many low-amplitude, moderately sharp-gradient 

anomalies that can be shown to originate from 

sources at or near the depth of known or seismic 

basement; however, only linear anomalies reflecting 

dikes and a few circular anomalies, perhaps reflecting small plutons, have amplitudes of over 100 

gammas. This suggests that many of these anomalies, particularly areas of low-amplitude button-like 

anomaly fields seem in the detailed 10-gamma contour aeromagnetic data, may originate from thin 

sources. 

Several possible lithologies could reasonably account for the smooth magnetic and gravity field 

south of line BeE,. From observations of the geophysical fields of exposed Piedmont rocks, these 

would include high-grade schist or gneiss, granitic 

rocks, or a deep basin of flat-lying or unmetamorphosed sedimentary rocks. Our interpretation is that 

most of the smooth field reflects a thick section of 

unmetamorphosed flat-lying clastic and volcanic 

rocks within a structural basin for the following 

reasons: 

1. The stra,ight boundaries BcB2 , B2-B,, and 

B3-B4 suggest faults. 

2. The general geophysical character of the entire 

southern province resembles that seen over some 

Triassic basins where a flat magnetic field is associated with stratified continental deposits, and anomalies are associated with exposures of mafic intrusive 

or extrusive rocks (see Kane and others, 1972) and, 

in some cases, secondary horst structures juxtaposing older rocks with the younger rocks. 

3. No high-grade schist or gneiss is known from 

drill holes in the smooth field, with the exception of 

drill holes 34 and 35, which are discussed later. Instead, all drill holes within the area have bottomed in 

unmetamorphosed flat-lying volcanic flows, volcaniclastic rocks, and tuffaceous clastic rocks (wells 

23-25, 37-55, table 1). These lithologies within the 

survey area include quartz-rhyolite porphyry, amygdaloidal basalt and diabase, volcanic ash, and arkosic 

to fine-grained sandstone. No felsic intrusive rocks, 

such as granites, are known from basement samples· 

south of the boundary B1-B. and north of Glynn, 

Pierce, and Coffee Counties, Ga. (fig. 6). 

In South Carolina, granitic basement has been 

suggested as the cause of the smoorth magnetic field 

(Taylor and others, 1968, p. 776; Daniels, 1974), on 

the basis of reported granite at the basement recovered from a well that was drilled in Screven County, 

Ga. (well 36, table 1) ; however, new information 

reveals that no basement sample was recovered from 

the Screven County well (Sam Pickering, Jr., oral 

commun., 1976) and the identification of basement 

material as granite was based on the resistance .to 

the drill. Seismic and magnetic evidence suggests 

that the "basement" in Screven County, Ga., is. composed of stratified rocks. Two sub-horizontal seismic 

refractors were recorded by Pooley (1960) (refraction line 4) only 3 km from the Screven County well, 

one at 0.7 km (the surface contoured in fig. 2) and a 

second at 2.1 km. No gravity or magnetic break is 

evident between the well location and seismic refraction line location. If the resistive rock penetrated in 

the Screven County well was a volcanic flow, it 

would explain the high basement velocity of 5.3 km/s 

recorded by Pooley and the deeper subbasement 

refractor. 

. 4. The shoreward extension of the Brunswick, Ga., 

branch of the East Coast magnetic high, discussed 

by Taylor, Zietz, and Dennis (1968), Emory and 

others (1970), and Rabinowitz (1974) touches the 

southern corner of our study area in area 3b. Along 

the shelf edge, the magnetic high, continuous with 

the Brunswick anomaly, has been interpreted as related to Mesozoic continental extensdon. 

5. Seismic, electrical, and magnetic analysis show 

that subhorizontal layers are present at several 

depths beneath the basalt (geophysical basement) in 

the Summerville, S.C., area (Ackermann, this volume; Campbell, this volume; Phillips, this volume). 

Subhorizontal refractors were also recorded below 

the geophysical basement in the area of smooth magnetic field in Jasper County, S.C., and Effingham 

County, Ga. (Pooley, 1960, refraction lines 10, 2). 

The most probable explanation for the high velocity, 

high-resistivity layers beneath the geophysical basement depth (fig. 2) is deeper volcanic flows or sills, 

or the true crystalline basement. 

We favor a Triassic ( ?) age rather than a Paleozoic age for the unmetamorphosed sedimentary and 
134 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

volcanic rocks within the structural basin for the 

following reasons: 

1. The abruptness of the boundary dividing the 

smooth field from the northeast-trending Piedmont 

anomalies suggests structure rather than a metamorphic gradient. 

2. All of the rock penetrated in the area of the 

smooth field sugges.t Triassic lithologies, except for 

the rhyolites and ignimbrites. The rhyolitic lithologies do not preclude a Triassic age, as rhyolites and 

ignimbrites of Triassic age are extensive in the 

southern Florida volcanic province (Barnett, 1975, 

p. 127). 

3. The area lies on the predictable continuation to 

the east-northeast of the deep Triassic graben system that underlies the re1gion of the Apalachicolasouthwest Georgia embayment in southwestern and 

south-central Georgia (Barnett, 1975; Marine and 

Siple, 1974) (fig. 2). In Florida and western Georgia, the graben system is more than 200 km wide 

(Barnett, 1975; Neathery and Thomas, 1975; Marine and Siple, 1974) and contains a number of secondary horst blocks of older Paleozoic sedimentary 

rocks and Precambrian ( ?) or lower Paleozoic ( ?) 

crystalline rocks. The various basins of the graben 

system are filled with coarse red feldspathic and 

arkosic clastics, and tabular, sometimes amygdular, 

diabases believed to be intrusive sills (Barnett, 

1975). 

The northern boundary of this graben system is 

structural, as a well in Pulaski County, Ga. (R. 0. 

Leighton-Dana No.1, Milton and Hurst, 1965), penetrated 1,176 m of coarse- to fine-grained sandstones 

and diabase layers of Triassic(?) age below the 

Upper Cretaceous Coastal Plain sedimentary rocks 

only 30 km southeast of wells in Houston County, 

Ga., that bottomed at basement depth in Piedmont 

rocks (Tricon Minerals-Gilbert No. 1, Milton and 

Hurst, 1965). There is a distinct gravity break between the Houston County, Ga., and the Pulaski 

County, Ga., wells (see Long and others, 1972). This 

break is similar to and along the strike of our magnetic break and corresponding gravity break BcB2 

(fig. 5), suggesting a similar cause. 

4. Northwest-trending anomalies probably reflecting mafic dikes cut the smooth field in South Carolina (fig. 7). These dikes are along the same trend 

and are assumed to be continuous with dike swarms 

of Triassic(?) or Jurassic(?) age that cut the exposed Piedmont rocks. Depth analyses on these dikes 

indicate that they have tops. at basement depth 

(basalt) (0.7 to 1 km) in South Carolina. This would 

put a minimum probable age of Jurassic(?) on the 

basement material in the area of the smooth field in 

South Carolina. 

5. There are no obvious structural breaks within 

the smooth field. Instead, magnetic data suggest 

that flow units are extensive in the basement and 

form zones of more or less localized, discontinuous 

bodies, which cause low-amplitude magnetic anomalies. The flows appear to be mixed with and separated by intervening zones or layers of clastic materials, causing areas of smoother aeromagnetic and 

gravity lows. 

Basement compressional velocities in the area of 

smooth magnetic field (Pooley, 1960, Bonini and 

Woollard, 1960) of 4.5-5.6 km/s are not compatible 

with velocities of Triassic sedimentary rocks (2.3-

4.5 km/s) but could be explained by the extensive 

volcanic flows or sills known to be present at the 

basement. 

Wells 34 and 35 are within the area of smooth 

magnetic field. These wells were reported to have 

bottomed ill! metamorphos;ed rocks (Milton and 

Hurst, 1965, p. 17). If the identification of basement 

in this area is correct, these rocks may occupy a 

small secondary horst structure within the proposed structural basin. Clearly, metamorphism is. nil 

to low grade in all other wells that have pentrated 

basement within the smooth magnetic. field. 

The shape and amplitudes of the aeromagnetic 

and gravity highs in areas 4a, 4b, 4c, 4d, 4e, 4f, 4g, 

and 4h (figs. 4 and 5) clearly indicate that these 

areas are underlain by mafic intrusive masses. Mafic 

intrusive masses of this abundance, shape, and size 

are not known elsewhere in the south Appalachian 

Piedmont. A similar, but less pronounced, occurrence of mafic plutons j:tlong the coast of Maine and 

Massachusetts was interpreted by Kane and others 

(1972) as marking a major crustal break resulting 

from adjustments between distinctive crustal blocks 

offshore and onshore. The association of the aeromagnetic and gravity highs in areas 4a, 4b, and 4c 

with the boundary between Piedmont-type metamorphic rocks and undeformed rocks, and the arrangement of the plutons within the ridgelike zone 

along an eastwest and northeast trend, suggest that 

the zone also marks a major crustal break. 

Anomalies 4e, 4f, and 4g have the classic gravity 

and magnetic forms of unmetamorphosed, stocklike 

mafic plutons, and may be feeders for basalt flows 

known to underlie the area (wells 23 and 24, table 

1) . Anomalies 4e and 4f are deep or may be produced by plutons with outward-dipping contacts, 

whereas 4g is typical of an anomaly from a steepsided, cylindrical, compositionally zoned pluton. 
GEOPHYSICAL BASEMENT BENEATH COASTAL PLAIN 135 

Depth analyses on anomalies 4e, 4f, and 4h by the 

technique of Vaquier and others (1951) and by 

Phillips (this volume) show that the tops of the 

main plutonic masses lie at about 1.5-km depth or 

below basement (basalt) depth. If the three small 

circular anomalies associated with the top of anomaly 4f are treated as separate sources, these anomalies originate at about 0.8 km below ground level, 

or the known depth to the basalt flows drilled in 

this area (drill hole 24, table 1). The small anomaly 

centered between drill hole 23 and 24 similarly originates from the basalt depth. Depth analyses by the 

same technique on anomaly 4g indicates a depth to 

the top of this pluton of about 1 km, or near the 

depth to the high velocity refractor (0.925 kmf in 

this area (Bonini and Woollard, 1960; Pooley, 

1960). 

Areas 4a, 4b, 4c, and 4d outline zones composed 

of a complex of mafic plutons which appear to intrude a mafic crust, perhaps similar to the Bays of 

Maine igneous complex (Chapman, 1968; Kane and 

others, 1972). Individual plutons in the zone are not 

isolated, as are anomalies 4e-4h, but discrete plutonic masses can be identified from both the gravity 

and the magnetic data. On figure 5 we have patterned the most prominent of these plutons within 

the zones. The plutons appear to be arranged reticularly along apparent north-northeast and east 

trends. 

The zones surrounding individual plutons in areas 

4a, 4b, and 4c, and zone 5 near plutons 4e, 4f, and 

4h. have an unusually high magnetic level. Our 

modeling and that of Phillips (this volume) in area 

5 suggest that in this area much of the magnetic 

buildup (broad wavelength anomalies) originates 

from a deep source; however, there is a strong possibility that at least some of the high magnetic level 

originates from the cumulative effect of many shallower, thin magnetic sources. Depth analyses show 

that many individual anomalies within this zone of 

high magnetic level originate near basement 

(basalt) depth. Our interpretation in area 5 and 

area 4c is that these areas of high level may, in 

part, outline areas of extensive mafic flows, although we were unable to model the broader sources 

as flows. 

There is a deep gravity low underlying Georgetown, S. C., and a corresponding high magnetic 

level in area 3c of the magnetic map. This gravity 

low has been interpreted by Talwani and others 

(1975) to be caused by a deep structural basin of 

low-density rock capped by a mafic sill or flow. The 

sill would explain high seismic velocities (6.7 km/s) 

(Bonini, 1957) and high magnetic level associated 

with the gravity low. A second interpretation, which 

would also fit the data, is that the gravity anomaly 

reflects a low-density basement rock, such as a 

granite body, coincidentally overlain by· diabase or 

basalt (Talwani and others, 1975). On the basis of 

the amplitude of the gravity low (35 mGals), the 

magnetic expression, which suggests a prismatic 

source, and the drill hole 7, which bottomed in 

chlorite schist, we favor the second interpretation, 

whereas Talwani favored the first. 

CONCLUSIONS 

The major point in our analysis is that the basement beneath southeastern South Carolina and eastcentral Georgia is not simply an extension of the 

Appalachian Piedmont, as generally believed, but 

differs strikingly from the Piedmont. The area 

near the Charleston earthquake zone is particularly anomalous, as it is underlain by a number of 

large mafic plutons and an extensive volcanic field. 

These plutons intrude nonmagnetic and undeformed 

layered rocks that could be as old as Paleozoic, although some evidence in the Charleston, S. C., area 

suggests that here they may be Triassic ( ?) and perhaps as young as Cretaceous. The presence of mafic 

plutons of this size and abundance suggest that they 

mark deep structural breaks interpreted to be of 

Mesozoic age. 

The boundary between the deformed rocks of the 

Piedmont and the undeformed rocks beneath the 

Coastal Plain is abrupt, marked along most of its 

length by a ridgelike zone of mafic plutons. The 

straight segments along much of the zone suggests 

a series of faults, rather than a metamorphic 

gradient. 

If the smooth magnetic field in South Carolina 

and south-central Georgia does reflect a complex 

structural basin of Triassic ( ?) age rocks, this basin 

is an order of magnitude larger than any exposed 

Triassic(?) basin in the Eastern United States, and 

is a major geologic feature requiring explanation. 

The apparent overlap of Florida has long been noted 

in most continental reconstructions (Bullard and 

others, 1965; Dietz and Holden, 1970). The proposed graben system could furnish a zone along 

which the overlap could be accommodated. Also, it 

is possible that Florida, during the initial stages of 

continental separation, occupied a separate crustal 

fragment attached to the trailing edge of the African-South American blocks and later became 

stranded with the North American plate. There are 
136 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

any number of interesting speculations; in fact, the 

extension of the graben system into South Carolina 

and eastern Georgia at this time is a speculation 

based on geophysics yet to be proved by drilling. 

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GEOPHYSICAL BASEMENT BENEATH COASTAL PLAIN 137 

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Magnetic Basement Near Charleston, 

South Carolina-A Preliminary Report 

By JEFFREY D. PHILLIPS 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, 

EARTHQUAKE OF 1886-A PRELIMINARY REPORT 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1028-J 

CONTENTS 

Page 

Abstract ----------------------------------------------------------------- 139 

Introduction ______ ~---- _____ ------ ___________ -------------- ___ ----------- 139 

Aeromagnetic data ------------------------------------------------------- 139 

Depth analysis ----------------------------------------------------------- 142 

Model studies ___ --------------------------------------------------------- 142 

Discussion of results ----------------------------------------------------- 145 

Depth contours ----------------------------------------------------------- 146 

Basalt horizon ----------- ___ ------------------------------------------ 146 

Crystalline basement _____________ ------------------------- ____ __ _ ____ 146 

Mafic bodies --------------------------------------------------------- 149 

References cited ---------------------------------------------------------- 149 

ILLUSTRATIONS 

FIGURE 1. Map showing location of the study area ---------------------

2. Aeromagnetic map of the study area -------------------------

3. Magnetic profile 66 and interpreted basement cross section ____ _ 

4. Magnetic profile 76 and interpreted basement cross section ____ _ 

5. Contour map of magnetic basement (deep solution) -----------

6. Contour map of magnetic 'basement (shallow solution) ---------

Page 

140 

141 

143 

145 

147 

148 

III 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886-

A PRELIMINARY REPORT 

MAGNETIC BASEMENT NEAR CHARLESTON, SOUTH CAROLINAA PRELIMINARY REPORT 

By JEFFREY D. PHILLIPS 

ABSTRACT 

Automated depth analysis has been performed on aeromagnetic profiles collected in an area of current and historical seismicity near Charleston, S. C. Model studies, based 

on the computer-generated depth estimates, have been used 

to construct basement cross sections along two north-south 

lines. These cross sections reveal that extensive surfaces of 

magnetization contrast are present at two different depths, 

with the deeper surface having the stronger contrast. The 

shallower surface corresponds to the seismically determined 

crystalline basement. The deeper surface is interpreted to 

be the top of a mafic intrusive complex. Linear zones of 

anomalously low magnetization within the crystalline rocks 

appear to be responsible for linear lows in the magnetic 

anomaly. Reversely magnetized volcanic flows are an alternative interpretation. Contour maps of the computer-generated depth estimates are used to study depths and trends 

of subsurface structures in the epicentral area. 

INTRODUCTION 

The aeromagnetic map of Charleston and vicinity, 

S.C. (U.S. Geol. Survey, 1975) is characterized by 

localized strong magnetic highs superimposed upon 

broad, but sharply defined regional highs. The overall pattern suggests that interesting structures and 

lithologies exist within the crystalline rocks underlying the South Carolina Coastal Plain. The definition of these structural and lithologic features is of 

particular interest because of the historical seismicity of the Charleston area (Bollinger, this volume; 

Bollinger and Visvanathan, this volume; Tarr, this 

volume). 

The magnetization contrasts responsible for magnetic anomalies usually are found at the boundaries 

of relatively homogeneous zones of magnetization. 

Such magnetization boundaries may be, found at the 

crystalline basement surface (the contact between 

buried crystalline rock and the overlying sedimentary rock), at lithologic boundaries within the crystalline rock, and at the surfaces of dikes, sills, and 

volcanic flows within the sedimentary column. In 

the Charleston region, there is evidence for all three 

forms of magnetization boundaries. 

To locate magnetization boundaries, an automated 

depth-analysis technique has been used on selected 

aeromagnetic profiles taken from the Charleston survey (U.S. Geol. Survey, 1975). Two complementary 

sets of depths have been calculated for each profile. 

Miodel studies, based on both sets of solutions, have 

been used to obtain basement cross sections along 

two north-south lines. These cross sections indicate 

the presence of at least-two extensive surfaces of 

magnetization contrast, the deeper surface having 

the stronger contrast. 

The shallower of these two surfaces is interpreted 

to be crystalline basement on the basis of seismicrefraction studie's (Ackermann, this volume). The 

deeper surface is interpreted to be the top of a 

mafic intrusive complex. In addition to defining 

these magnetic-basement surfaces, the depth estimates and model studies suggest that linear zones 

of anomalously low magnetization are present 

within the crystalline basement rocks. Contour maps 

of the computer-generated depth estimates are used 

to examine these linear features, as well as other 

apparent structures, in a 40 x 55 km area west 

of Charleston. 

This study was funded by the U.S. Nuclear Regulatory Commission, Office of Nuclear Regulatory 

Research, Agreement AT (49-25)-1000. 

AEROMAGNETIC DATA 

A total-field aeromagnetic survey was flown over 

the South Carolina Coastal Plain between lat 

139 
140 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

81 °00' 

33°30' 

30' 

0 

0 

LINE 

Regional 

magnetic 

high 

Broad 

magnetic 

low 

5 10 

10 15 

80°00' 45' 79°30' 

LINE 

15 20 25 30 MILES 

2 5 30 KILOMETERS 

FIGURE 1.-Map showing location of the study area. Magnetic profiles 66 and 76 are indicated. The line with tick marks 

is the zero contour of the aeromagnetic map (U.S. Geological Survey, 1975). 

33°30' N. and 32°30' N. in 1973. The flight lines 

were north-south at 1 mile (1.6 km) spacing. The 

flight elevation was 500 ft (152 m)·. The resulting 

total field anomaly map was released as an openfile report (U.S. Geol. Survey, 1975). 

The regional magnetic pattern consists of broad 

regional highs separated by broad belts of low magnetic intensity. Superimposed upon the regional 

highs are stronger, more localized highs. In figure 

1 the regional magnetic highs and lows are outlined, 

and the location of the detailed study area is indicated. The part of the aeromagnetic map covering 

this detailed study area is reproduced in figure 2. 

Indicated on this figure are the locations of Middleton Place, the Charleston Air Force Base, and the 

USGS corehole site (Clubhouse Crossroads corehole 

1) . Strong magnetic highs are found over the corehole site, north and southeast of Middleton Place, 

and along the coast in the southeast quadrant and 

the southwest corner of the mapped area. Middleton Place itself sits on an east-west linear magnetic 

low, bounded on three sides by strong closed magnetic highs and on the south by an east-west linear 

magnetic high. Both this linear high and the strong 

triple-peaked magnetic high over the USGS corehole site correspond to similar highs in the gravity 

anomaly (Long and Champion, this volume). In addition, the regional magnetic highs correspond, for 
MAGNETIC BASEMENT 141 

1 1 

LINE 76 LINE 66 

0 10 MILES 

I I I I 

0 5 10 15 KILOMETERS 

CONTOUR INTERVALS 50 GAMMAS 

FIGURE 2.-Aeromagnetic map of the study area (modified from U.S. Geological Survey, 1975). The southern ends of 

magnetic profiles 66 and 76 are indicated. 
142 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

the most part, to similar regional gravity highs. 

This correspondence suggests that both the strong 

magnetic highs and the regional highs are produced by mafic intrusive bodies at depth. 

DEPTH ANALYSIS 

In order to obtain magnetic-basement depth estimates, digital aeromagnetic data, as recorded along 

the flight lines, were first interpolated to a rectangular grid. The resulting interpolated profiles were 

oriented north-south, spaced at 1-mile (1.6 km) intervals, and sampled at quarter-mile (0.4 km) intervals. Selected profiles were analyzed for source 

depth using the automated high-resolution technique 

of Phillips (1975). In this technique a statistical 

source model is used to estimate depth from the 

autocorrelation function of the magnetic profile. 

The autocorrelation function is calculated within 

short windows ab:out each observation point, and 

compared with a theoretical autocorrelation function that would be produced by a two-dimensional 

basement having uncorrelated magnetization. This 

means that the magnetization contrast at the basement surface is assumed to be statistically independent from point to point. Where the fit between 

the observed and theoretical autocorrelation functions is good, a depth can be estimated. Where the 

fit is poor, it means the data violate the assumptions 

of the model, and no reliable depth estimate is possible. In practice then, the computer only locates 

the segments of the basement where the assumptions of two dimensionality and uncorrelated magnetization appear to be satisfied. When two slightly different statistical models (assuming zero-mean 

and nonzero-mean source magnetization) are used, 

two complementary solutions can be obtained-one 

emphasizing shallow sources and one emphasizing 

deep sources. The two solutions are combined in 

cross section form prior to structural or geologic 

interpretation. 

Because the depth-analysis technique uses a sliding data window to search for a continuous basement surface, its response to a sudden vertical 

change in the basement is often delayed, resulting 

in hyperbolic tails on the depth estimates. These 

computer artifacts are generally ignored in the subsequent interpretation. Horizontal shifts of the 

depth estimates due to phase effects of the magnetic 

anomaly are reduced in the technique, through use 

of the analytic signal (Nabigihian, 1972), which has 

its power centered directly over the sources. However, some horizontal shifts will always remain as 

a result of the technique's slow response to sudden vertical changes. 

One possible source of error in the estimated 

depths is the assumption that two-dimensional 

trends in the magnetic anomaly are perpendicular 

to the flight lines. Where this assumption is not 

satisfied, the depths will be somewhat overestimated. 

