Reflection Seismic Profiling of the Wabash Valley 

Fault System in the Illinois Basin

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1538-0

MISSOURI

~"3t3fc: «tr- ^t-i.

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).
Reflection Seismic Profiling of the Wabash Valley 

Fault System in the Illinois Basin

By R.M. Rene and F.L. Stanonis

INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE 

Edited by Kaye M. Shedlock and Arch C. Johnston

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1538-O

This research was jointly supported by the U.S. Geological Survey and 

ARPEX (Industrial Associates' Research Program in Exploration 

Seismology—Indiana University, University of Southern Indiana, 

Indiana Geological Survey)

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

Rene, R.M.

Reflection seismic profiling of the Wabash Valley fault system in the Illinois Basin / by 

R.M. Rend and F.L. Stanonis.

p. cm.—(U.S. Geological Survey professional paper; 1538-O) (Investigations of the 

New Madrid seismic zone ; O)

Includes bibliographical references. 

Supt. of Docs, no.: I 19.16:1538-0

1. Faults (Geology)—Illinois Basin. 2. Seismic reflection method. I. Stanonis, F.L. 

II. Title. III. Series. IV. Series: Investigations of the New Madrid seismic zone ; O. 

QE535.2.U6I59 1994 vol. O 

[QE606.5.U6]

551.2'2'09778985 s—dc20 

[551.8'7'00977] 94^4233

CIP
CONTENTS

Abstract........................................................................................................................... Ol

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

Regional Geology and Previous Studies......................................................................... 4

Seismic Data Acquisition................................................................................................ 9

Seismic Data Processing................................................................................................. 10

Interpretation of Reflection Events................................................................................. 14

Ste. Genevieve, New Albany, Maquoketa, and Knox Events............................... 14

Identification of the Eau Claire Event................................................................... 14

Thickness of the Eau Claire Low-Impedance Layer............................................. 18

Acoustic Basement Event..................................................................................... 27

Interpretations of Faults and Fault-Related Structures.................................................... 29

Wabash Island Fault.............................................................................................. 29

Hovey Lake Fault.................................................................................................. 31

Summary and Discussion................................................................................................ 31

References Cited ............................................................................................................ 32

FIGURES

1. Map of the Wabash Valley fault system showing locations of seismic lines and deep wells..................................... O2

2. Map showing locations of seismic lines 1-3, locations of selected wells, and structural contours at the top of the

Cypress Formation....................................................................................................................................................... 3

3. Maps showing Schwalb's (1982) interpretations of thicknesses of the Eau Claire Formation and the Mount

Simon Sandstone......................................................................................................................................................... 6

4. Interval velocity, vertical average velocity, and synthetic seismogram for the Cuppy well and west end of the

Hamilton County, Illinois, seismic line ...................................................................................................................... 7

5. Sexton and others' (1986) interpretation of the Grayville and New Harmony seismic profiles................................. 8

6. Stacking velocity, vertical-average velocity, interval velocity, and interval velocity function used for conversion

to depth sections.......................................................................................................................................................... 11

7. Plot of velocity spectrum for location 245 in line 1.................................................................................................... 11

8. Line 1 stacked data from (X6 to 1.5 s in CDP locations 400-500 before and after wave-equation migration............ 12

9. F-K spectrum of stacked data in figure 8A.................................................................................................................. 13

10. Line 1 stacked section and plot of CDP fold............................................................................................................... 15

11. Line 1 migrated section for locations 9-560............................................................................................................... 16

12. Line 1 interpreted migrated section showing the Hovey Lake and Wabash Island faults .......................................... 17

13. Line 1 interpreted depth section (locations 9-560)..................................................................................................... 18

14. Line 1 interpreted depth section (locations 200-560)................................................................................................. 19

15. Line 1 interpreted depth section (locations 9-380)..................................................................................................... 20

16. Line 2 stacked section and plot of CDP fold............................................................................................................... 21

17. Line 2 migrated data.................................................................................................................................................... 21

18. Line 2 interpreted migrated data showing faults D and E of the Hovey Lake fault.................................................... 22

19. Line 2 interpreted depth section.................................................................................................................................. 23

20. Line 3 stacked section (0-1 s), migrated data, and depth section with 3:1 horizontal exaggeration.......................... 24

21. Line 3 interpreted migrated data and interpreted depth section showing the Wabash Island fault............................. 25

22. Parts of sonic logs for the Cuppy, Streich, and Duncan wells showing slowness (reciprocal velocity) as a function

of two-way reflection time .......................................................................................................................................... 26

23. Modeled primary seismic wavelet, wavelet complexes 1-6, seismic data showing the Eau Claire event, and

corresponding velocity models.................................................................................................................................... 27

III
IV CONTENTS

TABLES

1. Elevations of tops of formations in deep wells........................................................................................................... O5

2. Stratigraphic section and elevations of formation tops and thicknesses of strata in the General Electric Water

Disposal No. 2 well, Posey County, Indiana............................................................................................................... 5

3. Seismic survey field parameters.................................................................................................................................. 10

4. Data processing sequence............................................................................................................................................ 10

5. Elevations of the top of the Cypress Formation (Upper Mississippian) and fault cuts, and thicknesses of strata

faulted out in selected wells........................................................................................................................................ 29
REFLECTION SEISMIC PROFILING OF THE WABASH VALLEY 

FAULT SYSTEM IN THE ILLINOIS BASIN

By R.M. Rene 1 and F.L. Stanonis2

ABSTRACT

Three common-depth-point (CDP) minihole reflection 

seismic profiles were recorded in southwestern Indiana near 

the junction of the Wabash and Ohio Rivers. Our objective 

was to image and interpret the deep structure of the Wabash 

Valley fault system in the Illinois Basin. The normal faults 

of this system are Late Pennsylvanian or younger and 

pre-Pleistocene in age. The seismic data were processed 

through CDP stack, wave-equation migration, and 

time-to-depth conversion. These data image the Wabash 

Island and Hovey Lake faults, which bound the Mt. Vernon 

graben in Posey County, Indiana. Northwest of Hovey Lake, 

the Wabash Island fault comprises several branches in a 

quasi-planar fault zone that dips about 65° east-southeast. 

Vertical displacement on the floor fault increases with 

increasing depth and is about 120 m at the Upper Cambrian 

Eau Claire Formation. Vertical displacement on the roof 

fault decreases with increasing depth. Northeast of Hovey 

Lake, we interpret that the Hovey Lake fault is a subsidiary 

antithetic fault to the Wabash Island fault. The fault is listric, 

and vertical displacement of strata decreases with increasing 

depth, although the fault clearly displaces the Eau Claire 

Formation. The Hovey Lake and Wabash Island faults 

apparently intersect within the Precambrian basement rocks. 

Two hanging-wall synclines and an anticline in the Mt. Vernon graben result from reverse and normal drag folding associated with the two bounding faults.

A strong reflection seismic event is interpreted as the 

response to a low-velocity layer of approximately 200-m 

thickness within the Upper Cambrian Eau Claire Formation. 

Our interpretation of the transit-time interval between the 

Eau Claire and acoustic basement events is consistent with 

the possible existence of an Upper Cambrian Mount Simon 

Sandstone basin extending into southwestern Indiana on

Indiana Geological Survey, Indiana University, Bloomington, IN 

47405.

School of Science and Engineering Technology, University of Southern Indiana, Evansville, IN 47712.

trend with the Reelfoot rift of the New Madrid rift complex. 

We do not, however, see evidence of pre-Mount Simon 

rift-fill associated with any large-displacement basement 

faults that may have been reactivated to generate the Wabash 

Valley fault system.

INTRODUCTION

In 1988-90 we shot three reflection seismic profiles 

across faults in the Wabash Valley fault system to study 

these faults and deep structures of the Illinois Basin. This 

fault system is about 90 km long and 50 km wide in southeastern Illinois, southwestern Indiana, and northwestern 

Kentucky near the deepest part of the Illinois Basin (fig. 1). 

The high-angle north-northeast- to northeast-trending normal faults of this system displace the youngest consolidated 

strata (Upper Pennsylvanian Mattoon Formation) but not the 

overlying Quaternary deposits. These faults are thus Late 

Pennsylvanian or younger and pre-Pleistocene in age. The 

maximum vertical displacement on an individual fault is 

about 145 m (Nelson, 1990a); however, the faults commonly 

bifurcate upward (Bristol and Treworgy, 1979; Ault and Sullivan, 1982). The faults and fault-related structures of this 

system partially controlled deposits of oil and gas in Mississippian and Pennsylvanian strata (Bristol and Treworgy, 

1979) and may have controlled accumulations of deeper, 

undiscovered hydrocarbons as well. These structures also 

affect mining of Pennsylvanian coal deposits (Nelson, 1981) 

and locations of waste-disposal wells. Seismicity in the area 

may be related to zones of crustal weakness associated with 

these structures.

