A Search for Paleoliquefaction and 

Evidence Bearing on the Recurrence Behavior 

of the Great 1811-12 New Madrid Earthquakes

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1538-H
Cover. Gray, shaded-relief map of magnetic anomaly data. Map area includes parts of 

Missouri, Illinois, Indiana, Kentucky, Tennessee, and Arkansas. Illumination is from the 

west. Figure is from Geophysical setting of the Reelfoot rift and relations between rift 

structures and the New Madrid seismic zone, by Thomas G. Hildenbrand and John D. 

Hendricks (chapter E in this series).
A Search for Paleoliquefaction and 

Evidence Bearing on the Recurrence Behavior 

of the Great 1811-12 New Madrid Earthquakes

By Steven G. Wesnousky and Lisa M. Leffler

INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE 

Edited by Kaye M. Shedlock and Arch C. Johnston

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1538-H

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1994
US. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

For Sale by U.S. Geological Survey, Map Distribution

Box 25286, MS 306, Federal Center

Denver, CO 80225

Any use of trade, product, or firm names in this publication is for descriptive purposes only and 

does not imply endorsement by the U.S. Government

Library of Congress Cataloging-in-Publication Data

Wesnousky, Steven G.

A search for paleoliquefaction and evidence bearing on the recurrence behavior of the 

great 1811-12 New Madrid earthquakes / by Steven G. Wesnousky and Lisa M. Leffler.

p. cm.—(Investigations of the New Madrid seismic zone ; H) 

(U.S. Geological Survey professional paper ; 1538-H) 

Includes bibliographical references. 

Supt.ofDocs.no. ; I 19.16: 1538H

1. Earthquakes—Missouri—New Madrid Region. 2. Soil liquefaction— 

Missouri—New Madrid Region. I. Leffler, Lisa M. II. Title. III. Series. 

IV Series: U.S. Geological Survey professional paper ; 1538-H. 

QE535.2.U6159 1994vol. H 

551.2'2'09778985 s—dc20

[551.2'2'09778985] 93-50779

CIP
CONTENTS

Abstract................................................................................................................................. HI

Introduction.......................................................................................................................... 1

Opportunity........................................................................................................................... 2

Methodology......................................................................................................................... 3

Observations......................................................................................................................... 4

Ditch No. 12............................................................................................................... 4

Buffalo Creek Ditch.................................................................................................... 8

Stateline and Belle Fountaine Ditches........................................................................ 14

Exit 4 Ditch................................................................................................................. 15

Discussion............................................................................................................................. 16

Conclusions.......................................................................................................................... 23

Acknowledgments................................................................................................................ 23

References Cited................................................................................................................... 24

FIGURES

1-2. Maps showing:

1. Size of the New Madrid earthquakes of 1811-12 compared to other major historical U.S. earthquakes .... H2

2. Location of earthquake epicenters in the New Madrid seismic zone............................................................ 2

3. Photograph of sands that were liquefied and extruded onto the surface during the 1811-12

earthquake sequence.............................................................................................................................................. 3

4. Aerial photograph showing nature of 1811-12 liquefaction................................................................................. 4

5-6. Maps showing:

5. Generalized Quaternary geology of the upper Mississippi Embayment....................................................... 5

6. Drainage ditches in the area of the St. Francis drainage basin ..................................................................... 6

7. Photograph of a section of Buffalo Creek ditch.................................................................................................... 6

8. Map of reexcavated ditches in the area of Blytheville, Ark.................................................................................. 7

9. Photograph and schematic diagram of exposure along Ditch No. 12 ................................................................... 8

10. Photograph of exposure along Ditch No. 12......................................................................................................... 9

11. Aerial photograph: Manila North, Arkansas, orthophotoquad.............................................................................. 10

12. Aerial photograph showing parts of Ditch No. 12 and Buffalo Creek ditch......................................................... 11

13. Schematic diagram of south side of section of Ditch No. 12................................................................................ 12

14-16. Photograph and schematic diagram of:

14. Site la, Ditch No. 12..................................................................................................................................... 13

15. Site Ib, Ditch No. 12..................................................................................................................................... 14

16. Site 2, Ditch No. 12....................................................................................................................................... 15

17. Photographs of site 2, Ditch No. 12 ..................................................................................................................... 16

18. Photograph and schematic diagram, site 3, Ditch No. 12 ..................................................................................... 18

19. Photomosaic of site 3, Ditch No. 12...................................................................................................................... 19

20. Photographs and schematic diagram of sand dikes and sills, site 4, Buffalo Creek ditch..................................... 20

21. Photomosaic showing part of site 4, Buffalo Creek ditch..................................................................................... 21

22. Oblique photograph and schematic diagram, site 5, Buffalo Creek ditch............................................................. 22

23. Photographs of Buffalo Creek ditch showing rapid revegetation and erosion following reexcavation................. 23

24. Aerial photograph: Arbyrd, Missouri, orthophotoquad......................................................................................... 26

25. Aerial photograph showing area around sites 6 and 7, Buffalo Creek ditch......................................................... 27

26. Schematic diagram of east side of section of Buffalo Creek ditch adjacent to crossing of Highway 164............ 28

III
IV CONTENTS

27-28. Photograph and schematic diagram of:

27. Site 6, Buffalo Creek ditch.............................................................................................................................H29

28. Part of site 6, Buffalo Creek ditch.................................................................................................................. 29

29. Photographs and schematic diagram, site 6, Buffalo Creek ditch.......................................................................... 30

30. Aerial photograph showing sites 8 and 9, Buffalo Creek ditch.............................................................................. 31

31-32. Photograph and schematic diagram of:

31. Site 8, Buffalo Creek ditch............................................................................................................................. 32

32. Site 9, Buffalo Creek ditch............................................................................................................................. 33

33. Photograph showing reexcavation of ditch ............................................................................................................ 34

34. Aerial photograph: Portion of the Denton, Missouri, orthophotoquad.................................................................. 35

35. Photograph and schematic diagram, site 10, Belle Fountaine ditch....................................................................... 36

36-37. Photographs of:

36. Part of exposure, site 10, Belle Fountaine ditch ............................................................................................ 37

37. View to northwest from Exit 4 ditch near Interstate 55................................................................................. 38

38. Aerial photograph: Portion of the Steele, Missouri, orthophotoquad.................................................................... 39

39. Aerial photograph showing site 11, Exit 4 ditch.................................................................................................... 40

40. Photograph and schematic diagram, site 11, Exit 4 ditch...................................................................................... 41

41. Graph of average repeat time versus body-wave magnitude for earthquakes in the New Madrid seismic zone,

1816-1983.............................................................................................................................................................. 42

TABLE

1. The New Madrid earthquake sequence.................................................................................................................. H2
A SEARCH FOR PALEOLIQUEFACTION AND EVIDENCE

BEARING ON THE RECURRENCE BEHAVIOR OF THE GREAT

1811-12 NEW MADRID EARTHQUAKES

By Steven G. Wesnousky1 and Lisa M. Leffler2

ABSTRACT

The New Madrid earthquake sequence consisted of four 

principal events, each of estimated surface-wave magnitude 

> 8, occurring on three separate days between December 

1811 and February 1812. Although arguably the largest historical earthquakes within the conterminous United States, 

data on the expected repeat time of such events are few and 

generally equivocal.

The U.S. Army Corps of Engineers maintains a large 

network of major drainage ditches within the St. Francis 

drainage basin for flood control and land reclamation. The 

Corps recently reexcavated tens of kilometers of these 

ditches in the area of the southern limb of the New Madrid 

seismic zone, where pervasive liquefaction occurred during 

the 1811-12 earthquake sequence. We have examined the 

freshly excavated ditches for geologic evidence of liquefaction features that predate the 1811-12 earthquakes. Radiocarbon dates indicate the resulting vegetation-free exposures 

afford examination of the last 5,000 to 10,000 yr of geologic 

record. Historical earthquake statistics have previously been 

the basis to estimate the repeat time of New Madrid earthquakes at between about 550 and 1,100 yr. In contrast, any 

evidence of paleoliquefaction seen during our search was 

equivocal, and no evidence of a widespread, prehistoric liquefaction event as occurred in 1811-12 was observed. 

Hence, although negative evidence is a less-than-desirable 

basis for interpretation, an implication of our search is that 

the recurrence of 1811-12-type earthquake disturbances is 

on the order of 5,000 to 10,000 yr or more.

'Center for Neotectonic Studies, University of Nevada, Reno, Reno, 

NV 89557.

2Center for Earthquake Research and Information, Memphis State 

University, Memphis, TN 38152 (currently at Department of Geological 

Sciences, Northwestern University, Evanston, IL 60201).

INTRODUCTION

The New Madrid sequence of earthquakes consisted of 

four principal events, each of estimated surface-wave magnitude > 8, and occurred on the days of December 11, 1811, 

and January 23 and February 7,1812 (table 1). The distribution of isoseismals (Nuttli, 1973), the recognition of a distinct zone of seismicity within the region of largest 

isoseismals (Stauder and others, 1976; Stauder, 1982), and 

the association of extensive liquefaction features that indicate severe ground motion proximal to that zone of seismicity (Fuller, 1912; Heyl and McKeown, 1978; Obermeier, 

1984) lend strong credence to the argument that the source 

of the 1811-12 earthquake sequence was the now wellknown New Madrid seismic zone (figs. 1 and 2). Although 

arguably the largest historical earthquakes within the conterminous United States, data bearing on the expected repeat 

time for earthquakes such as the 1811-12 events remain few 

and are generally equivocal.