Fortunately, the major two-dimensional features of 

the aeromagnetic map do trend at right angles to 

the flight lines. 

Although the required assumptions of two-dimensionality and uncorrelated source magnetization 

may seem unreasonable, this technique has been successfully tested, both on synthetic data (generated 

assuming uniformly magnetized bodies) and on real 

data collected in areas of known source depth. For 

this reason, we can have some confidence in the 

estimated depths. 

MODEL STUDIES 

Two-dimensional modeling techniques were used 

to obtain cross sections along profiles 66 and 76 (fig. 

1). Where possible, computer-generated depths were 

used to define the models. In areas where no computer-generated depths were available, simple 

models were used to match the general character 

of the anomaly and thus complete, the cross section. 

Uniform-induced magnetization in a small number 

of bodies was assumed in all models. It should be 

emphasized that model studies of this sort yield 

nonunique solutions, and commonly alternative solutions are reasonable. However, in areas where computer-generated depths are available, the present 

solutions fit both the amplitude and the correlation 

statistics of the observed magnetic profiles, thereby 

restricting the alternatives. 

Line 66 is near the eastern edge of the detailed 

study area, and extends beyond it to the north (see 

fig. 1). The magnetic profile shown at the top of figure 3 is characterized by broad magnetic highs in 

the north and south separated by a broad low. The 

northern high and the low are outside the detailed 

study area. The southern high contains three strong 

peaks, two of which flank the Middleton Place magnetic low (lat 32°54' N.). An interpreted basement 

cross section is shown at the bottom of the figure. 

The heavy lines on the cross section indicate depths 

obtained from the computer, and the lighter connecting lines define the model used to fit the magnetic anomaly. 

In the northern part of the cross section, a welldefined southward-dipping magnetic basement is 

seen at depths of 600-1,500 m below the ground 
MAGNETIC BASEMENT 143 

s PROFILE 66 N 

600 

600 

400 

Middleton 

Place 

low 

400 

I ""' Observed ~ / ', 200 

200 

(/) 

<( 

:2 

:2 0 

~ 

Calculated ':: 

4-~----~~--~~~~--------~~~----------+-~~--~==--T-10 

<( 

(:J 

-200 

-400 

-600-

Flight 

elevation 

32°30' 

0 

(/) 1000 a: 

UJ 

1--

UJ 2000 :2 

~ 3000 

:i 

1--

a.. 4ooo- UJ 

0 

5000 

s 

\ ' ..... 

VERTICAL EXAGGATION xs 

10 15 20 MILES 

-200 

-400 

-600 

~sooo 

N 

10 15 20 KILOMETERS 

FIGURE 3.-Magnetic profile 66 and interpreted basement cross section. The observed magnetic profile is given by the 

solid curve at the top of the figure. The computed magnetic profile is given by the dashed curve. Heavy lines on the 

cross section represent computer-generated depths. Lighter lines have been added to form the model. Magnetizations 

(J) are given in gauss. Depths are relative to ground level. 

surface. Because these depths correspond to the 

seismically determined crystalline basement depths 

south of Middleton Place (Ackermann, this volume), this surface has been interpreted to be crystalline basement. The underlying material has been 

assigned a weak magnetization of 5 x 10-• gauss, 

which corresponds to a susceptibility of 10-a, a reasonable value for granitic or metamorphic rocks. 

Because of the low magnetization contrast and 

low relief of this basement surface, it contributes 

very little to the calculated magnetic anomaly. Consequently it could just as easily be modeled as an 

unconformity in a thick nonmagnetic sedimentary 

sequence. in either interpretation, the surface is defined magnetically by the dikes or volcanic flows that 

contribute to the short wavelength part of the magnetic anomaly. No attempt has been made to include 

these features in the model. 

The computer-generated depths provide no information on intrabasement sources in the northern 

part of this line, but deep sources have been added 

to the model, based on results from nearby lines. 

These sources consist of a strongly magnetized body 

at 3.6 km depth in the north and a weakly magnetized or nonmagnetic body at similar depth under the broad magnetic low. The northern source 

has been interpreted to be a mafic intrusive body on 

the basis of the regional gravity map (Long and 

Champion, this volume), which shows a relative 

high over this feature. The modeled nonmagnetic 

body under the broad magnetic low does not make 

any significant contribution to the calculated magnetic anomaly, and it could easily be replaced by a 

thickened section of the overlying material. 

The three magnetic highs and the regional high 

in the southern part of the line appear to be pro-
144 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

duced at depths of between 2.4 km and 3.6 km by a 

strongly magnetized source, which is again interpreted to be a mafic intrusive body on the basis of 

a corresponding regional gravity high. 

The Middleton Place magnetic low (lat 32°54' N.) 

corresponds to a topographic high in the estimated 

magnetic basement. Depth analysis of adjacent 

magnetic profiles reveals that this apparent topographic high is a linear feature, extending to the 

west under the magnetic low. On the cross section 

the topographic high is interpreted to be the upper 

boundary of a nonmagnetic zone within the crystalline rock. The width of this hypothetical zone 

may be exaggerated by the depth-estimation technique. This nonmagnetic zone is shown extending 

down into the top of the mafic intrusive body, and 

in fact, this relief at the top of the mafic body can 

account for nearly all of the observed decrease in 

magnetic intensity. Although this suggests that the 

source of the magnetic low is at great depth, the 

correlation between the low and the shallower depth 

estimates is an argument for a source nearer the 

crystalline basement surface. The nonmagnetic zone 

is included in the model mainly on the basis of this 

correlation. 

This modeled nonmagnetic zone could represent 

a zone of alteration around a fault. Three types of 

evidence support this interpretation: (1) The 

linearity of the feature, (2) the close association 

with Middleton Place, an area of active seismicity 

(Tarr, this volume), and (3) the negative sign of 

the anomaly, which is what one would expect from 

a mechanically or hydrothermally altered zone 

within granitic rock. Although none of the other 

geophysical studies indicate a west-trending fault 

in the Middleton Place area, there is a pronounced 

east-west linear high in the gravity anomaly immediately to the south, along lat 32°52' N. (Long 

and Champion, this volume). 

An alternative explanation for the Middleton 

Place magnetic low requires reversely magnetized 

material at or above the crystalline basement. The 

presence of such material is a distinct possibility, 

as basalt flows were encountered in the USGS corehole at a depth of 750 m ( Gohn and others, this volume), and similar flows could be present at greater 

depths. In order to produce a magnetic low, basalt 

flows that have reversed remanent magnetization 

would be required. Topographic relief on the tops 

or bottoms of the flows would result in a magnetic 

anomaly. The presence of reversely magnetized flows 

of limited extent would help explain some of the 

differences between the magnetic and gravity 

anomalies. In the gravity anomaly linear lows are 

absent, and the gravity high is not broken up into 

separate peaks north and west of Middleton Place. 

Reversely magnetized basalt flows could be the 

source of the linear magnetic lows that break up 

this feature on the aeromagnetic map. 

The computer-generated surface at the southern 

end of the section (south of lat 32°45' N.) has been 

modeled as a low-angle fault. Although this surface 

is almost certainly a boundary of the mafic intrusive body at depth, displacement of the crystalline 

basement along this surface is hypothetical. At its 

northern end this apparent surface extends up into 

the sedimentary column and may level off at the top 

of the basalt horizon seen in the USGS corehole to 

the northwest. Computer artifacts (hyperbolic 

tails) may be responsible for the apparent continuity of this surface. 

Line 76 passes through the western end of the 

Middleton Place magnetic low (figs. 1 and 2). The 

magnetic profile, shown in figure 4, is similar to 

profile 66. The interpreted basement cross section 

differs from the previous one in several ways. Deep 

sources have been detected in the northern part of 

the section by using the technique of Phillips 

(1975). As before, these are modeled as a mafic intrusive body in the north and as a nonmagnetic 

body under the broad magnetic low. The magnetization of the northern mafic body has decreased to 

5 X 10-3 gauss, whereas the magnetization of the 

southern mafic body has increased to 9 X 10-3 gauss. 

The latter value is unusually large, even for mafic 

rock. Because of the oblique trends of the anomalies 

relative to the flight line (fig. 2), the depth of the 

southern mafic body is likely to be overestimated. 

A shallower body would not require as strong a 

magnetization to fit the observed anomaly. 

Another difference is the growth of the nonmagnetic zone overlying the southern mafic body. There 

are now two peaks in the upper boundary of this 

zone, which correlate with relative lows in the magnetic anomaly at lat 32°51' N. and 32°54' N. On the 

aeromagnetic map (fig. 2) the two magnetic lows 

appear to be separate features, but contour maps 

of the computer-generated depth estimates, to be 

covered later, suggest the lows can be connected 

along a north-northwest-trending line. Consequently, the section of figure 4 may be presenting a 

nearly longitudinal view .of an altered zone about 

a north-northwest-trending fault. An alternative 

interpretation, presented earlier, would explain the 

magnetic lows as the result of reversely magnetized 
MAGNETIC BASEMENT 145 

PROFILE 76 N 

200 (J) 

s 600 

400 

200 

0 

-200 

-400 

::: I 

~ oj~~--------~~~~~~~--------------~,~--------------~~~~--------~--~-1 <X: Calculated/\ 

<.:l -200 ', __ 

-400 

I -600 _j 

Flight 

elevation 

-600 

15' 33°30' 

0 33°00' 

~ 1000 w 

1- : ::::; 