We shot seismic lines 1-3 (fig. 2) across the Mt. Vernon 

graben, bounded by the Wabash Island and Hovey Lake 

faults in an area of low relief near the intersection of the Ohio 

and Wabash Rivers in southwestern Indiana. Figure'2 shows 

structural contours for the top of the Upper Mississippian 

Cypress Formation based on oil-well data. Anticlines F, G, 

and H (fig. 2) helped trap oil in Mississippian strata in the 

College Consolidated, Spencer Consolidated, and Powells 

Lake Consolidated fields, respectively. Although deep wells

01
O2 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

COCORP seismic line

Grayville 

seismic line

New Harmony 

seismic line

Hamilton County 

seismic line w

Study area (fig. 2)

EXPLANATION

Normal fault - bar and ball 

on downthrown side

Deep well (table 1) 

NMRC New Madrid rift complex 

SIA Southern Indiana arm

(Braile and others, 1982)

Figure 1. Map of the Wabash Valley fault system showing our reflection seismic study area and the COCORP, Hamilton 

County, Grayville, and New Harmony seismic lines. The: (1) Brown, (2) Weber-Horn, (3) Johnson, (4) Cisne, (5) Cuppy, (6) 

Bell, (7) Rollison, (8) Lewis, (9) Parley, (10) Streich, (11) Duncan, and (12) General Electric wells (table 1) are shown. The inset 

map shows the New Madrid rift complex and its Southern Indiana arm as postulated by Braile and others (1982). The small box 

within the inset map shows the area of the main map. Modified from Nelson (1990a).
REFLECTION SEISMIC PROFILING OF THE WABASH VALLEY FAULT SYSTEM IN THE ILLINOIS BASIN 03

EXPLANATION 

Selected shallow well

Normal fault 

downthrown

Anticline

Figure 2. Map showing seismic lines 1-3, with section-line indicia at 1-mi (1,.6-km) intervals. Wells with fault cuts, wells 1-13 (table 5), 

faults A-E, anticlines F-H, synclines I-J, and structure contours (in meters) at the top of the Cypress Formation (Upper Mississippian) are 

shown. Lines la and Ib (see text) overlap and were processed together as line 1. Line la extends eastward from the west flank of syncline 

J. Line Ib extends westward from a point near the axis of syncline J. Datum is mean sea level; contour interval is 5 m.

in the Wabash Valley fault system are sparse, wells less than 

1 km deep are plentiful. In areas of oil and gas production, 

wells are spaced at about 200-m (660-ft) intervals. The 

steeply dipping faults are intersected by these wells sporadically along the direction of strike, but, because the faults 

commonly bifurcate, reliable determinations of fault dips 

may be impossible using shallow wells alone. In Posey 

County, Indiana (area = 1,060 km2), which includes the

study area, Tanner and others (1980a, 1980b) mapped fault 

cuts with missing sections in 207 wells. The deepest of these 

fault cuts was 702 m below sea level in Mississippian strata. 

Many authors, including Butler (1967), Tanner and others 

(1980a, 1980b, 1981a, 1981b), and Ray (1986), have used 

well logs to map structures and thicknesses of Mississippian 

and Pennsylvanian strata in the study area. The faults have 

been only slightly exhumed. Coal-seam moisture content in
O4 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

the region indicates that only about 300 m of Late Pennsylvanian or younger strata were removed by erosion (Cluff and 

Byrnes, 1990).

Seismic lines 1-3 were acquired by students under our 

direction as part of a field course in seismic exploration at the 

University of Southern Indiana during the summers of 

1988-90. The data were recorded digitally with SERCEL 

SN338B and SN338HR recording systems and were processed by us at the data-processing facilities of Digicon Geophysical Corp. in Houston, Texas. Although the resultant 

seismic profiles are short, they successfully imaged faults 

and fault-related structures of the Wabash Valley fault system at depths as great as 4 km. A strong reflection event in 

these data is correlated with the Upper Cambrian Eau Claire 

Formation. From these seismic data, we derived tentative 

estimates of thickness for the Upper Cambrian Mount Simon 

Sandstone that are consistent with the possible existence of 

a basin in southwestern Indiana. The acoustic basement 

event, due perhaps to the interface between the Mount Simon 

Sandstone and underlying Proterozoic rocks, is only weakly 

defined. We did not observe in our reflection seismic data 

direct evidence for a previously postulated pre-Mount Simon 

rift in this region.

Acknowledgments.—We wish to thank the reviewers 

for their helpful suggestions. We also wish to thank Gulzar 

Aziz, Mark Duckworth, Steve France, Ben Gibson, John 

Hohman, Keith Might, Richard Mode, Fekri Zainoba, the 

many other students who participated in this study, the personnel of the Hovey Lake Fish and Wildlife Reserve, Mr. 

John Breiner, and many other helpful residents of Posey 

County, Indiana. This work was supported by the U.S. Geological Survey, Department of the Interior, under award 

number 14-08-001-G1927; by the Indiana Geological Survey; and through ARPEX (Industrial Associates' Research 

Program in Exploration Seismology—Indiana University, 

University of Southern Indiana, Indiana Geological Survey) 

by Amoco Production Company; Chevron USA; Conoco, 

Inc.; Digicon Geophysical Corp.; Grant Tensor Geophysical 

Corp.; Input/Output, Inc.; Pump and Irrigation Supply, Inc. 

(Evansville, Ind.); and SERCEL, Inc.

REGIONAL GEOLOGY AND 

PREVIOUS STUDIES

Table 1 provides elevations of tops of the Lower 

Ordovician and Upper Cambrian Knox Group, Upper Cambrian Mount Simon Sandstone, and Precambrian basement 

rocks in deep wells shown on figure 1. In the region of the 

Wabash Valley fault system, the deepest well, the General 

Electric Water Disposal No. 2 well (fig. 1), penetrates 93 m 

of the Knox Group. Table 2 shows the regional stratigraphy 

and elevations of tops of formations penetrated by the 

General Electric well.

According to Nelson (1990a, 1990b) and Kolata and 

Nelson (1990), the New Madrid rift complex comprises the 

northeast-trending Reelfoot rift (Ervin and McGinnis, 1975) 

and the east-trending Rough Creek graben (Soderberg and 

Keller, 1981). These grabens contain several kilometers of 

pre-Knox Group sedimentary strata. Braile and others (1982) 

proposed that the New Madrid rift complex includes a 

Southern Indiana arm (fig. 1) and a St. Louis arm extending 

northeast and northwest, respectively, from the intersection 

of the Reelfoot rift and Rough Creek graben. They based 

these interpretations on seismicity and patterns of correlated 

gravity and magnetic highs on the flanks of the hypothesized 

rifts. A similar pattern of positive gravity and magnetic 

anomalies, due to basic or ultramafic intrusives, flanks the 

Reelfoot rift (Hildenbrand and others, 1977).

Schwalb (1982) mapped thicknesses of the Upper Cambrian Eau Claire Formation (or its stratigraphic equivalent, 

the Bonneterre Formation) and the Mount Simon Sandstone 

(fig. 3) based on sparse well control. Schwalb postulated the 

existence of a Mount Simon Sandstone basin in southwestern Indiana based largely on the concept that a sag basin may 

have developed over the hypothesized Southern Indiana arm 

of the New Madrid rift complex. To the northeast of our survey area, Schwalb interpreted more than 610 m of Mqunt 

Simon strata. Perhaps Schwalb's interpretation was influenced by "jump correlations" of widely spaced, single 

reflection seismic records in southern Indiana shot by Rudman (1960). Rudman tentatively interpreted that the basement surface 40 km northeast of our survey area showed a 

northwest-trending depression of about 1 km below the 

regional slope of that surface in southwestern Indiana. Interpretations of basement depths using such data are generally 

unreliable due to the difficulty of distinguishing basement, 

intrabasement, and suprabasement reflections in parts of the 

Illinois Basin. This difficulty occurs even in good-quality 

common-depth-point (CDP) reflection seismic data. In 

selecting our survey site, we anticipated that a Mount Simon 

Sandstone basin associated with sag over the postulated 

Southern Indiana arm might be thicker in the vicinity of this 

site than to the northeast, as postulated by Schwalb (1982). 

In the postulated Southern Indiana arm, the only well penetrating rocks older than the Upper Cambrian and Lower 

Ordovician Knox Group is the Brown well (fig. 1, table 1), 

which penetrated an altered Precambrian(?) basalt possibly 

associated with a basic intrusive at the edge of the rift, as 

indicated by a positive gravity and magnetic anomaly (Braile 

and others, 1982).