The New Madrid seismic zone has no clear and unambiguously expressed fault trace at the surface (Schweig and 

Marple, 1991) and, hence, it is not known if the 1811-12 

earthquakes produced a single through-going zone of surface faulting, as is commonly observed for large earthquakes in the Western United States. However, the 1811-12 

earthquakes were associated with pervasive liquefaction 

phenomena that was concentrated in a zone approximately 

20-50 km wide and that trends southwestward for a distance of about 150 km through portions of Missouri, Arkansas, and Tennessee (fig. 2). Extruded sand covers as much 

as 25 percent of the land surface in much of this area. 

Expressed as light-colored, commonly irregular shapes on 

the dark-brown soils of the Mississippi Embayment, liquefied sand that was extruded during the 1811-12 earthquakes 

is still readily visible today both in the field (fig. 3) and on 

recent aerial photographs (fig. 4). It seems certain that the 

occurrence today of similar-sized earthquakes in the New 

Madrid region would cause equally pervasive liquefaction.

Hi
H2 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

Analogously, if similar events occurred in the past, we can 

reasonably expect similar deformations to be preserved in 

the geologic record. A systematic search for such geological 

evidence of pre-1811-12-type earthquakes is the basis of 

this paper.

OPPORTUNITY

Much of the New Madrid seismic zone lies within the 

St. Francis drainage basin of the Mississippi Embayment 

(fig. 2). The geology, geomorphology, and Quaternary history of the Mississippi Embayment have been described 

previously by Saucier (1974) and, more locally, by Guccione (1987). The St. Francis drainage basin has little 

topography (e.g., fig. 3), a high water table, and poor drainage. The surface deposits consist primarily of late Wisconsin glacial outwash deposited by braided streams. The 

transition of the Mississippi River drainage from a braidedstream system to the current meandering mode of deposition has been estimated to have taken place between about 

10 to 6 ka ago at about the latitude of Memphis (Saucier, 

1974). Hence, the majority of evidence for liquefaction 

rests upon abandoned late Wisconsin braided-stream terraces (fig. 5), which have been stable surfaces with only 

minor localized sedimentation since the formation of the 

Holocene Mississippi River meander belt.

Table 1. The New Madrid earthquake sequence.

[Surface wave (Ms) and body wave (raj,) magnitude estimates taken from Street and 

Nuttli (1984) as reported by Hopper (1985). Leaders (--) indicate no data]

91°

Date

Dec. 16, 1811

Dec. 16, 1811

Jan. 23, 1812

Feb. 7, 1812

Local time

2:15 a.m.

8:15 a.m.

9:00 a.m.

3:45 a.m.

Ms

8.6

—

8.4

8.7

mt

7.2

7.0

7.1

7.3

SAN FRANCISCO,

SAN FERNANDO, 

1971

CHARLESTON, 

1886

Figure 1. The large size of the 1811-12 earthquakes compared to 

other major historical U.S. earthquakes is shown by the relative extent of Modified Mercalli (MM) VI and VII (hachured) isoseismals 

for the respective earthquakes (Modified from Hamilton and 

Johnston, 1990).

O 4.0<M<5.0

o 3.0<M<4.0

o 2.0<M<3.0

o 0.0<M<2.0

36° -

Figure 2. The New Madrid seismic zone is defined by an alignment of earthquake epicenters (circles scaled according to magnitude) that extends southwestward from near Illinois to northwest of 

Memphis, Tenn. Analysis of aerial photographs by Heyl and 

McKeown (1978) and Obermeier (1989) show that the shaded area 

was characterized by extensive liquefaction during the 1811-12 

New Madrid earthquakes. The curved solid line marks the northern 

extent of the Mississippi Embayment.

The U.S. Army Corps of Engineers maintains a large 

network of major drainage ditches throughout the St. Francis 

drainage basin for flood control and land reclamation (fig. 

6). Two factors provided us a unique opportunity to search 

for evidence of paleoliquefaction along these ditches. The 

Mississippi Embayment and associated drainages were subject to an unusual drought during the late 1980's, with the 

record lowest stage of the Mississippi River being recorded 

during the summer of 1988. Simultaneously, the U.S. Army 

Corps of Engineers embarked on a program to reexcavate 

and widen several of the existing ditches. The combination 

of drought and excavation provided tens of kilometers of relatively vegetation-free exposures along the ditches that were 

used to characterize liquefaction features preserved in the 

geologic record (fig. 6).

Figure 7 is a photograph of one of the reexcavated 

ditches. Both sides of the ditch were heavily vegetated prior 

to reexcavation, as seen on the far side of the ditch. During 

reexcavation, the vegetation on one side of the ditch is
RECURRENCE BEHAVIOR OF THE GREAT 1811-12 NEW MADRID EARTHQUAKES H3

Figure 3. Liquefied sands that were extruded onto the surface during 1811-12 are still clearly visible as light-colored, circular patches on 

the dark-brown soil of this farm field at the intersection of Stateline (Main) ditch and State Highway 151 in northeastern Arkansas. The lack 

of significant relief shown here is characteristic of the entire study region.

removed, resulting in fresh exposures about 2-3 m high. 

Unless freshly excavated, the dense vegetation along the 

ditches completely obscures virtually all exposures. The purpose of this paper is to describe the character of liquefaction 

that we observed in these exposures and the implications of 

our observations on the expected recurrence time of great 

1811-12-type earthquakes. We focused our efforts on the 

region and ditches shown in figure 8. Within this region, we 

concentrated on documenting the location and detailed character of liquefaction features along the ditches.

METHODOLOGY

In the ditches we examined, the upper 2 to 3 m of 

braided-stream-terrace stratigraphy observed is quite simple 

and consists of fine to coarse sand overlain by a clay and siltrich top stratum of low permeability. However, the top stratum is not homogeneous but tends toward either of two distinct compositions.

One composition is a distinct cap of clay overlying the 

fine to coarse sand. Top stratum of this nature is illustrated 

by the photograph and accompanying schematic diagram in 

figure 9. Where the base of the clay top stratum is visible, it 

is invariably in sharp contact with the underlying sand. The 

tabular cross-bedding and thin interbeds of clay observed 

beneath the clay cap in figure 9 are consistent with deposition in a braided-stream environment. Top stratum of this

character is interpreted to reflect deposition of overbank or 

slackwater clay and silt during flood stages of the Mississippi River and its tributaries following abandonment of the 

braided-stream terrace (e.g., Saucier, 1974; Obermeier, 

1989).

The second kind of top stratum is a generally distinct, 

well-developed soil profile (fig. 10). The typical profile is 

capped by a 15- to 25-cm-thick A horizon that grades downward into a distinct B horizon. The B horizon is generally > 

1 m thick and, where sufficiently exposed, is observed to 

grade into unaltered silty sand or sand (C horizon). The characteristic profile is generally developed on a silty to sandy 

parent material, and pedogenesis appears to be dominated by 

the alteration of the parent silt and sand and translocation of 

clays through the soil column. Top stratum of this character 

appears associated with interfluves or bars of the original 

braided-stream surface.

Regardless of its origin or character, the top stratum 

observed forms a clay-rich, liquefaction-resistant layer generally more than 1 m thick that overlies water-saturated fine 

to coarse sand. Indeed, this stratigraphy provided ideal conditions for the tremendous liquefaction effects reported for 

the 1811-12 earthquakes (Fuller, 1912; Saucier, 1977; 

Obermeier, 1989). Thus, our search for evidence of 

paleoliquefaction initially entailed walking the entire length 

of the ditches shown in figure 8, looking for breaches or 

breaks in the top and bottom of the top stratum to systematically identify sites of sandblows, dikes, and rifts. Places
H4 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

Figure 4. The pervasive nature of 1811-12 liquefaction is clearly shown by the abundant sandblows and sand rifts seen in this 

1940 aerial photograph. The town of Dell, Ark., is within the New Madrid seismic zone and is located in the lower right quarter 

of the photograph. North is up on photograph.

where liquefaction phenomena were concentrated were later 

logged in detail to document the general character of liquefaction features and permanently record their location for 

later study. At our detailed study sites, we cleared the exposure by hand shovel or backhoe, logged it in greater detail, 

and examined it for evidence of prehistoric liquefaction. 

Because our emphasis was on identifying pre-1811-12 liquefaction, we limited analysis of individual geologic units 

to brief field descriptions. The results are described in following sections of this paper.

OBSERVATIONS 

DITCH NO. 12

Ditch No. 12 is located west of Big Lake Wildlife Refuge in Arkansas (fig. 8) and trends east-west, which is 

roughly normal to the general flow direction during deposition of the braided-stream terraces (fig. 11). A 1939 aerial

photograph shows numerous sand rifts or dikes crossing the 

ditch (fig. 12). A schematic diagram of about 1 km of the 

ditch is shown in figure 13. The numerous breaches in the top 

stratum further attest to the pervasive nature of liquefaction 

near the ditch.

The exposure shown in figure 14 is site 1 in figure 13. 

