Characterization of the Cottonwood Grove and 

Ridgely Faults Near Reelfoot Lake,Tennessee, 

from High-Resolution Seismic Reflection Data

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1538-1

MISSOURI 

ARKANSAS
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).
Characterization of the Cottonwood Grove and 

Ridgely Faults Near Reelfoot Lake, Tennessee, 

from High-Resolution Seismic Reflection Data

By William J. Stephenson, Kaye M. Shedlock, and Jack K. Odum

INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE 

Edited by Kaye M. Shedlock and Arch C. Johnston

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1538-1

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1995
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

For sale by U.S. Geological Survey, Information Services

Box 25286, 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

Stephenson, William J.

Characterization of the Cottonwood Grove and Ridgely faults near Reelfoot Lake, 

Tennessee, from high-resolution seismic reflection data / by William J. Stephenson, 

Kaye M. Shedlock, and Jack K. Odum. 

p. cm.—(Investigations of the New Madrid seismic zone : I) 

(U.S. Geological Survey professional paper: 1538) 

Includes bibliographical references. 

Supt.. of Docs. no.: 119.16: 15381

1. Faults (Geology)—Tennessee—Reelfoot Lake Region. 2. Seismic reflection 

method. I. Shedlock, Kaye M. II. Odum, Jack K. III. Title. IV. Series. 

V. Series: U.S. Geological Survey professional paper: 1538 

QE535.2.U6I59 1995 vol. I 

[QE606.5.U6] 

2'2'09778985 s—dc20

[551.8T0976812] 95-2235

CIP
CONTENTS

Abstract........................................................................................................................... II

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

Seismic Interpretation and Analysis............................................................................... 3

Mini-Sosie Line RDG-1......................................................................................... 3

Mini-Sosie Line RDG-2......................................................................................... 4

Mini-Sosie Line RDG-3 ......................................................................................... 5

Discussion....................................................................................................................... 6

Conclusions.................................................................................................................... 7

Acknowledgments.......................................................................................................... 7

References Cited............................................................................................................. 8

Appendix........................................................................................................................ 9

FIGURES

1. Map of Reelfoot Lake area, Tennessee...................................................................................................................... 12

2. Interpreted Mini-Sosie seismic profile RDG-1.......................................................................................................... 4

3. Interpreted Mini-Sosie seismic profile RDG-2.......................................................................................................... 5

4. Interpreted Mini-Sosie seismic profile RDG-3.......................................................................................................... 6

5. Map of faults imaged in high-resolution seismic reflection data............................................................................... 7

Al. Uninterpreted seismic profile RDG-1........................................................................................................................ 9

A2. Uninterpreted seismic profile RDG-2........................................................................................................................ 9

A3. Uninterpreted seismic profile RDG-3........................................................................................................................ 10

TABLES

1. Generalized Mini-Sosie data-acquisition parameters ................................................................................................ 13

2. Generalized processing steps used on Mini-Sosie seismic reflection data................................................................ 4

CHARACTERIZATION OF THE COTTONWOOD GROVE AND 

RIDGELY FAULTS NEAR REELFOOT LAKE, TENNESSEE, 

FROM HIGH-RESOLUTION SEISMIC REFLECTION DATA

By William J. Stephenson, 1 Kaye M. Shedlock,1 and Jack K. Odum1

ABSTRACT

High-resolution seismic reflection data acquired 2-10 

km south of Reelfoot Lake, Tennessee, more clearly delineate the Cottonwood Grove and Ridgely faults as well as 