Sexton and others (1986) and Braile and others (1986) 

obtained crooked-line Vibroseis seismic profiles along 

Hamilton County, Grayville, and New Harmony lines in Illinois and Indiana (figs. 1, 4, 5). Figure 4 shows a synthetic 

seismogram for the Cuppy well (fig. 1, table 1) and the west 

end of the Hamilton County, Illinois, seismic line. In wells 

in the Illinois Basin north of the Reelfoot rift and Rough 

Creek graben, the Upper Cambrian Mount Simon Sandstone
REFLECTION SEISMIC PROFILING OF THE WABASH VALLEY FAULT SYSTEM IN THE ILLINOIS BASIN O5

Table 1. Elevations of tops of formations in deep wells.

[Datum is mean sea level. Well locations are shown on figs. 1 and 3. Names in italics are those used in the text to identify these wells. Except for well 12, data are from Buschbach 

and Kolata (1990). NP, not penetrated]

Map 

no.

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

Well name, County, and State

Indiana Farm Bureau No. 1 Brown, Lawrence Co., Ind.

Humble Oil No. 1 Weber-Horn, Fayette Co., HI.

Texaco No. 1 Johnson, Marion Co., HI.

Union Oil of California No. 1 Cisne Community, Wayne Co., HI.

Texaco No. 1 Cuppy, Hamilton Co., HI.

Exxon No. 1 Bell, Webster Co., Ky.

Citizens Gas and Coke No. 9 Rollison, Greene Co., Ind.

Atlantic Richfield No. 77 Lewis, Lawrence Co., HI.

Texas Pacific Oil No. 1 Parley et al., Johnson Co., fll.

Texas Pacific Oil No. 1 Streich Community, Pope Co., fll.

Exxon No. 1 Duncan, Webster Co., Ky.

General Electric Water Disposal No. 2, Posey Co., Ind.

Elevations of tops (in meters)

Knox

-415

-1,249

-1,474

-2,156

-2,245

-1,644

-875

-1,428

-1,522

-2,007

-2,175

-2,227

Mount Simon

-1,416

-1,936

-2,411

-3,247

absent

-3,975

-1,855

-2,569

-3,802

^,257

NP

NP

Basement

-1,783

-2,340

-2,630

-3,356

-3,833

-4,222 1

NP

NP

NP

NP

NP

NP

*A K/Ar age of 478±25 Ma was determined for crystalline rocks near the bottom of the Bell well.

Table 2. Stratigraphic section in southwestern Indiana, elevations of formation tops and thicknesses of strata in the General Electric Water Disposal No. 2 well in Posey County, Indiana.

[Datum is mean sea level. NP, not penetrated. Leaders (--) indicate no data]

Description, age, and dominant rock types Elevation 

(m)

Thickness 

(m)

Quaternary (unconsolidated sediments)...................................

Pennsylvanian (shales and sandstones)....................................

Mississippian (shales, sandstones, and limestones)..................

New Albany Shale (Early Mississippian to Middle Devonian). 

New Harmony (Early Devonian) and Muscatatuck

(Middle Devonian) Groups (carbonates)..............................

Silurian carbonates..................................................................

.+120. 

..+79..

..41 

.503

.-1,262 ........... 103

Maquoketa Group (Late Ordovician shale)...................................

Trenton Limestone (Late and Middle Ordovician), 

Black River Group (Middle Ordovician), and upper 

part of Middle Ordovician Ancell Group (carbonates)...............

St. Peter Sandstone (Middle Ordovician)......................................

Knox Group (Lower Ordovician and Upper Cambrian dolomites).

Davis Formation (Late Cambrian carbonates)...............................

Eau Claire Formation (Late Cambrian carbonates)........................

Mount Simon Sandstone (Late Cambrian)....................................

Rift-fill(?) (Middle Cambrian-Late Proterozoic) 1 •••••••••••••••••••••••••

Crystalline rocks (Proterozoic layered sequence?)2 •••••••••••••••••••••••

.-1,365 ...........345

.-1,710...........126

.-1,836 ............96

1,932

2,241

2,276 .

. 309 

..35

. NP. 

NP.

1 Interpreted in seismic profile by Sexton and others (1986).

2 Interpreted in seismic profile by Pratt and others (1989).

lies unconformably on crystalline basement rocks, except in 

the Cuppy well where the Upper Cambrian Eau Claire Formation may rest directly on weathered granite or arkose. In 

the Grayville and New Harmony lines (fig. 5), Sexton and 

others (1986) interpreted the existence of the Grayville graben as part of the hypothesized Southern Indiana arm of the 

New Madrid rift complex. They interpreted that Precambrian or Cambrian rift-fill lies below the Mount Simon Sandstone and that the Wabash Valley fault system resulted from 

reactivation of basement faults associated with the Grayville

graben. Vertical displacements of basement rocks across 

these older faults are as great as 500 m, according to Sexton 

and others (1986) (fig. 5). Nelson (1990b) suggested, however, that these seismic data show faults in Paleozoic rocks 

that lose displacement downward and do not detectably offset the Upper Cambrian Eau Claire Formation above the 

basement rocks. Greb (1989) suggested that the Southern 

Indiana arm might roughly coincide with the Wabash Valley 

fault system and thus trend north-northeast, instead of 

northeast.
06 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

89° 88° 87°

39°

38°

39°

B

ARPEX 

STUDY AREA 

(Shown on fig. 2)

38°

Figure 3. Schwalb's (1982) interpretation of thicknesses (in meters) of A, the Eau Claire Formation 

(Upper Cambrian) and B, the Mount Simon Sandstone (Upper Cambrian). Contour interval is 250 ft (76.2 

m). Solid circles indicate wells. Thicknesses were determined for the (1) Brown, (2) Weber-Horn, (3) 

Johnson, (4) Cisne, (5) Cuppy, (6) Bell, (7) Rollison, (8) Lewis, (9) Parley, and (10) Streich wells (table 1). 

Modified from Schwalb (1982).
REFLECTION SEISMIC PROFILING OF THE WABASH VALLEY FAULT SYSTEM IN THE ILLINOIS BASIN O7

TOPS OF

STRATIGRAPHIC

UNITS

Ste. Genevieve 

Limestone

New Albany Shale ——

Maquoketa Group

Knox Group

Eau Claire 

Formation

Igneous rock

0.0 -

0.5 -

to Q

O 

&5

CO

UJ

5

1.6 -

2.0 -

2.5 -1

Vp(km/s)

048

1 km

0.0

K^, NEW ALBANY

2.5

Figure 4. Interval velocity, vertical average velocity, and synthetic seismogram for the Cuppy well and west end of the Hamilton County, 

Illinois, seismic line showing the New Albany, Knox, and Eau Claire reflection events. Modified from Sexton and others (1986).
O8 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

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REFLECTION SEISMIC PROFILING OF THE WAB ASH VALLEY FAULT SYSTEM IN THE ILLINOIS BASIN O9

COCORP (Consortium for Continental Reflection Profiling) reflection seismic data, in a profile about 20 km north 

of the Grayville and New Harmony lines (fig. 1), defined a 

Proterozoic layered sequence (Pratt and others, 1989). These 

rocks may comprise Middle Proterozoic crystalline basement of the eastern granite-rhyolite province, which may 

form a veneer over older crustal rocks of Early Proterozoic 

age. Published (Heigold, 1990) and unpublished seismic 

data acquired by industry for oil and gas exploration also 

show layering in basement rocks and basinal features predating the New Madrid rift complex. The COCORP seismic line 

did not image a Late Proterozoic or Cambrian graben containing pre-Mount Simon rift-fill, according to Nelson 

(1990b) and Pratt and others (1990), who suggested that 

reflectors interpreted by Sexton and others (1986) as the base 

of pre-Mount Simon rift-fill (fig. 5) are instead intrabasement reflectors of the Middle Proterozoic layered sequence. 

The COCORP line extends eastward in Indiana across the 

postulated Mount Simon Sandstone basin, across the maximum isopach (610 m) contoured by Schwalb (fig. 3fi), and 

north of the maximum depression of the basement tentatively interpreted by Rudman (1960). Pratt and others (1990) 

interpreted the COCORP profile as having "no significant 

thickening of lower Paleozoic strata like that which characterizes the Reelfoot and Rough Creek basins." Nelson 

(1990a) also stated that well control and COCORP reflection 

seismic data show that the region of the hypothesized St. 

Louis arm does not contain a graben analogous to the Reelfoot rift and Rough Creek graben. Nelson thus concluded 

that the Reelfoot rift and Rough Creek graben together comprise a dogleg graben and that the term "New Madrid rift 

complex" should be discarded. He did not suggest a replacement name, however, for the dogleg graben. The "Reelfoot-Rough Creek graben complex" might be appropriate, 

albeit lengthy.