Initial examination of this exposure showed the clay top stratum overlying and in sharp contact with tabular cross-bedded, fine to medium sand (unit A). However, further 

examination revealed clear evidence of liquefaction beneath 

the top stratum. The sand of unit C flowed upward through 

the section to the base of the overlying clay, but it was unable 

to propagate through the impermeable top stratum and 

flowed horizontally, forming thin sills in the basal part of the 

clay. Thus, the top stratum behaved as an impenetrable cap 

in this instance. In addition, the thin anastomosing character 

of bedding within the sand unit B is likely due to the liquefaction of sand to the point of incipient mass flow. The gradual degradation of cross-bedding laminations from east to
RECURRENCE BEHAVIOR OF THE GREAT 1811-12 NEW MADRID EARTHQUAKES H5

•.... KENTUCKY 

:. '.TENNESSEE

EXPLANATION

Modern Mississippi meander belt

Older Mississippi meander belts

Late Wisconsin braided 

stream terraces

Early Wisconsin braided 

stream terraces

Loess deposits

Figure 5. Generalized Quaternary geologic map of the upper Mississippi Embayment (adapted from Saucier, 1974). Sand ejected during 

the 1811-12 earthquakes comprise from greater than 1 to 25 percent of the surficial deposits in a region (shown by asterisk pattern) that 

extends from north of New Madrid, Mo., southwestward to Marked Tree, Ark. (Obermeier, 1989).

west across unit A may also be evidence of incipient liquefaction. Indeed, we seldom found evidence of original and 

undisturbed bedding within the sand immediately underlying 

the top stratum. More commonly, the sand beneath the top 

stratum commonly contained disturbed bedding or flow 

structures that we attributed to liquefaction. Site Ib (fig. 13) 

is another example that illustrates the disturbed character of 

bedding in the sand (fig. 15).

Site Ib is about 10 m west of site la (fig. 13), and details 

of the exposure are shown in figure 15. Here, the top stratum 

is unbroken and consists of a generally impermeable clay 

and clay loam. The underlying sand shows more evidence of 

liquefaction as compared to site la. No evidence of undisturbed original bedding is observed. The disrupted and generally anastomosing character of bedding within the 

underlying sand (unit AS, fig. 15) is interpreted to represent 

incipient flow due to liquefaction. In turn, the sill of white 

sand (unit WS) is apparently the result of impeded upward

flow of sand due to the impermeable and unbroken nature of 

the overlying clay top stratum (unit TS). A similar interpretation may explain the sill of lignite sand (unit LG). Pressures were sufficient nearby to breach the top stratum and 

result in the expulsion of sand (e.g., unit WS) and lignite 

(e.g., unit LG) in the vicinity of this site—this is evidenced 

by the presence of extruded sand of similar composition on 

the surface (unit SC). Site 2, located about 400 m east of this 

site, shows the character of such a break in the top stratum.

The exposure at site 2 is capped by about 1 m of artificial levee fill (fig. 16). Beneath the levee fill is about 1 to 2 

m of clean fine to medium sand. The sand is fed by a dike at 

the base of the exposure. Soil on the sand is immature, consisting of a 5- to 10-cm-thick A horizon and no significant B 

horizon. The immaturity of the soil profile on the ejected 

sand (fig. 17A) suggests that the deposit on which it formed 

is very young, most likely a result of the ejection of sand to 

the surface in 1811-12. The internal structure of the ejected
H6 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

50 KILOMETERS 

I

Figure 6. The U.S. Army Corps of Engineers maintains a network of drainage ditches (open lines) throughout the St. Francis 

drainage basin. Ditches that were reexcavated and widened during the course of our study and examined for evidence of paleoliquefaction are shown by solid lines. Areas where 1811-12 

liquefaction deposits still comprise > 1 percent and > 25 percent 

of the surface area are shaded by light and dark stippling, respectively. The principal area that is discussed in this paper is outlined 

by the box. Circled numbers 1 through 5 correspond to sections 

of Ditch No. 9, Little River, Honey Cypress ditch, Blackfish Bayou, and the St. Francis River, respectively. See figure 8 for detailed map of study area.

Figure 7. Photograph of a section of Buffalo Creek ditch taken 

during the spring of 1987, shortly after reexcavation by the U.S. 

Army Corps of Engineers. The vegetation on one side of the 

ditch was removed during reexcavation, resulting in clean exposures about 2 to 3 m high. The water level in these ditches may 

reach the rim or overflow it during the heaviest winter storms. 

Flow is limited during the summer but, even during the severe 

drought conditions of 1988, spring flow from the sides of ditches 

is generally maintained.

sand shows two, distinct, thin layers of silt and lignite (fig. 

17A). The thin layers probably represent brief hiatuses of the 

sand-blow eruption and the attendant settling of finer 

grained, lighter materials; the lack of any soil development 

or oxidation indicates that the layers were exposed for a relatively brief time. Saucier (1989) interpreted similar features at a liquefaction site in northeastern Arkansas in a 

similar manner and suggested that the distinct packages of 

sand may represent individual events of the 1811-12 New 

Madrid earthquake sequence.

In contrast to the immature soil developed on the 

ejected sand at site 2, the buried surface on which the ejected 

sand rests is characterized by a much more well developed 

soil profile, consisting of a 10- to 15-cm-thick A horizon 

(2Ab) and a B horizon (2Bb) that is about 1 m thick (fig. 

17Q. The maturity of the 2Ab-2Bb soil profile suggests that 

the surface on which the sand was ejected was stable for a 

relatively long period of time prior to being breached by liquefied sand in 1811-12. The buried 2Ab-2Bb profile grades 

further downward into clean sand. Unique to this site, however, we observed that the buried sand rests in sharp contact 

with another buried surface on which the 3Ab-3Bb soil profile is developed (figs. 16 and 17C). A possible interpretation is that the 2Ab-2Bb profile is developed on sands 

ejected at the time of a prehistoric earthquake. A sand fissure 

feeding the buried sand and breaking the 3 Ab horizon would 

be conclusive evidence of a liquefaction origin for the sand. 

However, such was not observed along the exposed sand3Ab contact, and we followed this contact for about 15 m to
RECURRENCE BEHAVIOR OF THE GREAT 1811-12 NEW MADRID EARTHQUAKES H7

^ Western limit of Holocene 

\ Mississippi meander belt

Figure 8. Map of reexcavated ditches (thick solid lines) where we concentrated on documenting the location and character of liquefaction 

features. Detailed studies were conducted in parts of Ditch No. 12, Buffalo Creek ditch, Stateline ditch, and the Belle Fountaine ditch. The 

western limit of the Holocene Mississippi meander belt is shown by dashed line. Area of this figure is shown in figure 6 as the "principal 

area of study." Circled numbers and letters are State and County Highway numbers.

the west of the vent until it dipped beneath the water table. 

Also, paleomagnetic sampling of unit 2Bb shows it to maintain a continuous secular variation curve, suggesting that it 

was emplaced gradually over a period of time (Stephen Salyards, Southern California Earthquake Center, University of 

California at Los Angeles, oral, commun., 1993). Hence, 

although an interpretation for the buried sand unit invoking 

liquefaction is tempting, an alluvial origin for the buried 

sand cannot be ruled out.

Another break in the top stratum along Ditch No. 12 is 

labeled site 3 in figures 12 and 13 and is shown in figure 18. 

The top stratum at this location is very dark clay and is 

sharply interrupted by the intrusion and ejection of very light 

gray, locally oxidized, very fine to fine-grained sand. Again, 

the soil profile developed on the extruded sand is immature, 

composed of a thin A horizon and virtually no B horizon. Its 

weak development indicates that it most likely formed since 

1811-12. Again, a very well developed soil is present on the

surface broken by the liquefied sand, suggesting considerable antiquity and stability to the surface on which it is developed. The composite photographs of the site in figure 19 

further illustrates both the character of soil development on 

the top stratum and the ubiquitous and pervasive flow structures that characterize the liquefied sand.

Brown clay loam forms the lower meter of the top 

stratum to the east of the extruded sand at site 3 (fig. 18). 

The light-gray silty clay at the top of the loam may be a 

buried E horizon associated with an older surface. Large 

pieces of bark-covered wood were recovered from two 

sites within the clay loam (fig. 18) and were tentatively 

identified as bald cypress (Donna Christensen, U.S. Forest Products, written commun., 1990). The two samples 

have conventional radiocarbon dates of 5,090160 and 

11,100±100 radiocarbon yr B.P., respectively (Beta Analytic Inc.; lab sample numbers Beta-38311 and Beta41984). The wood immediately overlying the liquefied
H8 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

EAST WEST

sand has an age of 11,100±100 radiocarbon yr B.P. Thus, 

the overlying soil profiles represent some 5,000 to 10,000 

yr of development, and our observations here show no evidence of prehistoric liquefaction during that same period 

of time.

BUFFALO CREEK DITCH

The Buffalo Creek ditch, which trends northerly 

through the area of study (fig. 8), occupies an abandoned, 

relict channel on the braided-stream terrace surface (fig. 11). 

We excavated and logged several sites along the ditch.