reveal a new, potentially major, fault with approximately 40 

m of apparent vertical displacement, which is located east of 

the Ridgely fault. This new fault trends northwest, opposite 

in trend direction to the Cottonwood Grove and Ridgely 

faults, and dips vertically. The northeast-trending 

Cottonwood Grove fault has as much as 30 m of apparent 

vertical displacement on all imaged strata, from the 

Cretaceous/Paleozoic boundary to the middle Eocene 

horizon. This displacement suggests that faulting began 

post-middle Eocene. The northeast-trending Ridgely fault 

appears to be a zone of several fault strands bounding a 

horst-like structure. Apparent vertical displacements on 

strata across the easternmost strand of the Ridgely fault 

suggest recurrent displacement, with roughly 22-26 m of 

apparent offset on the Cretaceous/Paleozoic boundary and 

18-22 m of apparent offset on middle Eocene deposits. The 

Quaternary/Eocene boundary was not sufficiently imaged on 

any seismic profile to determine if faulting has occurred later 

than post-middle Eocene.

'U.S. Geological Survey, Mail Stop 966, P.O. Box 25046, Denver 

Federal Center, Denver, CO 80225.

INTRODUCTION

The area surrounding Reelfoot Lake, Tennessee, is 

important for understanding the seismotectonics of the 

Mississippi Embayment—this is because the Reelfoot Lake 

area is a region of major historic and current seismicity in the 

New Madrid seismic zone (Stauder, 1982; Johnston and 

Shedlock, 1992) and because it has identifiable surface 

features related to recent faulting (less than 2,000 years old; 

Russ, 1982). The Lake County uplift, west of Reelfoot Lake 

(fig. 1), is an irregularly shaped topographic feature with as 

much as 10 m of topographic relief above the general level 

-of the Mississippi River valley (Russ, 1982; Kelson and 

others, 1992). As described by Stearns (1979), the Lake 

County uplift contains numerous physiographic bulges. One 

of the most prominent of these is Ridgely ridge (fig. 1), rising 

5 m above the level of the river valley. Vibroseis data 

acquired south of Reelfoot Lake resulted in the identification 

of the Cottonwood Grove and Ridgely faults (Zoback, 1979; 

Hamilton and Zoback, 1982), which are coincident with 

Ridgely ridge and possibly related to its uplift.

Using Vibroseis and Mini-Sosie seismic data, Zoback 

and others (1980) and Sexton and Jones (1986) inferred the 

displacement of middle Eocene deposits across the Cottonwood Grove fault (fig. 1). Shedlock and Harding (1982) 

further delineated the Cottonwood Grove fault, which 

crosses the Mississippi River 5 km southeast of Caruthersville, Mo., from seismic data collected along the Mississippi 

River. These studies suggested that the apparent vertical displacement on the Cottonwood Grove fault diminishes to both 

the northeast and the southwest. The Ridgely fault (fig. 1) 

essentially has been inferred from well data and has only
12 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

Missouri

Kentucky

Lake County 

uplift f Tennessee

Reelfoot Lake

Ridgely 

fault Mississippi 

River EXPLANATION 

«~ Vibroseis data

— Mini-Sosie data

— Fault

Study Area

\ Ridgely ridge

Caruthersville
CHARACTERIZATION OF FAULTS FROM HIGH-RESOLUTION SEISMIC REFLECTION DATA 13

Figure 1 (facing page). Study area with seismic profiles and surficial features shown. Geomorphic features possibly related to faulting include the Tiptonville dome, Ridgely ridge, and the Lake 

County uplift. Seismic profile locations include Mini-Sosie lines 

RDG-1, RDG-2, and RDG-3 and Vibroseis lines S-4, S-5, and R-l. 

Surface locations of the Cottonwood Grove and Ridgely faults are 

based on projections from seismic reflection data (Zoback and others, 1980; Shedlock and Harding, 1982).

been observed in seismic data by Zoback (1979) and Zoback 

and others (1980).

We acquired three high-resolution Mini-Sosie seismic 

reflection profiles (fig. 1) across the northeastern 

Cottonwood Grove and Ridgely faults near Reelfoot Lake, 

Tennessee, (1) to better constrain their location and apparent 

vertical displacements, (2) to better characterize the faults 

and their faulting history, and (3) to map additional structures associated with these faults.