Seismicity in the Illinois Basin north of the New 

Madrid seismic zone defines the Wabash Valley seismic 

zone (Nuttli, 1974, 1979), and liquefaction features in 

Holocene sediments of the Wabash Valley have provided 

evidence of strong paleoseismicity (Obermeier and others, 

1991, 1992; Munson and others, 1992). This seismic zone is 

in the Midcontinent stress province of regional east-west to 

east-northeast-west-southwest compression. The stress field 

results from plate-tectonic processes, according to Sbar and 

Sykes (1973). The normal faults of the Wabash Valley fault 

system developed in an extensional regime different from 

the present stress field. Seismicity in the Wabash Valley 

seismic zone may be localized by crustal inhomogeneities 

related to the Wabash Valley fault system, the New Madrid 

rift complex (fig. 1), or older structures in crystalline basement rocks. The potential for reactivation of normal faults in 

the Wabash Valley fault system with reverse or strike-slip 

components of motion depends on whether these faults cut

basement rocks and their orientation relative to the present 

stress field. The nature of these faults at depth is largely 

unknown because of the scarcity of published 

common-depth-point reflection seismic data and sparseness 

of deep wells.

SEISMIC DATA ACQUISITION

Seismic lines 1-3 (fig. 2) were shot in an area of low 

relief where near-surface, fine-grained (largely clay) alluvial 

sediments helped couple the seismic energy for deep penetration. The profiles were obtained by minihole pattern 

shooting using field parameters given in table 3. Distances 

were measured in the English system of units (feet). The 

nominal shot pattern comprised five equispaced holes in a 

70-ft (21-m) in-line array detonated with seismic pattern 

electrical detonators. Two-component seismic explosives 

were armed in the field for safety and facilitation of transportation and storage. Despite use of 0.7-kg charges in 3- to 

4.5-m shot holes, most holes did not blow due to careful 

tamping and confinement of the shot by dense clayey soil 

below or near the water table. Some shot holes partially collapsed before the explosives were loaded and, therefore, 

shallower and smaller charges were used. Some shots were 

skipped for buildings, pipelines, a highway, and a bridge.

Geophones were planted in 140-ft (43-m), in-line arrays 

of 12 equispaced sensors with parallel-series connections. In 

rare cases, the first or last six geophones were inactive, due 

to a break in the wire, and the array length became 70 ft (21 

m). Geophones were planted at intervals of about 11.7 ft (3.6 

m), except at road intersections where it was necessary to 

bunch the sensors together. Line 1 (fig. 2) was shot in two 

parts; the eastern part, la, in 1988 and the remainder, Ib, in 

1990. Line la was shot across a field of crops and along a 

gravel road from east to west by "pushing the cable;" that is, 

the end-on geophone spread was west of the shot. Because 

the geophone group interval was twice the shot interval, the 

rollalong switch was generally advanced with every other 

shot. Line Ib was shot from west to east along a gravel road 

by pushing the cable eastward until the far-offset geophone 

group reached a highway 0.8 km west of line 2. Shooting 

then continued eastward with a stationary split-spread geophone layout until the shot location reached the highway. 

Finally, shooting continued east of the highway, with a stationary end-on geophone spread west of the highway, until 

the westernmost shotpoint of line la was approached. Line 2 

was shot in 1989 along gravel and dirt roads from south to 

north by "pushing the cable" north in end-on configuration 

until it reached woods at the edge of the Ohio River. Line 3 

was shot in 1990 from west to east along a gravel road into a 

stationary 1.6-km (1-mi) spread of geophone arrays. Except 

for the first few shots, it was shot with a split-spread configuration. Line la was recorded with a 48-channel SERCEL 

SN-338B seismic recording system; whereas, lines Ib, 2,
O10 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

Table 3. Seismic survey field parameters. 

[Field geometry measured in feet]

Table 4. Data processing sequence.

[CDP, common-depth-point]

Shot pattern .......................5 holes, equispaced

Shot-hole interval............... 14 ft (4.3 m)

Shot-array length................70 ft (21 m)

Shotpoint interval...............70 ft (21 m)

Shot-hole depth..................10-15 ft (3-4.5 m)

Explosives/hole,................. 1.5 Ib (0.7 kg)

Explosives/shot..................7.5 Ib (3.4 kg)

Detonators .........................seismic pattern, electrical

Geophones.........................10-Hz, vertical-motion

Geophone array.................. 12 sensors, equispaced

Array length.......................140 ft (43 m)

Array spacing.....................140 ft (43 m)

Near-trace offset.................455-525 ft (138-160 m)

Arrays/layout:.....................47 (line la);

...............53-59 (lines Ib, 2);

...............36 (line 3)

Far-trace offset:..................2.1 km (line la);

...............2.5 km (lines Ib, 2);

...............0.8-1.6 km (line 3)

Recorder (line la)..............SERCEL SN338B, 48 channels

Recorder (lines Ib, 2-3).....SERCEL SN338HR, 96 channels

Sampling interval...............2 ms

Record length.....................6 s

Antialiasing filter............... 125 Hz, 72 dB/octave

Notch filter ........................60 Hz_______________

and 3 were recorded with a 96-channel SERCEL SN-338HR 

system. All data were recorded for 6 seconds at 2-ms 

intervals with a 125-Hz antialiasing filter and a 60-Hz notch 

filter.

SEISMIC DATA PROCESSING

Table 4 shows the data processing sequence. The data 

were processed using record lengths of 6 s, but only the first 

2.3 s of data are shown in this report. Each application of 

automatic gain compensation used 200-ms data windows. 

Spiking decon volution before stack applied minimum-phase, least-squares predictive 120-ms operators with 

1 percent pre-whitening. Filter design window lengths for 

autocorrelation were 1-1.5 s, depending on source-receiver 

offset. Zero-phase pre-stack, post-stack, and post-migration 

filters specified a trapezoidal band-pass with 0, 1, 1, and 0 

amplitude response at 10, 20, 60, and 80 Hz, respectively. 

The band-pass filter used a convolutional (time-domain) 

302-ms operator truncated by a Hanning taper (equivalent to 

smoothing the trapezoidal amplitude response in the frequency domain).

Shot-lead static corrections, using up-hole geophone 

response and repeat tones in an auxiliary trace, corrected a 

temporary problem in shot-recorder synchronization. ElevaDemultiplexing

Automatic gain compensation

Data editing

Spiking deconvolution

Band-pass filter

Automatic gain compensation

CDP gather

Shot-lead statics (line la)

Elevation statics

Refraction statics (line 1)

Automatic statics

Re-gather (lines la and Ib)

Automatic statics (line 1)

Normal moveout correction

Mutes

CDP stack

Gapped deconvolution

Automatic gain compensation

Band-pass filter

Migration

Mutes

Band-pass filter

Automatic gain compensation

Time-to-depth conversion

tion static corrections reduced the data to a datum 350 ft (107 

m) above sea level using a datum velocity of 914 m/s. The 

maximum change in elevation along a single line, 5 m, 

occurred in line 1. Refraction statics were computed and 

applied in line 1 after interpretation of velocity-reduced 

common-receiver and common-shot gathers to compute and 

correct for delays by low-velocity sediments associated with 

a slough occupied by an intermittent pond. Surface-consistent automatic statics corrections were computed by use of 

crosscorrelation techniques in moveout-corrected CDP gathers with variable data windows, multiple applications, and 

some manual intervention.

Normal moveout corrections used a spatially constant 

stacking velocity function (fig. 6), derived from the data in 

lines 1-2 by standard analysis methods guided by sonic log 

velocities of the Cuppy well (fig. 4). Although moveout 

velocities for reflection events in the Mt. Vernon graben 

should decrease slightly due to greater thickness of Pennsylvanian strata in the graben, the effect was not resolved by 

velocity analysis. Figure 7 is a representative velocity spectrum showing coherence versus moveout velocity and 

two-way reflection time for a CDP gather of good-quality 

data in line 1. Mutes were applied before stack to eliminate 

refraction arrivals and other early-arriving noise from CDP 

stacks. In central parts of the lines, a mute was also applied 

to shorten near-range traces and eliminate late-arriving
REFLECTION SEISMIC PROFILING OF THE WAB ASH VALLEY FAULT SYSTEM IN THE ILLINOIS BASIN 011

VELOCITY, IN KILOMETERS PER SECOND

2345678

VELOCITY, IN KILOMETERS PER SECOND

23456

Figure 6. Velocity functions: A, Stacking velocity (rms velocity); B, vertical-average velocity; C, interval velocity (assuming 

stacking velocity equals rms velocity); andD, interval velocity used 

for conversion of seismic data to depth sections.

noise, mainly surface waves. The data were CDP gathered 

and stacked with a 35-ft (10.7-m) trace interval. Gapped 

least-squares predictive deconvolution was applied after 

stack using a prediction distance of 32 ms, a 

prediction-operator length of 160 ms, and a 2.5-s filter 

design window for autocorrelation from 0.5 to 3.0 s.