Site 4 is located about 150 m south of the ditch crossing with State Highway 77 between Manila and Leachville, 

Ark. (fig. 11). The location of the site with respect to the 

local geomorphology is illustrated by the aerial photograph 

in figure 12. The stratigraphy at the site (fig. 20) consists 

of a dark-brown A horizon resting on a light-gray B horizon composed of FeO-stained loam. Downward, the B 

horizon grades into unaltered, fine- to medium-grained 

alluvial sand interbedded with thin clay beds. Sand dikes 

and sills (units SI, S2, and S3) intrude and disrupt the host 

stratigraphy (fig. 20).

o n

1 -

2 -

^Ground surface

Ditch spoils

and 

slope wash

Gray Clay

Figure 9 (facing column and above). Photograph and schematic 

diagram of an exposure along Ditch No. 12, Arkansas, illustrating 

the nature of the top stratum or "clay cap" along many of the drainage ditches. String grid in photograph indicates 1-m intervals. In 

this exposure, a thick clay cap overlies a sequence of tabular crossbedded sand and thin interbeds of clay. The tabular cross-beds are 

consistent with deposition in a braided-stream environment. The 

sand of unit A is fine to medium grained, stained reddish yellow, 

and contains distinct topset, foreset, and bottomset beds. The lightgray, fine- to medium-grained sand of unit B contains faint, undulatory laminations. See text for further discussion.

Site 4 provides insight into both the mechanics of the 

liquefaction process as well as the past history of liquefaction events at the site (fig. 20). Impermeable clay layers play 

a controlling role in the liquefaction process, limiting the 

upward migration of liquefied sand. This is demonstrated by 

the presence of sand sills (stippled) that extend horizontally 

from the central pipe to distances of approximately 5 m or 

more, each directly beneath relatively non-liquefiable clay 

or clay-rich layers. Cross-cutting relations further indicate 

several phases of sand injection whereby the injection of 

unit SI was followed by units S2 and S3, respectively. The 

sharpness of the cross-cutting relations and the relative ages 

of the respective sand units are shown more clearly by the 

larger scale photomosaic shown in figure 21.

Although cross-cutting relations reveal evidence of 

three distinct episodes or phases of liquefaction, there is no 

evidence at site 4 to suggest that the hiatus between 

emplacement of units SI, S2, and S3 spanned any significant
RECURRENCE BEHAVIOR OF THE GREAT 1811-12 NEW MADRID EARTHQUAKES H9

amount of time. Additionally, the sand (unit S3) that did 

reach the surface is characterized by the absence of significant soil development. The simplest interpretation of this is 

similar to the previous exposure: that is, the liquefied sand is 

the result of the 1811-12 earthquake sequence, and, possibly, 

the separate units of liquefied sand may be attributed to the 

separate earthquakes of that same sequence.

Site 5 is several hundred meters north of site 4 and 

about 150 m north of the Highway 77 bridge crossing (figs. 

8, 11, and 12). The top stratum is composed of a well-developed soil profile (fig. 22) similar in color and composition to 

that observed at site 4. Unlike site 4, the liquefied sand forms 

a clear break in the top stratum and is responsible for venting 

more than 1 m of white, fine to medium sand onto the surface. Again, the soil on the top stratum is much more mature 

compared to soil on the ejected sand (fig. 22). In this case, 

pedogenesis since ejection of the sand has formed an A horizon only a few centimeters thick and virtually no B horizon. 

The incipient soil development on the extruded sand indicates the youthfulness of the ejected sand, and, hence, our 

interpretation is that liquefied sand vented in 1811-12.

The magnitude of the liquefaction at site 5 is further 

illustrated by the upper photograph of figure 23. The ejected 

sand forms a layer that is as much as 2 m thick and extends 

3(M€ m along the ditch. The lower photograph shows the 

condition of the ditch at site 5 about 4 months after it was 

excavated and logged. The vegetation has seriously 

degraded the exposure. This comparison illustrates the 

unique opportunity provided by the excavations of the Corps , 

of Engineers.

Buffalo Creek ditch continues north of site 5 (fig. 24), 

as does evidence for 1811-12 liquefaction. An aerial photograph of the ditch near Highway 164 is shown in figure 25. 

Figure 26 is a schematic diagram of about 3/4 km of ditch 

where it crosses Highway 164. Breaches in the top stratum 

are common and, although remnant cross-beds are present, 

the sand beneath the unbreached top stratum more typically 

exhibits secondary flow structures that can most likely be 

attributed to liquefaction. A significant break in the top 

stratum is located 400 m south of the Highway 164 bridge 

and is labeled as site 6 in both the aerial photograph of the 

site (fig. 25) and the schematic diagram (fig. 26). A photograph and schematic diagram of the exposure at site 6 are 

shown in figure 27.

Site 6 and site 2 in Ditch No. 12 (fig. 16) share strong 

similarities. The photograph and schematic diagram (fig. 

27) show a large breach in the top stratum. The top stratum, 

which is defined by a well-developed soil profile, represents a relatively long period of stability (fig. 28). In contrast, the sand that was extruded through the top stratum 

has only a 1-cm-thick A horizon and virtually no B-horizon 

development. Similar to sites 2 and 4, the weak soil on the 

extruded sand is consistent with the sand blow forming in 

1811-12. We found no relations that suggested older episodes of liquefaction.

I

B;hort2on

'

Hfc

1st

Figure 10. Photograph of an exposure along Ditch No. 12, Arkansas, illustrates the nature of the top stratum or "clay cap" 

along many of the ditches. The clay cap has a well-developed 

soil, which is formed on a silty top stratum. A typical profile is 

capped by a dark-brown A horizon, 15-25 cm thick, which 

grades downward into a thick B horizon composed of a light 

brownish gray, silty loam with distinct strong brown mottling due 

to oxidation. Local farmers refer to the material as "buckshot 

clay" because it contains numerous, circular iron-oxide concretions. String grid indicates 1-m intervals.

Site 7, located to the north of the Highway 164 bridge 

crossing (fig. 26), illustrates the character of the top stratum 

and the intensity of liquefaction-induced disruption beneath 

unbreached parts of the top stratum (fig. 29). The blocky clay 

of the top stratum is underlain by a very fine, sandy loam 

(unit B, fig. 29). The silty loam is cut by two distinct sand 

units, SI and S2, respectively. The intruding sand (unit S2) 

has torn away part of the overlying clay top stratum. The 

exposure illustrates the erosion that occurs at the base of the 

top stratum due to the liquefaction and flow of underlying 

sand. Unit SI is a very fine to medium-grained, light-gray 

sand. The sand of unit S2 is similar in grain size but white in 

color, indicating that the two units had different sources.
H10 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE 

i

Figure 11. Manila North, Arkansas, orthophotoquad showing geomorphic character of braided-stream surface on which Buffalo Creek ditch and Ditch No. 12 are excavated. Buffalo Creek ditch is excavated along the axis of a relict channel. In contrast, 

Ditch No. 12 cuts across an interfluvial portion of the braided-stream terrace between Buffalo Creek ditch and Big Lake. Total 

elevation difference between relict channels and interfluve regions is about 1 m. Specific excavations are marked by site numbers. North is up on photograph.
RECURRENCE BEHAVIOR OF THE GREAT 1811-12 NEW MADRID EARTHQUAKES Hll

Figure 12. A 1939 aerial photograph showing part of Ditch No. 12 and Buffalo Creek ditch. Patches of light-colored 

ground mark numerous rifts or blows of liquefied and ejected sand in the vicinity of the ditches. Arrows locate sites 2 

through 5. North is up on photograph. Note: Some white dots on this image are caused by chemical changes in the negative 

of the aerial photograph.

Cross-cutting relations show that unit S2 was emplaced 

before SI, but we saw no evidence to argue a significant 

period of time separating emplacement of the two units. In 

that regard, the simplest interpretation is that the two units 

resulted from the 1811-12 earthquake sequence.

Farther to the north, the articulated skeletal remains of 

an extinct, stout-legged llama (Paleolama nitrified) were 

exposed in the western bank of Buffalo Creek ditch, 150 m 

south of the County Road N bridge crossing (site 8, fig. 30) 

and about 5 km south of Senath, Mo. (Graham, 1990). The 

Paleolama skeleton was found near the base of the section in 

a massive, fine to medium sand (fig. 31). The sand is generally 

overlain by a top stratum of silty to clayey loam and clay. The 

sand both encompasses and occurs within a gleyed, dark-gray 

clay. The complex stratigraphic relations between the sand 

and the gleyed clay are interpreted to be the result of liquefaction. The gleyed clay originally rested directly on the sand 

enclosing the Paleolama skeleton, but the basal sand liquefied

and flowed during the 1811-12 New Madrid earthquakes, 

breached the overlying gleyed clay, and formed a sill between 

the gleyed clay and overlying loam and clay deposits. This 

interpretation is supported by the presence of sand dikes originating from this same sand—these dikes clearly breach the 

entire top stratum at nearby sites, such as site 9, about 250 m 

to the north (fig. 32). Thus, after eliminating the effects of liquefaction, the Paleolama was preserved within the sand 

directly below the silty and clayey loam and clay units of the 

top stratum.