SEISMIC INTERPRETATION AND 

ANALYSIS

Data acquired with the Mini-Sosie method have been 

well-documented throughout the Mississippi Embayment 

(Sexton and Jones, 1986; Luzietti and others, 1992; 

VanArsdale and others, 1992; Odum and others, in press). 

This seismic acquisition method and its application are 

discussed by Wiles (1979) and Barbier (1983).

The data presented here were recorded with 28-Hz resonant-frequency, vertical-component geophones in a cluster 

array. All data were acquired using an end-on spread, a minimum receiver offset of 60 m, 15.24-m group intervals, and 

24 receivers per shot (acquisition parameters are shown in 

table 1). The majority of the signal bandwidth of these data 

is between 30 and 140 Hz (40 to 80 Hz dominant bandwidth). The generalized processing steps used on these data 

are shown in table 2. Processing was conventional with the 

possible exceptions of adaptive deconvolution and 

post-stack, 90° finite-difference time migration (Yilmaz, 

1987), which further enhanced data resolution.

Vertical resolution of the Mini-Sosie data acquired for 

this study varies from about 4.5 m at 100 ms two-way travel 

time (TWTT) to about 8 m at 600 ms TWTT. Spatial resolution, expressed as the first-Fresnel-zone radius (Yilmaz, 

1987), is on the order of 30 m at 100 ms and 85 m at 600 ms 

TWTT, although migration increases the resolution to less 

than a Fresnel zone. Correlations of reflections to local and 

regional lithologic units are based on the studies of Zoback 

and others (1980), Sexton and Jones (1986), and Odum and 

others (in press). The horizons interpreted on each of the 

respective lines are the Quaternary/Eocene unconformity 

(Q/E), the top of the middle Eocene Memphis Sand (Tms),

Table 1. Generalized Mini-Sosie data-acquisition parameters.

[gp, group]

Parameter Description

Source type ...................Earth tampers (Wackers)

Source array..................Three Wackers spaced 3.1 m(10 ft)

apart, parallel to seismic line 

Source point interval ..... 15.24 m (50 ft) 

Source duration.............2,000 Wacker impacts summed

per source point 

Geophone type ............. .28-Hz resonant frequency,

vertical component 

Geophone array .............12 geophones in 1-m point cluster

Geophone gp interval ....15.24 m (50 ft)

Shooting spread.............24 channels, end-on;

61-m near-channel offset1

41 1.6-m far-channel offset2 

Field filters...................60-Hz notch;

40-Hz low cut, 120-Hz high cut,

24 dB/octave rolloff 

Recording system ..........Input/output DHR 2400

Sampling rate................1 ms

Trace length..................! s_________________

1 3Q.5 m for Mini-Sosie line RDG-1. 

2381.1 m for Mini-Sosie line RDG-1 .

the top of the Paleocene Porters Creek Clay (Tpc), and the 

Cretaceous/Paleozoic unconformity (K/PZ).

In addition to flexure of reflections, interpretations of 

faults in these data are often based on changes in frequency 

content across an interpreted structure as well as reflection 

terminations. All apparent vertical displacements estimated 

on each seismic profile are measured from the maximum to 

the minimum depth of a horizon across a given fault.

MINI-SOSIE LINE RDG-1

Mini-Sosie line RDG-1 was acquired across the (linear) 

surface projection of the Ridgely fault, over a section of U.S. 

Geological Survey (USGS) Vibroseis line S-5 of Hamilton 

and Zoback (1982), in an effort to identify any near-surface 

deformation possibly associated with this structure. Because 

the resolution of RDG-1 is higher than previously achieved 

with the Vibroseis data, the Mini-Sosie data successfully 

image reflectors into the middle Eocene (Tms) and permit a 

more detailed interpretation (fig. 2). Specifically, an upwarp 

observed on the Vibroseis data appears in the Mini-Sosie 

data to be a horst bounded by near-vertical fault strands that 

displace middle Eocene deposits (between stations 142 and 

195). The fault splays bounding this horst probably represent 

the northeastern continuation of the Ridgely fault. The westernmost of these faults also apparently splays at around 400 

ms TWTT.
14 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

Table 2. Generalized processing steps used on Mini-Sosie 

high-resolution seismic reflection data, Ridgely, Tenn., area.