Figure 8A shows stacked data from line 1 in a window 

from 0.6 to 1.5 s for CDP locations 400-500, which includes 

part of the Wabash Island fault. The steeply dipping events 

are diffraction limbs generated by shallow diffractors. Figure 

9 shows the F-K spectrum of the windowed data in figure 8A 

after zero-padding in the x-t domain. The wavenumber 

(reciprocal wavelength) is normalized with respect to the 

sampling wavenumber or reciprocal of the trace spacing, 35 

ft (10.7 m). Strong peaks for positive wavenumbers in the 

frequency range of 22-30 Hz indicate unaliased west-dipping events with time-dips, 5-9 ms per trace interval, equal 

to wavenumber divided by frequency. Band-reject frequency 

filtering is unsuitable for attenuation of the diffraction noise 

because the spectrum of this noise overlaps that of reflection 

seismic events. Although post-stack multicomponent filtering, for example F-K filtering, could attenuate these diffractions, wave-equation migration sufficiently improved 

interpretability of the data so that premigration filtering was

Q

O 

O

UJ

(/> 1

UJ

Figure 7. Velocity spectrum, for location 245 in the central part 

of line 1, showing contours of coherency as a function of moveout 

velocity and reflection time. The peak at 1.6 s is the Eau Claire 

reflection event.

unnecessary. Figure &B shows the data of figure 8A after 

application of migration and postmigration automatic gain 

compensation and band-pass filtering. The east-dipping 

event at 0.72 s and CDP location 460 is a primary reflection 

event from within the fault zone of the Wabash Island fault. 

Migration of this segment has moved it to its correct 

position, and the edge of a fault is clearly defined at 0.7 s and 

CDP location 467. The alternative of CDP gathering at 70-ft 

(21.4-m) intervals, with consequent depth-point smear and 

attenuation of dipping events, was not used because it was 

believed that closer trace spacing, at 35-ft (10.7-m) intervals, 

would aid interpretation of the migrated data.

Wave-equation migration was applied with a 

finite-difference algorithm. The laterally constant stacking 

velocity function (fig. 6) was specified for the migration 

algorithm as the root-mean-square velocity from which the 

interval velocity function (fig. 6) was derived assuming 

horizontal layering. Mutes were applied to migrated traces 

to eliminate data preceding the start of non-zero values in 

the corresponding input stacked traces. Because a 302-ms 

zero-phase band-pass filter operator was applied before 

migration, the postmigration mute only eliminated data that 

preceded the start of the corresponding unfiltered stacked 

traces by more than 150 ms. A band-pass filter and automatic gain compensation were then applied to the migrated 

data. Finally, an approximate time-to-depth conversion 

used a laterally constant velocity function (fig. 6) derived 

by approximating the interval velocity function with seven 

constant-velocity layers having two-way interval transit 

times of 200-500 ms. Choice of horizontal layers that did 

not cut across the principal reflection events aided inter-
O12 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

1 km EAST

1.4

480 460 440 420

LOCATION NUMBERS

400 500

B

480 460 440 420

LOCATION NUMBERS

400

Figure 8. Line 1 stacked data from 0.6 to 1.5 s in CDP locations 400-500, which includes part of the Wabash Island fault: A, before 

migration and B, after wave-equation migration and postmigration automatic gain compensation and band-pass filtering. Trace interval is 

35 ft (10.7m).
REFLECTION SEISMIC PROFILING OF THE WABASH VALLEY FAULT SYSTEM IN THE ILLINOIS BASIN O13

-0.5 0.0 0.5

NORMALIZED WAVENUMBER (k/ka , see text)

Figure 9. F-K spectrum of stacked data in figure 8A. Strong peaks with positive wavenumbers are unaliased west-dipping noise; levels of shading in increments of 10 dB; kg (sampling wavenumber) = 10.7 nTl .
O14 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

pretability of the depth sections and avoided distortions of 

those events by variable wavelet stretch or contraction 

where these events were displaced by faults. Although the 

depth sections aid structural interpretation, time intervals 

and interval velocity estimates were used directly to estimate depths and thicknesses.

INTERPRETATION OF 

REFLECTION EVENTS

Seismic reflection profiles of lines 1, 2, and 3 are 

shown in figures 10-15,16-19, and 20-21, respectively. For 

each line, the uninterpreted stacked sections and migrated 

sections are shown first, then interpreted migrated time and 

depth sections are shown. Section-line indicia at 1-mi 

(1.6-km) intervals are shown in these displays and on the 

map (fig. 2). Except on the west end of line 1, where the line 

followed a bend in the road, profiles were shot within 5 m of 

section lines. The CDP fold, or number of traces in each 

CDP gather after editing, is shown above the sections in figures 10, 16, and 21.

STE. GENEVIEVE, NEW ALBANY, 

MAQUOKETA, AND KNOX EVENTS

The interpreted sections of lines 1-3 (figs. 12-15, 

18-19, and 21) show correlations of events with reflecting 

interfaces. For the Ste. Genevieve Limestone, New Albany 

Shale, Maquoketa Group, and Knox Group events, correlations are apparent from examination of depth sections, elevations of formations in the General Electric No. 2 Water 

Disposal well (table 2), and sonic logs of the Cuppy well 

(fig. 4) and other deep wells. The General Electric well 

penetrates the top of the Upper Cambrian and Lower 

Ordovician Knox Group in the Mt. Vernon graben 6.1 km 

north of the intersection of seismic lines 1 and 2 (fig. 2). 

The top of the Upper Mississippian Cypress Formation is 

about 15 m deeper in the General Electric well than in 

wells in the central part of the graben near line 1. Mississippian and Pennsylvanian strata above the Upper Mississippian Ste. Genevieve Limestone are predominantly shales 

and sandstones. The top of the Cypress Formation, mapped 

in figure 2, is about 90 m above the top of the Ste. Genevieve Limestone. The strong New Albany and Maquoketa 

events result from low-velocity and low-density shales of 

about 100-m thickness overlain and underlain by faster and 

denser rocks, mainly carbonates. The Knox event results 

from reflection off the top of the Knox Group, which is 

faster and denser than the overlying Middle Ordovician St. 

Peter Sandstone. Most of the Knox Group is dolomite that

is nearly acoustically transparent. The velocity of Knox 

Group strata increases gradually with increasing depth. In 

southern Illinois, the Knox Supergroup includes the Upper 

Cambrian Franconia Formation (stratigraphic equivalent of 

the Davis Formation (table 2)) and the Upper Cambrian 

Eau Claire Formation (Sargent, 1990). In southern Indiana, 

the Munising Group, comprising the Davis and Eau Claire 

Formations, is excluded from the Knox Supergroup (Droste 

and Patton, 1985).

IDENTIFICATION OF THE 

EAU CLAIRE EVENT

The strong Eau Claire reflection event is identified in 

lines 1-3 (figs. 10-21) by its similarity (in strength, coherence, and relative arrival time) to an event in an unpublished 

industry reflection seismic profile between the Cuppy and 

Duncan wells (fig. 1) and the Hamilton County, Grayville, 

and New Harmony profiles in Illinois and Indiana (figs. 4 

and 5). The Cisne> Cuppy, and Streich wells are the closest 

wells in Illinois to penetrate the Eau Claire Formation (fig. 

1). The nearest well to this formation in Kentucky is the 

Duncan well. Sexton and others (1986) tied the west end of 

the Hamilton County profile to the Cuppy well with a synthetic seismogram (fig. 5). In that well, the Eau Claire Formation is a low-velocity 260-m interval of shaley carbonates 

underlying faster strata of the Knox Group and overlying 

weathered granite or arkose on a basement high, the Mount 

Simon Sandstone being absent. Although the velocity of the 

Eau Claire Formation varies rapidly with depth in the Cuppy 

well (fig. 4), all the Eau Claire strata have velocities less 

than those of the overlying lower part of the Knox strata. In 

the Cisne, Cuppy, and Duncan wells (figs. 1 and 4) the 

velocity of lower Knox strata, 100 m above the Eau Claire 

Formation, is about 7,000 m/s.

In the Cisne well (fig. 1) velocities of the Eau Claire 

and Mount Simon Formations are 5,187 and 4,689 m/s in 

291- and 109-m intervals, respectively (Heigold and Oltz, 

1990). The normal-incidence reflection coefficient for particle displacement due to velocity contrast only is Ry = 

(V2-Vj)/(V2+Vi), where Vj and V2 are velocities above 

and below an interface. For velocities of lower Knox strata, 

Eau Claire Formation, and Mount Simon Sandstone of 

7,000, 5,200, and 4,700 m/s, respectively, Rv is -0.15 and 

-0.05 at the top and bottom of the Eau Claire interval. 