A radiocarbon age for the Paleolama, determined from 

accelerator mass spectrometry (AMS) techniques applied to 

amino acids extracted from the preserved bones, is 10,890±30 

yr B.P. (Graham, 1990). From our observations and prior studies (e.g., Saucier, 1974; Guccione and others, 1990), the sand 

underlying the top stratum and encompassing the Paleolama 

skeleton is interpreted as a braided-stream deposit, and the 

sequence of clay and loam are deposits that accumulated in
H12

EAST

850m

INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

900 m 950 m 

-Ground surface

WEST

1,000 m

1,250 m

Site 2

1,350 m 1,400 m

METERS

r- 0

— 4

1,450 m

Site 1a

1,500 m 1,550 m Site 1b

Site 3 

1,600 m

1,650 m 1,700 m 1,750 m 1,800 m

1,850 m 1,900 m 1,950 m 2,000 m

Figure 13. Schematic diagram of the south side of a section of Ditch No. 12 near Manila, Ark. The upper 0.5 to 1.0 m of the section is 

levee fill resulting from excavation of the ditch. The top stratum is clay rich and generally non-liquefiable in character. The shaded unit is 

fine to coarse sand that shows evidence of liquefaction. Evidence of original bedding is rare beneath the top stratum. Solid boxes show sites 

along the trench that were documented in greater detail. Horizontal distances are measured with respect to west edge of bridge crossing 

shown in figure 12. Note vertical exaggeration.
RECURRENCE BEHAVIOR OF THE GREAT 1811-12 NEW MADRID EARTHQUAKES H13

EAST WEST

^r^^-.- /.- ' .- -

Figure 14. Photograph and schematic diagram of Ditch No. 12 at site la near Manila, Ark. See figure 13 for details of location. Exposure 

shows tabular cross-beds and the confinement of liquefaction features beneath a relatively impermeable clay top stratum. The sand of unit 

C flowed upward to the base of the overlying clay, at which point it was unable to propagate through the top stratum and flowed horizontally, 

forming thin dikes beneath the clay top stratum (arrows indicate flow direction). Unit A consists of cross-bedded, brownish-yellow and 

light-gray fine- to medium-grained sands. Unit B is composed of thin anastomosing lenses and beds of light-gray and gray, fine- to mediumgrained sand. Unit C is light-gray, fine- to medium-grained sand—this sand is generally massive near the base of the exposure and occurs 

in thin horizontal beds directly beneath the overlying clay top stratum. The disturbed character of bedding in the sand labeled unit B indicates 

that the sand also liquefied but that mass flow was minimal. The incipient nature of liquefaction in unit A is evidenced by the gradual degradation of cross-beds from east to west across the unit. String grid in photograph indicates 1-m intervals. No vertical exaggeration.
H14 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

EAST WEST

Ground surface

0 -i

Figure 15 (above and facing column). Photograph and schematic 

diagram of site Ib along Ditch No. 12 near Manila, Ark. (see fig. 

13). Sand underlying the clay top stratum (TS) shows disrupted 

bedding and laminae, which are interpreted to indicate deformation 

due to liquefaction subsequent to deposition. The top stratum (TS) 

is unbroken, and, hence, flow due to liquefaction was confined beneath the top stratum at this particular site. Note the clean white 

sand (WS), which appears to represent lateral flow beneath the top 

stratum, resulting in emplacement of a sill of sand. String grid in 

photograph indicates approximate 1-m intervals.

low-energy backswamp and slackwater settings that collected since the terrace was abandoned approximately 11,000 

yr B.P. The stratigraphy and radiocarbon dates at this site and 

site 3 (fig. 18) are virtually identical, lending support to the 

idea that the deposits exposed in the ditch represent about 

5,000 to 10,000 yr of time in the vicinity of Buffalo Creek 

ditch and Ditch No. 12.

STATELINE AND BELLE FOUNTAINE 

DITCHES

The Stateline and Belle Fountaine Ditches, which trend 

easterly from the Big Lake Wildlife Refuge (fig. 8), were 

reexcavated to a significantly greater width than Ditch 12 or 

Buffalo Creek ditch (fig. 33), and, although the ditch walls 

had a shallow slope, they provided about 5 m of vertical 

exposure. In contrast to the deposits along Ditch No. 12 and 

Buffalo Creek ditch, the base of the gray, blocky top stratum, where present, was not observed at any point along the 

base of the ditches. The thicker top stratum characteristic of 

the Stateline and Belle Fountaine ditches is consistent with 

the interpretation of Guccione (1987) that these ditches are 

excavated into thick, backswamp deposits.

Numerous sand blows are present in fields adjacent to 

the ditches (fig. 34), but our search revealed only one

EXPLANATION

SC Thin interbeds of light-gray fine to medium sand and brown

fine to medium sand containing abundant lignite.

Bioturbated(?) 

TS Top stratum of gray and grayish-brown clay and clay loam.

Mottling of color and texture suggestive of Krotovina 

WS Fine to medium white sand containig abundant gray clay

clasts (cc) 

LG Sand- to granule-size lignite. Lignite granules are well

rounded 

AS Anastomosing lenses of pale-brown and gray, fine to

medium sand containing numerous small clay clasts (cc).

Interpreted direction of flow marked by arrows

major break in the top stratum near the eastern end of the 

studied section of Stateline ditch (fig. 8). The occurrence 

of relatively few large breaks in the top stratum are probably the result of the thick top stratum along these ditches as 

compared to Ditch No. 12 and the Buffalo Creek ditch. 

The sand blows were typically expressed in cross section 

as 0.5- to 1-m-thick layers of sand at the top of the section, 

as shown at site 10 (fig. 35).

A 1-m-thick layer of extruded sand is connected to several dipping sand dikes at site 10 (fig. 35). The stratigraphy 

and structure of the vented sand layer indicates four distinct 

episodes of venting or sand extrusion. More specifically, 

there exist four approximately flat-lying layers of sand (fig. 

36). These episodes are represented by four nearly flat-lying 

packets of sand whose contacts are characterized by concentrations of silt and lignite, some flare structures, and, along 

the uppermost internal contact, preserved worm-hole casts. 

The lower three layers are composed of distinct, finingupward sequences. The contacts thus represent hiatuses in 

venting of the sand, but the absence of soil development or 

oxidation on these buried surfaces implies a brief period of 

time between deposition of the individual packages. Most
RECURRENCE BEHAVIOR OF THE GREAT 1811-12 NEW MADRID EARTHQUAKES H15

EAST WEST

-^ A

Levee fill 

Post-1811-12 around surface

likely, the silt and lignite at the contacts represent a latestage settling of the finer grained fraction of the vented 

material. Although the surface is disturbed, soil development on the upper surface of the extruded sand is minimal. 

The weak soil development on the surface of the 

extruded sand is consistent with deposition during the 

1811-12 earthquake sequence, and the absence of soil 

development or oxidation on the interval between sand layers is consistent with the interpretation that the layers are due 

to separate liquefaction episodes during the 1811-12 

sequence. Hence, we observed no evidence in this and similar exposures along these ditches that favors a pre-1811-12 

origin for the liquefaction features.

EXIT 4 DITCH

The Exit 4 ditch, which strikes in a southerly direction 

from its intersection with Interstate 55 about 2 km south of 

exit 4 (fig. 8), is a local farm-field drainage ditch (fig. 37)

Figure 16 (above and facing column). Photograph and schematic 

diagram of site 2 along Ditch No. 12 near Manila, Ark. String grid 

in photograph indicates 1-m intervals. Note vertical exaggeration 

of schematic diagram. Labels along right side of schematic diagram refer to soil horizons. See text for discussion.

located within the Holocene Mississippi meander belt (fig. 

38). Because it is in the Holocene meander belt, the surface 

has probably been stable for a shorter period of time. The 

large-scale aerial photograph in figure 39 shows numerous 

arcuate lineaments that trend across the ditch, and the intersection of one lineament with the ditch is marked as site 11.

The photograph and schematic diagram of site 11 

(fig. 40) show that the arcuate trends are from sand 

extruded onto the surface, most likely because of seismically induced liquefaction. The extruded sand in this area 

forms arcuate lineaments because they follow the course 

of abandoned meander belt point-bar deposits. The source 

beds of the sand are likely shallowest above the abandoned point-bar deposits and, hence, are most likely to fail 

here during liquefaction.

Site 11, like many others and those documented previously, shows evidence of multiple episodes of liquefaction, but the lack of significant pedogenesis on the 

surface sand suggests a recent genesis for the deposits. 

Similarly, the contact between units S1 and S2 (fig. 40) is 

marked only by a concentration of silt, suggesting that the 

units were emplaced within a short time of each other. 

Here again, the evidence of liquefaction is consistent with 

an 1811-12 genesis.
H16 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

DISCUSSION

Many of the exposures we examined show evidence of 

multiple episodes of liquefaction. The vented sand is commonly composed of distinct packets, each separated by a hiatus in deposition marked by concentrations of silt and lignite, 

occasional flare structures, or preservation of worm-hole 

casts (e.g., figs. 16, 17, 35, and 36). In all cases, the lack of 

soil development or oxidation at layer contacts indicates that 

the hiatuses were very brief, perhaps on the order of minutes 

or hours to months. Moreover, soil development on the surface of the extruded sand is invariably weak, generally characterized by a 1- to 2-cm-thick A horizon and virtually no B 

horizon, which indicates that the sand deposit is relatively 

young (e.g., figs. 17 and 28). The 1811-12 earthquake 

sequence consisted of four great earthquakes on three different days within a period of 3 months (table 1). The multiple 

episodes of liquefaction we interpret in the vented packages 

of sand are best explained to be the result of individual 

events of the 1811-12 earthquake sequence. Multiple episodes of liquefaction are commonly shown by cross-cutting 

relationships between intruded dikes and sills (e.g., fig. 20). 

The consistent lack of alteration, oxidation, or diagenesis 

between the different sets of dikes and sills argues for an 

1811-12 genesis for all of these features. In summary, our 

search has revealed no evidence of liquefaction that cannot 

be best attributed to the 1811-12 earthquake sequence.