fu 4000 0 

5000 

s 

10 15 20 MILES 

1000 

2000 

3000 

4000 

5000 

N 

~~~~--~~--L_~ 

10 15 20 KILOMETERS 

FIGURE 4.-Magnetic profile 76 and interpreted basement cross section. Symbols are as in figure 3. 

basalt flows. In this interpretation no nonmagnetic 

intrabasement zones would be required. 

In a final difference, crystalline basement is shown 

deepening to the south above the southern mafic 

body. This brings the model into agreement with 

the gravity interpretation of Long and Champion 

(this volume) which places a fault with a similar 

sense of motion in this location. The shallow (,-I 

km) depth estimates at lat 32°43' N. would have to 

result from intrasediment volcanics in this. interpretation. An alternative model more in agreement 

with the seismic refractiion data (Ackermann, this 

volume) would have crystalline basement remaining flat and shallow at about 1,200 m depth, passing through the shallow depth estimates. This modification would not significantly affect the calculated 

anomaly. 

DISCUSSION OF RESULTS 

Both the depth estimates and the model studies 

suggest that several different crystalline materials 

are present beneath the Coastal Plain sediments. 

The shallowest of these is the basalt unit encountered in the corehole. Below is the weakly magnetic 

granitic or metamorphic material which forms the 

cryg,talline basement. Because of the weak magnetization, depths to this basement can only be estimated where dikes or volcanic flows are present. 

South of Middleton Place this surface is known to 

be crystalline basement from the seismic refraction 

results (Ackermann, this volume). If further geophysical studies should prove that a shallow crystalline basement is absent in the northern part of the 

section, then the shallow magnetic sources there 

could be reinterpreted as dikes or volcanic flows at 

a surface of unconformity within a thick sedimentary column. 

The model studies have shown that most of the 

power in the magnetic anomalies is produced by 

strongly magnetized sources at depth. On the basis 

of the strong magnetization and the associated 
146 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

gravity highs (Long and Champion, this volume), 

these sources have been interpreted to be mafic intrusive bodies. Although some mafic material may 

extend up to the crystalline basement in parts of 

the study area, the mafic bodies seen in the cross 

sections generally appear to be covered by a kilometer or more of weakly magnetic crystalline material. Mafic intrusive bodies are absent beneath the 

broad magnetic and gravity low to the north of 

Summerville. 

Recent earthquake hypocenters under Middleton 

Place cluster at depths of 1-8 km (Tarr, this volume) . According to our models, the top of the mafic 

intrusive complex in this area is located at depths 

of 2.5-3.5 km; thus, the shallower seismic events 

could be occurring within the crystalline rock near 

the surface of the mafic intrusive bodies, as proposed by Kane (this volume). On both cross sections crustal magnetization appears to be homogeneous below about 4.5 km, so nothing can be said 

about structures associated with the deeper seismic 

events. 

DEPTH CONTOURS 

In order to examine more fully the relation between the computer-generated depth estimates and 

the aeromagnetic anomalies, contour maps of the 

depth estimates have been prepared. There are difficulties in interpreting such maps. The contours 

do not represent geologic surfaces such as the crystalline basement or the tops of the mafic bodies. Instead, they indicate spots or patches on these surfaces where the correlation statistics of the magnetic profiles could be used to estimate depth. These 

patches are often surrounded by deeper contours, 

which represent the fictitious surfaces of the hyperbolic tails. It follows that topographic highs in the 

contoured depth estimates are more reliable indicators of geologic surfaces than are gradients. However, our model studies have shown that some 

gradients can have a geologic interpretation. The 

depth-estimation technique introduces distortion by 

exaggerating the widths of vertical bodies, and by 

overestimating depths when anomaly trends are not 

perpendicular to the flight lines. In addition, in 

many areas depth estimates are unavailable because of unacceptable behavior of the correlation 

statistics. Despite these difficulties depth estimates 

often show remarkable consistency from line to line, 

and, when contoured, show good correlation with 

features of the aeromagnetic map. 

In figures 5 and 6 the "deep" and "shallow" computer-generated depth solutions have been contoured. These figures only contain information of 

the type shown by the heavy lines in figures 3 and 

4. Blank areas indicate regions where no reliable 

depth estimates could be obtained. 

The shallower features of these contour maps 

will be compared with the seismic interpretation of 

Ackermann (this volume). The deeper features will 

be analyzed using the gravity data of Long and 

Champion (this volume). 

BASALT HORIZON 

The seismic interpretation places the basalt horizon above 900 m depth east of Middleton Place and 

west of long 80°15' W. Magnetic-basement depth 

estimates above 900 m are found on the "deep" 

solution (fig. 5) at the center right and on the 

"shallow" solution (fig. 6), both northeast of the 

corehole and within an east-west belt around lat 

32°45' N. These depth estimates, which are shallower than 600 m in places, probably represent the 

basalt horizon. The seismic interpretation shows a 

north-south trough in the basalt horizon west of 

Middleton Place. Maximum depth to the horizon 

within the trough is 1 km. Closed highs in the magnetic basement contours at depths above 1.2 km 

just west and south of Middleton Place (figs. 5 and 

· 6) may indicate the depressed region of the basalt 

horizon, or they may indicate crystalline basement. 

CRYSTALLINE BASEMENT 

The seismic interpretation has crystalline basement dipping southeast, increasing in depth from 

900 m near the corehole to 1,300 m under Middleton Place, and flexing to 2,000 m further southeast. 

Magnetic-basement de.pth estimates in the range 

1.2-1.5 km are found throughout the detailed study 

area, not just to the southeast of Middleton Place. 

This depth range includes the apparent east-west 

linear topographic high passing through Middleton 

Place, and the apparent north-northwest linear 

topographic high halfway between Middleton Place 

and the corehole (fig. 6). If the tops of these linear 

topographic highs are located at the crystalline 

basement, then the basement appears to be at a 

fairly constant depth of 1.2 km. There is no evidence of a southeast dip or flexure. 

The linear topographic highs in the basement 

have been modeled as nonmagnetic zones within the 

crystalline rocks. These topographic highs are associated with relative lows in the magnetic anomaly 

(fig. 2) and can be interpreted either as altered 

zones about faults within the crystalline rocks or as 
MAGNETIC BASEMENT 

Charleston AFB 

ttl 

32'45' 

32°30'L_ ______________ __j_ ___________________ ---.J 

10 KILOMETERS 

CONTOUR INTERVAL 

305 METERS BETWEEN 0-1524 METERS 

610 METERS BETWEEN 152~572 METERS 

10 MILES 

FIGURE 5.-Contour map of depths to magnetic basement corresponding to the computer-generated 

"deep" solution within the study area. Contours are dashed where inferred. Blank areas represent regions where no depth estimates were generated. 

147 
148 

33°00' 

STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

I 

I 

I 

I 

~ IJ I 

I I I \ I I (") 

~~ ~ 

Yo.." ~ ';'Jf'i-<" I I I/. \ 

32°30' L_ ______________ ..J__ __________________ _____J 

5 10 MILES 

0 10 KILOMETERS 

CONTOUR INTERVAL 

305 METERS BETWEEN G-1524 METERS 

610 METERS BETWEEN 1524-4572 METERS 

FIGURE 6.-Contour map of depths to magnetic basement corresponding to the computer-generated 

"shallow" solution. Contours are dashed where inferred. Blank areas represent regions where no 

depth estimates were generated. 
MAGNETIC BASEMENT 149 

reversely magnetized volcanic flows on top of the 

crystalline basement. 

A third interpretation may be advanced for the 

north-northwest-trending linear topographic high. 

The feature is located along the eastern boundary 

of the strong magnetic high over the USGS corehole 

site. If the top of the mafic body responsible for 

this magnetic high is at the crystalline basement 

as the gravity interpretation of Long and Champion 

(this volume) suggests, then the linear topographic 

high in the magnetic-basement depth estimates may 

represent a vertical contact between crystalline 

basement material to the east and mafic material 

to the west. Similar contacts may exist on other 

sides of the mafic body as well, as indicated by the 

1.5-km depth estimates northwest and southeast of 

the corehole site in figure 6. 

MAFIC BODIES 

The estimated depths to magnetic basement conboured in figure 5 reflect what are interpreted to be 

mafic intrusive bodies at depths of 2-4.5 km. These 

sources are responsible for the strong magnetic 

highs and the regional magnetic high in the aeromagnetic map (fig. 2). The mafic bodies are shallowest in the northern part of the study area, where 

the magnetic anomalies are the strongest. They 

deepen to the south, most rapidly along the southward-dipping surface appearing in the southeast 

quadrant of figure 5. Mafic bodies are absent under the broad magnetic low immediately north of 

the study area (fig. 1). 

In discussing the mafic bodies, we will ignore 

contours above a depth of 2 km in figure 5, such as 

those near Middleton Place and those near the 

center of the figure. These contours represent the 

shallow magnetic sources discussed earlier. 

Shallow mafic sources, indicated by the magnetic 

highs north of the Middleton Place magnetic low in 

figure 2, are found in figure 5 to have estimated 

depths of between 2.0 and 2.7 km. Similar depths 

are indicated under the magnetic high to the southeast of Middleton Place (figs. 2, 5) . 

Apparent small-scale relief on the magnetic basement, such as the V -shaped trough northwest of 

Middleton Place in figure 5, is most likely a computer artifact resulting from nonperpendicularity 

of the magnetic contours to the flight lines. It is interesting, however, that one leg of the trough 

trends northwest along the trace of a nodal plane 

of the 22 November 1974 earthquake (Tarr, this 

volume), and the other leg trends northeast along 

a lineation defined by the gravity anomaly (Long 

and Champion, this volume). Both legs of the trough 

correspond to saddles in the magnetic anomaly (fig. 

2). 

The positive magnetic anomaly over the USGS 

corehole site (fig. 2) is the strongest magnetic high 

in the area, and it is coincident with the strongest 

positive gravity anomaly (Long and Champion, this 

volume). The strength of the magnetic anomaly and 

the results of the gravity modeling suggest that the 

3.2-4.5 km depths indicated under this feature in 

figure 5 are unlikely to represent the top of the 

source body. It is more likely that the top is at the 

crystalline basement and that the contours of figure 5 represent either the bottom of the source 

body or a mineralization boundary within the source 

body. This is probably the shallowest mafic body 

in the study area. None of the other mafic sources 

appear to extend up to the crystalline basement. 

The large elongate magnetic high in the southeast quadrant of the study area (fig. 2) corresponds 

to a gravity low (Long and Champion, this volume). 

This suggests that the material responsible for this 

magnetic high differs from the mafic material to 

the north. In our model studies, the magnetic source 

has been placed at depths of 2.7-3 km. 

A final strong magnetic high is found in the southwest corner of the study area (fig. 2). A corresponding gravity high (Long and Champion, this volume) 

indicates a mafic source body. According to figure 5 

the body is at a depth of 1.5 km. 

REFERENCES CITED 

Nabigihian, M. N., 1972, The analytic signal of two-dimensional magnetic bodies with polygonal cross-section: 

Its properties and use for automated anomaly interpretation: Geophysics, v. 37, no. 4, p. 507-517. 

Phillips, J. D., 1975, Statistical analysis of magnetic profiles and geomagnetic reversal sequences: Stanford, 

Calif., Stanford Univ., Ph.D. dissert. p. 81-134. 

U. S. Geological Survey, 1975, Aeromagnetic map of Charleston and vicinity, South Carolina: U.S. Geol. Survey 

open-file rept. 75-590. 

Bouguer Gravity Map of the 

Summerville-Charleston, South Carolina, 

Epicentral Zone and Tectonic Implications 

By LELAND TIMOTHY LONG and J. W. CHAMPION, .JR. 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, 

EARTHQUAKE OF 1886-A PRELIMINARY REPORT 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1028-K 

CONTENTS 

Page 

Abstract ----------------------------------------------------------------- 151 

Introduction ------------------------------------------------------------- 151 

Regional gravity --------------------------------------------------------- 153 

Analysis of line data ___ ____ _ _ ___ _ __ _ _ ___ _ __ _ _ __ _ __ _ __ __ _ _ _ _ __ _ _ ___ _ ____ __ _ 153 

Residual gravity anomalies _ _ _ _ _ ___ _ ___ _ __ _ _ _ _ _ _ _ _ ___ _ _ _ __ _ _ ___ _ __ ____ _ ___ _ 160 

Three-dimensional models ______ _ ___ _ ____ __ __ _ _ ___ ___ __ _ ___ _ _ _ _ _ _ __ _ _ ______ 161 

Possible earthquake mechanisms _ _ _ __ _ _ ___ _ __ _ _ _ __ _ __ _ __ _ _ _ __ _ _ __ _ _ __ ____ _ _ 163 

Earthquake locations and Sloan's intensity map ------------------------------ 163 

Conclusion --------------------------------------------------------------- 166 

References cited ---------------------------------------------------------- 166 

FIGURE 1. 

2. 

3. 

4. 

5-10. 

ILLUSTRATIONS 

Simple Bouguer anomaly map of Georgia and South Carolina __ _ 

Index map of southern South Carolina showing the location of the 

area of study ------------------------------------------- Simple Bouguer gravity map of the Summerville-Charleston, S.C., 

epicentral zone ------~----------------------------------­ Index map showing the locations of the detailed gravity lines, the 

profile, and the earthquake epicenters ---------------------

Profiles of: 

5. Detailed gravity line G-G' showing the horizontal cylinder, sphere, and simple fault model interpretations 

for three anomalies ------------------------------

6. Line L-L' showing a model for the central positive 

anomaly --------------------------------------- 7. Line A-A' compared with the' theoretical anomaly from 

a fault model -----------------------------------

8. Line F -F' compared with the theoretical anomaly from 

Page 

152 

154 

155 

156 

157 

158 

158 

a horizontal cylinder ----------------------------- 158 

9. Eastern part of line D-D' compared with the theoretical 

anomaly for a two-dimensional rectangular structure -------------------------------------------- 159 

10. Line /-/' compared with a simple fault model _________ 159 

11. Residual gravity map of the Summerville-Charleston, S.C., epicentral zone -------------------------------------------- 160 

12. Map showing the elevation contours of the interpreted subbasement surface -------------------------------------------- 161 

13. Diagrams showing three-dimensional modeling of the gravity 

anomalies by use of polygons of anomalous density in stacked 

vertical sheets at intermediate depths and at maximum depths 162 

14. Map showing superposition of isoseismal contours of Earl Sloan 

on Bouguer gravity anomalies ---------------------------- 164 

III 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886-

A PRELIMINARY REPORT 

BOUGUER GRAVITY MAP OF THE SUMMERVILLE-CHARLESTON, 

SOUTH CAROLINA, EPICENTRAL ZONE AND TECTONIC IMPLICATIONS 

By LELAND TIMOTHY LoNG1 and J. W. CHAMPION, .JR.~ 

ABSTRACT 

A new Bouguer anomaly map of the Summerville-Charleston, S.C., epicentral zone is interpreted to reveal a mafic intrusive body and associated flows and a northeast-trending 

Triassic ( ?) basin. Two shallow structures interpreted from 

the gravity data and associated with the Triassic ( ?) basin 

may be significant in determining the mechanism for -the 

1886 Charleston earthquake. The first is a border fault on 

the northwest side of the basin striking N. 45° E., and the 

second is a linear positive anomaly striking east. The first 

structure suggests the more conventional earthquake mechanism of reactivation of a basement fault. The second structure suggests a newly proposed mechanism of stress amplification in the anomalously rigid structure responsible for 

the linear positive anomaly. Intensity data from the August 

31, 1886, Charleston earthquake and epicenters of recent 

events favor stress amplification as the more likely explanation for earthquake activity in the Summerville-Charleston 

epicentral zone. 

INTRODUCTION 

The lack of a confirmed tectonic mechanism for 

the Charleston, S.C., earthquake of August 31, 1886, 

and for its foreshocks and aftershocks has been a 

major obstacle in the development of a realistic 

evaluation of seismic hazard in the Eastern United 

States. Although more than 400 events (Taber, 

1914; Bollinger, 1972) have been felt in the region 

since 1886, no fault to which the activity can be 

definitely attributed has been observed at the surface. The probable reason that no tectonic mechanism has yet been agreed upon is that the basement 

structures responsible are not only unknown but 

also hidden by more than 0.79 km of post-Paleozoic 

sedimentary and extrusive rocks. 

The Summerville-Charleston epicentral zone does 

not lie near an active plate boundary. Hence, the 

1 School of Geophysical Sciences, Georgia Institute of Technology, Atlanta, Ga. 

2 Chevron Oil Co., Houston, Tex. 

association of the Summerville-Charleston events 

with plate tectonics would have to be indirect. Intraplate movements near the epicentral zone, if present, 

are obscured by a lack of appropriate data except, 

perhaps, recent releveling data. Within the context 

of the theories of plate tectonics, the Charleston 

earthquake is one manifestation of intraplate tectonics that as yet has not been satisfactorily 

explained. 

Taber (1914), in one of the earliest attempted explanations of the seismic activity near Charleston, 

hypothesized a fault in -the crystalline basement. On 

the basis of intensity data only, he sugges,ted that the 

unobserved fault trended in a general northeastsouthwest direction and was near Woodstock, S.C., 

8 km southeast of Summerville. A deep well near 

Summerville bottomed in basaltic rocks (diabase) 

(Cooke, 1936). The 0.26 km of sedimentary rocks 

directly above the diabase was interpreted to be Triassic (Cooke, 1936). Mansfield ( 1936) placed this 

section in the Cretaceous. Woollard, Bonini, and 

Meyer (1957) and Pooley, Meyer, and Woollard 

(1960), assuming that Mansfield was correct, suggested that the tectonics of the Charleston epicentral 

area might be related to a topographic feature of the 

basement surface, the Yamacraw Ridge, and the associated basement valley to the north, rather than to 

a Triassic basin perhaps related to the Florence 

Triassic basin. Bollinger (1973) conjectured that a 

general relation existed among seismicity, regional 

uplift, and old Appalachian structures. Oliver and 

lsacks (1972) and Fletcher, Sbar, and Sykes (1974) 

suggested that the Charleston activity and other 

earthquakes of the South Carolina belt are related to 

the landward extension of a major transform fault 

151 
81 ' 

FIGURE 1.-Simple . South Carolina (taken from Bouguer anoma I Y map of Georgia Talwam, and . an d Bridges, 1975). 

IOOKILOMETERS fl,,2!5 510 715 I 

5 AND 10 MILLIGALS CONTOUR INTERVALS EAS Of LOWER GRAVITY HACHURES INDICATE AR 

Long, Bn ·d ges, and Dorman, 1972 • and Long, 
BOUGUER GRAVITY MAP OF THE EPICENTRAL ZONE AND TECTONIC IMPLICATIONS 153 

and structures associated with the early opening of 

the Atlantic Ocean. 

The first objective of this paper is to present an 

analysis and structural interpretation of gravity 

data covering the Summerville-Charleston epicen .. 

tral zone. The gravity data consist of approximately 

1,000 regional observations at a mean separation of 

1.0 km and an additional 1,000 observations at a 

mean separation of 0.3 km along selected lines. The 

gravity analysis presented herein is largely a condensation of the master's thesis of the second author 

(Champion, 1975). A listing of the gravity data and 

details concerning its reduction are given in Champion ( 1975). Standard reduction techniques were 

used, and the theoretical gravity was computed using 

the 1931 international gravity formula. 

The second objective of this paper is to discuss the 

interpretation of the structure in terms of possible 

mechanisms for the Charleston earthquake of 

August 31, 1886. In particular, we propose that 

stress amplification within an anomalousJy rigid 

crustal structure could have been responsible for the 

1886 Charleston earthquake. The hypothesis of stress 

amplification should be given serious consideration 

as new data become available. 

The gravity data were obtained by the second 

author during the summer of 197 4. His fieldwork, 

the data reduction, and the analysis were supported 

by the U.S. Geological Survey (grant 14-08-0001--

G-127). Studies on the stress amplification mechanism were supported by the National Science Foundation under grant DES75-15756. 

REGIONAL GRAVITY 

The regional Bouguer gravity pattern of the South 

Carolina and Georgia Coastal Plain is characterized 

by numerous sharp positive anomalies and smoother, 

less pronounced negative anomalies (fig. 1). The 

sharp positive anomalies range in magnitude from 

+ 15.0 to + 70.0 mGal. Those that were studied in 

detail have the size and character of mafic volcanic 

plugs and associated basaltic flows and dikes (Long, 

1974). The negative anomalies could be explained by 

shallow basins, perhaps of Triassic age, or by blocks 

of less dense or thicker continental crust. In general, 

the gravity data imply a highly inhomogeneous upper crust beneath the Coastal Plain. 

The area of detailed gravity coverage (fig. 2) includes one of the sharp positive anomalies and a 

major part of the suspected epicentral zone of the 

1886 earthquake, as well as the epicenters of more 

recent seismic events. The borders of the area investigated are defined by the coordinates 32°37'30" N., 

80° W., and 33°07'30" N., 80°22'30" W. The gravity 

map (fig. 3) is contoured at 1.0 mGal from individual gravity observations and has an estimated precision of 0.2 mGal. 

The gravity isogals in figure 3 indicate that the 

Summerville-Charleston epicentrai zone is near the 

contact between a sharp positive anomaly, here interpreted as a volcanic plug, and a negative anomaly, 

here interpreted as a Triassic basin. In the western 

part of the study area (fig. 3), a positive anomaly 

having a peak value of 15.0 mGal exhibits a steep 

gravity gradient of 2.0-3.0 mGal/km on both its 

northern and its southern sides. To the east of this 

feature, the gravity gradient becomes less steep·, and 

the isogals spread to form a noselike feature. To the 

south and to the northeast, negative anomalies appear to form an al'C around the noselike feature. The 

northwestern part of the study area is characterized 

by a reasonably constant negative anomaly of ap~ 

proximately - 3.0 mGal. 

Three prominent zones of alinement in the contour 

lines and anomalies can be observed. The trend of 

the strongest alinement of contour lines is approximately east-west and is formed by the steep gradient 

south of the central positive anomaly. Another alinement of contour lines is defined by the trend of the 

isogals north of the central positive anomaly and 

bears approximately N. 50° W. These two contour 

alinements appear to be a consequence of the shape 

of the central positive anomaly. A third alinement is 

defined by the western termination of the northeastern and 1southern negative anomalies. The northwestern edges of these negative regions define an 

alinement of isogals trending N. 40°-50° E. (labeled 

NE linear anomaly on fig. 3) that intersects the central positive anomaly in the region where the isogals 

begin spreading to form the noselike positive 

anomaly. 

ANALYSIS OF LINE DATA 

Approximately one-half of the new data were obtained along lines at an average separation of 0.3 

km. However, many of these lines (see fig. 4) were 

restricted to major rights- of-way or were obtained 

prior to knowledge of the strike of the crustal structures. The lines that proved to be normal to the strike 

of the crustal structures could be used for interpretation of depths and structures using simple twodimensional models. Lines G-G', the north part of 

A-A', and a profile L-L', which all cross the positive 

anomalies in the north part of the map, give information on the depths to these structures. Lines A-A' 
154 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

81" 

BAMBERG 

Ridgeland 

0 

JASPER 

Bowman 

0 

St. George 0 

DORCHESTER CO. 

Cottageville 0 

Walterboro 

0 

COLLETON CO. 

Greenpond 

0 

80" 

FIGURE 2.-Index map of southern South Carolina showing the location of the area of study. 
BOUGUER GRAVITY MAP OF THE EPICENTRAL ZONE AND TECTONIC IMPLICATIONS 155 

33°07'30" 

32°52'30" 

80°22'30" 

0 10 KM 

EXPLANATION 

-2- Bouguer gravity contour; contour 

interval, 1 milligal. Hachures 

indicate areas of lower gravitY 

e Epicenter of recent earthquake 

CCC 1 ® Clubhouse Crossroads corehole 1 

80°00 ' 

\ 

FIGURE 3.-Simple Bouguer gravity map of the Summerville-Charleston, S.C., epicentral zone (taken 

from Champion, 1975). Epicenters of recent earthquakes are from Tarr (this volume). 
156 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

32°52'30" 

80°2 2'30" 

EXPLANATION 

Gravity line 

Profile 

10 KM 

e Epicenter of recent earthquake 

- Faultlike structure 

CCCI 

0 Clubhouse Crossroads corehole 1 

/ 

~ I 

\ 

FIGURE 4.-Index map showing the locations of the detailed gravity lines and the profile. Epicenters of 

rec,ent earthquakes (Tarr, this volume) are plotted on the gravity map of figure 3. 
BOUGUER GRAVITY MAP OF THE EPICENTRAL ZONE AND TECTONIC IMPLICATIONS 157 

and F -F' are used to model the negative anomaly in 

the northeast. Line D-D' provides information on 

the depth and size of the eastward protruding positive anomaly. Lines/-/', G-G' and F-F' give information on a possible northwest-trending structure. 

Simple two- or three-dimensional models (Nettleton, 

1976) are used in the analysis. Corrections for end 

effeds in two-dimensional models would' not significantly affect the results. Similarly, more detailed 

models that remove the deviations of the observed 

gravity from the modeled gravity would not change 

any of the conclusions. Most of the irregularities that 

have magnitudes less than 1.0 mGal are inversely 

proportional to the elevation. However, the implied 

Bouguer reduction densities are often unreasonably 

low, or even negative. The explanation probably relates to a fundamental difference between near-surface materials in the dry elevated areas and those in 

the river bottoms. 

The northern part of line G-G' crosses two positive anomalies. The anomaly at 4.0 km on line G-G' 

(see fig. 5) can be modeled with a horizontal cylinder 

that has a 1.3-km depth to its center and a radius of 

0.45 km at a density contrast of 0.3 g/cm3 • The 

anomaly at 9.0 km can be modeled by a sphere that 

has a depth to its center of 1.7 km and a radius of 

0.9 km at a density contrast of 0.3 g/cm3 • Both of 

these anomalies are consistent with a depth of 0.8 

km to the tops of these structures. 

G 

12 

(1J 

(!) NORTHEAST 

E 

Profile L-L', which was interpolated from the contours because of the lack of appropriate rights-ofway for a detailed profile, crosses the largest positive anomaly (fig. 6). Examination of this anomaly 

indicated that the steepest gradient lies on the north 

side and has a half-width of about 2.0 km. The central peak was modeled as a 4.0-km-wide two-dimensional structure that has its top at a depth of 1.5 km 

and its bottom at 4.0 km (fig. 6). The interpretation 

of a ,structure at depths less than 1.5 km along line 

L-L' is difficult because of the smoothing that is inherent in the interpolation from contours. The sides 

of the anomaly can be modeled with a thinner or less 

dense structure that also has its top at 1.5 km and 

it's bottom at 4.0 km. The depth to the top of the 

largest positive anomaly is consistent with depths 

to basement structures toward the northeast. The 

negative gravity values to the south are modeled by 

a less dense basin. 

Line A-A' intersects the prominent negative 

anomaly in the northeastern part of the study area. 

The structure under line A-A' (fig. 7) can be modeled as a nearly vertical fault that offsets a block 0.3 

g/cm" denser than the overlying material. The fault 

is interpreted as striking N. 40° E. (labeled NE 

linear anomaly in fig. 3) and intel"sects line A-A' at 

6.0 km (fig. 4). The throw of the fault is 0.65 km, 

and the upper boundary of the upthrown block on 

the northwest is at a depth of 0.8 km. The positive 

residual at 5.0 km is derived in part from the posi-

.... 

G' 

.... .. ···· 

·soUTHWEST 

z Cylinder 

8 

Z,1.3 

Sphere 

Z,1.7 

R,0.9 

Jlp,0.3 

Simple fault 

model .. >-' 

..J 

<( R,0.45 ~ Jlp,0.3 0 

z 4 

<( 

a: 

w 

:::> 

(!) 

:::> 0 

0 

Ill 

Z,1.0 

T,0.2 

Jlp ,0.3 

777[/~~ .. · ~-rr~· ... 

.··.· .... 

EXPLANATION 

• • • • • Observed gravity points 

--Theoretical gravity anomaly 

Z Depth to center, in km 

R Radius, in km 

llp Density contrast, in glcm3 

T Thickness, in km 

- 4 oL_ __ ~ __ _J4 __ --~ __ _l ____ l===~,t2~~L_--~,6~--~---2~0~--~--~2~4----l_--~2~8----L---~3~2--~ 

DISTANCE, IN KILOMETERS 

FIGURE 5.-Detailed gravity line G-G' showing the horizontal cylinder (at 4.0 km) and sphere (at 9.0 km) interpretations 

for the two northern positive anomalies and the simple fault model interpretation for the anomaly at 16.0 km. The 

location of G-G' is shown in figure 4. 
158 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

16 

L L 

-12 

co 

(.9 

E 

z 

>-' 8 ...J 

<( 

~ 

0 

z 

<( 4 

0:: 

w 

::J 

(.9 

::J 

0 

co 0 

NORTH 

5 10 15 20 25 30 

DISTANCE, IN KILOMETERS 

~ 0~----~----~------+------r------r-----~ 

z 2 

~ 4 a.. 

~ 6 

/1p=0.15 

EXPLANATION 

• • • • Gravity anomaly interpolated from observed contours 

-- Theoretical gravity anomaly 

11p Density contrast, in g/cm3 

FIGURE 6.-Profile L-L' showing a model for the central positive anomaly. This profile was interpreted from the contour lines. 

tive density anomalies on the upthrown block related to the two positive anomalies of line G-G', previously noted. It may also be derived in part from 

the inverse relation of gravity to elevation caused by 

applying a Bouguer reduction density of 2.67 to 

Coastal Plain consolidated sedimentary rocks. Line 

B-B' gives similar results (Champion, 1975). 

Line F-F' (see fig. 8) was used to estimate the 

extent of the feature responsible for the negative 

anomaly-a possible basin-corresponding to the 

downthrown side of the fault interpreted under lines 

A-A' (fig. 7) and B-B'. A horizontal cylinder was 

used for the model and indicated a depth to its center of 3.7 km and a radius of 1.8 km at a density contrast of -0.2 g/cm". Maximum depths to the tops of 

two-dimensional structures can be computed using 

0.65 times the ratio of the maximum anomaly to the 

maximum gradient. The positive anomalies on the 

north end of line F -F' are an extension of the posi-

-2 

A A' 

EXPLANATION 

co • • • • • Observed gravity points 

(.9 --Theoretical gravity anomaly 

E -4 

z 

>-' 

...J 

<( Vertical fault model 

~ Depth to top, 0.8 km 0 

z -6 Throw, 0.65 km 

<( 

a: 

w 

::J 

(.9 

::J 

0 

co -8 

NORTHWEST SOUTHEAST 

0 4 8 12 16 

DISTANCE, IN KILOMETERS 

FIGURE 7.-Line A-A' compared with the theoretical anomaly 

from a fault model having a density contrast of 0.3 gjcm". 

2 

co F F' (.9 EXPLANATION 

E 0 .. ... · · · · · · Observed gravity points 

z -- Theoretical gravity anomaly 

>-' -2 --- Gravity corrected for near-. .· .·. ...J surface anomalies <( 

~ -4 

0 

z 

<( -6 a: 

w 'I· 

'I ::J 

(.9 -8 _.;..;; ::J NORTH 0 SOUTH co -10 

0 4 8 12 16 20 24 

DISTANCE, IN KILOMETERS 

FIGURE 8.-Line F-F' compared with the theoretical anomaly 

from a horizontal cylinder that has a depth of 3.7 km to 

its center and a radius of 1.8 km at a density contrast of 

-0.2 gjcm". 

tive anomaly at 4.0 km in line G-G'. Its northern 

gradient and its maximum anomaly (respectively, 

1.1 mGal/km and 3 mGal) indicate a maximum 

depth of 1.8 km, which is consistent with, or s.Iightly 

deeper than, the structures along line G-G'. However, the northern and :southern edges of the basin 

have respective gradients of 2.0 and 1.2 mGal/km 

for a maximum anomaly of -8.0 mGal. The respective maximum depths to the tops of the northern and 

southern edge of the basin would be 2.6 and 4.3 km. 
BOUGUER GRAVITY MAP OF THE EPICENTRAL ZONE AND TECTONIC IMPLICATIONS 159 

Furthermore, the scatter in the gravity data on the 

southern edge of the basin can be almost completely 

removed by using a correction factor proportional to 

the elevation. Consequently, the negative anomaly is 

interpreted as a basin in the depth range of 0.8 

(from line G-G') to perhaps 5.5 km. The westward 

extension of the basin is interpreted as being truncated by a fault. The northern edge could also be 

interpreted to be a fault. The southern edge is deeper 

and probably represents a density contrast within 

or below the basin. The maximum depth of the ba,sin 

cannot be estimated without better control on the 

density contrast. 

The southeastern part of line D-D' crosses the 