Pre-Knox strata are about 1 km shallower in the Cisne well 

than in the seismic survey area where Eau Claire strata 

probably have higher velocities. Figure 22 shows parts of 

sonic logs that were smoothed and converted to functions 

of two-way time relative to the top of the Eau Claire 

low-velocity layer in the Cuppy, Streich, and Duncan wells.
REFLECTION SEISMIC PROFILING OF THE WABASH VALLEY FAULT SYSTEM IN THE ILLINOIS BASIN 015

2km

I EAST

700 600 500 400 300

LOCATION NUMBERS

200 100 20

Figure 10. Line 1 stacked section and plot of CDP fold. Section lines (S) are marked at 1-mi (1.6-km) intervals. At location 83, line 1 

ties line 2. Trace interval is 35 ft (10.7 m).

Pre-Knox strata in the Streich well are at about the same 

depth as in the survey area. The average velocity of the Eau 

Claire strata in the Streich well is about 5,800 m/s, about 

the same as the velocity of the deepest Mount Simon strata 

in this well. For velocities of 7,000 and 5,800 m/s above 

and below the top of the Eau Claire Formation, Rv is about 

-0.9. Density contrast enhances reflectivity of this interface. It probably produces a strong reflection event in most 

of the Illinois Basin. The apparent two-way interval transit 

time between the tops of the Knox Group and the Eau 

Claire Formation is about 460 ms as measured by a 

peak-to-trough separation within the graben in line 1. The 

interval velocity is probably about 6,400 m/s, as in the 

Cuppy well (fig. 4). The corresponding thickness of the
O16 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

1 km__. EAST

0.0 -

0.5 -:

o

O

UJ

2.0

560 500 400 300 200 

LOCATION NUMBERS

100 20

Figure 11. Line 1 migrated section for locations 9-560 with section lines (S) at 1-mi (1.6-km) intervals. Numbers in circles are 

projected locations of wells 3-7. At location 83, line 1 ties line 2. Trace interval is 35 ft (10.7 m).
REFLECTION SEISMIC PROFILING OF THE WAB ASH VALLEY FAULT SYSTEM IN THE ILLINOIS BASIN 017

1 km EAST

CO

o

z 

o

CJ

UJ 

(O

1IN

M

K

;- x

560 500 400 300 200 

LOCATION NUMBERS

100

Figure 12. Line 1 migrated section (locations 9-560) showing the Hovey Lake fault (H), the floor (A) and roof (B) faults of the Wabash 

Island fault, and section lines (S). Numbers in circles are projected locations of wells 3-7. Interpreted events (labeled along right side of 

figure) are: S, Ste. Genevieve Limestone; N, New Albany Shale; M, Maquoketa Group; K, Knox Group; E, Eau Claire Formation; and X, 

acoustic basement.
O18 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

1 km EAST

o —

S

N

M 

K

560 500 400 300 200

LOCATION NUMBERS

100 20

Figure 13. Line 1 depth section (locations 9-560) showing the Hovey Lake fault (H), the floor (A) and roof (B) faults of the Wabash 

Island fault, and section lines (S). Numbers in circles are projected locations of wells 3-7. Interpreted events (labeled along right side of 

figure) are: S, Ste. Genevieve Limestone; N, New Albany Shale; M, Maquoketa Group; K, Knox Group; E, Eau Claire Formation; and X, 

acoustic basement. Horizontal lines are at 1,000-ft (305-m) intervals.

Knox Group is approximately 1,470 m. Also, using the 

depth to the top of the Knox Group in the General Electric 

well, we estimate that the top of the Eau Claire Formation 

in the center of the graben beneath line 1 is approximately 

3,680 m below sea level.

THICKNESS OF THE EAU CLAIRE 

LOW-IMPEDANCE LAYER

The Eau Claire event is a wavelet complex due to 

interference of two or more reflections. The first trough of
REFLECTION SEISMIC PROFILING OF THE WABASH VALLEY FAULT SYSTEM IN THE ILLINOIS BASIN 019

CO

cc

I

o

t

UJ

o

1/2 km EAST

o -

2 -

560 500 4OO 300

N

M

K

LOCATION NUMBERS

Figure 14. Line 1 depth section (locations 200-560) showing the floor (A) and roof (B) faults of the Wabash Island fault and section 

lines (S). Numbers in circles are projected locations of wells 3-5. Interpreted events (labeled along right side of figure) are: S, Ste. Genevieve Limestone; N, New Albany Shale; M, Maquoketa Group; K, Knox Group; E, Eau Claire Formation; and X, acoustic basement. Horizontal lines are at 1,000-ft (305-m) intervals.
O20 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

, 1/2 km , EAST

o -

.

I

o

380 300 200

N

M

LOCATION NUMBERS

Figure 15. Line 1 depth section (locations 9-380) showing the Hovey Lake fault (H) and section lines (S). Numbers in circles are projected locations of wells 5-7. Interpreted events (labeled along right side of figure) are: S, Ste. Genevieve Limestone; N, New Albany Shale; 

M, Maquoketa Group; K, Knox Group; E, Eau Claire Formation; and X, acoustic basement. Horizontal lines are at 1,000-ft (305-m) intervals.
REFLECTION SEISMIC PROFILING OF THE WABASH VALLEY FAULT SYSTEM IN THE ILLINOIS BASIN O21

1 km NORTH 1 km NORTH

UJ

100 200

LOCATION NUMBERS

300

Figure 16. Line 2 stacked section and plot of CDP fold with 

section-line indicia (S). Number in circle is projected location of 

well 10. At location 305, line 2 ties line 1. Trace interval is 35 ft 

(10.7 m)

20 100 200

LOCATION NUMBERS

300

Figure 17. Line 2 migrated data with section-line indicia (S). Number in circle is projected location of well 10. At location 305, line 2 ties line 1. Trace interval is 35 ft (10.7 m).
O22 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

1 km NORTH

o 

o

LLI

LLI

5

1.0

1.5 -

2.0 -

100 200

LOCATION NUMBERS

300

Figure 18. Line 2 migrated data showing faults D and E of the Hovey Lake fault 

and section lines (S). Number in circle is projected location of well 10. Interpreted 

events (labeled along right side of figure) are: S, Ste. Genevieve Limestone; N, New 

Albany Shale; M, Maquoketa Group; K, Knox Group; E, Eau Claire Formation; and 

X, acoustic basement.
REFLECTION SEISMIC PROFILING OF THE WAB ASH VALLEY FAULT SYSTEM IN THE ILLINOIS BASIN O23

1 km NORTH

S

N

M 

K

6 -

100 200

LOCATION NUMBERS

300

Figure 19. Line 2 depth section showing faults D and E of the Hovey Lake fault and 

section lines (S). Number in circle is projected location of well' 10. Interpreted events 

(labeled along right side of figure) are: S, Ste. Genevieve Limestone; N, New Albany 

Shale; M, Maquoketa Group; K, Knox Group; E, Eau Claire Formation; and X, 

acoustic basement. Horizontal lines are at 1,000-ft (305-m) intervals.

this event is correlated (interpreted) in figures 12-15, 

18-19, and 21. In lines 1-2 the event generally has eight 

successive legs (fig. 23C): (1) a weak initial peak, (2) an 

anomalously strong trough, (3) a strong peak generally 

weaker than the first trough, (4) a moderate- to

high-amplitude trough, (5) a peak near the zero-deflection 

line, (6) another moderate- to high-amplitude trough, (7) a 

peak of moderate strength, and (8) a trough of moderate 

strength. All seismic sections for lines 1-3 have normal 

Society of Exploration Geophysicists (S.E.G.) polarity for
024

B

0.0 i

INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

1/2 km . EAST

CO 

Q

O 

O

{/) 0.5 —

w

5

ICO 

Q

O 

O

CO 0.5

5

ICO 

(C

w

O

UJ

Q

140

I I 

120 100 80

LOCATION NUMBERS

I

80

I 

40

f

Figure 20. Line 3: A, stacked section (0-1 s) with section-line indicia (S); B, migrated data; and C, depth section and numbered CDP 

locations; horizontal exaggeration is approximately 3:1. Horizontal lines are at 1,000-ft (305-m) intervals.
REFLECTION SEISMIC PROFILING OF THE WABASH VALLEY FAULT SYSTEM IN THE ILLINOIS BASIN O25

EAST

2.0

6 -

140 40

LOCATION NUMBERS B

140 40

LOCATION NUMBERS

Figure 21. Line 3: A, migrated data and B, depth section, with plot of CDP fold, showing the Wabash Island fault (W) and section lines (S). Interpreted events (labeled along right sides of seismic 

sections) are: S, Ste. Genevieve Limestone; N, New Albany Shale; M, Maquoketa Group; K, Knox 

Group; E, Eau Claire Formation; and X, acoustic basement. Trace interval is 35 ft (10.7 m).
O26 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

SLOWNESS, IN MICROSECONDS PER METER

300 

-300

-200

100 300 100 300 100

CO 

Q

O -100

O 111 

CO

i

II

i

- E

111

I

111 

cc

100

200

300

400

- EM

Cuppy

Hamilton Co.,

Streich

Pope Co., III.

Duncan

Webster Co., Ky.