Our observations of liquefaction features centered principally on a late Wisconsin braided-stream terrace in the 

vicinity of Big Lake, Ark. Saucier (1977) estimated that the 

terrace was abandoned about 9,500 yr ago. Our radiocarbon 

dates at site 3 (fig. 8) and site 8 (fig. 31), each on samples 

collected adjacent to the contact between outwash sands and 

the overlying top stratum (which is interpreted to have developed since abandonment of the terrace), range from 10,380 

to 11,100 radiocarbon yr B.P. These ages generally agree 

with Saucier's (1974) estimate of 9,500 yr B.P. Similarly, 

backswamp sedimentation in Big Lake, Ark., is estimated to 

have started more than 9,900 yr ago (Guccione, 1987) and 

more than 6,500 yr ago for a site farther east, near Belle 

Fountaine ditch (fig. 8). The apparent absence of older liquefaction features in the geologic record similar to those attributed to the 1811-12 earthquake supports an argument that 

similar liquefaction events have not occurred in approximately 10,000 yr prior to the 1811-12 sequence.

At this stage, we should place our observations in the 

context of prior geological and seismological efforts to estimate the expected recurrence interval of 1811-12 New 

Madrid-type earthquakes. The search for geological evidence bearing on the repeat time of 1811-12 earthquakes is 

not new. As early as 1971, Saucier (1977) examined the 

geological effects of the 1811-12 earthquakes and clearly 

recognized the potential value of geological studies of liquefaction features for predicting the recurrence interval of 

infrequent major earthquakes in the region. Saucier (1991)

A

-W11

sift

reported observations of liquefaction features at eight 

archaeological sites but found no evidence of ground disturbance or liquefaction that could not be attributed to the 

1811-12 earthquakes. Moreover, based on archaeological 

age estimates, the inferred that the lack of evidence for liquefaction-inducing events prior to 1811-12 extended back 

500 to 1,000 yr or more. To our knowledge, Saucier's work 

was the first attempt to use liquefaction features to unravel 

the paleoearthquake history of a fault zone.
RECURRENCE BEHAVIOR OF THE GREAT 1811-12 NEW MADRID EARTHQUAKES H17

Figure 17 (facing column and above). A, Soil profile developed 

on the ejected sand at site 2 along Ditch No. 12 (see fig. 16) is 

characterized by a thin, black A horizon and a very weak B horizon. Although overlain by artificial levee fill, the abundant wormhole casts within the A horizon attest to the undisturbed nature of 

the surface of the ejected sand. B, The internal structure of the 

ejected sand (see fig. 16) is characterized by thin layers of silt and

lignite that separate thicker units of sand. Sampling of the ejected 

sand for paleomagnetic signature caused small holes evident in 

this photograph. The A horizon shown in A is also shown at the 

top of B. See text for further discussion. C, Photograph of area 

shown in part of schematic diagram (in fig. 16) that includes sand 

vent and section to the west of vent. String grid in photograph indicates 1-m intervals.

The first reported geologic evidence for 

paleoearthquakes and, hence, an estimate of recurrence 

intervals for large New Madrid earthquakes is from trenching of the Reelfoot scarp (Russ and others, 1978; Russ, 

1979). The fault strikes northwesterly from the southwestern end of Reelfoot Lake to the Mississippi River (fig. 6). It 

is perhaps the only feature in the region that shows unambiguous evidence of Holocene movement. The oldest 

deposits in the trench are about 2,000 yr old. Structural, 

stratigraphic, and geomorphic data revealed evidence of 

two episodes of fault movement prior to 1811-12. Combining the geologic observations with the historical record, 

Russ (1979) interpreted that there may have been three 

earthquakes of sufficient size to produce liquefaction during the last 2,000 yr and, on that basis, suggested a recurrence time of 600 yr or less for such events in the region. 

At first glance, Russ' (1979) observations conflict with the 

10,000-yr-long absence of liquefaction events prior to

1811-12, as implied by our observations. However, it 

should be noted that Russ (1979) found insufficient evidence to prove that any of the faults or liquefaction features 

in the trench were produced during the 1811-12 earthquakes. Moreover, earthquakes as small as mi, = 6.2 can 

produce liquefaction at distances of 15 to 20 km from the 

earthquake source (e.g., Youd and Wieczorek, 1982). We 

suggest that one or more of the paleoearthquakes interpreted by Russ (1979) do not represent a recurrence of 

1811-12-type earthquakes but, rather, the occurrence of 

smaller earthquakes in the northern part of the New Madrid 

seismic zone.

Recently, Saucier (1991) reported stratigraphic evidence of two liquefaction events during the past 1,300 yr at 

an archaeological site about 30 km northwest of Reelfoot 

Lake. Noting that liquefaction was induced by a nearby m^, 

= 6.2 earthquake in 1895 and also by the 1811 and 1812 

earthquakes, (treating the 1811-12 sequence as a single
H18 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

EAST WEST

Clay

(A horizon) 

(E? horizon)

Spodic horizon (Bs)

Loamy sand 

Silty clay (2Eb)

Loam (2Bb)

Gleyed sand

Levee fill

A horizon developed on surface 

formed in 1811-12

24 METERS

Figure 18. Photograph and schematic diagram of site 3 along Ditch No. 12 near Manila, Ark. Circled numbers 1 and 2 indicate 

sites of two wood samples dated at 5,090±60 and 1 1,100±100 radiocarbon yr B.P., respectively. String grid in photograph indicates 

1-m intervals. Note vertical exaggeration of schematic diagram. See text for further discussion.
w 

a

=

>

oyeH ffi 

WOwH 

oo

T

i

OI

o

Figure 19. Large-scale photomosaic of figure 18. String grid in photograph indicates 1 -m intervals; outcrop is labeled from 1 to 23 from east (left) to west (right) along the exposure. Wood recovered for radiocarbon dating was taken from panel 2. The pervasive nature of the flow accompanying liquefaction of the underlying sands is evidenced by the diapiric flow 

structures, the presence of numerous clasts of top stratum within the liquefied sands, and the accompanying break in the top stratum.
H20 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

SOUTH NORTH

Levee fill

1 -

EXPLANATION

A Medium-grained sand with

cross-beds

S1, S2, S3 Intruded fine to medium sand 

D Clay

C Fine-grained sand with 

cross-beds

E Fine to medium clayey sand 

F Fine to medium sand

Figure 20. Photographs and schematic diagram of sand dikes and sills in Buffalo Creek Ditch, about 150 m south 

of the Highway 77 bridge crossing between Leachville and Manila, Ark. Location is site 4 in figure 12. Note vertical 

exaggeration of schematic diagram. Exposure consists of two faces separated by a step, each gridded at 1-m intervals, 

except adjacent to central sand dike (S2) where grid is 0.5 m.

earthquake), and assuming uniformly spaced intervals, Saucier estimated an average recurrence rate of 468 yr for liquefaction-inducing events near New Madrid, Mo. Like Russ 

(1979), the scale of paleoliquefaction features Saucier 

observed were small compared to those reported in 1 811-12. 

Hence, as stated by Saucier (1991), any inference of the 

repeat time of great New Madrid earthquakes from these 

observations remains equivocal, and, more likely, the 

paleoliquefaction features represent the recurrence of 

smaller magnitude events in the New Madrid seismic zone. 

Earthquake-frequency statistics have been the basis 

for estimating the average recurrence interval of 1811-12- 

type earthquakes. The most recent estimate using

earthquake-frequency statistics yields a recurrence interval of M > 8 earthquakes of 550 to 1,100 yr (Johnston and 

Nava, 1985). In contrast, the apparent lack of a widespread paleoliquefaction event in the geologic record may 

imply a repeat time of 5,000 to 10,000 yr or more for the 

occurrence of 1811-12-type earthquakes (fig. 41). 

Johnston and Nava's (1985) estimate is based on the 

extrapolation of about 10 yr of instrumental data and historical records for the period after 1811. This represents a 

relatively small part of the expected repeat time. Furthermore, an assumption of stationarity is implicit to the 

extrapolation of earthquake-frequency statistics to determine the repeat time of larger, less frequent earthquakes.
r.

Figure 21. This large-scale photomosaic of a part of the lower photograph in figure 20 shows the sharp cross-cutting relationships associated with the injection of sand dikes and sills. 

The location is site 4 along Buffalo Creek ditch (see fig. 12) and encompasses the lower and central part of the schematic diagram shown in figure 20. The wispy character of crossbedding in units A and D (see fig. 20) may result from incipient liquefaction. Horizontal strings indicate 1-m intervals, and vertical strings indicate 1-m or 2-m intervals.

d

8IT)

»

g5s70S

Hffi W

o

B
H22 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

SOUTH

The discrepancy between our observations and the repeattime estimates based on seismicity may simply show that 

the historical record is too short to accurately portray the 

behavior of faults in the region. In addition, estimates of 

repeat time of large earthquakes based on the linear 

extrapolation of the recurrence of small events may be 

inaccurate because it is now known that earthquake-frequency curves are commonly non-linear throughout the 

entire magnitude range for all fault zones (e.g., Youngs 

and Coppersmith, 1985). Our observations in the New 

Madrid region, if correct, would imply that the earthquake-frequency curve should truncate sharply at the largest expected magnitude (fig. 41).