[AGC, automatic gain control; DMO, dip moveout; FK, frequency-wave number; 

Dyn, dynamic; FX, frequency-distance]

West 

Station 2rjrj

LINE RDG-1

180 160 140 120

East

100

Processing step Parameters/comments

Geometry........................ Surface coordinates, elevations to

trace headers 

Trace edit........................ Bad traces removed from

processing 

AGC...............................400ms operator length

Bandpass filter................ Zero-phase, 25-40-140-170 Hz

(0%-100%-100%-0% filter points)

pass band 

Resample........................2-ms sample rate

Adaptive deconvolution... L2-norm spiking, 200 ms operator

length 

Trace muting................... Top mute (first arrivals) and bottom

mute (ground roll), 5-ms mute taper 

Elevation statics .............. 1 ,000 m/s weathered-layer velocity

Normal moveout. ............. Apply best velocity function of

as many as three determined from

constant velocity analysis 

Residual statics............... Apply best solutions of as many as

three surface-consistent passes;

10-ms time shift allowed per pass 

DMO.......................... ....Common offset FK DMO

Normal moveout.............. Remove pre-DMO normal moveout;

apply velocity function of postDMO analysis 

Stack........................... ....Fold normalized

Bandpass filter................ Zero-phase, 25-40-140-170 Hz

(0%-100%-100%-0% filter points)

pass band 

AGC...............................400ms operator length

Dyn signal/noise filter..... 20-170 Hz FX signal enhancement

Migration........................ Steep-dip finite-difference time

migration

Apparent vertical displacement across these two faults 

is estimated to be 20 to 26 m on all reflectors. The Tms 

horizon has apparent vertical displacement of 20 to 21 m 

across both fault strands, whereas the K/PZ horizon has an 

apparent vertical displacement of 24 to 26 m across these 

strands. This suggests that fault movement has been recurrent (or episodic) on these structures since pre-middle 

Eocene time; however, the vertical resolution of these data is 

less than the differences in offset between the respective 

horizons, making this recurrence interpretation equivocal. 

The Tpc horizon is poorly imaged on the eastern half of the 

line but has a faulted appearance at station 140 similar to the 

Tms and K/PZ horizons between stations 150 and 200. 

Unfortunately, the Quaternary/Eocene boundary (interpreted 

at 125 ms TWTT between stations 100 and 130) was not 

successfully imaged across the horst; thus, any 

late-Eocene-to-Quaternary fault movement cannot be 

determined.

900

Vertical exaggeration^.? . 500 m ,

920(?)

Figure 2. Mini-Sosie line RDG-1 reveals two fault strands bounding a horst beneath the surface projection of the Ridgely fault. The 

Quaternary/Eocene boundary (Q/E), the top of the middle Eocene 

Memphis Sand (Tms), the top of the Paleocene Porters Creek Clay 

(Tpc), and the Cretaceous/Paleozoic boundary (K/PZ) are interpreted 

on the seismic profile. Deeper, approximate depths on the profile 

are queried because of poor seismic velocity control. Vertical exaggeration is estimated from an averaged, single stacking-velocity 

function. Uninterpreted section is shown in the Appendix as 

figure Al.