Figure 22. Parts of sonic logs for the Cuppy, Streich, and Duncan wells showing slowness (reciprocal velocity) as a function of 

two-way reflection time relative to that of the top of the Eau Claire 

Formation (E). Approximate tops of Precambrian rocks (P) and the 

Mount Simon Sandstone (M) are shown.

an explosive source (Thigpen and others, 1975). First 

upward motion of the geophone case produces a trough 

(negative deflection) in these wiggle-trace, variable-area 

displays. Zero-phase band-pass filtering produces precursory deflections, but these are negligible in our data and do 

not affect polarity interpretations of the Eau Claire event or 

first-arrival critical refractions (head waves). For an impulsive source with first motion of the incident wave 

downgoing and away from the source, reflection from a 

low-impedance layer yields downward first motion of the 

reflected wave at the surface and a peak in normal-polarity 

displays. Generally, the second leg of the primary seismic 

wavelet has much greater amplitude than the first leg in data

recorded and processed with parameters similar to those 

used here. Therefore, in data with high signal-to-noise ratio, 

a strong (high-amplitude) event from an isolated, highly 

reflective, low-impedance layer begins with a weak peak 

followed by a strong trough. That the first anomalously 

large deflection, leg 2, of the Eau Claire event is a trough, is 

consistent with reflection from a highly reflective 

low-impedance layer.

Legs 4-6 of the Eau Claire event together form a 

broad trough interrupted by a minor peak (fig. 23 C), a feature that may result from destructive interference. To further interpret the waveform of the Eau Claire event, 

wavelet complexes (fig. 235) corresponding to simple 

velocity models (fig. 23£>) were considered. In these models, density variations were ignored, a reference velocity 

of 7,000 m/s for the lower part of the Knox strata was 

used, and modeled reflection coefficients were scaled arbitrarily to get reasonable velocity estimates. The modeled 

primary seismic wavelet (fig. 23A) was generated by convolution of the first derivative of a Gaussian error function 

with a series of three equispaced spikes of alternating 

sign (Rene, 1992). The dominant period of the wavelet, 

33 ms, is twice the separation between extrema of the 

derivative of the Gaussian function and twice the interval 

between successive spikes in the time series with which 

this derivative was convolved. The modeled wavelet has 

four legs, the second of which has the largest amplitude. 

The simplest velocity model is a low-velocity 

(low-impedance) layer (model 1 in fig. 23£>) with 

two-way interval transit time, 72 ms, equal to the separation between the second and seventh legs of the wavelet 

complex. The modeled waveform may better approximate 

the Eau Claire event by inclusion of layering within the 

low-impedance layer (models 2-5 in fig. 23£>). The solution of a low-impedance layer is not unique; however, the 

Eau Claire event can also be modeled by several step-like 

decreases in velocity (model 6 in fig. 23D) or by other 

models with transitional layers.

Interval velocities of the Eau Claire Formation are 

about 5,200 and 5,800 m/s in the Cisne (Heigold and 

Oltz, 1990) and Streich (fig. 22) wells, respectively. For 

velocities of 5,000-6,000 m/s, a 72-ms two-way interval 

transit time corresponds to an interval of 180- to 216-m 

thickness. Using sparse well control, Schwalb (1982) 

mapped the Eau Claire Formation (fig. 3A) and interpreted a thickness of about 360 m in our study area, 

slightly greater than in the Parley well. For velocities of 

5,000-6,000 m/s, the two-way interval transit time for a 

360-m layer is 144 to 120 ms. If the Eau Claire event is 

due to a low-impedance layer with two-way interval transit time of 72 ms, then either that interval is only part of 

the Eau Claire Formation or the Eau Claire Formation is 

only about 200 m thick, much thinner than mapped by
REFLECTION SEISMIC PROFILING OF THE WABASH VALLEY FAULT SYSTEM IN THE ILLINOIS BASIN O27

0 1

WAVELET

Model: 123456

WAVELET COMPLEXES

VELOCITY, IN KILOMETERS PER SECOND 

4686868686868

SEISMIC DATA

B

VI \

23456

VELOCITY MODELS

D

Figure 23. A, Modeled primary seismic wavelet; B, modeled wavelet complexes 1-6; C, the Eau Claire event in line 1 data after 

wave-equation migration (from within the Mt. Vernon graben); and D, corresponding velocity models 1-6. Successive legs numbered 1-8 

are identified in the wavelet complexes and the Eau Claire event.

Schwalb (1982). Considering the indications of layering 

in the Eau Claire Formation shown by geophysical logs 

from deep wells in the Illinois Basin, we interpret that the 

Eau Claire event is probably generated by reflections at 

the top of the Eau Claire Formation and other interfaces in 

the upper 200 m of that formation.

ACOUSTIC BASEMENT EVENT

The acoustic basement event in lines 1-3 is tentatively 

defined by trough X, which follows the first trough of the 

Eau Claire event by about 250 ms (figs. 12-15, 18-19, and 

21). The coherent events arriving after the Eau Claire event 

and including trough X may include multiple reflections, 

especially long-period interbed multiples with little differential moveout relative to primary reflections. Correlations 

across faults and apparent terminations at interpreted fault 

cuts in line 1 may indicate that primary reflections dominate 

these sub-Eau Claire events (figs. 12-15). Coherency 

decreases directly below the fault cuts of the Eau Claire Formation. This may indicate fault-shadow effects (Tucker and 

Yorston, 1973) of nonhyperbolic moveout, wherein, for a 

given CDP gather, some paths to or from a sub-Eau Claire 

footwall reflector cross the fault where lower Knox strata are 

faulted out, and other ray paths to or from that same reflector

cross the fault whe're Eau Claire strata, with much slower 

velocities, are faulted out. If trough X is part of the response 

to reflection from geologic basement, defined as the top of 

igneous or metamorphic basement rocks, then coherency of 

troughs and peaks in the interval between trough X and the 

Eau Claire event is probably due to reflectivity of the 

interface between the Eau Claire and Mount Simon Formations and layering within those formations.

Except for the Weber-Horn well, wells in the map area 

of figure 3 penetrated 30 m or less of Precambrian crystalline 

rocks, and sonic velocities were generally reduced by effects 

of weathering. The Weber-Horn well penetrated about 400 

m of Mount Simon Sandstone, with an average velocity of 

4,450 m/s, overlying 122 m of Precambrian crystalline 

rocks, including a rhyolite porphyry. The velocity of basement rocks a short distance below the Cambrian-Precambrian contact is 5,240 m/s, and the top of basement rocks 

produces a strong reflection event in nearby CDP seismic 

data (Heigold and Oltz, 1990). Basement is only 2.3 km 

below sea level in this well. The average velocity of Mount 

Simon Sandstone is 4,689 m/s in the Cisne well, 3.3 km 

below sea level (Heigold and Oltz, 1990). Christensen 

(1982) measured compressional wave velocities of 

5,710-6,520 m/s for 19 samples of granite at 0.1 GPa, which 

approximates the pressure at the top of basement rocks in the 

survey area. For velocities of Mount Simon Sandstone of 

4,700-5,000 m/s and velocities of granite of 5,700-6,500
O28 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

m/s, reflection coefficients for particle displacement due to 

velocity contrast, Ry, are from 0.13 to 0.16, about the same 

in absolute magnitude as was calculated for the Knox-Eau 

Claire interface (Ry = -0.15) with velocities of 7,000 and 

5,200 m/s above and below that interface, respectively.

In lines 1-3, the reflection event that includes trough X 

is much less coherent than the Eau Claire event. This may 

result from low reflectivity of the basement due to greater 

velocities of Mount Simon Sandstone than are measured in 

Illinois Basin wells, or it may result from the presence of 

basement rocks with lower velocities than unweathered 

granite, for example rhyolites. We do not interpret 

pre-Mount Simon rift-fill beneath lines 1-3, although this 

cannot be ruled out. Rift-fill sedimentary or igneous rocks, 

as postulated by Sexton and others (1986), and sedimentary 

or metasedimentary strata in a Proterozoic layered sequence, 

may not be distinguishable in these data from other basement 

rocks, including unlayered granites. For purposes of seismic 

interpretations, we will refer here to the combined Eau Claire 

and Mount Simon Formations as the pre-Knox sedimentary 

rocks.