eastward protruding positive anomaly. This structure is modeled (fig. 9) a1s a rectangular bar whose 

width is 8.0 km, depth to top is 1.5 km, and depth to 

bottom is 4.0 km on the basis of a density contrast 

of 0.2 g/cm3

• The actual depth to the bottom may be 

greater since density contrasts become more difficult 

to discriminate at greater depths. The residuals are 

4 

OJ 

(.!) 

E 

z 

~ ...J 

<I: 

~ 

0 

z 

<I: 

a: 

w 

::::> 

(.!) 

::::> 

0 

a:J 

NORTHWEST SOUTHEAST 

30 36 38 40 42 44 

DISTANCE, IN KILOMETERS 

or-+--r-I~-+-I~-+-4L~+L--~~+I--J+-~L--+-1-l~l I I I I I I I I I I I 

E 

-"' -

~+-------------------~ 

z 2-

::i 

1-

a.. 

- ~p =0.2 

~ ~ 4 ~----------------__J 

EXPLANATION 

• • • • Observed gravity points 

--Theoretical gravity anomaly 

~p Density contrast, in g/cm3 

FIGURE 9.-Eastern part of line D-D' compared with the 

theoretical anomaly for a two-dimensional rectangular 

structure. 

(,J "' 

E 

z 

>-' 

...J 

<{ 

::2: -2 

0 

z 

<{ 

0::: 

UJ 

:J 

(,J 

:J 

0 

I I' 

NORTH SOUTH 

aJ -4L-----~-------L------~------~----_...J 

0 2 4 6 8 10 

DISTANCE, IN KILOMETERS 

I I I _l 30r-----~-------+------~------+------4 I I I I 

(/) 

0::: 

~ 1- UJ 

::2: 

z 

-_ 20 1-

z 

0 

i= 

:; - UJ 

...J 

UJ 

EXPLANATION 

• • • • • Observed gravity points 

--Theoretical gravity anomaly -

--- Gravity corrected for nearsurface anomalies -

-

10L_----~------~------~------~----~ _1. i I i 

FIGURE 10.-Line I-1' compared with a simple fault model 

that has a depth of 0.8 km to its center and a throw of 0.2 

km at a density contrast of 0.3 gjcm' . 

within the precision of the data. The maximum 

gradient of 2.4 mGal/km and maximum anomaly of 

12 mGal imply a maximum depth of 3.25 km to the 

top of the structure. On the basis of this computation and the depth computations for line F -F', the 

top of the eastward-protruding positive anomaly 

may be deeper than the tops. of the other structures 

to the northwest. The difference in depths to the tops 

of the structures is consistent with the fault interpretation for line A-A'. 

In an analysis of earthquakes and structures near 

Bowman, S.C., McKee (1974) noted an alinement of 

epicenters N. 40° W. parallel to Bollinger's (1973) 

transve11se South Carolina-Georgia seismic belt. 

Tarr (this volume) also noted the N. 40° W. alinement of epicenters. Lines 1-1', G-G', and F-F' are 

normal to this trend (fig. 4) and have been examined 

for evidence of a faultlike structure. Line 1-1' and 

part of line G-G' are consistent with the model for a 

thin faulted slab with the downthrown side assumed 

to be infinitely deep (,see Nettleton, 1976, p. 195). 

The depth to its center is 0.8 km, and its thickness is 

0.2 km at a density contrast of 0.3 g/cm3 • The thin 

faulted slab model is mathematically identical to a 
160 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

semi-infinite horizontal sheet and does not necessarily require interpretation as a fault. Line /-/' indicates a possible thin slab truncated at 5.5 km from 

the rsouth end (fig. 10; see fig. 4 also). Line G-G' 

shows a possible thin slab truncated at 16.0 km from 

the northeast end (fig. 5). The scatter in the data 

about the theoretical anomaly for the thin faulted 

slab in line/-/' correlates inversely with the elevation (see fig. 10). The scatter is related to the nearsurface density variations which correlate with the 

topography, and, hence, the scatter can be reduced 

prior to computation of the model parameters. However, the proportionality constant is often too large 

to be explained completely by an improper Bouguer 

reduction density and implies that near-surface 

structures are controlled in part by their elevation. 

Line F -F' has a negative deviation from the theoretical anomaly (fig. 8) at 15.0-16.0 km and again 

at 12 km from the north end. However, the interpretation that these deviations result from a thin 

faulted •slab is inappropriate because they can be 

virtually eliminated by a correction factor proportional to the elevation and, hence, are related to nearsurface structures. The two thin faulted slab models 

line up along a strike of N. 70° W. This strike is not 

consistent with theN. 40° W. alinement of regional 

epicenters noted by Bollinger (1973), McKee 

(1974), and Tarr (this volume). The gravity data 

do not indicate the existence of a continuous fault 

that has vertical displacements greater than 200 m 

oriented N. 40° W. TheN. 70° W. alinement is consistent with, but displaced from, some recent shallow 

epicenters plotted in figure 4 (Tarr, this volume). 

However, the interpretation that the alinement of 

the thin faulted models is a single fault irs not unique. 

An alternate interpretation that these features are 

the edges of basalt flows is preferred by the authors 

since this would be consistent with the interpretation 

that the positive anomalies are volcanic plugs and 

associated flows; also the regional data and lack of a 

fau1

tlike structure along line F-F' do not support a 

continuous linear structure. 

RESIDUAL GRAVITY ANOMALIES 

In order to facilitate further analysis, gravity 

values were computed at a regular grid interval of 

1.0 km using a distance-weighted mean-value interpolation algorithm. The area of the interpolated 

gravity data encompassed the area defined by the 

simple Bouguer gravity map. A regional field was 

obtained by convolving the gravity data with a 

smoothing operator which has an effective half-width 

of 2.5 km. The residual gravity map (fig. 11) is the 

FIGURE 11.-Residual gravity map of the SummervilleCharleston, S.C., epicentral zone. Contour interval, 0.5 

mGal. Hachures are used to indicate the negative side of 

the zero and all negative contour lines. 

difference between the simple Bouguer gravity map 

and the regional field already described. Positive 

residual anomalies are shown in the central part of 

figure 11 and are located in the same positions as the 

positive anomalies in the original map (fig. 3), implying that parts of the source of these anomalies are 

less than 2.5 km deep (the radius of the smoothing 

operator). The westernmost large positive anomaly 

i's resolved by the residual anomalies into two peaks. 

These two peaks are in a line with the two positive 

anomalies to the northeast. The line strikes N. 45 o E. 

A long, narrow negative residual anomaly that also 

strikes N. 45° E. occurs approximately 4.0 km southeast of the line of positive anomalies. This negative 

residual anomaly connects the northwest edge of the 

basin (where a fault, shaded on fig. 3, was interpreted along line A-A') and the northwest edge of a 

negative simple Bouguer anomaly (fig. 3) in the 

southwest part of the area shown on the map. This 

long, narrow negative residual anomaly is interpreted as evidence of the southwest continuation of 

the edge fault for the basin interpretation of the 
BOUGUER GRAVITY MAP OF THE EPICENTRAL ZONE AND TECTONIC IMPLICATIONS 161 

negative Bouguer anomaly near 80° W., 33° N. The 

negative residual anomaly occurs on the downthrown 

block of a fault. The positive anomaly protruding to 

the east (fig. 11) is smoother than the peaks to the 

northwest and supports the hypothesis of a deeper 

source for this anomaly. 

The northeastern and southwestern negative Bouguer anomalies may be part of one continuous basin 

(see fig. 1). The total depth of the basin is unknown 

but could be as deep as 5.5 km on the basis of the 

horizontal cylinder model applied to line F-F' (fig. 

83. Mann and Zablocki (1961) noted very similar 

anomalies associated with the Jonesboro fault, a 

border fault on the southeast edge of the Deep River 

Triassic basin in North Carolina. However, they interpreted the density contrast to be -0.1 g/ cm3 • If a 

density contrast of 0.1 g/ cm3 applies to the basin 

near Charleston, its depth may exceed the 5.5-km 

estimate from the cylinder model applied to· line 

F -F'. The displacement of shallow or more recent 

flows near the fault could be significantly less or even 

nonexistent, since some of the volcanic activity and 

the faulting could have been contemporaneous. 

THREE-DIMENSIONAL MODELS 

Although gravity data generally do not allow a 

unique ·structural interpretation, the addition of constraints on the acceptable structures will often allow 

a direct inversion that provides insight into the distribution of the anomalous masses. One simple constraint is to· assume that the anomalies are derived 

from a variation in the thickness of less dense rocks 

near the surface. In this model, the sedimentary 

rocks or less dense volcanic rocks were assumed to 

provide a density contrast of 0.3 g/ cm3 above mo·re 

dense basic volcanic rocks or intrusive rocks. A lower 

density contrast or greater depth would lead to 

numerical instability for the shallow anomalies in 

the northwest part of the study area. Coastal Plain 

sediments were neglected in this model. An iterative 

process was used to effect a perfect fit of the theoretical anomaly to the data interpolated at a grid 

interval of 1.0 km. In this type of reduction, shallow 

anomalies are made more sharp, while the deeper 

sources remain smooth. The effect is similar to a 

downward continuation of the gravity field. 

The elevation contours of the interpreted subbasement (fig. 12) are similar to those of the gravity 

anomalies, except that they show steeper gradients 

and tend to emphasize some of the structural contacts. In this model, the sharp peaks in the northwest 

part of the study area are at depths equivalent to 

0.7-2.1 km. The eastward-protruding positive anom0 2 4 6 8 10 KILOMETERS 

FIGURE 12.-Elevation contours of a surface derived by 

modeling Bouguer gravity anomalies assuming a density 

contrast of 0.3 g; cm". The contours are in kilometers above 

an arbitrary surface at a depth of 3.5 km. Hachures indicate areas below 3.5 km. Epicenters of recent earthquakes 

(solid circles) are from Tarr (this volume). CCC 1, Clubhouse Crossroads corehole 1. 

aly now appears as a ridge and has an average gradient significantly less than those on the edges of the 

large positive anomaly to the northwest. The smooth 

gradient provides additional support for the hypothesis of a possible deeper structure as the cause 

of this anomaly. 

Figure 13 shows two results of three-dimensional 

modeling of the gravity anomalies using the method 

of Talwani and Ewing (1960). Regional gravity 

data to the west of the area were included in this 

modeling to minimize the edge effects related to the 

po·sitive anomaly. The models were obtained by assuming a structure compatible with the line data and 

perturbing the model until the computed gravity 

anomaly varied no more than ±2 mGal from the observed data. Regional data, interpolated onto a grid 
162 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

A 

A 

111111 + 0.23 g/cm3 

- + 0.13 g/cm3 

~ - 0.27 g/cm3 

0 10 20 30 40 50 

KILOMETERS 

Depth, in 

kilometers 

2.5 

4.5 

4.5 

6.5 

6.5 

8.5 

EXPLANATION 

---Map area 

8 

8 

• + 0.33 g/cm3 

- 0.27 g/cm3 

Depth, in 

kilometers 

2.5 

3.5 

3.5 

4.5 

4.5 

7.5 

7.5 

16.5 

FIGURE 13.-Diagrams showing three-dimensional modeling of the gravity anomalies following the method of Talwani 

and Ewing (1960). This method uses polygons of anomalous density in stacked vertical sheets at intermediatedepths (A) and at maximum depths (B). The dashed lines on the top blocks outline the area of the gravity 

map in figure 3. The vertical dimension is exaggerated by a factor of five, and the sheets are separated for 

clarity. The maximum error for either model is 10 percent. 

with a 5.0-km separation, were used to the west of 

the study area for the comparison. In the study area, 

the data interpolated to a 1.0-km grid were used for 

the comparison, and the maximum error allowed was 

1.0 mGal. Resolution of models or structures at 

depths less than 2.5 km was not practical for data 

interpolated to a 1.0-km grid interval. 

Figure 13A shows a model based on the depths and 

structures interpreted from the line data. The top 

sheet contains most of the sources for the positive 

anomalies. These extend over parts of the second and 

third sheet where no anomalous masses are shown. 

Hence, some of these may be interpreted as nearsurface flows or sills. The second sheet contains the 
BOUGUER GRAVITY MAP OF THE EPICEN'l'RAL ZONE AND TECTONIC IMPLICATIONS 163 

sources for the negative anomalies and the eastward 

extension of the positive anomalies. The third sheet 

contains only a source for part of the eastward protruding anomaly. 

Figure 13B shows the result of extending the modeled structures as deep as possible. However, in both 

models, shallow structures (2.5-4.5 km) are required to maintain a satisfactory fit to the observed 

data; only the core of the large positive anomalies 

can be extended to significantly greater depths. Both 

models suggest that a vertical offset of the structure 

responsible for the eastward-protruding positive 

anomaly is compatible with the gravity data. 

POSSIBLE EARTHQUAKE MECHANISMS 

Two large-scale features of the interpreted structures are considered significant to the mechanism of 

the 1gg6 Charleston earthquake. The first is a fault 

in the basement interpreted as the northwest edge of 

a basin. The fault strikes generally N. 45° E., but is 

displaced to the northwest by more than 6.0 km 

from the hypothesized Woodstock fault described by 

Taber (1914). The offset on the fault is estimated to 

be at least 0.6 km on the basis of the interpretation 

of the gravity data for the zones that cross this feature. The 0.6-km vertical displacement is reasonable 

for basins associated with rift zones and is comparable to the displacement of the Deep River basin in 

North Carolina (Reinemund, 1955). The second significant large-scale feature is the linear positive 

anomaly extending east from the positive high. This 

is interpreted to be a ridge or barlike structure of 

high-density material in the depth range of 1.0-6.0 

km or greater in the crust. High density rocks typically have high seismic velocities. Higher velocities 

would imply that this protrusion has a higher modulus of rigidity than would be expected for the surrounding basin materials. 

These two large-scale features of the interpreted 

crustal structure pose two independent explanations 

for the occurrence of earthquakes near Charleston. 

The first explanation, and perhaps the more conventional, is that the earthquakes are the result of the 

reactivation of the northeast-striking basement 

fault. This mechanism is essentially that proposed by 

Taber (1914), except that the fault interpreted from 

gravity data is farther to the northwest than the 

proposed Woodstock fault. In this first explanation, 

earthquake epicenters and intensities should be 

closely associated with the fault trace. 

The second explanation is that the earthquakes 

are the result of fracture of the structure responsible 

for the eastward protruding positive anomaly. The 

contrast between the rigidity of this structure and 

the rigidity of the surrounding sedimentary or igneous rocks would allow the concentration of stress 

through the mechanism of "stress amplification." In 

stress amplification, the geometry of the structure is 

such that regional shear stress is concentrated in an 

anomalously rigid crustal unit, and the stress within 

the anomalously rigid unit is amplified at geometrically appropriate locations. Consequently, stress amplification could lead to stress levels significantly 

higher than expected for an homogeneous medium. 

During a steady change in regional ambient stress, 

fracture will occur first at geometrically appropriate 

locations in the more rigid structures. The existence 

of contemporary stress changes related to a flexure 

of the crust is implied by differential vertical movement (Meade, 1971; Brown and Oliver, 1976) measured along the South Carolina coast. However, appropriate data prior to the 1gg6 Charleston earthquake are not available. Nevertheless, bending of the 

east-west axis of the structure could account for the 

concentration of stress necessary for the occurrence 

of earthquakes in or near the structure. 

Earthquakes in this model would be expected to 

occur at points of weakness or stress concentration, 

such as where the structure thins or joins a larger 

structure. For the mass of rigid material identified 

near Charleston, one possible point of weakness or 

stress concentration would be near lat 32° 52' 20" N. 

between long goo 7' 30" W. and goo 12' W. Near this 

point, the structure in the inversion model (fig. 12) 

shows a slight thinning and is near its junction with 

the larger structure. The east-west strike of the 

structure would imply a higher susceptibility to 

stress amplification from regional shear stress oriented normal to the strike. These stresses would be 

conducive to a generally north-south strike to a plane 

of rupture caused by stress amplification. 

EARTHQUAKE LOCATIONS AND SLOAN'S 

INTENSITY MAP 

Sufficiently precise epicenters and intensity maps 

might now allow identification of one of the two 

above-described mechanisms as the more likely 

mechanism of the Charleston earthquake. Unfortunately, the reported epicenters for the historic activity near Charleston are based largely on intensity 

reports or seismograms written at distant stations. 

The precision of such data is insufficient for a resolution of mechanism of the Charleston earthquakes. 

The November 22, 1974, earthquake, however, was 

recorded by the U.S. Geological Survey's recently installed seismic net as well as by more distant sta-
164 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

EXPLANATION * Dutton's epicenters 

X X X tsoseismal contours of Earl Sloan; 

X • X • X range from most intense to least 

intense 

e Recent earthquake epicenter 

@ Epicenter of November 22, 1974, 

earthquake 

- Interpreted fault in basement, 

dotted where questionable 

®CCC 1 Clubhouse Crossroads corehole 1 

/ 

+ 

~ I 

10 KILOMETERS 

FIGURE 14.-Superposition of isoseismal contours of Earl Sloan (Dutton, 1889) on Bouguer gravity anomalies of figure 

3. The solid line indicates the near-surface position of the interpreted basement fault. Epicenters of recent earthquakes are from Tarr (this volume). 

tions, and consequently its hypocenter should be more 

precise (see fig. 14). The hypocenter (Tarr, this volume) falls 7.0 km southeast of the proposed basement fault, but less than 2.0 km north of the center 

of the eastward-protruding ridge. The hypocenter of 

an aftershock of the November 22, 1974, earthquake 

was near the center of the protruding ridge. These 

hypocenters are compatible with the hypothesized 

hypocenters for the stress amplification mechanism. 

Their depths of 4.1 km and 2.2 km, respectively, are 
BOUGUER GRAVITY MAP OF THE EPICENTRAL ZONE AND TECTONIC IMPLICATIONS 165 

close to or within the structures modeled. Unfortunately, both the precision of the hypocenter depth 

computations and the maximum depth of the structure are unknown and difficult to compute with existing data. Many of the other events occur where the 

gravity model indicates dense, shallow, and hence 

more rigid structures, such as near-surface flows. 

If these events are shallow they could be attributed 

to stress amplification in the shallow structures. This 

could explain part of the apparent scatter in the 

epicenters. Unfortunately, the gravity data are not 

sufficient to resolve the details of these shallow structures. 

The isoseismal contours according to Earl Sloan 

(Dutton, 1889) are shown in figure 14 for comparison to the epicenters, gravity contours, and crustal 

structure. Unfortunately, Sloan's map was not completely true to scale, and the contours have been adjusted to fit the known locations of still-existing 

towns or stable physiographic features shown on 

his map. The intensity data are distributed so as 

to form two apparent "maximum intensity areas" 

at the ends of a linear zone of maximum intensity 

striking N. 20° E. This distribution prompted Taber 

(1914) to propose the Woodstock fault. The isoseismal contours do not correspond to an intensity distribution that would be expected from reactivation 

of the basement fault interpreted from the gravity 

data. While the intensity contours may be partially 

controlled by the near-surface soils and the distribution of intensity observations, the predominance of 

the higher intensities to the southeast of the fault 

would be difficult to explain completely by variations 

in near-surface soils. The distribution of the intensities given by Sloan does, however, correspond remarkably well to the intensity that one would expect 

from an earthquake resulting from fracture in the 

eastward protruding structure because of stress amplification. Consequently, the epicentral zone of the 

1886 earthquake may be presumed to be midway between the dual epicenters of Dutton (1889) and subsequently near the epicenter of the November 22, 

1974, earthquake. However, this immediate epicentral zone was sparsely populated, and remains so 

today. Although the completeness of the data and 

the effects of soil response to intensities in the immediate epicentral zone are questionable, the distributions of intensities near the two macroseismic epicenters were well documented. Remarkably, the 

crustal structure interpreted from the gravity data 

is consistent with the intensity pattern. In the stress 

amplification mechanism, the seimic waves would 

originate largely in the more rigid, higher velocity 

structure and would propagate into the lower velocity adjacent basins. Because of a possible combination of focusing of the seismic waves and a change 

in acoustical impedance near the edge of the structure, the seismic waves could undergo dynamic 

amplification near the observed dual epicenters. In 

general, Sloan's intensities are lower where the 

gravity data imply denser and, consequently, higher 

velocity crustal structures. As a tribute to Sloan's 

evaluation of the intensities about 5.0 km northnorthwest of Dutton's northern epicenter (see fig. 

14), we note that even the apparent reduction in the 

intensities-which was discounted by Dutton (1889) 

-is supported by the crustal structures interpreted 

from the gravity data and the supposition that the 

intensities over the more rigid crustal rock were subdued. 

The intensity data for the historic and recent 

Summerville-Charleston earthquakes show that 

audible sounds are associated with these earthquakes 

(Louderback, 1941). Louderback (1941) also suggested that these unusual sounds imply the fracturing of fresh rock under high stress rather than 

movement along established faults. These sounds 

may imply anomalously high corner frequencies and, 

hence, the existence of a greater proportion of 

energy at frequencies higher than generally observed 

for earthquakes of equivalent magnitudes occurring 

in. the other seismic zones. By consideration of the 

spectral theory of earthquakes (Randall, 1973), 

these conditions imply relatively high stress drops 

for the Summerville-Charleston earthquakes. Furthermore, the width of the eastward protruding 

ridge would allow an effective fault radius of about 

6 km if the entire structure ruptures according to 

the stress amplification mechanism. A magnitude 

(mv) range of 6.8-7.1 (Bollinger, this volume) is 

implied by intensity data. Since mb is equivalent to 

Mr, in the 6.0-7.0 magnitude range, these magnitudes 

and a fault radius of 6 km would theoretically allow 

stress drops of 40-200 bars (Randall, 1973). According to Gibowicz (1973), a magnitude-7.0 event 

would normally have a stress drop of about 22 bars 

and (after Randall, 1973) a fault radius of 25 km. 

A 50-km-long fault is not reasonable for the Charleston event. If correct, the maximum intensity and a 

reasonable fault radius imply an abnormally high 

stress drop for the 1886 Charleston earthquake. 

These observations are consistent with the stress 

amplification mechanism for the SummervilleCharleston earthquakes. 
166 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

CONCLUSION 

Of the two mechanisms-reactivation of a basement fault and stress amplification-suggested by 

the structures interpreted from the gravity data, 

the stress amplification mechanism better satisfies 

the historic intensity data and recent-event epicenters. Stress amplification should be considered carefully as a probable mechanism for the great 

Charleston earthquake of 1886 as more data become 

available. 

REFERENCES CITED 

Bollinger, G. A., 1972, Historical and recent seismic activity 

in South Carolina: Seismol. Soc. America Bull., v. 62, 

no. 3, p. 851-864 

--- 1973, Seismicity and crustal uplift in the southeastern 

United States: Am. Jour. Sci., in The Byron N. Cooper 

Volume 273-A. p. 396-408. 

Brown, L. D., and Oliver, J. E., 1976, Vertical crustal movements from leveling data and their relation to geologic 

structure in the Eastern United States: Rev. Geophysics and Space Physics, v. 14, no. 1, p. 13-35. 

Champion, J. W., Jr., 1975, A detailed gravity study of the 

Charleston, South Carolina, epicentral zone: Atlanta, 

Georgia Inst. of Tech., Master's thesis, 97 p. 

Cooke, C. W., 1936, Geology of the Coastal Plain of South 

Carolina. U.S. Geol. Survey Bull. 867, 196 p. 

Dutton, C. E., 1889, The Charleston earthquake of August 

31, 1886: U.S. Geol. Survey Ann. Rept. 9, 1887-88, p. 

203-528. 

Fletcher, J. P., Sbar, M. L., and Sykes, L. R., 1974, Seismic 

zones and travel time anomalies in eastern North America related to fracture zones active in the early opening 

of the Atlantic [abs.]: in EOS (Am. Geophys. Union 

Trans.), v. 55, no. 4, p. 447. 

Gibowicz, S. J., 1973, Stress drop and aft.ershocks: Seismol. 

Soc. America Bull., v. 63, no. 4, p. 1433-1446. 

Long, L. T., 1974, Bouguer gravity anomalies of Georgia, in 

Symposium on the petroleum geology of the Georgia 

Coastal Plain: Georgia Geol. Survey Bull. 87, p. 141-166. 

Long, L. T., Bridges, S. R., and Dorman, L. M., 1972, Simple 

Bouguer gravity map of Georgia: Georgia Geol. Survey. 

Long, L. T., Talwani, P., and Bridges, S. R., 1975, Simple 

Bouguer gravity map of South Carolina: South Carolina 

Div. Geology. Map. Ser. 21, 27 p. 

Louderback, G. D., 1941, The personal record of Ada M. 

Trotter of certain aftershocks of the Charleston earthquake of 1886: Seismol. Soc. America Bull., v. 31, no. 

4, p. 199-206. 

Mann, V. I., and Zablocki, F. S., 1961, Gravity features of 

the Deep River-Wadesboro Triassic basin of North 

Carolina: Southeastern Geology, v. 2, no. 4, p. 191-215. 

Mansfield, W. C., 1936, Some deep wells near the Atlantic 

Coast in Virginia and the Carolinas: U.S. Geol. Survey 

Prof. Paper 186-I, p. 159-161. 

McKee, J. H., 1974, A geophysical study of microearthquake 

activity near Bowman, South Carolina: Atlanta, Georgia 

Inst. of Tech., Master's thesis, 65 p. 

Meade, B. K., 1971, Report of the sub-commission on recent 

crustal movements in North American: Internat. Assoc. 

Geodesy, 15th General Assembly, Moscow, USSR. 

Nettleton, L. L., 1976, Gravity and Magnetics in oil prospecting: New York, McGraw-Hill Inc., 464 p. 

Oliver, Jack, and !sacks, Bryan, 1972, Seismicity and tectonics 

of the eastern United States [abs.] Earthquake Notes, 

v. 43, no. 1, p. 30. 

Pooley, R. N., Meyer, R. P., Woollard, G. P., 1960, Yamacraw 

Ridge, pre-Cretaceous structure beneath South CarolinaGeorgia Coastal Plain [abs.]: Am. Assoc. Petroleum 

Geologists Bull., v. 44, no. 7, p. 1254-1255. 

Randall, M. J., 1973, The spectral theory of seismic sources: 

Seismol. Soc. America Bull., v. 63, no. 3, p. 1133-1144. 

Reinemund, J. A., 1955, Geology of the Deep River coal field, 

North Carolina: U.S. Geol. Survey Prof. Paper 246, 

159 p. 

Taber, Stephen, 1914, Seismic activity in the Atlantic Coastal 

Plain near Charleston, S.C.: Seismol. Soc. America Bull., 

v. 4, no. 3, p. 108-160. 

Talwani, Manik, and Ewing, W. M., 1960, Rapid computation of gravitational attraction of three-dimensional 

bodies of arbitrary shape: Geophysics, v. 25, no. 1, p. 

203-225. 

Woollard, G. P., Bonini, W. E., and Meyer, R. P., 1957, A 

seismic refraction study of the subsurface geology of 

the Atlantic Coastal Plain and continental shelf between 

Virginia and Florida: Wisconsin Univ., Dept. Geology 

Geophysics Sec., 128 p. 
Exploring the Charleston, South Carolina, 

Earthquake Area with Seismic RefractionA Preliminary Study 

By HANS D. ACKERMANN 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, 

EARTHQUAKE OF 1886-A PRELIMINARY REPORT 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1028-L 

CONTENTS 

Page 

Abstract ----------------------------------------------------------------- 167 

Introduction ------------------------------------------------------------- 167 

The survey -------------------------------------------------------------- 167 

Results ------------------------------------------------------------------ 169 

Character of refracted arrivals ---------------------------------------- 169 

Variations in velocity ------------------------------------------------- 169 

Structural interpretations _ __ _ __ _ ____ _ __ __ ___ __ _ _ _ __ _ ____ _________ _____ 169 

Discussion --------------------------------------------------------------- 173 

References cited ---------------------------------------------------------- 175 

FIGURE 1. 

2. 

3-5. 

ILLUSTRATIONS 

Location map showing area of study ------------------------

Map showing lateral variations in compressional velocity of intermediate horizon _____________________________________ _ 

Contour maps showing: 

3. Depths to the marker horizon within the Santee LimePage 

168 

170 

stone------------------------------------------------ 171 

4. Depths to the intermediate marker horizon ------------- 172 

5. Depths to crystalline basement horizon ---------------- 174 

III 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886-

A PRELIMINARY REPORT 

EXPLORING THE CHARLESTON, SOUTH CAROLINA, EARTHQUAKE AREA 

WITH SEISMIC REFRACTION-A PRELIMINARY STUDY 

By HANs D. AcKERMANN 

ABSTRACT 

Seismic refraction soundings northwest of Charleston, 

S.C., show: 

1. A marked decrease in the velocity of an approximately 

800-m-deep basalt layer (of Cretaceous or older age). 

2. A possible small downwarp in this basalt layer and the 

shallower sedimentary section. 

3. A flexure or fault in the 1,000- to 2,000-m-deep crystalline basement. 

The spatial near coincidence of these three features with 

the high-intensity zone of the 1886 earthquake and recent 

earthquake epicenters may strengthen the argument that 

the Charleston seismic trend is an area of high stress along 

a preexisting fault zone. 

INTRODUCTION 

During the spring of 1975, 12 seismic-refraction 

spreads, each approximately 2,600 m long, were recorded near Charleston, S. C. The purpose of this 

work was to investigate deformations that may be 

related to the historical earthquakes of the area. The 

problem is twofold- ( 1) to find deformations, and 

(2) to determine whether they are recent. 

One possible approach to this problem is to identify deformations that involve recent geologic features. On the Atlantic Coastal Plain, this approach 

would mean locating basement faults that extend 

into the shallow sedimentary section. The seismicreflection method is well suited for this purpose. 

This approach presents two problems, however. First 

of all, an earthquake-generating fault need not disrupt shallow rocks. Second, although seismic reflection is very sensitive for delineating vertical 

displacements, it cannot detect strike-slip displacements. Nevertheless, a high-resolution seismic-reflection survey was seriously considered in the early 

stages of this project. We felt that in order to investigate recent earthquakes, the survey should 

focus to depths between at least 200 and 1,000 m, 

the latter having been the assumed depth to the 

crystalline basement. In addition, resolution must 

be sufficient to detect vertical displacements as 

small as 15 m, and the survey should be sufficiently 

extensive to cross the Charleston structure if one 

exists. The cost of contracting a survey to meet these 

minimum requirements was prohibitive. 

A seismic-refraction survey, on the other hand, 

also permits the study of recent tectonism, but from 

a different point of view. In refraction, the path 

traveled by the recorded signal is largely horizontal 

instead of vertical. Hence, although the refraction 

method is considerably less accurate than the reflection method for delineating vertical displacements, the long horizontal travel path permits the 

accurate calculation of lateral velocity variations in 

the layers recorded. One important cause for lateral 

velocity changes in a layer is inhomogeneity resulting from changes in fracture porosity (Wyllie and 

others, 1956; Ackermann and others, 1975). One 

may certainly expect large variations in fracture 

porosity in a zone of recent earthquakes because 

fractures caused by the large stresses have not had 

the opportunity to close. Hence, we chose to use 

seismic refraction to search for lateral velocity variations in the deep rocks of the Charleston area. 

Furthermore, refraction is a powerful reconnaissance tool, and the results are extremely valuable 

for possible later high-resolution reflection studies. 

This work was supported by the U.S. Nuclear 

Regulatory Commission, Office of Nuclear Regulatory Research, Agreement no. AT (49-25)-1000. 

THE SURVEY 

Locations of the 12 seismic spreads are shown in 

figure 1. Also shown are the centers of highest in167 
168 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

(!) 

CCC 1 

f--

t----1 

+ 

X 

/ 

/ 

EXPLANATION 

Seismic 

Epicenter 

spread 

of November 1974 earthquake 

~~ 

~ 

Center of highest intensity of 1886 earthquake {i(G~~,~ Clubhouse Crossroads corehole 1 \ _/~-