The possibility exists that pre-1811-12 events may 

have occurred without producing liquefaction if water-table 

conditions were unfavorable. Of course, such a possibility 

would obviate the implications of our work. However, the

Figure 22 (facing column and below). Oblique photograph and 

schematic diagram of exposure at site 5 (see fig. 12) along Buffalo Creek ditch. Site is about 150 m north of the intersection of the 

ditch with Highway 177 between Manila and Leachville, Ark. 

The well-developed soil profile has about 50 cm of apparent extension across a fissure through which more than 1 m of sand was 

extruded on the surface. The soil development on the surface of 

the ejected sand is minimal in comparison to that observed on the 

breached top stratum. Vertical and horizontal dimensions of 

string grid shown in photograph are 1 m and 0.5 m, respectively.

NORTH

Ejected white, fine to medium sand
RECURRENCE BEHAVIOR OF THE GREAT 1811-12 NEW MADRID EARTHQUAKES H23

Figure 23. The portion of ditch wall logged in figure 22 is at lower left of upper photograph. Extruded sand is white, in contrast to 

the dark A horizon on the top stratum. The buried soil cuts from left 

to right across the photograph and outcrops at the 1-m-long stake 

emplaced vertically along the face of the ditch. Renewed growth 

along the ditch wall is most rapid where the organic-rich soil crops 

out. The line of vegetation between the stake and the telephone pole 

marks the base of the extruded sand, which is as much as 2 m thick 

and extends about 30 to 40 m along the strike of the ditch. The lower photograph shows approximately the same view of the site, taken 

4 months subsequent to logging the exposure. Rapid revegetation 

and erosion quickly degrades the exposures provided by the reexcavations of the Corps of Engineers.

possibility that such conditions existed in the past 10,000 yr 

should be tempered by pollen data of core in the Big Lake 

area that indicates that the region has supported backswamp 

vegetation throughout the Holocene (Guccione, 1987). Furthermore, even during the record low stages of the Mississippi River, which occurred during the drought period of 

1988, the water table remained relatively high, as evidenced by persistent flow in ditches that was maintained by 

springs along ditch edges. Thus, it seems reasonable that if 

an 1811-12-sized earthquake occurred during the last 5,000 

to 10,000 yr, it would have induced liquefaction that would 

be recorded in the geologic record.

CONCLUSIONS

Excavations by the U.S. Army Corps of Engineers 

provided an opportunity to examine the subsurface characteristics of liquefaction over a significant area of the 

1811-12 meizoseismal zone. Deformation due to 

1811-12 liquefaction is pervasive throughout the region. 

In contrast, we observed in the geologic record no evidence for prehistoric liquefaction similar in character or 

extent to that which occurred in 1811-12. Prior studies 

and radiocarbon age limits that we have placed on specific exposures indicate that the ditch exposures generally 

encompass about 5,000 to 10,000 yr of geologic record. 

Although lack of evidence provides less than a desirable 

basis for interpretation, we interpret from our observations, and our perception that similarly pervasive liquefaction would have accompanied similar prehistoric events, 

that earthquakes of similar size to the great 1811-12 New 

Madrid earthquakes have not occurred during 5,000 to 

10,000 yr or more prior to 1811-12.

ACKNOWLEDGMENTS

We thank Steve Obermeier for originally suggesting 

that we take advantage of the excavations of the U.S. Army 

Corps of Engineers. Tony Crone and John Tinsley provided 

very useful reviews of an early version of the manuscript. 

Ingrid Ramos kindly proofed this version of the paper. Joe 

Keithly and John Monroe kindly kept us informed of the 

excavation activities of the Corps during this study. Don 

Johnson's comments regarding the description of soils were 

particularly valuable. In addition, we would like to thank 

Bob Dziak, Mike Froehme, Rob Mellors, Silvio Pezzopane, 

Jill Stevens, and Guang Yu, all of whom, at various times, 

helped with aspects of cleaning, logging, and surveying various liquefaction sites. Arch Johnston of Center for Earthquake Research and Information (CERI) kindly provided a 

small amount of seed monies to initiate this project. The 

majority of the research was supported by U.S. Geological 

Survey grant awards numbered 14-08-0001-G1682, -G1791, 

and -G1928.
H24 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

REFERENCES CITED

Fuller, M.L., 1912, The New Madrid earthquake: U.S. Geological 

Survey Bulletin 494, 119 p.

Graham, R.W., 1990, The extinct stout-legged llama (Paleolama 

mirificd), lower/central Mississippi River valley, in Guccione, 

M.J., and Rutledge, E.M., eds., Friends of the Pleistocene Field 

Guide to the Mississippi Alluvial Valley, Northeast Arkansas 

and Southeast Missouri: Fayetteville, University of Arkansas, 

p. 207-210.

Guccione, M. J., 1987, Geomorphology, sedimentation, and chronology of alluvial deposits, northern Mississippi County, Arkansas, in A Cultural Resources Survey, Testing, and 

Geomorphic Examination of Ditches 10,12, and 29, Mississippi County, Arkansas: Mid-Continental Research Associates 

Report No. 86-5, [Memphis District, Corps of Engineers Contract No. DACW66-86-C-0034], p. 67-99.

Guccione, M.J., Lafferty, R.H. HI, and Cummings, L.S., 1990, An 

evolving Holocene alluvial system and human settlement, Big 

Lake, Arkansas, in Guccione, M.J., and Rutledge, E.M., eds., 

Friends of the Pleistocene Field Guide to the Mississippi Alluvial Valley, Northeast Arkansas and Southeast Missouri: Fayetteville, University of Arkansas, p. 211-214.

Hamilton, R.M., and Johnston, A.C., 1990, Tecumseh's prophecy: 

Preparing for the next New Madrid earthquake: U.S. Geological Survey Circular 1066, 30 p.

Heyl, A.V., and McKeown, F.A., 1978, Preliminary seismotectonic 

map of central Mississippi valley and environs: U.S. Geological Survey Miscellaneous Field Studies Map MF-1011, scale: 

1:500,000.

Hopper, M.G., 1985, Estimation of earthquake effects associated 

with large earthquakes in the New Madrid seismic zone: U.S. 

Geological Survey Open-File Report 85-457, 140 p.

Johnston A.C., and Nava, S.J., 1985, Recurrence rates and probability estimates for the New Madrid seismic zone: Journal of 

Geophysical Research, v. 90, p. 6737-6753.

Nuttli, O.W., 1973, The Mississippi valley earthquakes of 1811 

and 1812—Intensities, ground motion, and magnitudes: Seismological Society of America Bulletin, v. 63, p. 227-248.

Obermeier, S., 1984, Liquefaction potential for the central Mississippi valley: U.S. Geological Survey Open-File Report 84- 

770, p. 391^46.

————1989, The New Madrid earthquakes—An engineeringgeologic interpretation of relict liquefaction features: U.S. 

Geological Survey Professional Paper 1336-B, 114 p.

Russ, D.P., 1979, Late Holocene faulting and earthquake recurrence in the Reelfoot Lake area, northwestern Tennessee: Geological Society of America Bulletin, v. 90, p. 1013-1018.

Russ, D.P., Stearns, R.G., and Herd, D.G., 1978, Map of exploratory trench across Reelfoot scarp, northwestern Tennessee: U.S. 

Geological Survey Miscellaneous Field Studies Map MF-985.

Saucier, R., 1974, Quaternary geology of the lower Mississippi 

River valley: Arkansas Archaeological Survey Research Series No. 6, 26 p.

————1977, Effects of the New Madrid earthquake series in the 

Mississippi alluvial valley: U.S. Army Engineer Waterways 

Experiment Station Miscellaneous Paper S-77-5, 10 p.

————1989, Evidence for episodic sand-blow activity during the 

1811-12 New Madrid (Missouri) earthquake series: Geology, 

v. 17, p. 103-106.

-1991, Geoarchaeological evidence of strong prehistoric

earthquakes in the New Madrid (Missouri) seismic zone, 

Geology, v. 19, p. 296-298.

Schweig, E.S., and Marple, R.T., 1991, Bootheel lineament: A possible coseismic fault of the great New Madrid earthquakes: 

Geology, v. 19, p. 1025-1028.

Stauder, W., 1982, Present-day seismicity and identification of active faults in the New Madrid seismic zone, in McKeown, 

F.A., and Pakiser, L.C., eds., Investigations of the New 

Madrid, Missouri, Earthquake Region: U.S. Geological Survey Professional Paper 1236, p. 21-30.

Stauder, W., Kramer, M., Fischer, G., Schaeffer, S., and Morrissey, 

S.T., 1976, Seismic characteristics of southeast Missouri as indicated by a regional telemetered microearthquake array: Seismological Society of America Bulletin, v. 66, p. 1953-1964.

Street, R., and Nuttli, O.W., 1984, The central Mississippi River 

valley earthquakes of 1811-12: Proceedings of Missouri 

Academy of Sciences Meeting, Cape Girardeau, Missouri, 

April 27-28, 1984, 34 p.

Youngs, R., and Coppersmith, K., 1985, Implications of fault slip 

rates and earthquake recurrence models to probabilistic hazard 

estimates: Bulletin of the Seismological Society of America, v. 

75, p. 939-964.

Youd, T.L., and Wieczorek, G.F., 1982, Liquefaction and secondary ground failure, in The Imperial Valley, California, earthquake of October 15, 1979: U.S. Geological Survey 

Professional Paper 1254, p. 223-246.