MINI-SOSIE LINE RDG-2

Mini-Sosie line RDG-2 was acquired along the linear 

projection of the Cottonwood Grove fault, as previously 

located with Vibroseis data (Hamilton and Zoback, 1982; 

Zoback and others, 1980). As seen in figure 3, our data indicate the fault intersects the Tms horizon 320 m west of the 

projected surface location as determined in previous 

Vibroseis studies. Apparent vertical displacements on both 

the interpreted K/PZ and Tms horizons are approximately 30 

m, suggesting fault activity has occurred since the middle 

Eocene. This interpretation is in general agreement with 

those of both Sexton and Jones (1988) and Zoback and others (1980), and our interpretation also supports the hypothesis that apparent vertical displacement on the Cottonwood 

Grove fault decreases to the northeast (Zoback and others, 

1980). These data, like those of RDG-1, do not clearly 

resolve the Quaternary/Eocene boundary or Quaternary
CHARACTERIZATION OF FAULTS FROM HIGH-RESOLUTION SEISMIC REFLECTION DATA 15

West 

Station

LINE RDG-2 East

780 760 X740 720 700

soo-vc :.;. "'-' :^.^-•"">'. ."•*?' 785<?)

900 -

Vertical exaggeration~2.7 875(?)

500m

Figure 3. The Cottonwood Grove fault is imaged as two strands 

beneath Mini-Sosie line RDG-2. The location of the fault is approximately 320 m west of a linear surface projection (arrow) previously 

inferred from Vibroseis data. The Quaternary/Eocene boundary 

(Q/E), the top of the middle Eocene Memphis Sand (Tms), the top of 

the Paleocene Porters Creek Clay (Tpc), and the Cretaceous/Paleozoic boundary (K/PZ) are interpreted on the seismic profile. Deeper, 

approximate depths on the profile are queried because of poor seismic velocity control. Vertical exaggeration is estimated from an 

averaged, single stacking-velocity function. Uninterpreted section 

is shown in the Appendix as figure A2.

units; hence, possible recurrent motion after the middle 

Eocene cannot be determined. A fault splay is apparent west 

of the interpreted main Cottonwood Grove fault, displacing 

the K/PZ horizon. No other faults were apparent in section 

RDG-2, as evidenced by the generally strong and continuous 

appearance of all reflections east of station 760. The disruption in the Tms reflection below station 720 is believed to be 

a stratigraphic feature, perhaps the edge of a paleochannel.

MINI-SOSIE LINE RDG-3

Mini-Sosie line RDG-3 consists of three, interconnected, two-dimensional Mini-Sosie lines merged into a

single profile (figs. 1 and 4), with stations 210 to 260 positioned over a section of Vibroseis line R-l (Zoback, 1979). 

The Mini-Sosie data reveal a much more complex subsurface fault system than had been previously inferred, with 

four faults interpreted. A horst between two near-vertical to 

steeply east dipping fault strands is apparent between stations 200 and 255. This structure had been previously 

imaged in Vibroseis data by Zoback (1979), and many of the 

reflections between 300 and 800 ms TWTT match well 

between the two data sets (although the reflector depths 

estimated by Zoback (1979) differ from those estimated in 

this study, which is probably a function of the different 

velocity functions calculated from the two data sets).

The apparent vertical displacement of the K/PZ reflector 

across the horst is approximately 20 m on the eastern fault 

and 22 m on the western fault. The apparent vertical displacement of the Tms reflector across both faults is about 18 

m. The K/PZ and Tpc horizons dip gently eastward across the 

horst, suggesting rotation during faulting, whereas the Tms 

horizon appears primarily to be arched rather than rotated.

Between stations 155 and 180, RDG-3 changes direction from east-west to north-south. An apparent structure 

between stations 160 and 170 on the K/PZ horizon is most 

likely an out-of-plane reflection from the fault between 

stations 200 and 210; the reflection may be caused by the 

close proximity of this fault to the profile between stations 

160 and 180. Evidence for this reflection being from out of 

the plane include the similar displacement on the K/PZ 

horizon and the lack of apparent displacement on the T^ 

horizon (the Fresnel zone is much smaller at 200 ms TWTT 

than at 650 ms TWTT; hence, the reflected wavelet did not 

sample as far laterally at shallow depth).