~~~ 

/ ~f;f?_/ ----

0 5 10 15 KILOMETERS 

_l_ ____ _j 

FIGURE !.-Location map showing area of study near Charleston, S. C. 
EXPLORING EARTHQUAKE AREA WITH SEISMIC REFRACTION 169 

tensity (Dutton, 1889) for the 1886 MM intensity 

X earthquake; the location of the 792-m-deep Clubhouse Crossroads corehole 1 (CCC 1) ; and the epicenter, near the historic Middleton Place plantation, of the Nov. 22, 1974, magnitude-3.8 earthquake 

(Tarr, this volume). The plan was to tie the CCC 

1 to the refraction profiles and to extend coverage 

towards the most southern of Dutton's centers and 

also to the Middleton Place epicenter. The seismic 

spreads were recorded with sufficient shot points 

to obtain full reverse coverage from a basement 

horizon 600-1,000 m deep, and partial reverse coverage from shallower horizons within the sedimentary sequence. 

RESULTS 

The refraction interpretations revealed three distinct seismic marker horizons that were continuous 

throughout the area surveyed. The shallowest and 

intermediate refracting horizons were penetrated 

by CCC 1 and are evident on both the geologic and 

sonic well logs. The deepest horizon is below the 

total depth of the hole (792 m). 

The shallowest refractor correlates with a thin, 

well-indurated crossbedded calcarenite at the base 

of the Santee Limestone (Eocene), which is about 

100 m deep at the well site. The velocity of this 

calcarenite member of the Santee is 2.5-2.7 km/s. 

Its higher velocity is a result of cementation by carbonate rocks dissolved from the overlying section. 

The intermediate horizon corresponds to the top 

of the Cretaceous ( ?) basalt lava flows, intersected 

by CCC 1 at a depth of 750 m. (See Gottfried and 

other geophysical data to obtain a preliminary crustbasalt.) Its velocity near the well site is 5.8 km/s. 

Drilling was terminated after 42 m of basalt had 

been cored. 

The deepest horizon recorded has a velocity of 

about 6.3-6.5 km/s. This undoubtedly represents the 

crystalline basement. 

We note, once again, that shot locations were 

planned to provide complete reverse coverage for 

a single high-velocity basement horizon 600-1,000 m 

deep. The recordings revealed two high-velocity 

layers; one, the basalt, which was within the expected interval, and the other, the deeper crystalline 

basement. Full coverage was not obtained from the 

crystalline basement. Consequently, velocity and 

depth control are incomplete for this layer. 

The sonic well log showed several layers between 

the shallow Santee Limestone (Eocene) and the 

Cretaceous ( ?) basalt that have velocities slightly 

more than 2.7 km/s. However, the position of these 

layers in the sedimentary section did not permit 

them to appear as conspicuous events on a refraction record. Thus, for all practical purposes, the 

refraction data revealed only the three above-mentioned layers. 

CHARACTER OF REFRACTED ARRIVALS 

The arrivals recorded from the marker horizon 

in the Santee attenuate rapidly and cannot be identified on the recordings beyond 700 to 1,100 m from 

any shot point. Apparently, the high-velocity-sandstone part of the Santee is too thin to transmit a 

seismic wave efficiently. 

Similarly, arrivals from the basalt layer also attenuate rapidly and are generally shingled. A 

shingle is a form of multiple arrival (Spencer, 

1965; Cassinis and Borgonovi, 1966) associated with 

a high-velocity layer imbedded in a lower velocity 

medium. Therefore, we infer that the basalt is 

again underlain by lower velocity rocks, possibly a 

pre-Upper Cretaceous sedimentary sequence. 

VARIATIONS IN VELOCITY 

Interpretations for the intermediate horizon, 

which correlates with the basalt at CCC 1, are that 

its velocity ranges from 4.3 to 5.8 km/ s. Significant 

velocity variations for the shallow marker horizon 

in the Santee Limestone, on the other hand, were 

not identified. Furthermore, data from the deep 

crystalline basement rocks were insufficient to calculate velocity changes for this layer. 

Figure 2 shows the lateral variations in compressional velocity of the intermediate (basalt) horizon. 

We see a general eastward decrease in velocity. The 

focus of the November 22, 197 4, magnitude-3.8 

earthquake (Tarr, this volume) was at a depth of 

4.1 km, directly under the area of lowest velocity. 

STRUCTURAL INTERPRETATIONS 

Figures 3 and 4 are contour maps of interpreted 

depths to the marker horizon within the Santee 

Limestone and to the intermediate (basalt) marker 

horizon, respectively. Depths were calculated using 

a vertical velocity function obtained from the sonic 

log of CCC 1. By so doing, the countoured depths 

for these two horizons agree with their actual 

measured depths at the well site. We point out, 

however, that because of the shingling of the basalt 

arrivals, depth calculations for this horizon are 

based, in part, on subjectively shifting recorded 

data. Thus, to some extent, the interpreted depths 

and structure for the basalt horizon are uncertain. 
170 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

80"15' 80°00' 

(!) 

CCC 1 

~5.8 

32°45' t-----

EXPLANATION 

t-----1 Seismic spread 

+ Epicenter of November 1974 earthquake 

X Center of highest intensity of 1886 earthquake 

(!) Clubhouse Crossroads corehole 1 

Boundary between zones of different 

compressional velocity of the intermediate 

(basalt) horizon. Given in km/s 

0 5 10 15 KILOMETERS 

~ ~~~--------L-------~ 

FIGURE 2.-Lateral variations in compressional velocity of the intermediate (basalt) horizon. 
EXPLORING EARTHQUAKE AREA WITH SEISMIC REFRACTION 171 

80"15' 80°00' 

(!) 