Published in the Central Region, Denver, Colorado 

Manuscript approved for publication December 10, 1993 

Edited by Richard W. Scott, Jr. 

Graphics prepared by Wayne Hawkins 

Photocomposition by Carol A. Quesenberry
FIGURES 24-41
H26 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

$v' f" * '

u,-/ F -'r,Xr

)mnMCM *•..-. i *, i'liBB " r^^" ">"TM'j v ""•*-- " T. • ^o ?*

s ii6J<. '-^ t y

Figure 24. Arbyrd, Missouri, orthophotoquad showing Buffalo Creek ditch following the course of a relict channel on an abandoned braided-stream terrace of late Wisconsin age. Sites 6 through 9 are discussed in the text. North is up on photograph.
RECURRENCE BEHAVIOR OF THE GREAT 1811-12 NEW MADRID EARTHQUAKES H27

Figure 25. Aerial photograph showing geomorphology in the vicinity of sites 6 and 7 along Buffalo Creek ditch, which follows 

a relict stream channel of late Wisconsin age. Sites 6 and 7 are discussed in text. North is up on photograph.
INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

150m

Liquefied sands 1

SOUTH

100m 50 m NORTH SOUTH

South side 

of Highway 164 

bridge crossing

100m 150m 200m

250m 300 m 350m

METERS

[— 0

"— 4

Site 6

450 m

500m

Figure 26. Schematic diagram of the east side of a section of Buffalo Creek ditch adjacent to the crossing of Highway 164 (see figs. 24 

and 25). The upper unit is levee fill from excavation of the ditch. The top stratum is generally a clay-rich, non-liquefiable deposit. The shaded 

unit is fine to coarse sand that shows evidence of liquefaction. Evidence of original bedding is rare beneath the top stratum. Sites 6 and 7 

were documented in greater detail and are marked by the solid boxes. Horizontal distances are measured in meters with respect to the south 

and north sides of the Highway 164 bridge crossing, respectively. Note vertical exaggeration.
RECURRENCE BEHAVIOR OF THE GREAT 1811-12 NEW MADRID EARTHQUAKES H29

Figure 27. Photograph and schematic diagram of major breach in 

top stratum at site 6 along Buffalo Creek ditch. The buried log rests 

on the A horizon developed on the surface at the time of the 

1811-12 earthquakes. The Ab soil horizon is a dark-gray, clay loam 

that averages 20 to 25 cm in thickness and grades downward into 

the B horizon, which is a light yellowish brown, very fine, sandy 

loam that extends below the exposure. The A horizon on the extruded sand is an approximately 1-cm-thick, dark-brown, silty clay 

loam. The sharp color and compositional contrast of this A horizon 

with underlying sand may be accentuated by the settling out of finer 

grained clays subsequent to the extrusion of the sands. The extruded 

sands are light gray to brownish yellow in color, medium to coarse 

grained, generally devoid of a silt or clay fraction, and contain 

abundant small clay clasts. Shovel and spade provide scale. A larger 

scale diagram of the portion of the photograph adjacent to the spade 

is shown in figure 28.

EAST WEST

0 -

Figure 28. Photograph and schematic diagram of the portion of 

site 6 adjacent to the spade shown in figure 27. This figure further 

illustrates the character of soil development on the top stratum and 

extruded sand. View is to the south.
H30 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE
RECURRENCE BEHAVIOR OF THE GREAT 1811-12 NEW MADRID EARTHQUAKES H31

Figure 30. Aerial photograph of Buffalo Creek ditch showing sites 8 and 9, which are south and north of Missouri County Road N bridge crossing, respectively. The articulated remains of a stout-legged llama (Paleolama mirifica) were unearthed at site 8. Both sites are located in a relict channel on an abandoned late Wisconsin braided-stream terrace. North is 

up on photograph.

Figure 29 (facing page). Photographs and schematic diagram of 

site 6 along Buffalo Creek ditch showing the erosion at the base of 

the top stratum due to the liquefaction and flow of underlying 

sands, which most likely took place during the 1811-12 earthquakes. Lower photograph and schematic diagram show central 

part of upper photograph. See text for discussion.
H32 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

WEST METER

Ditch spoil and slope wash 

Original grou nds

Metalliferous oxide concretions 

Dark-brown silt loam

EAST

~-3~I~I~I Grayjsandy cla\rioam -~ ~

^-^-^-^-^r=r^-^

Yellowish-brown

Trench floor

Figure 31. Photograph and schematic diagram of site 8, Buffalo 

Creek ditch. A 1-m grid, shown on the photograph, shows the location of the schematic diagram. Small survey flags at base of excavation mark the location of skeletal remains of a Paleolama 

mirifica. A radiocarbon date places the age of the skeletal remains 

at about 10,380±380 yr B.P. The skeletal remains were located in 

the fine to medium sand beneath a gleyed, dark-gray clay.
RECURRENCE BEHAVIOR OF THE GREAT 1811-12 NEW MADRID EARTHQUAKES H33

NORTH

Figure 32. Photograph and schematic diagram of site 9 showing breach of clay loam top stratum by small dikes along Buffalo Creek ditch near Missouri County Road N. String grid in photograph indicates 1-m intervals.
H34 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

Figure 33. Reexcavation of the Stateline and Bell Fountaine ditches produced about 5 m of vertical exposure, although sides of 

the ditches had a relatively shallow slope. The drag line in the distance provides a measure of scale, and the width of the ditch prior 

to reexcavation is visible in the distance.
RECURRENCE BEHAVIOR OF THE GREAT 1811-12 NEW MADRID EARTHQUAKES H35

Figure 34. Portion of the Denton, Missouri, orthophotoquad showing site 10 along Belle Fountaine ditch surrounded by numerous sand blows in the adjacent fields. North is up on photograph.
H36 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

I 2 —

Figure 35. Photograph and schematic diagram of exposure at site 10, Belle Fountaine ditch. Sand vented onto the surface through dikes 

in the clay top stratum form a layer about 1 m thick. Internal contacts (dashed) within the ejected, very fine to fine sands (dotted and stippled) 

indicate four distinct episodes of venting, all of which are most likely due to the 1811-12 earthquake sequence. The dashed box is the location of the larger scale photograph in figure 36 that shows details of the internal stratigraphy of vented sand. String grid in photograph indicates 1-m intervals. See text for further discussion.
RECURRENCE BEHAVIOR OF THE GREAT 1811-12 NEW MADRID EARTHQUAKES H37

K Very fine to fine sand

"*- Silty layer, worm-hole casts 

> Very fine to fine sand, fining upward

•" • Erosional unconformity

Very fine to fine sand, fining upward

• Silty, lignitic layer, flare structures

•> Very fine to fine sand, fining upward

Figure 36. Photograph of part of exposure shown in figure 35. Four distinct layers of yellowish-brown sand are visible. Contacts 

between the sand layers are marked by a concentration of silt and lignite, abrupt changes in grain size, and the presence of flare 

structures and worm casts. The three lower packages show fining-upward sequences. The contact between the levee fill and sand 

has been disturbed, but pedogenesis appears minimal at the uppermost contact of the sand. The contacts between the sand packages 

are interpreted to reflect brief hiatuses between separate episodes of venting resulting, possibly, from the earthquakes of the 

1811-12 sequence. String grid in photograph indicates 1-m intervals.
H38 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

Figure 37. View to the northwest along the Exit 4 ditch in southeastern Missouri. Car at left edge of view is on Interstate 55. Site 11 is 

the excavation behind the person standing in the ditch.
RECURRENCE BEHAVIOR OF THE GREAT 1811-12 NEW MADRID EARTHQUAKES H39

Figure 38. Portion of Steele, Missouri, orthophotoquad showing location of Exit 4 ditch and numerous abandoned meander 

scars of the Mississippi River system. Holland, Mo., is located directly above the site 11 label. North is up on photograph.
H40 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

Figure 39. Aerial photograph showing location of site 11 along Exit 4 ditch with sharp white lineations caused by liquefaction 

and extrusion of sand along trend of abandoned point-bar deposits.
RECURRENCE BEHAVIOR OF THE GREAT 1811-12 NEW MADRID EARTHQUAKES H41

Figure 40. Photograph and schematic diagram of site 11, Exit 4 ditch, in southeastern Missouri. See figure 39 for aerial view of the area 

and text for further discussion. String grid in photograph indicates 1-m intervals horizontally and 0.5-m intervals vertically.
H42 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

.01

10

100

600

1,200

10,000

100,000

1811-12 New Madrid 

earthquakes (Ms>8.3) 

(mb>7.0)

\

\ —

23456789 

BODY-WAVE MAGNITUDE (mb)

Figure 41. Average repeat time of earthquakes of size greater 

than or equal to a given body-wave magnitude (mj,, solid dots) for 

the New Madrid seismic zone (adapted from Johnston and Nava, 

1985). The largest earthquake reported during the period since 

1811-12 is mj, = 6.2. Extrapolation (dashed line) of earthquake statistics covering the period since 1811-12 implies a 550- to 1,100-yr 

repeat time for 1811-12-type earthquakes (Ms > 8.3). The lack of 

geologic evidence for widespread paleoliquefaction may reflect a 

significantly longer repeat time, on the order of 5,000 to 10,000 yr 

or more, for such events in the region.

* U.S. GOVERNMENT PRINTING OFFICE: 1994-673-046/86067