A third major, and previously unidentified, fault is 

imaged beneath station 120 on RDG-3. Approximately 40 m 

of apparent vertical displacement, down to the east, is 

observed on the K/PZ horizon. Apparent vertical displacement on the Tms horizon is approximately llm, suggesting 

that vertical movement on this fault has been recurrent (or 

episodic) after formation of the K/PZ horizon and that faulting has occurred since the middle Eocene. This structure was 

not imaged on either Vibroseis line R-l or on the north-south 

segment of line RDG-3.

We thus infer that the structural trend of this fault must 

be generally northwest-southeast because of its absence on 

Vibroseis line R-l and the surficial geometric relationship 

between lines R-l and RDG-3 (fig. 1). Interestingly, 

O'Connell and others (1982) interpreted a fault with the 

same sense of vertical displacement and with a surface projection (based on a focal mechanism) that trends at about N. 

20° W., toward and roughly parallel to this third interpreted 

fault on line RDG-3. The relationship of this easternmost 

imaged fault to the surface projection of the fault plane as 

derived by O'Connell and others (1982) is shown in figure 5.
16

West

Station 26o 240 220 

0-4

INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

LINE RDG-3

140 120

East

100

900 Vertical exaggeration^.? 500m

900(?)

Figure 4. Four separate fault strands are interpreted on Mini-Sosie line RDG-3. The western two bound a horst that is probably also observed on RDG-1. The interpreted fault beneath station 145 has approximately 5 m of apparent vertical displacement. The easternmost fault 

is a previously unknown strand that has approximately 40 m of apparent vertical displacement across the K/PZ horizon. The 

Quaternary/Eocene boundary (Q/E), the top of the middle Eocene Memphis Sand (Tms), the top of the Paleocene Porters Creek Clay (Tpc), 

and the Cretaceous/Paleozoic boundary (K/PZ) are interpreted on the seismic profile. Deeper, approximate depths on the profile are queried 

because of poor seismic velocity control. Vertical exaggeration is estimated from an averaged, single stacking-velocity function. Uninterpreted section is shown in the Appendix as figure A3. See text for explanation of heavy vertical lines.

DISCUSSION

We have purposefully used the phrase "apparent vertical displacement" to describe the fault offsets observed in 

these data because they could be caused by normal, thrust, 

strike-slip, or some combination of faulting. Strike-slip 

faulting can cause apparent vertical displacement when

observed on a two-dimensional seismic profile because of 

bed dip and changes in bed thicknesses. Determining the 

type of faulting observed in these two-dimensional data is 

necessarily equivocal.

The interpreted faults are generally located on flexures 

in the reflections, even though some of the reflections may 

be continuous across an interpreted fault. This is acceptable
CHARACTERIZATION OF FAULTS FROM HIGH-RESOLUTION SEISMIC REFLECTION DATA 17

in interpreting these data, as shown by the modeling of 

Mini-Sosie data acquired across the Cottonwood Grove fault 

(Sexton and Jones, 1986). The modeling results of Sexton 

and Jones (1986) indicated that, given the resolution of these 

data, the small relative displacements of fault strands across 

this fault system can yield flexed but fairly continuous 

reflections similar to those observed in our Mini-Sosie data. 

Essentially, the lateral smearing effects are caused by the 

relatively small apparent vertical fault displacements in 

relation to the Fresnel zone size. Alternately, it has been 

suggested that flexures of this type have the geometric 

characteristics of fault-bend folds (e.g., Suppe, 1983). Yet, 

until a cogent model is developed that can kinematically 

explain such features in this tectonic setting, we prefer to 

interpret the cause of these flexures as faults that have 

propagated into or through the respective horizons.

The horst structure observed on both lines RDG-1 and 

the western end of RDG-3 correlates between the two lines 

and is interpreted to be the Ridgely fault (fig. 5). Previous 

studies did not project the Ridgely fault as far to the northeast, perhaps due to the lack of shallow, higher resolution 

information. The fault strands bounding the horst are 

interpreted to dip steeply to the southeast or are nearly 

vertical. If they do dip southeast, their relation to the southwest-dipping thrust plane determined from focal mechanisms (Chiu and others, 1992) is unclear.