CCC1 

a 

EXPLANATION 

t------i Seismic spread 

+ Epicenter of November 1974 earthquake 

X Center of highest intensity of 1886 earthquake 

(!) Clubhouse Crossroads corehole 1 

-1 OQ- Contour showing interpreted depth to marker 

horizon within Santee Limestone. Given in 

meters below ground surface; contour interval, 10 m 

0 5 10 15 KILOMETERS 

~~~~-L-------~------~ 

FIGURE 3.-Contour map of interpreted depths to the marker horizon within the Santee Limestone. Ground-surface elevation approximately 7.5 m. 
172 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

EXPLANATION 

t----f Seismic spread 

+ Epicenter of November 1974 earthquake 

X Center of highest intensity of 1886 earthquake 

(!) Clubhouse Crossroads corehole 1 

-750- Contour showing interpreted depth to 

intermediate (basalt) marker horizon . Given in meters below ground surface; 

contour interval, 50 m 

0 

LL____j_____j 

5 10 15 KILOMETERS 

FIGURE 4.-Contour map of interpreted depths to the intermediate (basalt) marker horizon. 
EXPLORING EARTHQUAKE AREA WITH SEISMIC REFRACTION 173 

Figure 3 shows that the Santee is nearly horizontal throughout the area surveyed. The data suggest, however, that the Santee contains an approximately 20-m-deep north-trending troughlike depression near the eastern edge of surveyed area. 

The most striking feature of the basalt-horizon 

contours (fig. 4) is also a north-trending broad 

troughlike depression which is offset slightly westward from the axis of the overlying Santee trough. 

The size of this depression may exceed 50 m, though 

it is difficult to determine because it modulates the 

regional dip which is to the southeast. The axis of 

this trough also parallels the trend of the basaltvelocity variations noted above, though offset several 

kilometers westward from the velocity minimum. 

Figure 5 is a contour map of interpreted depths 

to the deep crystalline basement. Because data from 

this horizon are incomplete, structural details could 

not be determined. In particular, the downward continuation of the troughlike feature from the Santee 

and basalt horizons could not be calculated. Crystalline basement depths were calculated, assuming a 

constant 4.2-km/s velocity between basement and 

the overlying basalt. If a sedimentary section underlies the basalt, its average velocity may be less than 

4.2 km/s. If so, the calculated crystalline basement 

depths are too large. In any case, the basalt and 

basement horizons diverge southeastward. Near 

CCC 1, the distance between the two may be less 

than 200 m. In the southeastern part of the area surveyed, it may be 1,000 m. The more tightly spaced 

depth contours in the southeastern part of the area 

indicate either a flexure or a fault in the crystalline 

basement. Unfortunately, data for this horizon are 

insufficient to make a definitive judgment. 

DISCUSSION 

The seismic-refraction data allow one to map 

three horizons, the upper two of which were identified in CCC 1. The intermediate horizon correlates 

with a Cretaceous ( ?) basalt at the depth of 750 m 

in the corehole. The velocity of this horizon is definitely variable, decreasing from a high value of 

about 5.8 km/s at the well to about 4.5 km/s along 

the eastern edge of the area surveyed, which includes the epicenter of the November 22, 1974, 

earthquake. Furthermore, a north-trending troughlike feature, which parallels the velocity trend, has 

been tentatively identified in the intermediate horizon. The axis of this trough is offset a few kilometers west of the velocity minimum. The data also 

suggest a similar but smaller depression in the 

shallowest horizon, which is within the 100-m-deep 

Santee Limestone. 

Shingling in the refracted arrivals for the intermediate (basalt) horizon indicates that this horizon 

is underlain by lower velocity materials, possibly a 

pre-Upper Cretaceous sedimentary section, which 

thickens southeastward. 

The deepest of the three mappable horizons is 

the true crystalline basement. Because data from 

this horizon are incomplete, details of its structure 

and velocity cannot be calculated. However, the data 

do indicate either a flexure or a fault of the crystalline basement in the southeastern part of the area 

surveyed. Neither the intermediate (basalt) nor the 

shallow Santee horizons show evidence of this structure. Furthermore, the velocity of the intermediate 

(basalt) layer attains a minimum value in the immediate area of this basement flexure or fault. In 

addition, the troughlike depression in the basalt and 

one of the two centers of highest intensity (Dutton, 

1889) are just a few kilometers westward. 

Thus we see the near coincidence of four events 

or features: (1) a line of earthquake activity defined by the Dutton high-intensity points and the 

recent epicenter at Middleton Place; (2) a compressional velocity minimum of a Cretaceous ( ?) basalt 

layer; (3) possible downwarping of this basalt 

layer and a shallower Eocene horizon; and ( 4) a 

flexure or fault in the crystalline basement. The spatial proximity of these four suggests a genetic relationship. 

Sbar and Sykes (1973) delineated a region of 

high horizontal compressive stress in eastern North 

America. They proposed that the Charleston seismic 

trend is due to these high stresses acting along a 

zone of weakness, such as an unhealed fault or the 

continental extension of a major oceanic fracture 

zone. Our interpretation of the Charleston seismic 

data then suggests the possibility that the flexure 

or fault found in the crystalline basement may actually be a manifestation of such a zone of crustal 

weakness. Additional data are necessary to define 

this structure clearly and to determine its trend. 

The small downwarp tentatively identified in the 

two shallower horizons may then be the product of 

more recent earthquake activity. We further note 

the decrease in compressional velocity of the intermediate (basalt) layer and suggest that this may 

be due to increased fracture porosity also resulting 

from earthquake activity over an extended period 

of time. Another possible explanation for the low-
174 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

80"15' 

EXPLANATION 

1----i Seismic spread 

+ Epicenter of November 1974 earthquake 

X Center of highest intensity of 1886 earthquake 

@ Clubhouse Crossroads corehole 1 

-1000- Contour showing interpreted depth to crystalline 

basement horizon. Given in meters below ground 

surface; contour interval, 100 m 

0 5 10 15 KILOMETERS 

~~.~~--L---------L-------~ 

80°00' 

FIGURE 5.-Contour map of interpreted depths to the crystalline basement horizon. 
EXPLORING EARTHQUAKE AREA WITH SEISMIC REFRACTION 175 

ered compressional velocity is that it simply represents the termination of the basalt layer and that 

the arrivals recorded there are from the rocks that 

elsewhere underlie the basalt. The velocity of 4.5 

km/s, for example, is an acceptable value (Stewart 

and others, 1973) for Triassic sedimentary rocks. 

REFERENCES CITED 

Ackermann, H. D., Godson, R. H., and Watkins, J. S., 1975, 

A seismic refraction technique used for subsurface investigations at Meteor Crater, Arizona: Jour. Geophys. 

Research, v. 80, no. 5, p. 765-775. 

Cassinis, R. and Morgonovi, L., 1966, Significance and implications of shingling in refraction records: Geophys. 

Prospecting, v. 14, no. 4, p. 547-565. 

Dutton, C. E., 1889, The Charleston earthquake of August 

31, 1886: U.S. Geol. Survey, Ann. Rept. 9, 1887-1888, 

p. 203-528. 

Sbar, M. L., and Sykes, L. R., 1973, Contemporary compressive stress and seismicity in eastern North America; 

an example of intraplate tectonics: Geol. Soc. America 

Bull., v. 84, no. 6, p. 1861-1881. 

Spencer, T. W., 1965, Refraction along a layer: Geophysics, 

v. 30, no. 3, p. 369-388. 

Stewart, D. M., Ballard, J. A., and Black, W. W., 1973, A 

seismic estimate of depth of Triassic Durham basin, 

North Carolina: Southeastern Geology, v. 15, no. 2, p. 

93-103. 

Wyllie, M. R. J., Gregory, A. R., and Gardner, L. W., 1956, 

Elastic wave velocities in heterogeneous and porous 

media: Geophysics, v. 21, no. 1, p. 41-70. 

A Preliminary Shallow Crustal Model Between 

Columbia and Charleston, South Carolina, 

Determined from Quarry Blast Monitoring 

and Other Geophysical Data 

By PRADEEP TALWANI 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, 

EARTHQUAKE OF 1886-A PRELIMINARY REPORT 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1028-M 

CONTENTS 

Page 

Abstract ----------------------------------------------------------------- 177 

Introduction -------------------------------------------------------------- 177 Data collection _ __ ____ _________ ________ ____ _ _____ _ __ _ _ ____ __ _________ _____ 177 

Results ------------------------------------------------------------------ 178 Discussion _____ -------------- _____ ____ ____ _______ _ __ ___ _ __ ___ _ __ _ __ ___ _ __ 179 

References cited ---------------------------------------------------------- 185 

ILLUSTRATIONS 

FIGURE 1. Location map around Charleston, S.C., showing study area, quarries monitored, refraction lines, permanent seismograph stations, refraction shot points, and interpreted Triassic basins ___________ _ 

2. Traveltime curves for quarry blasts in the Coastal Plain of South Carolina -----------------------

3. Velocity models southeast of Columbia --------------·--------------------------------------------

4. Simple Bouguer anomaly map of area around Charleston, S.C., showing location of refraction data __ 

5. Observed gravity profile and three interpretative shallow crustal models -----------------------------

III 

Page 

178 

180 

185 

186 

187 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886-

A PRELIMINARY REPORT 

A PRELIMINARY SHALLOW CRUSTAL MODEL BETWEEN COLUMBIA AND 

CHARLESTON, SOUTH CAROINA, DETERMINED FROM QUARRY BLAST 

MONITORING AND OTHER GEOPHYSICAL DATA 

By PRADEEP TALWANI 1 

ABSTRACT 

To obtain the velocity model under the Coastal Plain of 

South Carolina, blasts at five quarries were monitored. The 

data, incorporated with other refraction and gravity data, 

suggest that the crustal model is extremely complicated. 

A Triassic ( ?) graben is inferred near Summerville, and its 

border faults may be associated with the seismicity observed 

in the Summerville-Charleston area. 

INTRODUCTION 

The 10-station South Carolina seismographic network went into operation in May 1974 (Tarr, this 

volume). To best use the data accumulated by this 

network for the location of hypocenters, we must 

first determine the subcrustal velocity structure. 

Data pertinent to the velocity structure of the Coastal Plain of South Carolina were obtained at five 

quarries. These data have been incorporated with 

other geophyhical data to obtain a preliminary crustal model between Columbia and Summerville. 

This study was supported by U.S. Geological Survey Contract No. 14-08-0001-14553. I am grateful 

to my students, Donald Stevenson, David Amick, 

and Robert Van Nieuwenhuise, for their help in 

carrying out the fieldwork, and to the various 

quarry superintendents for their cooperation. I 

thank Hans Ackermann for allowing me to use some 

of his unpublished seismic refraction data. I also 

benefited from the discussions with A. C. Tarr of 

the U.S. Geological Survey and Prof. Donald T. 

Secor of the University of South Carolina. I also 

thank Dr. John Sumner of Lehigh University, 

who reviewed the manuscript and offered valuable 

comments. 

1 Dept. of Geol., University of South Carolina, Columbia, S.C. 29208. 

DATA COLLECTION 

Locations.-Most of the blast data were collected 

in the summers of 1975 and 1976. Of the five quarries monitored, two are in the crystalline rocks near 

the Fall Line, and the others are in the Coastal 

Plain (fig. 1). The Columbia quarry (COQ) and 

the Cayce quarry (CAQ) produce granite and are 

in the northwest quadrant of the study area. 

Berkeley quarry (BEQ) produces fine-grained clastic limestone of the Santee Limestone, and the 

Georgetown (GTQ) and Bass (BAQ) quarries produce indurated recrystallized limestone of the lower 

part of the Santee Limestone. BEQ, GTQ, and BAQ 

provided data from the southeast quadrant of the 

study area. Locations of various shots at BEQ and 

GTQ were determined from quarry maps (1 inch 

= 200 feet). The location of each shot was determined to ±0.01' (about 20 m) by tieing the shot 

point to a Coast and Geodetic Survey triangulation 

station. The blasts were monitored at remote station 

sites lying along the various refraction lines (fig. 1). 

The locations of stations within 6 km of the blast 

site were determined from the quarry map or from 

aerial photographs of the area surrounding the quarry ( 1 inch= 800 feet). Thus, the accuracy of locating 

stations close to the blast site was ± 0.02' ( ± 40 m). 

The locations of more distant stations were determined from 7.5' topographic quadrangle maps or 

county maps, and the accuracy was ± 100 m. 

All remote stations were within 45 km of the blast 

site, as beyond that distance the blast could not be 

detected on portable seismographs. 

Traveltime.-The origin times of all quarry blasts 

were obtained by recording the shot at the quarry 

177 
178 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

EXPLANATION * Quarry monitored GTO 

- ·Refraction line \ • Permanent seismograph station of South Carolina BAO 

seismic network 

(!) Refraction shot point of Woollard and others (1957) 

~------~--,_----~ 

/:Eo 

51 0 / PBS "'Summerville 

0 \ I 0 52 «2> 

50 ~ \ S G S (!) 

53 

Middleton Place+ 

osc .\ \ ([/) • ~\ Bowman HBF •$ CCC1 J 

0 20 40 60 KILOMETERS 

FIGURE 1.-Location map around Charleston, S.C., showing study area, quarries monitored, refraction lines, permanent 

seismograph stations of the South Carolina seismographic network, refraction shot points of Woollard and others 

(1957), and interpreted Triassic (Tr). The locations of the center of seismic activity, Middleton Place, and 

of the wells to the basalt at the Clubhouse Crossroads core hole 1 (CCC 1) are also shown. The town of Orangeburg is 6 km west of OSC. Abbreviations: COQ, Columbia quarry; CAQ, Cayce quarry; BEQ, Berkeley quarry; 

GTQ, Georgetown quarry; BAQ, Bass quarry. Seismograph station abbreviations, coordinates, and instrumentation are discussed by Carver, Turner, and Tarr (1977). 

on a portable seismograph equipped with a paper 

speed of 300 mm/ min. Origin times at quarry sites 

and the P- and S-wave arrival times on seismographs 

at remote stations were read to an accuracy of at 

least ± 0.02 s by using a low-power microscope. A 

WWVB time signal was recorded on all seismograms 

to obtain a uniform absolute time. Traveltimes from 

various blasts to stations of the seismographic network were also incorporated wherever they were 

available. 

RESULTS 

Velocity values from most traveltime data presented below were obtained by drawing an eyeball fit 

curve through the data. Local geology and the quality of the first arrivals were incorporated where a 

single line did not pass through all the data points. 

The velocity was also calculated by a method of least 

squares. The standard deviation and the coefficient of 

determination, r 2 , were also determined by linear regression. The velocity values obtained by the two 

methods agree well, and the values obtained by eyeball fit were used in computing depths. The least 

square values are given in figure captions 2C-F. 

The two quarries, located on either side of the 

Congaree River to the south of Columbia (COQ and 

CAQ), are about 1 km apart. The traveltime data for 

the Columbia blasts recorded in a southeast direction 

were plotted, and those for COQ and CAQ were 

grouped together (fig. 2A). The data suggest a Pwave velocity ( v P) of 6.0 km/ s. This velocity is reasonable for crystalline basement, which outcrops 

near Columbia. 

Figure 2B shows two possible interpretations of 

traveltime data for blasts at BEQ and recorded within 8 km in a northwest direction. In the first interpretation (a), the traveltimes for the near stations 

(within 1 km) and for the distant stations (near 5 
A PRELIMINARY SHALLOW CRUSTAL MODEL 179 

km and 8 km) lie on a 3.65 km/s line. Both near stations lie in the Berkeley quarry, and 3.65 km/s 

probably represents the velocity of Santee Limestone. From borehole data north of Santee River 

(Alan-Jon Zupan, oral commun., 1977), Santee 

Limestone is known to be less than 100 m thick. 

Traveltime data from BEQ, in a northwest direction 

beyond 7 km, lie on 5.70 km/s curve (fig. 2C). A 

simple two-layer example of a 3.65-km/s overlying a 

5.70-km/s layer would imply that the 3.65-km/s layer is 1.8 km thick. North of BEQ, Santee Limestone 

is known to overlie Black Mingo and Peedee Formations, which are a few hundred meters thick. Thus, a 

3.65-km/s layer, if it exists, has to be younger than 

the Black Mingo Formation. In interpretation a (fig. 

2B), data from a station 1.74 km distant were not 

incorporated. These data indicate a 2.2-km/s layer 

(interpretation b). In this latter interpretation, data 

from the two nearer stations have been neglected on 

the assumption that they represent the thin Santee 

Limestone, which has a higher P-wave velocity because of its greater induration. The sedimentary 

rocks, which have a P-wave velocity of 2.2 km/s, in 

turn overlie a 0.56-km-deep layer with a 5.70-km/s 

P-wave velocity. This depth, 0.56 km, appears to be 

more reasonable in view of a 5.5 km/s layer 0.5 km 

deep at Woollard's (1957) station 53 (fig. 1). 

Figure 2C shows the preferred traveltime data for 

blasts at BEQ recorded in a northwest direction out 

to a distance of about 31 km. This profile lies almost 

completely on the mapped Santee Limestone (see, 

for example, the Coastal Plain geology taken from 

Cooke (1936) and incorporated on the gravity map 

on South Carolina (Talwani and others, 1975). If 

interpretation b from figure 2B is accepted, the 5.70-

km/s layer is offset by 0.7 km, 5 km from BEQ. The 

postulation of a fault is based on data from a single 

station. If data from that station are neglected, the 

depth to the 5.70-km/s layer is 0.90 km. The P-wave 

velocity of 5.70 km/s suggests a basalt flow, and the 

implications thereof will be discussed later. 

In recording blasts at BEQ to the south (fig. 2D) 

there are no data within 3 km. Assuming that the 

velocity of the near-surface material is 2.2 km/s, the 

calculated depth to the 5.2-km/s layer is 0.8 km. If 

we assume that the true P-wave velocity of this layer 

(basalt flow) is 5.70 km/s, then an apparent velocity 

of 5.2 km/s suggests a southerly dip of 2.3 o. 

Figure 2E shows the reversed profile between 

GTQ to the north of Santee River and BAQ to the 

south. Sedimentary rocks that have a P-wave velocity of 2.05 km/s overlie a 6.0 km/s layer (crystalline 

basement), which dips from a depth of 0.48 km below BEQ to 0.63 km below GTQ. 

In figure 2F, two interpretations are presented for 

travel-time data for blasts at GTQ and BAQ recorded to the southwest. The data from the two quarries are grouped together in figure 2F. Two interpretations were made owing to the uncertainty resulting from a lack of data between 11 and 24 km. 

In interpretation a, a layer with an apparent velocity 

of 5.70 km/s. underlies a 2.0 km/s. sedimentary layer. The underlying layer is 0.57 km deep and dips 1 o 

to the southwest. Alternatively, >if we assume that a 

6.0-km/s. layer underlies the sedimentary rocks (interpretation b), it is 0.57 km deep, and somewhere 

between 11 and 24 km from BAQ, it is downthrown 

by 0.64 km. 

DISCUSSION 

The quarry blast data presented above are sparse 

and somewhat inconclusive. However, by incorporating gravity, magnetic, and other seismic refraction 

data, some constraints can be applied and a preliminary interpretation made. 

Figure 3A shows seismic refraction data of Woollard and others ( 1957). Only profiles at locations 48, 

49, and 53 were reversed. A low velocity of 4.82 

km/s. at location 51 together with an aeromagnetic 

low has been inferred by Daniels (1974) to indicate 

a possible Tria:ssic basin. This basin lies to the northeast of the Dunbarton basin, where red beds of assumed Triassic age are known to occur in the subsurface (fig. 1) (Marine and Siple, 1974). 

Data from Figures 2A and 2C were combined with 

those from figure 3A to obtain a schematic model 

along a line southeast from Columbia (fig. 3B). 

Seismic refraction data obtained at BEQ (and recorded to the south) were insufficient to obtain a 

velocity model in the Summerville area. However, 

other refraction data are available in the area (Ackermann, this volume, and written commun.). These 

were combined with drill-hole data at Clubhouse 

Crossroads and the gravity map of the area to obtain a velocity model. 

Figure 4 shows a part of the Bouguer anomaly 

map of South Carolina (Talwani and others, 1975). 

The location of the seismic refraction profiles from 

quarries, and those of Ackermann (unpub. data, and 

this volume) are also shown. BEQ and the Clubhouse Crossroads corehole 1 both lie on broad gravity highs, which are separated by an east-we:st gravity low. This gravity low coincides with a broad low 

seen on the aeromagnetic map of the area (Phillips, 

this volume). Unpublished refraction data from 
180 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

6.--------------.-------------,-------------,-------------,--------------,---------~---. 

5 

(/) 

0 

z 84 

LU 

(/) 

~3 

LU 

::2! 

~2 ...J 

LU 

> <( 

0::1 

Ivp =6.0 km/s 

EXPLANATION 

® CAQ 

0 coo 

OOL-----------~------------~------------~------------J_ ____________ L_ ___________ ~ 

5 1 0 15 20 25 30 

COO,CAQ SE DISTANCE, IN KILOMETERS · 

A 

FIGURE 2.--Traveltime curves for quarry blasts in the Coastal Plain of South Carolina. A, Shots at Columbia (COQ and 

CAQ) recorded in a southeast direction. 

Interstate (I), Knightsville (K) profiles (Ackermann, written commun.) and tho•se at Middleton 

Place (MP), Clubhouse Crossroads (CC), County 

Line East (CLE) and Bees Ferry (BF) (Ackermann, this volume) were extrapolated to a northsouth profile from BEQ (fig. 4). The direction of 

extrapolation was along strike of the structures suggested by the gravity contou~s. This profile passes 

through BEQ in the north, and through the eastern 

end of a gravity high to the south of Summerville. 

Ackermann (this volume) noted that some seismic 

refractions were shingled. These were interpreted as 

being caused by a thin basalt flow, and the P-wave 

velocity was found to vary between 4.5 and 5.8 km/s. 

Figure 5 shows the observed gravity profile and 

three proposed shallow crustal models. In making 

the gravity models, the density values used were 

those obtained at the Clubhouse Crossroads corehole 

1: 2.1 g/cm3 and 2.9 gjcm3 for Tertiary and Upper 

Cretaceous sedimentary rocks and the basalt, respectively (Brenda Higgins, written commun.). 

Below the sedimentary rocks that have Vp=2.0 

-2.2 km/s., seismic data at BF and I indicated an 

absence of the 5.8 km)s. horizon, which had been observed at BEQ and CC. At CLE and K, a velocity of 

5.0-5.4 km/s was obtained, and the refractions were 

associated with shingling. At Middleton Place (MP), 

the velocity decreased from 5.5 to 4.5 km/ s. eastward. This is interpreted as the edge of the ba,salt 

flow. A 6.2 km/s. horizon (crystalline basement) was 

observed at BF, CLE, and MP. 

The low-velocity, low-density sediments of the 

Coastal Plain are 600-950 m thick. If the standard 

Bouguer density of 2.67 g/cm3 is used in reduction 

of gravity data, the contribution of these sediments' 

is -20 mGal for a - 0.6-g/cm3 density contrast and 

an 800-m thickness. Since the Coastal Plain is only 

a few tens of meters above sea level, a normally compensated crust would have a slightly negative Bouguer anomaly associated with it. However, the Simple Bouguer gravity values in the area are positive, 

ranging from 0 to 10 mGal and indicating a thinned 

continental crust in this part of the Coastal Plain. 

To model the near-surface geology (to a depth of 

2.5-3 km), a datum density value of 2.5 g/cm3 rather 

than the standard 2.67 g/cm3 was used. This has the 

effect of removing the regional gravity gradient due' 

to a deep basement structure. 

The gravity models were constrained by the depths 

obtained from refraction data (short thick lines, 

fig. 5). In the first model, a 500-m-thick basalt flow 

is assumed below CC, a sedimentary basin below I, 

and a basalt flow below BEQ. The basalt flow below 

CC is at least 100 million years old, and possibly as 

old as Triassic (Gottfried and others, this volume), 

which suggests that the sedimentary horizon ( Vp 

=4.4 km/s) is older--possibly of Triassic age. A 

density of 2.4 g/cm3 was used to model this horizon. 
2 

Interpretation a 

0 

en 

0 

z 

00 

u 0 LLJ 2 

en BEQ 

z 

uJ 

~ s2 

LLJ 

> <( 

0:: 

IInterpretation b 

A PRELIMINARY SHALLOW CRUSTAL MODEL 

3.65 km/s 

3 4 5 6 7 

DISTANCE, IN KILOMETERS 

8 9 

181 

10 

NW. 

0~------L-______ L_ ______ L_ ______ ~------~------~------~-------L-------L------~ 

0 

BEO 

B 

2 3 4 5 6 

DISTANCE, IN KILOMETERS 

7 8 9 10 

NW. 

FIGURE 2.-Continued. B, Shots at BEQ recorded in a northwest direction within 8 km of the site-two possible interpretations (&ee text for discussion). 
182 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

7.-----------,----------,-----------,-----------,----------.-----------.-----------. 

i= Ld2-

> <( 

a: t-1-

5 10 15 20 

DISTANCE, IN KILOMETERS 

25 30 35 

NW. 

7,----------,-----------,-----------,-----------,-----------,----------~ 

(/) 

0 

z 

0 

u 

UJ 

(/)4 

z 

UJ 

~ 

i= 

....J 

UJ 

~ 2 

a: 

1-

km/s 

o~-----------L5------------~----------~------------J-----------~------------~ 10 15 20 25 30 

BEO DISTANCE, IN KILOMETERS S. 

D 

FIGURE 2.-Continued. C, Shots at BEQ recorded in a northwest direction for distances greater than 7 km from the site. 

Curve is projected to zero time at distances shorter than 7 km and shows that if interpretation b (fig. 2B) is accepted, 

faulting is suggested close to BEQ. Velocity obtained by eyeball fit ( 5. 70 km/ s) agrees well with that obtained by the 

method of least squares (5.68 km/s, standard deviation 0.18, and r"=0.994). D, Shots at BEQ recorded to the south. 

Dashed line represents the assumed velocity of near-surface material. Velocity by eyeball fit (5.2 km/s) agrees with that 

obtained by method of least squares (5.07 km/s, standard deviation 0.06, and r'=0.9985). 

This value was used by Marine (1974) to model 

postulated Triassic rocks at Dunbarton basin. A 

graben is required to model the gravity low. The 

Bouguer anomaly due to a basalt flow ( -500 m 

thick) below CC is insufficient to match the observed 

gravity anomaly. 
(j) 

0 

z 

0 

u 

LU 

(j) 

z 

w' 

~ 

i= 

_J 

LU 

> <( 

a: 

I-

(j) 

a: 

LU 

ILU 

~ 

0 

_J 

~ 

GTO 

NW. 

0 

E 

A PRELIMINARY SHALLOW CRUSTAL MODEL 183 

2 3 4 5 6 7 8 10 

DISTANCE, IN KILOMETERS BAO 

SE. 

2.05 km/s 

6.0 km/s 

VERTICAL EXAGGATION X2.5 

FIGURE 2.-Continued. E, Reversed refraction profile between blasts at GTQ and BAQ, as well as an interpretative model. 

Velocities by eyeball fit ( 6.5 km;s and 5.5 km;s) agree well with those obtained by method of least squares ( 6.29) km/s, 

standard deviation 0.26, r"=0.992; and 5.49 km;s, standard deviation 0.07, r"=0.999, respectively). The near-surface 

velocity of 2.05 km;s obtained at GTQ was also used at BAQ. 
184 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

5~--------~--------~----------,----------,--------~~~----~ 

4 

3 

2 

(/) 1 

0 

z 

Interpretation a 

Swoo~ __________ _L __________ ~------------~----------~----------~25~--------~30 5 10 15 20 

(/) DISTANCE, IN KILOMETERS z 

w5~----------,-----------,------------,-----------r---------r~~r-------~ ~ 

i= 

....1 

w 

~4 

a: 

1-

3 

2 

Interpretation b 

-------- EXPLANATION 

EB BAQ 

0 GTQ 

~~~~~---L----------~------------~----------~2~----------2~5~--------~30 5 10 15 0 

GTO, BAO DISTANCE, IN KILOMETERS SW. 

F 

FIGURE 2.-Continued. F, Shots at GTQ and BAQ recorded in a southwest direction. Two interpretations are given. Velocity values obtained by eyeball fit ( 5. 70 and 6.0 km;s agree with 'those obtained by the method of least squares ( 5.65 

km;s, standard deviation 0.09, r"=0.9988; and 6.12 km;s, standard deviation 0.12, 1""=0.9988, respectively). 

In the second model, the basalt flow below CC is 

replaced by a broad volcanic plus having an umbrellalike flow at the top. The shingling of refractions 

and Vp<5.8 km/s observed at CLE, MP and K is 

interpreted to be due to thin basalt flows around the 

plug, whose stem, lying below CC, is associated with 

no shingling and a velocity of 5.8 km/s. BF and I lie 

outside the plug where the post-Cretaceous sedimentary rocks (Vp=2.0-2.2 km/s and underlain by 

Triassic sedimentary rocks ( v P = 4.4 km/ s) . The 

crystalline basement ( Vp= 6.2 km/s) dips gently to 

the south and extends from BEQ to the south of 

BF, being interrupted by a volcanic plug at CC. The 

Bouguer anomaly associated with this model fits the 

observed data over the gravity highs on the ends of 

the profile but does not match the gravity low. To 

match the gravty low, a buried graben is required 

below I (model3). 

Thus, model 3 represents the preferred interpretation of the observed gravity data using constraints 

supplied by seismic refraction data and drilling. 

Some of the features of this model are: 

a. A broad volcanic plug was punched into a broad 

Triassic basin. 

b. The seismic velocity is 5.8 km/s in the stem of 

this plug, while on the flanks (associated with 

basalt flows) it decreases to 5.0 km/s and 

causes shingling of refractions. 
A PRELIMINARY SHALLOW CRUSTAL MODEL 185 

ORANGEBURG ESCARPMENT __ 50 .. ___ _ ----- ------- 51 

--~----------~--- ~ 

SEA LEVEL 

(/) 

a: 

w 

1--

100 

w 200 ~ 

z 

I 300 1--

a.. 

w 

0 

400 

500 

A 

NW. 

B 

1.73~- -----------------

SE. 

5.7 

FIGURE 3.-Velocity models southeast of Columbia. A, Model between Columbia and location 53 of Woollard and others 

(1957). The numbers 47-53 are the refraction locations (see fig. 1), and the others are the observed seismic velocities 

(km/s). B, Interpreted model along a line southeast from Columbia through location 52 to the Berkeley quarry. Seismic velocity values in km;s are incorporated. 

c. The broad lows on the aeromagnetic and gravity 

maps are due to a broad Triassic basin belo·w 

Summerville. 

d. Middleton Place lies on top of the southern flank 

of the graben, and the observed seismicity 

there may be associated with the border faults 

of this graben. 

e. The gravity high at BEQ is associated with a 

shallow crystalline basement having a thin 

basalt cap. (This is suggested by an absence of 

the basalt on the southwest profile from GTQ 

fig. 4). 

These results are preliminary, and this summer 

(1977) H. D. Ackermann and I will collect more 

data to test the model. 

REFERENCES CITED 

Carver, David, Turner, L. M., and Tarr, A. C., 1977, South 

Carolina seismological data report, May 1974-June 1975: 

U.S. Geo. Survey open-file report 77-429, 66 p. 

Cooke, C. W., 1936, Geology of the Coastal Plain of South 

Carolina: U.S. Geol. Survey Bull. 867, 196 p. 

Daniels, D. L., 1974, Geologic interpretation of geophysical 

maps, central Savannah River area, South Carolina and 

Georgia: U.S. Geol. Survey Geophys. Inv. Map GP-893 

[1975]. 
186 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

81° 80° 79° 34°~------------------------------------~~-------------------------------------. 

Columbia 

6. Quarry (see fig. 1 for names) 

f----1 Ackermann's seismic refraction profile 

-1s:3 Woollard's refraction profile 

f!r- Seismic refraction profile from quarry 

- ·10- Bouguer anomaly (mgal) from Talwani and 

(1975) 

Middleton Place 

Clubhouse Crossroads corehole 1 

FIGURE 4.-Simple Bouguer anomaly map (modified from Talwani and others, 1975) of the area around Charleston, S.C., 

showing the location of refraction data from Ackermann (this volume and written commun.). Location of a north-south 

profile from BEQ is also shown. This profile was extrapolated from unpublished refraction data from Interstate (I) 

and Knightsville (K) profiles (Ackermann, written comrnun.), as well as profiles at Middleton Place (MP), Clubhouse 

Crossroads (CC), County Line East (CLE), and Bees Ferry (BF) (Ackermann, this volume). The direction of extrap-
FIGURE 5.-0bserved gravity profile and three interpretative shallow crustal models. The P-wave velocities in km/s of the 

Tertiary and Upper Cretaceous sedimentary rocks, Triassic ( ?) sedimentary rocks, basalt, and crystalline basement 

are, respectively: 2.0-2.2, 4.4, 5.7-5.8, and 6.2. The corresponding density values (in parentheses) are 2.1, 2.4, 2.9 and 

2.7 gjcm'. Computed gravity due to model 1 (circles), model 2 (triangles), and model 3 (squares) is also shown along 

with the observed gravity profile. Locations such as BF and, CLE, extrapolated to the north-south profile, are shown in 

figure 4. The short thick lines at velocity boundaries show depths obtained from refraction data. 

Marine, I. W., 1974, Geohydrology of buried Triassic basin 

at Savannah River plant, South Carolina: Am. Assoc. 

Petroleum Geologists Bull., v. 58, no. 9, p. 1825-1837. 

Marine, I. W., and Siple, G. E., 1974, Buried Triassic basin 

in the central Savannah River area, South Carolina and 

Georgia: Geol. Soc. America Bull., v. 85, no. 2, p. 311-

320. 

Talwani, P., Long, L. T., and Bridges, S. R., 1975, Simple 

Bouguer anomaly map of South Carolina: South Carolina Div. Geology Map Ser. MS-21. 

Woollard, G. P., Bonini, W. E., and Meyer, R. P., 1957, A 

seismic refraction study of the subsurface geology of 

the Atlantic Coastal Plain and Continental Shelf between 

Virginia and Florida: Wisconsin Univ., Dept. Geology 

Geophys. Sec., 128 p. 

Electric and Electromagnetic Soundings Near 

Charleston, South CarolinaA Preliminary Report 

By DAVID L. CAMPBELL 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, 

EARTHQUAKE OF 1886-A PRELIMINARY REPORT 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1028-N 

CONTENTS 

Page 

1\bstract ----------------------------------------------------------------- 189 

Background -------------------------------------------------------------- 189 

1\udio-frequency magnetotelluric soundings -------------------------------- 190 

Vertical electric soundings ----------------------------------------------- 193 

Cross sections ------------------------------------------------------------ 195 

Interpretation and some speculations -------------------------------------- 197 

References cited ---------------------------------------------------------- 198 

FIGURE 

TABLE 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

ILLUSTRATIONS 

Page 

Sketch of electric microlaterolog of Clubhouse Crossroads core- hole 1 _ _ ___ __ _ __ _ _ _ __ __ __ ___ __ ___ _ _________ _ __ ____ ___ __ 190 

Map showing locations of vertical electric soundings (VES) and 

audio-frequency magnetotelluric (1\MT) resistivity soundings --------------------------------------------------- 191 

Hand-contoured maps of 1\MT apparent resistivities at six frequencies for north-south oriented E (electrical)-field ______ 192 

Hand-contoured map of 1\MT apparent resistivities at six frequencies for east-west oriented E-field ___________________ 194 

Interpreted VES projected onto section A-A' ----------------- 196 

Interpreted VES projected onto section B-B' ----------------- 196 

Interpreted VES projected onto section C-C' __________________ 197 

TABLE 

Page 

1. Interpreted VES solutions ---------------------------------- 196 

III 

STUDIES RELATED TO THE CHA~LESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886-

A PRELIMINARY REPORT 

ELECTRIC AND ELECTROMAGNETIC SOUNDINGS NEAR 

CHARLESTON, SOUTH CAROLINA-A PRELIMINARY REPORT 

By DAVID L. CAMPBELL 

ABSTRACT 

In an attempt to outline structural features which may 

bear on earthquake activity near Charleston, S. C., the 

U.S. Geological Survey has completed 9 Schlumberger d.c. 

resistivity soundings and 18 audio-frequency magnetotelluric 

(AMT) soundings in the region. Typical soundings show 

up to 60 m of surface sediments of variable resistivity, underlain by 100-250 m of 15-25 ohm-m material and 500-

1,000 m of 4--10 ohm-m material. 

The resistivity soundings failed to detect a basalt (Cretaceous or older) encountered at 750 m depth in U.S. Geological Survey Clubhouse Crossroads corehole 1. Drilling had been 

stopped after penetrating 42 m into this basalt. We now 

estimate this flow to be less than 75 m thick; it is underlain by low-resistivity material. Interpretation of the soundings indicates that the depth to high-resistivity electric basement near the corehole is approximately 1,300 m. 

The AMT data outline a higher resistivity zone approximately 11 km wide, trending northeast-southwest, roughly 

corresponding to the higher isoseismal region of the 1886 

earthquake. This zone seems to be bordered on the northwest by a lineament interpreted by Long and Champion in 

1975, on the basis of gravity, to represent a steeply dipping 

fault with the southeast side downthrown. Three d.c. soundings over this zone, however, show shallower electric basement (around 900 m) than those outside it. If this basement represents a thickened version of the Cretaceous ( ? ) 

basalt encountered in the corehole, some 150 m of vertical 

displacement would be indicated along this fault since Cretaceous time. 

BACKGROUND 

On August 31, 1886, Charleston, S.C., was shaken 

by a large earthquake which was felt throughout 

the eastern United States. Dutton (1889) studied 

this earthquake, finding maximum isoseismals along 

an elongated northeast-trending region between 

Charleston and the town of Summerville, which is 

about 35 km inland. The seismicity of South Carolina has been studied by Bollinger (1972), who 

finds historical earthquakes occurring in a northwest-trending band across South Carolina through 

Charleston and Summerville, roughly perpendicular 

to the coast and the Appalachian Mountains. Tarr 

(this volume) reports that a magnitude 3.8 earthquake occurred November 22, 1974, and 15 km west 

of Charleston, at a depth of 4.1 km. The focal 

mechanism of this earthquake was well determined 

and involved either a reverse fault or a thrust that 

strikes N. 42° W. Thus the scene is set: earthquakes 

seem to occur at shallow depths in a northwesttrending belt which passes under Charleston, but a 

northeast-trending feature, perhaps only in the shallow subsurface between Charleston and Summerville, transmitted and focused the shaking of the 

1886 quake. 

In the winter of 1975, the U.S. Geological Survey 

drilled a deep corehole near Clubhouse Crossroads, 

24 km southwest of Summerville. This corehole 

(Clubhouse Crossroads corehole 1) was located on 

an aeromagnetic and gravity high; geophysical 

analysis predicted a mafic basement at about 1,300 

m depth. Instead, at least two successive basalt 

flows were encountered, beginning at 750 m depth. 

The core had penetrated 42 m into these basalts before the core barrel became wedged in the hole and 

the hole was abandoned. Gottfried and others (this 

volume) reports that K-Ar ages of 94.8±4.2 m.y. 

and 109±4 m.y. for the basalt must be considered 

minimum ages because geochemical studies indicate 

that all samples are altered somewhat. The K-Ar 

ages are consistent, however, with a Late Cretaceous age for the overlying Cape Fear Formation 

(Hazel and others, this volume). 

Figure 1 shows an electric log ( microlaterolog) of 

Clubhouse Crossroads corehole 1, with a tentative 

stratigraphic description by Gohn and others (this 

189 
190 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

STRATIGRAPHY 

COOPER 

FORMATION 

SANTEE 

>- LIMESTONE a: 

<( 

f= 

a: 

~ BLACK MINGO 

(/) 

:J 

0 

w 

u 

~ w 

a: 

u 

. ,.... <(- f-(/) 

w=> a:O 

uw u 

FORMATION 

BEAUFORT(?) 

FORMATION 

PEEDEE 

FORMATION 

BLACK CREEK 

FORMATION 

MIDDENDORF 

FORMATION 

CAPE FEAR 

FORMATION 

BASALT 

MICROLATEROLOG 

10 100 1000 ohm-m 0 

100 

200 

300 

(/) 

a: 

w 

tw 

::!; 

400 ~ 

:r:' 

fa.. 

w 

0 

500 

600 

TO 792 BOO 

FIGURE !.-Sketch of electric microlaterolog of Clubhouse 

Crossroads corehole 1 near Clubhouse Crossroads, S. C. 

Also shown is a tentative stratigraphic identification by 

Gohn and others (this volume). TD, total depth. 

volume). In general, the logged resistivities do not 

seem particularly indicative of lithologic or stratigraphic boundaries. An exception is the thin 80 

ohm-m zone between 116 and 126m in depth, which 

corresponds to the tight calcareous sands at the base 

of the Santee Limestone. Below this zone, resistivities vary between 2 and 20 ohm-m throughout the 

sedimentary section. The interface between freshwater and saltwater should be no deeper than 220 

m at this location, but no specific resistivity drop on 

the log is identified as due to this cause. The microlaterolog shows a resistivity of 600 ohm-m for the 

basalt at the bottom of the corehole. 

In June 1975, the U.S. Geological Survey completed further geophysical work in the Charleston 

area, including 6 refraction seismic spreads, 18 

audio-frequency magnetotelluric (AMT) resistivity 

soundings, and 9 Schlumberger d.c. vertical electric 

soundings (VES). The results of the refraction seismic work are reported by Ackerman (this volume), 

and this paper discusses the resistivity results. The 

locations of the VES and AMT soundings are shown 

on figure 2. 

This study has been funded by the U.S. Nuclear 

Regulatory Commission, Office of Nuclear Regulatory Research, Agreement No. AT (49-25)-1000. 

Charles Tippens and Harold Kaufmann made the 

AMT soundings. 

The material in this report was presented orally 

March 26, 1976, at the Combined Meeting of the 

Northeastern-Southeastern Sections of the Geological Society of America, at Arlington, Va. 

AUDIO-FREQUENCY MAGNETOTELLURIC 

SOUNDINGS 

A general description of audio-frequency magnetotelluric (AMT) techniques and theory may be 

found in Chapter IV of Keller and Frischknecht 

(1966). Each AMT measurement described here 

yielded 11 apparent 'resistivity values for a given 

site, each value corresponding to one of 11 different 

frequencies in the band from 7.5 Hz to 18.6 Hz . 

Schematically, one may regard each apparent resistivity value as a weighted average of true resistivities in the earth below that site, with successively lower frequencies weighting successively 

deeper resistivities more heavily. In the Charleston 

area, near-surface resistivities were too low for very 

deep penetration of audio-frequency electromagnetic 

waves, so that negligible weights resulted at even 

the lowest AMT frequency for depths greater than 

about 700 m. 

The equipment used in the Charleston area received electromagnetic waves broadcast by the lightning strokes in thunderstorms. Ideally, the equipment should be oriented to measure the maximum 
ELECTRIC AND ELECTROMAGNETIC SOUNDINGS 191 

80"15' 80"00' 

Ll6 

l27 

FIGURE 2.-Map showing locations of vertical electric soundings (VES) (heavy lines) and audio-frequency magnetotelluric (AMT) resistivity soundings (heavy L's) described in this report. Also shown are the locations of Clubhouse Crossroads corehole 1 (CCC 1), the historical plantation Middleton Place (MP), and section lines A-A', 

B-B', and C-C' (figs. 5, 6, and 7). The broken line indicates a trend which Long and Champion (this volume) 

picked on the basis of gravity to represent a basement fault with the southeast side dropped 0.65 km. In the present study we prefer that Long and Champion's line be shifted somewhat to the position indicated by heavy railroad bars. 

horizontal electric field ' at each frequency; in practice, however, the direction to the particular 

storm (s) in progress is unknown, and therefore the 

direction of maximum field is unknown. Therefore, 

two electric fields are measured, in north-south and 

east-west directions, and later combined in a way 

1 Magnetotelluric technique actually involves simultaneous measurement of horizontal magnetic fie!d, too, in a direction perpendicular to that of the electric field. In practice, however the electrical field is of chief concern to us. as it is found to vary in magnitude much more than the magnetic field. 

which varies with the interpreter. According to 

Stodt (oral commun., 1975), this azimuthal uncertainty can give rise to a scatter of as much as an 

order of magnitude in the derived apparent resistivity values. Other problems with AMT data involve changes in relative calibrations from frequency to frequency due to drift in the electronic 

gear, contamination by cultural noise, and near 

field effects due to very local storms (in Charleston 
192 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

80'15' 

285Hz (8/2= 51 METERS) 

0 5 

1 1111 11 1 I I I 

10MILES 

I 

5 10 KILOMETERS 

C. 1., 20 ohm-m 

80'15' 

14Hz (8/2=310 METERS) 

0 5 10 MILES 

11 111111 I I I I 

0 5 10 KILOMETERS 

C. 1., 20 and 40 ohm-m 

80'00' 

80'00' 

[3p , 

~0 I 

0 

1 11 11 11 1 

32"45'f----· 

0 5 

1 1111111 I I 

C. 1.. 20 ohm-m 

80'15' 80'00' 

76Hz (8/2 = 120 METERS) 

80'15' 80'00' 

FIGURE 3.-Hand-contoured maps of AMT apparent resistivities at six frequencies for north-south oriented E (electrical)-

field. Each L represents a station, and the number in the L gives observed apparent resistivity in ohm-meters at that 

frequency and location. Here a equals skin depth in 20 ohm-m material; a; 2 values are given to indicate roughly the 

depth to which each map applies. Contours are schematic; note that the contour interval (C.I.) varies from map to map. 

MP is Middleton Place, and CCC 1 is Clubhouse Crossroads corehole 1. 

in June, such storms were often visible on the horizon). 

Figures 3 and 4 are contour maps of apparent 

resistivities at the six lowest AMT frequencies for 

north-south and east-west measurements respectively. For the reasons given above, the exact apparent 

resistivity values shown are not considered significant, though general magnitudes and trends may be 

of interest. A representative depth is given on each 

map, equal to half the skin depth o for a uniform 

halfspace of resistivity 20 ohm-m, a fair average 

for the Charleston area near-surface. Such values 

are meant to be only approximate, given to show 

roughly the depth to which each map applies; they 

have no rigorous meaning. 

We make the following generalizations about figures 3 and 4: 

1. On any given map the north-south values are 

usually higher than the east-west ones. This 

is probably an artifact of geometrical direc-
ELECTRIC AND ELECTROMAGNETIC SOUNDINGS 193 

0 5 

1 11 1 111 1 I I I 

0 5 10 KILOMETERS 

C. 1 ..40 ohm-m 

80'15' 80'00' 

12h33 7.5 Hz (cS/2 = 420 METERS) 

Lss 

0 5 

1 1 11 " 1 1 I I I 

0 5 10 KILOMETERS 

C. 1 .. 100 and 200 ohm-m 

FIGURE 3.-Continued. 

tion to dominant nea.rby storm activity (See 

Goldstein and Strangway, 1975), but conceivably could indicate east-west trends in nearsurface lithologies. (Electric current usually 

flows more readily along layers than across 

them, so that the lower resistivity direction is 

along the layers.) 

2. The contours on the two shallower maps (285 

and 76 Hz) appear to trend generally northsouth. The contours on the four deeper maps 

(27, 14, 10, and 7.5 Hz) appear to trend generally northeast, especially in the vicinity of 

Middleton Place. A change in orientation of 

geologic grain of the area below about 150 m 

depth therefore may be indicated. We may expect to find northeast trends in the deep 

structure near Middleton Place. 

3. The dominantly northeast-trending pattern 

seems to be crossed in the southwestern part 

of the map by a single, constant low-resistivity 

zone. The uniformly high apparent resistivity 

values found on AMT soundings 3 and 8 (locations shown on fig. 2) may be due to cultural 

and (or) instrumental difficulties at those two 

sites. 

There are various reasorns for focusing on the 

northeast-trending feature indicated in figures 3 

and 4. First, Dutton's isoseismals were elongated 

to the northeast in precisely this area, so that we 

may be picking up the geological structure responsible for this effect. Second, this feature is roughly parallel to and bounded on the northwest by a 

line picked by Long and Champion (this volume) 

on the basis of gravity to represent a steeply dipping vertical fault. Third, certain characteristics of 

the interpreted VES (discussed next), as well as the 

refraction seismic interpretations (Ackerman, this 

volume), may be explained by postulating such a 

northeast-trending feature. 

VERTICAL ELECTRIC SOUNDINGS 

A general description of Schlumberger vertical 

electric sounding (VES) technique and theory may 

be found in Zohdy, Eaton, and Mabey (1974). Near 

Charleston we worked along existing roads, placing 

as much as 10 km of wire on the ground in order 

to get the necessary 1% km depth penetration. The 

field data were processed according to standard U.S. 

Geological Survey procedure-curve segments from 

different potential-electrode spacings were shifted 

to form a single continuous curve, this curve was 

smoothed by splining and sampled at uniform intervals, and the sampled points then inverted by automatic computer to give resistivity layering versus 

depth (Zohdy and others, 1973; Zohdy, 1974a; and 

Zohdy, 1975). This layer model was then simplified 

using the Dar Zarrouk technique (Zohdy, 1974b) to 

give the most conservative solution (that with 

fewest layers) which would still fit the (smoothed) 

field data. In this way, spurious apparent layers 

due to noise in the field data were suppressed. At 

the same time, however, certain thin but probably 

real layers such as the 80 ohm-m base of the Santee 

Limestone were also suppressed. To the extent allowed by the field data, the solutions for adjacent 

soundings used similar resistivities at similar 

depths, and all these values were made to correspond 
194 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

Bll"15' BO"OO' 

14Hz (ll/2= 310 METERS) 

I 0 KILOMETERS 

C. I. 20 ohm-m 

FIGURE 4.-Hand-contoured maps of AMT apparent resistivities at six frequencies for east-west oriented E-field. Each L 

represents a station, and the number in the L gives observed apparent resistivity in ohm-meters at that frequency 

and location. Here o equals skin depth in 20 ohm-m material; o/ 2 values are given to indicate roughly the depth to 

which each map applies. Contours are schematic, and the contour interval (C.I.) varies from map to map. MP is Middleton Place, and CCC 1 is Clubhouse Crossroads corehole 1. 

in a general way with the resistivities seen on Clubhouse Crossroads corehole 1 well log. Depths were 

not specified in any way, however; all were determined solely by the interpretation scheme. Electric 

basement was assumed to have a resistivity of 200 

ohm-m everywhere. This value is arbitrary. The 

field data indicate only that basement resistivity is 

high with respect to that of the overlying sediments 

(more than 100 ohm-m) but do not give its exact 

value. The poor resolution of this parameter is not 

serious, giVmg a probable uncertainty in depth to 

basement of the order of 10 percent. 

Interpreted solutions for the nine VES are given 

in table 1. With the exceptions of VES 4 and VES 

6, all depths are thought to have an uncertainty of 

10 percent or less. Owing to severe contamination 

of the raw data by cultural noise, the entire solution for VES 6 and the depth to electric basement 

at VES 4 are thought to be good to only 20 percent. Resistivities shown are averages in the Dar 
ELECTRIC AND ELECTROMAGNETIC SOUNDINGS 195 

80"15' 

27 Hz (o/2= 170 METERS) 

32"45'f-------

0 5 

I •'• •'• I I I 

0 5 

C. 1., 20 ohm-m 

80"15' 

FIGURE 4.-Continued. 

80"00' 

80"00' 

Zarrouk sense (Zohdy, 197 4b) of the true resistivity 

versus depth function below each sounding. 

Not one of the nine VES showed a high-resistivity 

layer near 750 m depth which would correspond to 

the basalt encountered art the bottom of Clubhouse 

Crossroads corehole 1. We infer that this basalt is 

either absent or quite thin below the VES locations. 

A useful rule of thumb for VES interpretations is 

that a layer of sufficient (more than 20 times) resistivity contrast will be indicated on d.c. soundings 

whenever its thickness to depth ratio exceeds 1/ 20. 

Clubhouse Crossroads corehole 1 penetrated 42 m 

into this basalt, a sufficient minimum thickness under the 1/ 20 rule that a basalt layer maintaining 

this thickness everywhere should have been indicated on all soundings. As it was not, we conclude 

that the basalt flow, if present at all, was (a) 

deeper, (b) thinner, and (or) (c) of lower resistivity at the VES locations than at the corehole location near Clubhouse Crossroads. Computer modeling indicates that such a basalt layer, 750 m deep, 

could be up to a maximum of 75 m thick and still be 

missed, providing its resistivity were only 50 ohmm, one twelfth the logged value. I consider this the 

extreme possible thickness-resistivity estimate. 1 

Because electric basement was indicated at about 

1,300 m on several soundings near the corehole site 

(VES 1, 3, 8, and 9), I infer that about one-half 

kilometer of sediment lies below the basalt flow but 

above electric basement. Interpreted resistivities at 

these depths are all in the range 1-10 ohm-m, values 

appropriate for water-saturated sediments. A series 

of alternating very low resistivity sediments and 

thin basalt flows would, however, also fit the data. 

If, for example, 90 percent of the section consists 

of 1 ohm-m sediments, and the remaining 10 percent 

is thin 100 ohm-m basalt flows, a net apparent resistivity of 3.4 ohm-m would be seen at the surface 

VES (Campbell, 1977). In that case, the one-half 

kilometer of sediments could be replaced by only 160 

m of interleaved sediments and basalts and still give 

the observed VES curves. Then, however, depth to 

true electric basement (910 m) would no longer 

agree with magnetic basement depth estimates of 

more than 1,000 m (Phillips, this volume). The most 

likely interpretation is that there are few, if any, 

additional basalt flows in the sedimentary section below the flow encountered in Clubhouse Crossroads 

corehole 1. 

CROSS SECTIONS 

Under VES 2, 4, and 7, electric basement is near 

900 m depth; elsewhere it is at depths greater than 

1,000 m. These three shallow basement locations are 

on, or immediately east of, the Long-Champion 

trend (fig. 2), which may represent a steeply dipping fault. Sections A-A' and B-B' on figures 5 and 

6 show interpreted VES 1-8, including the LongChampion conjectured fault. Near VES 7, the fault 

is shown shifted 2 km to the northwest from its 

originally inferred position in order to include VES 

7 with the other shallow-basement soundings to the 

east (both original and shifted positions are also 

1 Additional information was received on May 10, 1977. Anoth.er U .S. Geological Survey corehoie, 2.6 km southwest of the center of VE~ 1, encountered basalt between 774 m and 1,0~1 m depth, and pass~d mto well-indurated sediments below 1,031 m depth. The total basalt th1ckness at this location is 257 m compared with 75-m maximum thickness I have 

interpreted from data at the YES 1 site. 
196 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

TABLE !.-Interpreted VES solutions 

[p, resistivity of layer in ohm-m; d, depth to bottom of layer in meters I 

NORTHWEST 

A 

VES 8 

0 75~ 

(J) 

a: 

w 

ti; 

::!!; 

~ 

~-

fu 1000 0 

23 

VES 1 

P= 

d= 

VES 2 

P= 

d= 

VES 3 

P= 

d= 

VES 4 

p= 

d= 

VES 5 

P= 

d= 

VES 6 

P= 

d= 

VES 7 

P= 

d= 

VES 8 

P= 

d= 

VES 9 

p= 

d= 

810 90 

1.5 4,9 

1200 256 

2.6 10.1 

80 146 

2.3 4.9 

120 25 

1.5 8 

1200 300 

1.5 14 

45 91 

1.65 5 

320 64 

1.7 4.4 

1000 74.5 

2.3 25 

700 72 

10.6 70.5 

VES 3 VES 4 

4 

z '·' ./~~"' ! ..... 

0 

200 ohm-m --' 

313 

6.6 

75 

64 

63 

27 

60 

26 

15 

64 

21 

14.5 

302 

11.3 

38.4 

68.4 

15 

226 

VERTICAL EXAGGERATION x 25 

39 

30 

14 

310 

7 

59 

16 

110 

40 

96 

40 

47 

20.6 

182 

124 

139.2 

6 

1300 

SOUTHEAST 

A' 

VES 5 

7 

FIGURE 5.-Interpreted VES projected onto section A-A'. 

Thin lines indicate divisions between different electrical 

layers. Numbers are resistivities in ohm-meters. Dotted 

horizons indicate features inferred from other evidence, 

but not seen in the VES data. 

shown on fig. 2). A second fault in the subsurface is 

shown parallel to the Long-Champion trend and 11 

km southeast of it in order to separate the different 

resistivity structures of VES 4 and 5. The position 

23 71 10.8 1.63 200 

125 166 689 1319 00 

4.5 200 

190 00 

25 8 200 

194 1186 00 

50 4 200 

150 900 00 

7 200 

1350 00 

10.6 4.2 200 

409 1113 00 

52.1 4.8 200 

320 965 00 

23 7.6 200 

889 1475 00 

200 

00 

NORTHWEST 

600 

(J) 

a: 

w 

1-

w 

::!!; 800 

;?; 

:i 

1-

a.. 1000 w 

0 

1200 

1400 

1600 

11 ? 

4.5 

_/4.8 

H 

1- -

1

·

6 5 -------------- 200 ::1. 200 _.. ...... . 

z ....... - 0 

0:: 

::!!; 

<1: 

:I: 

u -------1 

200 ~ 

0 

...I 

? 

VERTICAL EXAGGERATION x 25 

SOUTHEAST 

8' 

FIGURE 6.-Interpreted VES projected onto section B-B'. 

Thin lines indicate divisions between different electrical 

layers. Numbers are resistivities in ohm-meters. Dotted 

horizons indicate features inferred from other evidence, 

but not seen in the VES data. 
ELECTRIC AND ELECTROMAGNETIC SOUNDINGS 197 

of this fault has been chosen to coincide with some 

linear segments on the aeromagnetic contour map. 

Both faults are conjectural and interpreted as faults 

mainly to separate soundings of differing layer 

thicknesses and resistivities. Though the conjectured 

faults also separate regions of shallow and deep 

electric basement, any two adjacent basement depths 

may be connected with slopes not exceeding 5°. A 

rather gentle anticline would therefore fit the basement depth data as well as the faulted structure 

shown on sections A-A' and B-B'. 

Section C-C' (fig. 7) trends northeast between the 

two conjectured faults. We see that the shallow 

electric basement of VES 2 and 4 has been lost to 

the southwest under VES 9. 

INTERPRETATION AND SOME SPECULATIONS 

The original gravity interpretation of Long and 

Champion (this volume) involved downdrop of the 

block to the southeast of the Long-Champion line. 