CONCLUSIONS

Mini-Sosie lines RDG-1, RDG-2, and RDG-3 better 

delineate the Cottonwood Grove and Ridgely faults south of 

Reelfoot Lake (fig. 5) and indicate significant deformation 

as recently as post-middle Eocene on all imaged structures. 

Additionally, a previously unidentified fault with approximately 40 m of apparent vertical displacement on the Paleozoic surface, apparently trending to the northwest, was 

imaged east of the Ridgely fault. The Quaternary/Eocene 

boundary was not sufficiently imaged in either the 

Mini-Sosie or previously interpreted Vibroseis data (Hamilton and Zoback, 1982; Zoback and others, 1980) to determine if faulting has occurred later than post-middle Eocene 

in this area. Faulting does not appear to have been recurrent 

(or episodic) on the Cottonwood Grove fault. Conversely, 

apparent vertical displacements on strata across the Ridgely 

fault weakly suggest recurrence, with 22 to 26 m of apparent 

displacement of the K/PZ boundary and 18 to 22 m on the 

Tms horizon. Vertical displacement does not appear to 

decrease to the northeast on the Ridgely fault, as is observed 

on the Cottonwood Grove fault.

Tiptonville\;| 

dome

Ridgely 

fault

0 2km 

S-4 i____i

EXPLANATION 

„„, Vibroseis data

Mini-Sosie data

_ Previously 

inferred fault 

Interpreted 

fault

Figure 5. Surface projections (heavy black lines) of the Cottonwood Grove and Ridgely faults, inferred from this study. Locations 

of the Ridgely and Cottonwood Grove faults originally inferred 

from Vibroseis data are shown by thin lines. The Cottonwood 

Grove fault occurs very close to its previously inferred linear projection on line RDG-2. The Ridgely fault appears to continue northeast of its previously determined location (Zoback and others, 

1980), across RDG-1. The surface projection of the fault plane from 

O'Connell and others (1982) is shown as a heavy line with an 

asterisk. D, downthrown side; U, upthrown side.

ACKNOWLEDGMENTS

This work was supported by the U.S. Geological 

Survey through grants from the National Earthquake 

Hazards Reduction Program. The authors thank Dave 

Worley, John Michael, Rob Williams, Richard Dart, Susan 

Rhea, Dave Nicholas, Dave Kibler, Mike Ellis, Buddy 

Schweig, and students from the University of Arkansas and 

the University of Memphis for their efforts and support 

during data acquisition.
18 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

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Published in the Central Region, Denver, Colorado 

Manuscript approved for publication December 20, 1994 

Edited by Richard W. Scott, Jr. 

Graphics prepared by Denny Welp, use made of

author-drafted material 

Photocomposition by Wayne Hawkins
CHARACTERIZATION OF FAULTS FROM HIGH-RESOLUTION SEISMIC REFLECTION DATA

APPENDIX

Three uninterpreted, high-resolution seismic reflection profiles acquired south of

Reelfoot Lake, Tennessee.

19

West

Station 200

LINE RDG-1 East

180 160 140 120 100

900 920(?)

Vertical exaggeration^.?

Figure Al. Uninterpreted, high-resolution, Mini-Sosie seismic 

reflection profile RDG-1.

West 

Station 739 

0-

LINE RDG-2 East

760 740 720 700

900 Vertical exaggeration^.? 875(?)

Figure A2. Uninterpreted, high-resolution, Mini-Sosie seismic 

reflection profile RDG-2.
no

West

Station

INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

LINE RDG-3

200 180 160

900 Vertical exaggeration^.? 900(?)

Figure A3. Uninterpreted, high-resolution, Mini-Sosie seismic reflection profile RDG-3.

*U.S. GOVERNMENT PRINTING OFFICE: 1995- 673-046/86091