The VES interpretations shown on sections A-A' 

and B-B', however, show shallower basements 

southeast of this line. I would reconcile these two 

interpretations by postulating that the "basement" 

seen on VES 2, 4, and 7 is, in fact, a thickened interval of the Cretaceous ( ?) basalt encountered in 

Clubhouse Crossroads corehole 1. If the LongChampion fault were already active in the Late 

Cretaceous, some surface relief may have been expressed along it at that time. The basalt floods 

which inundated the area at that time would have 

filled the valley southeast of the fault resulting in 

greater basalt thicknesses there. Computer models 

indicate that a 100-m thickness of 200 ohm-m basalt, 

even when underlain by one-half kilometer of lowresistivity sediments, would be sufficient to give an 

"electric basement" signature equal within experimental error to those obtained from VES 2, 4, and 

7. 

The hypothesis of a thickened basalt interval under VES 2, 4, and 7 may explain the apparent 

change in basement depth seen along section C-C'. 

The deep basement seen at VES 9 would represent 

crystalline basement some one-half kilometer below 

the basalt flow. The flow itself presumably is too 

thin to be seen at the VES 9 location. The basalt is 

present at 750 m Clubhouse Crossroads corehole 1 

to the west of the fault, but (according to the thickened basalt hypothesis) at around 900 m under VES 

2, 4, and 7 east of it. Thus, some 150 m of postCretaceous vertical offset could be indicated across 

the Long-Champion line in the vicinity of these 

particular soundings. Long and Champion's (this 

(/) 

a: 

LJJ 

t;; 

:2 

SOUTHWEST 

VES 9 VES 2 VES 4 

NORTHEAST 

C' c 

0~--------~~-----~~=--~~=~-----------~ 

_!__3_ ~ }2_ /16 60 

15 I 50 

14 

-~~ 

4 

4.5 

6 

~ 800-

:I: 

1-

a.. 

LJJ 

D 

·-··---------- 7 ------- - -----

. 200 200 ohm-m 

--- - 7 - ----------··----------· 

200 . 

VERTICAL EXAGGERATION X 25 

FIGURE 7.-Interpreted VES projected onto section C-C'. 

Thin Jines indicate divisions between different electrical 

layers. Numbers are resistivities in ohm-meters. Dotted 

horizons indicate features inferred from other evidence, 

but not seen in the VES data. 

volume) gravity interpretation involved a 600-m 

vertical offset in the basement across this line at a 

location 12 km further northeast, indicating either 

that displacement increases northeasterly, or that 

substantial vertical displacement was already there 

before the basalt flow came. I tend to favor the first 

interpretation, on the grounds that the interpreted 

basement offset in the southeast is small, with no 

significant difference between VES 1 and VES 9. 

The structure east of the Long-Champion line 

may be a Cretaceous ( ?) analog of the Atlantic 

coast Triassic and Jurassic basins farther to the 

north. The Long-Champion fault would be the western border fault of this basin with the postulated 

thickened basalt and west-dipping flow within its 

sedimentary pile. (Some west dip seems likely between VES 2 and 7 as shown on section B-B'.) The 

lower resistivity seen above basement within the 
198 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

structure ( 4 ohm-m as opposed to 10 ohm-m outside 

it) could be indicative of ground water pooled in 

such a basin. 

Though the question is not closed, indications are 

that present-day earthquake activity has little to do 

with the postulated Long-Champion fault. The one 

well-determined earthquake focal mechanism (Tarr, 

this volume) and general seismicity trends (Bollinger, 1972) are at nearly right angles to it. There 

is no longer any surface expression of the LongChampion fault. Its only significance for presentday earthquake planners may be the transmission 

and concentration of shaking along its associated 

shallow basin in response to large earthquakes 

which take place deeper in the section. 

A second U.S. Geological Survey corehole, 2.6 km 

southwest of the center of VES 1, encountered 

basalt between 77 4 m and 1,031 m depth, and passed 

into well-indurated sediments below 1,031 m depth. 

The total basalt thickness at this location is 257 m 

compared with 75-m maximum thickness I have in·· 

terpreted from data at the VES 1 site. 

REFERENCES CITED 

Bollinger, G. A., 1972, Historical and recent seismic activity 

in South Carolina: Seismol. Soc. America Bull., v. 62, 

no. 3, p. 851-864. 

Campbell, D. C., 1977, A model for estimating electric macroanisotropy coefficient d fractured aquifers: Geophysics, v. 42, no. 1, p. 114-117. 

Dutton, C. E., 1889, The Charleston earthquake of August 

31, 1886: U.S. Geol. Survey Ann. Rept. 9, 1887-88, p. 

203-528. 

Goldstein, M. A., and Strangway, D. W., 1975, Audio-frequency magnetotellurics with a grounded electric dipole 

source: Geophysics, v. 40, no. 4, p. 669-70. 

Keller, George, and Frischknecht, Frank, 1966, Electrical 

methods in geophysical prospecting: New York, Pergamon Press, 519 p. 

Zohdy, Adel A. R., 1974a, A computer program for the 

automatic interpretation of Schlumberger sounding 

curves over horizontally stratified media: U.S. Natl. 

Tech. lnf. Service PB-232703/ AS, 25 p. 

--- 1974b, Use of Dar Zarrouk curves in the interpretation of vertical electrical sounding data: U.S. Geol. Sur~ 

vey Bull. 1313-D, 41 p. 

--- 1975, Automatic interpretation of Schlumberger 

sounding curves, using modified Dar Zarrouk functions: 

U.S. Geol. Survey Bull. 1313-E, 39 p. 

Zohdy, Adel A. R., Anderson, L. A., and Muffler, L. J. P., 

1973, Resistivity, self-potential and induced polarization 

surveys of a vapor-dominated geothermal system: Geophysics, v. 38, no. 6, p. 1130-1144. 

Zohdy, Adel A. R., Eaton, G. P., and Mabey, D. R., 1974, 

Application of surface geophysics to ground-water investigations, Chapter D1, of Book 2 of Techniques of 

water-resources investigations of the U.S. Geol. Survey: 

Washington, D. C., U.S. Govt. Printing Office, p. 10-22. 
Correlation of Major Eastern Earthquake 

Centers With Mafic/Ultramafic Basement Masses 

By M. F. KANE 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, 

EARTHQUAKE OF 1886-A PRELIMINARY REPORT 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1028-0 

FIGURE 

CONTENTS 

Page 

Abstract ----------------------------------------------------------------- 199 

Introduction ------------------------------------------------------------- 199 

Comparison of gravity anomalies and earthquake areas --------------------- 199 

A possible source mechanism -------------------------------------------- 201 

References cited ---------------------------------------------------------- 203 

ILLUSTRATIONS 

1. Sketch maps showing gravity and seismicity data for seven major earthquake regions in eastern 

North America ___________________________________________________________________________ _ 

2. Sketch maps showing gravity and contemporary epicenter data for the New Madrid, Mo., and CharlesPage 

200 

ton, S.C., earthquake areas ----------------------------------------------------------------- 202 

III 

STUDIES RELATED TO THE CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886-

A PRELIMINARY REPORT 

CORRELATION OF MAJOR EASTERN EARTHQUAKE CENTERS WITH 

MAFIC/ULTRAMAFIC BASEMENT MASSES 

By l\1. F. KANE 

ABSTRACT 

Extensive gravity highs and associated magnetic anomalies 

are present in or near seven major eastern North American 

earthquake areas. The seven include the five largest of 

these centers. The immediate localities of the gravity anomalies are, however, relatively free of seismicity, particularly 

of the largest seismic events. The anomalies are presumably 

caused by extensive mafic or ultramafic masses embedded in 

the crystalline basement. Laboratory experiments show that 

serpentinized gabbro and dunite fail under stress in a creep 

mode rather than in a stick-slip mode. A possible explanation of the correlation between the earthquake patterns and 

the anomalies is that the mafic/ultramafic masses are serpentinized and can sustain only low-stress fields, thereby 

acting to concentrate regional stress outside their boundaries. 

The proposed model is analogous to the hole-in-plate problem of mechanics whereby stresses around a hole in a 

stressed plate may reach values several times the average. 

INTRODUCTION 

Earthquakes of the Eastern United States are 

markedly lower in frequency and magnitude than 

those of the western regions, particularly when compared with those occuring along the San Andreas 

fault of California. Because of the low damping of 

earthquake energy in the Eastern United States, 

however, relatively high intensities are anticipated 

when compared with the intensities resulting from 

corresponding magnitudes of the western earthquakes (Nuttli, 1973). A second aspect of the eastern earthquake region that contrasts with that of 

western regions is the sparsity of readily identifiable major faults. To some extent, this lack may be 

attributed to a thick cover of incompetent sedimentary strata, but it seems surprising that ongoing 

studies have not uncovered direct evidence of major 

fault systems in the major eastern earthquake 

regions. 

As part of the earthquake investigation program 

of the U.S. Geological Survey, aeromagnetic and 

gravity studies of the New Madrid, Mo., and 

Charleston, S.C., earthquake areas began in 1972. 

Coverage of much of these regions was completed 

by 1975, although surveys in the New Madrid area 

are still underway. The initial efforts were directed 

towards discernment of linear magnetic or gravity 

features that could be attributed to major faults in 

the crystalline, presumably magnetic, basement 

rocks, but evidence of such features was not detected, at least not in the sense of readily apparent 

lineaments or discontinuities. Major magnetic and 

gravity highs were recognized in the near-epicentral 

regions of both the New Madrid and Charleston 

areas, but coincidence seemed to be the most plausible explanation. Positive magnetic and gravity 

anomalies have now been identified, however, for 

the seven major Eastern United States earthquake 

areas as defined by Hadley and Devine (1974), so 

that implications other than coincidence must be 

considered. 

COMPARISON OF GRAVITY ANOMALIES AND 

EARTHQUAKE AREAS 

Figure 1 illustrates the comparison of earthquake 

epicenter areas with gravity anomalies for seven 

well-identified eastern North American earthquake 

regions. The dashed line shown on each map of the 

figure is the maximum frequency contour line showing the total number of earthquakes per 10• km2 

from 1800 to 1972 that have had an intensity of 

Modified Mercali III or larger (Hadley and Devine, 

197 4). As explained by Hadle,y and Devine, the 

contours are "only * * * a guide for estimating 

regional seismicity." Also shown on figure 1 is the 

199 
200 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

32oL-~~-~IO~L------U----~--------~ 

B, Charleston, S. C., area 

EXPLANATION 

0 

Bouguer gravity contour in milligals 

relative to sea level; dashed in 

areas of sparse data. Hachures 

indicate areas of relatively lower 

gravity 

----64----

Maximum frequency contour showing total number of seismic events 

per 104 km2 from 1800 to 1972 

Approximate location of largest 

seismic event for each region. 

Two events of equal intensity .are 

shown for Cape Ann, Mass., 

area (C) 

0 50 100 KILOMETERS 

FIGURE 1.-Sketch maps showing gravity and seismicity data for seven major earthquake regions in eastern North 

America. Seismicity data were modified from Hadley and Devine (1974). Gravity data in A and B are from 

American Geophysical Union (1964); gravity data in C and D from Kane and others (1972); gravity data in 

E from Heiskanen and Uotila (1956); gravity data in F from Revetta and Diment (1971); and gravity data in G 

from Thompson and Garland (1957). 
CORRELATION OF EARTHQUAKE CENTERS WITH MAFIC BASEMENT MASSES 201 

earthquake of maximum intensity within each region. The fact that these largest ea.rthquakes are 

all within the maximum contour lines gives assurance that the contour lines also locate the areas of 

maximum energy release. 

An examination of the small-scale maps of figure 

1 shows that positive gravity anomalies of 10 milligals or greater and horizontal extents of more than 

30 km are present in each of the earthquake regions. 

The New Madrid, Mo., area (fig. lA) is notable for 

two large circular anomalies northwest and south 

of the zone of maximum epicenter frequency. The 

largest seismic event is also located between the 

gravity highs. In the Charleston, S.C., area (fig. 

lB), the largest event and the center of maximum 

epicenter frequency are both just east of a gravity 

high that has an easterly elongation. In the Cape 

Ann, Mass. (fig. lC), Anna, Ohio (fig. lE), and 

Attica N. Y. (fig. lF), areas the zones enclosed by 

the contour of maximum epicenter frequency are 

elongated, one end of the zone overlapping the gravity high in each area. In each of these last three 

areas, the event of maximum intensity is near but 

outside the locus of the gravity high. In the Cape 

Ann area (fig. lC) two events of approximately 

equal intensity are indicated; the second event is 

north of the seismicity zone, well removed from any 

notable gravity high. The strongest known earthquakes of this area, however, took place in the early 

and mid-18th century and are approximately located 

in the region east of the gravity high (Richard Holt 

written commun., 1976). In the Massena, N.Y. (fig. 

lD), and Baie St. Paul, Quebec (fig. lG), areas, the 

gravity highs are quite broad and have local highs 

superimposed. The maximum frequency contour is 

within the broad high; the events of maximum intensity are near but outside the superimposed 

gravity highs. 

In general the gravity anomalies, and hence their 

sources, tend to be peripheral to the earthquake 

maximum frequency contour. As this contour encloses, for the most part, the earthquake of maximum intensity this relation also indicates that the 

sources of the gravity highs are outside the region 

of maximum strain energy release. 

Figure 2 illustrates a more precise comparison 

of earthquake incidence and gravity anomalies for 

the New Madrid, Mo., and Charleston, S.C., areas. 

The earthquake plot for the New Madrid area (fig. 

2A) (Stauder and others, 1976) represents cumulative seismic events from June 29, 197 4, ·to March 

31, 1976. Events in the patterned zones are too close 

to be shown individually. In figure 2A, the earthquake epicenters are shown, for the most part, between the two prominent gravity highs north and 

south of the earthquake zone. A suggestion of an 

arcuate zone is seen southeast of the northern 

gravity high. Earthquakes are sparse or lacking in 

the immediate vicinity of the gravity highs. In the 

Charleston area (fig. 2B), the earthquakes (A. C. 

Tarr, this volume; C. E. Dutton, 1889) are east of 

the gravity high, which in detail has the shape of a 

sharp nose (Long and Champion, this volume). In 

both areas, depths to the earthquakes generally are 

less than 15 km (A. C. Tarr, this volume, William 

Stauder, oral commun., 1976). 

A POSSIBLE SOURCE MECHANISM 

In reviewing possible causal relationships between the gravity anomalies and the earthquakes, 

we have considered isostatic effects, intrusive activity, and anomalies in the distribution of regional 

stress. Isostatic effects would appear to be negligible 

as the loads represented by the gravity highs are 

small compared with surface loads imposed by 

topography. Intrusive activity might be a factor, 

but the anomaly in the Baie St. Paul area is associated with mafic masses of Precambrian age, seeming to rule out this possibility for at least one of 

the areas. Of the three factors, the most plausible 

one would seem to be a relationship between the 

distribution of the regional stress field and crustal 

lithology. Long (this volume), in reporting on the 

gravity high in the Charleston, S.C., earthquake 

area, suggested that stress amplification caused by 

lithologic contrast may be related to the occurrence 

of the earthquakes. 

In a study of the relations between rock type, 

stress, and mechanical failure, Byerlee and Brace 

(1968) concluded that serpentinized gabbro and 

dunite, limestone, and porous tuff failed by creep 

rather than by stick slip, a small-scale analog to 

earthquakelike failure. When one considers the 

gravity anomalies in the region of the earthquakes 

shown in figure 1, plausible sources of the anomalies 

are large masses of mafic and (or) ultramafic rock 

imbedded in a crust of generally more silicic rock. 

If these masses are serpentinized, they may, as suggested by Byerlee and Brace's results, deform continuously by creep rather than intermittently by 

stick slip as regional stress changes. The behavior 

of the stress in the host rock enclosing these masses 

might, therefore, be similar to that which takes 

place in a rigid plate near a hole or plastic plug. 

Timoshenko and Goodier (1951, p. 78-82) showed 
202 

0 

STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

A,New Madrid, Mo., area 

50 100 KILOMETERS 

B, Charleston, S. C., area 

EXPLANATION 

Bouguer gravity contour in milligals 

relative to sea level. Hachures 

indicate areas of relatively lower 

gravity 

• 

Location of a well-determined 

recent seismic event 

Area where seismic events are too 

closely grouped to be shown 

separately 

Isoseismal zone of the 1886 

Charleston, S. C., earthquake 

FIGURE 2.-Sketch maps showing gravity and contemporary epicenter data for the New Madrid, Mo., and Charleston, 

S. C., earthquake areas. Sources of gravity data are given in figure 1. Epicenter data in the New Madrid, Mo., 

area are from Stauder and others (1976). Epicenter data in the Charleston, S. C., area are from Tarr (this volume). Isoseismal boundary is from Dutton (1889). 
CORRELATION OF EARTHQUAKE CENTERS WITH MAFIC BASEMENT MASSES 203 

that stresses are localized at the margin of a hole 

in a plate and attain values several times those of 

the applied stresses. The thrust of this model is 

that large rock masses that have distinctive deformation contrasts may distort regional stress fields 

in much the same way that distinctive magnetization and density contrasts distort the magnetic and 

gravity fields. 

The role of serpentine in the mode of deformation of the San Andreas fault has been commented 

on by Allen (1968). He noted the "great abundance" 

of serpentine in the part of the fault zone characterized by creep and suggested that the creep may 

be related to the presence of serpentine. Although 

th geometry of the model described above and that 

of the San Andreas fault zone are greatly different, 

the two situations may be linked by the unusual deformation properties of serpentine. 

The stress concentration near holes in plates is 

dependent, among other things, on the direction and 

type of stresses, shapes of the holes, and on the relative location of plate boundaries. The arcuate zone 

(fig. 2A), for example, might be analogous to the 

high-stress zone that exists between a hole-in-a-plate 

and a nearby boundary. In the New Madrid, Mo., 

area, a boundary may be indicated by the southwesttrending zone for earthquakes that is southwest of 

the arcuate zone (fig. 2A). As such the zone would 

represent a fault influenced by the location of serpentinized mafic/ultramafic masses near either end. 

Similarly, the earthquakes near the eastern nose of 

the gravity anomaly in the Charleston region (fig. 

2B) might be analogous to high-stress zones associated with the ends of narrow cracks in plates when 

tension is applied normal to the crack. 

Undoubtedly, the model of the hole-in-a-plate, if 

valid, is greatly oversimplified, as the masses are 

more analogous to plastic plugs, and geologic bodies 

are three dimensional. Uncertainties are also present in other aspects of the data including the precise cause of the gravity anomalies, the directions 

and types of stress, the shapes and orientations of 

the anomalous masses, and the dimensions and 

boundaries of the host rock in which the anamalous 

masses are embedded. The only densities, however, 

that could reasonably explain the high positive gravity amplitudes, are those associated with mafic or 

ultramafic rocks. At present, no direct evidence of 

serpentinization exists. 

Perhaps the major question that arises about a 

relationship between mafic basement masses and 

stress-field distribution is why other regions in 

eastern North America underlain by large positive 

gravity anomalies do not have associated earthquake 

activity. Lack of serpentinization would be the most 

obvious answer. Other possible answers include the 

lack of a sufficiently large or changing regional 

stress field, or ina.ppropriate geometric relations between the causative masses and stress-field directions. 

The present evidence indicates, for example, that 

most, if not all ,the masses so far considered are at 

depths where they would be enclosed in highly 

competent basement. Mafic masses in softer, less 

competent sedimentary strata that yield more easily 

would presumably not give rise to the same stress 

concentrations. Possibly, also, the continental stress 

field, probably imparted by plate-tectonic conditions, 

is strongly zoned in a regional sense. The southwest 

alinement of earthquake areas from the Gulf of St. 

Lawrence to the New Madrid region and the similar 

trend in the broad earthquake region of the Appalachians indicated by the seismotectonic map of 

Hadley and Devine (1974) may be expressions of 

regional zoning of the continental stress field. 

In summary, a correlation has been shown to exist 

between major eastern North American earthquake 

areas and the presence of mafic-ultramafic masses 

as evidenced by gravity anomalies. It is not true, 

however, that all mafic-ultramafic masses are associated with earthquake areas. A model has been proposed whereby stress is concentrated near the margin of these masses in much the same manner as 

stress concentrations take place near the margins of 

defects or holes in plates under stress. This model 

has major implications in the consideration of eastern North America seismicity, as it suggests. that 

larger earthquakes are restricted to relatively local 

areas. The model may also explain why major 

through-going faults of continental or subcontinental dimensions are not evident in eastern North 

America. Presumably the faults associated with the 

localized stress zones would be similarly localized 

and of relatively small dimensions, perhaps 10 km 

long or less. 

REFERENCES CITED 

Allen, C. R., 1968, The tectonic environments of seismically 

active and inactive areas along the San Andreas fault 

system, in Dickinson, W. R., and Grantz, Arthur, eds., 

Proceedings of Conference on geologic problems of San 

Andreas fault system: Stanford Univ. Pub. Geol. Sci., 

v. 11, p. 70-80. 

American Geophysical Union, Special Committee for the 

Geophysical and Geological Study of the Continents, 

1964, Bouguer gravity anomaly map of the United 
204 STUDIES RELATED TO CHARLESTON, SOUTH CAROLINA, EARTHQUAKE OF 1886 

States (exclusive of Alaska and Hawaii): Washington, 

D.C., U.S. Geol. Survey, 2 sheets, scale 1:2,500,000. 

Byerlee, J. D., and Brace, W. F., 1968, Stick slip, stable 

sliding, and earthquakes-Effect of rock type, pressure, 

strain rate, and stiffness: Jour. Geophys. Research, v. 

73,no. 18,p. 6031-6037. 

Dutton, C. E., 1889, The Charleston earthquake of August 

31, 1886: U.S. Geol. Survey Ninth Ann. Rept., p. 203-

528. 

Hadley, J. B., and Devine, J. F., 1974, Seismotectonic map of 

the Eastern United States: U.S. Geol. Survey Misc. 

Field Studies Map MF-620. 

Heiskanen, W. A., and Uotila, U. A. K., 1956, Gravity survey 

of the State of Ohio: Ohio Div. Geol. Survey, Rept. Inv. 

30, 34 p. 

Kane, M. F., Simmons, Gene, Diment, W. H., Fitzpatrick, 

M. M., Joyner, W. B., and Bromery, R. W., 1972, 

Bouguer gravity and generalized geologic map of New 

England and adjoining areas: U.S. Geol. Survey 

Geophys. Inv. Map GP-839. 

Nuttli, Otto, W., 1973, The Mississippi Valley earthquakes 

of 1811 and 1812: intensities, ground motion, and magnitudes, Seismol. Soc. America Bull., v. 63, no. 1, p. 227-

248. 

Revetta, F. A., and Diment, W. H., 1971, Simple Bouguer 

gravity anomaly map of western New York: New York 

State Mus. Sci. Service, Geol. Survey, Map and Chart 

Series 17. 

Stauder, William, Schaefer, Stephen, Best, John, and Morrisey, S. T., 1976, 1 January-31 March 1976: St. Louis 

Univ. Southeast Missouri Regional Seismic Network 

Quart. Bull. 7, 25 p. 

Thompson, L. G. D., and Garland, G. D., 1957, Gravity 

measurements in Quebec (south of latitude 52° N): 

Ottawa Dominion Observatory Pub., v. 19, no. 4, p. 

111-167. 

Timoshenko, S., Goodier, J. N., 1951, Theory of elasticity: 

New York, McGraw-Hill, 506 p. 



\