At least some of the events arriving after trough X may 

be surface multiples, long-period interbed multiples, diffractions generated by nonlayered intrabasement heterogeneities 

(Gibson and Levander, 1988,1990), or sideswipe from Paleozoic reflectors having steep dips due to drag folding associated with the Wabash Island and Hovey Lake faults. Some of 

these events, however, may be primary reflections from 

within the basement rocks, perhaps from interfaces in the 

Proterozoic layered sequence defined in COCORP and other 

reflection seismic data from the region of the eastern granite-rhyolite province (Pratt and others, 1990). Some of these 

sub-acoustic basement events terminate at interpreted fault 

cuts. An apparent footwall cutoff of a reflection event by the 

Wabash Island fault is observed at CDP location 310 at a 

depth of about 4.8 km in line 1 (fig. 13). Possibly, this event 

should be designated as the acoustic basement because it can 

be tentatively correlated across the Wabash Island and 

Hovey Lake faults. With the caveat that acoustic basement is 

not definable with certainty in the reflection data of seismic 

lines 1-3, we shall tentatively interpret the thickness of 

pre-Knox sedimentary strata assuming that trough X is generated by reflection from the top of basement rocks.

The onset of the wavelet or wavelets that include trough 

X is indeterminate due to superposition of suprabasement 

reflections. Intrabasement reflectors may be subparallel to 

suprabasement reflectors, but it is unlikely that angular discordance would be so slight that intrabasement reflections 

would contribute to coherence of the sequence of deflections 

between the Eau Claire event and trough X over distances of 

several kilometers. For a basement velocity of 6,000 m/s, 

angular discordance of 3° between Paleozoic layering and an 

intrabasement reflector would produce divergence of reflections by 17.5 ms, about half the dominant period of the primary seismic wavelet, over a distance of 1 km. Because the

data are shown with normal S.E.G. polarity convention, 

trough X may be the third or fifth leg of a wavelet reflected 

from the top of high-impedance basement rocks. Estimates 

of two-way interval transit time from the top of the Eau 

Claire Formation to basement are about 202 or 234 ms 

according to whether trough X is the fifth or third leg of the 

wavelet reflected from basement. For interval velocities of 

5,000-6,000 m/s and two-way interval transit times of 202 or 

234 ms, thickness estimates of 505-606 m or 585-702 m, 

respectively, are computed for pre-Knox sedimentary rocks. 

In the survey area, Schwalb (1982) interpreted about 640 m 

of pre-Knox sedimentary rocks comprising 360 m of Eau 

Claire Formation and 280 m of Mount Simon Sandstone (fig. 

3). For a two-way transit time of 202 ms and a thickness of 

640 m, an average interval velocity of 6,340 m/s is implied. 

This is much greater than indicated by sonic velocities in 

wells. For two-way transit time of 234 ms and thickness of 

640 m, the interval velocity is 5,470 m/s, which is reasonable. If Schwalb's interpretations of thicknesses in the area 

are correct, trough X is more likely the third than the fifth leg 

of a wavelet reflected from the top of basement rocks. In 

view of the application of prestack spiking deconvolution to 

the data, the fifth leg of the wavelet may be so small that it 

would not account for trough X.

In the Streich well, pre-Knox sedimentary strata are at 

about the same depth as in the survey area. The average 

velocity of the Eau Claire strata is about 5,800 m/s, about the 

same as the velocity of the deepest Mount Simon strata penetrated in this well (fig. 22). For an interval velocity of 5,800 

m/s and thickness of 360 m, the computed two-way interval 

transit time for the Eau Claire Formation in the study area is 

124 ms and the remaining two-way transit time for the 

Mount Simon Sandstone is thus about 78 or 110 ms, according to whether trough X is the fifth or third leg of the wavelet 

reflected from basement. For velocities of 5,000-6,000 m/s 

and two-way interval transit times of 78 or 110 ms, thickness 

estimates of 195-234 m or 275-330 m, respectively, are 

computed for the Mount Simon Sandstone. In both cases 

estimated thicknesses are greater than indicated by Rupp 

(1991), who interpreted less than 150 m of Mount Simon 

Sandstone in the survey area (more precisely, no contours 

were mapped south of a 152-m (500-ft) contour). If the Eau 

Claire Formation is much thicker than 360 m or much slower 

than 5,800 m/s, then the Mount Simon Sandstone may be 

less than 150 m thick, as interpreted by Rupp, even if trough 

X is part of the geologic basement reflection.

Assuming 360 m of Eau Claire Formation with a velocity of 5,800 m/s, and assuming that trough X is the third leg 

of the wavelet reflected from the basement, we estimate 

275-330 m of Mount Simon Sandstone beneath lines 1-3. 

Our seismic survey area is about halfway between the Cuppy 

and Bell wells. The thickness of the Mount Simon Sandstone 

is about 265 m in the Bell well (table 1) and this formation is 

absent in the Cuppy well, according to Buschbach and 

Kolata (1990). Thus, a thickness of about 300 m of Mount
REFLECTION SEISMIC PROFILING OF THE WABASH VALLEY FAULT SYSTEM IN THE ILLINOIS BASIN O29

Simon Sandstone beneath seismic lines 1-3 is consistent 

with the existence of a Mount Simon Sandstone basin in 

southwestern Indiana on-trend with the Reelfoot rift but perhaps not extending as far north as the COCORP seismic line. 

The Cisne well (table 1) penetrated only 109 m of Mount 

Simon Sandstone north-northeast of the Cuppy well. As 

interpreted by Schwalb (1982) (fig. 35), the Mount Simon 

Sandstone may be regionally thinner in the vicinity of these 

two wells. Alternatively, relief on the eroded Precambrian 

surface may account for isolated changes in thickness of the 

Eau Claire and Mount Simon Formations (Pratt and others, 

1990). Interpretations of regional structure are speculative, 

given only the sparse well control and estimates of thickness 

based on reflection seismic data presently available. Using 

the depth to top of the Knox Group in the General Electric 

well and interpreted thickness estimates of 1,470, 360, and 

300 m for the Knox Group, Eau Claire Formation, and 

Mount Simon Sandstone, respectively, we estimate that the 

top of the Precambrian basement rocks is about 4,340 m 

below sea level in the center of the Mt. Vernon graben 

beneath seismic line 1.

INTERPRETATIONS OF FAULTS AND 

FAULT-RELATED STRUCTURES

Table 5 summarizes fault cuts and elevations of formation tops in selected shallow wells (fig. 2). Locations of some 

wells are projected along strike to locations shown at the top 

of the seismic sections. In a time section where velocity 

increases with depth, a planar fault will give the false appearance of being listric, or concave upward, and the geometry 

of a fault may be interpreted more easily in a depth section. 

All depth sections, except figure 20C, are shown without 

vertical or horizontal exaggeration. The datum for time and 

depth sections is 107 m (350 ft) above sea level. There are 

potential pitfalls, however, in interpreting the depth sections, 

including fault-shadow effects and effects of approximations 

in time-to-depth conversion using the laterally constant 

velocity function of figure 4.

WABASH ISLAND FAULT

Figures 12-15 show interpreted migrated time and 

depth sections of line 1. In the depth sections (figs. 13 and 

14), we interpret the Wabash Island fault as a fault zone 

about 220 m wide along the east-west direction of the seismic profile. Figure 14 shows part of the depth section that 

includes the Wabash Island fault at an expanded scale for 

depths less than 16,000 ft (4.9 km) and details of interpretation in the fault zone. The fault zone appears to be quasi-planar with an apparent east dip of about 64°. For an 

approximate strike of N. 20° E. (fig. 2), the estimated true 

dip of the fault zone is about 65° east-southeast. Faults A and

Table 5. Elevations of the top of the Cypress Formation (Upper 

Mississippian) and fault cuts, and thicknesses of strata faulted out 

in selected wells shown in figure 2.

[Elevations are relative to mean sea level and are shown in meters. Thickness faulted 

out shown in meters. Except for well 6, data are from Tanner and others (1980b). NP, 

not penetrated. Leaders (--) indicate no data]

Well

no.

1.........

2.........

3.........

4.........

5.........

6.........

7.........

8.........

9.........

10........

11.........

12........

13........

Elevations

Cypress Fm.

............592..............

............595..............

............593..............

............678..............

............664..............

............675..............

...........-581..............

............586..............

— .

— ..

............ NP...............

—

........ .... — .. .... .... .

............ NP...............

............646..............

............587..............

............589..............

Fault

-167.........

,.-67..........

, -190 .........

...—............

...—... ........

...—............

—

-255.........

-362.........

^75.........

-533.........

-167.........

-207.........

-280.........

-105.........

-310.........

..-2...........

-117.........

Thickness

faulted out

..............59

..............55

..............87

...............—

—

..............15

..............34

..............18

..............27

..............23

..............30

..............27

..............24

..............23

.............113

..............94

B are identified as the floor and roof faults of the fault zone, 

respectively.

Fault A is well defined by footwall cutoffs of the New 

Albany, Maquoketa, Knox, and Eau Claire events (figs. 

12-13). It apparently extends into basement rocks and cuts 

the acoustic basement event about 0.3 km east of the fault cut 

of the Eau Claire event. The footwall and hanging-wall cutoffs of the Eau Claire and New Albany events are offset by 

about 34 and 20 ms, respectively. Using a velocity of 7,000 

m/s for Knox strata faulted out at the footwall cutoff of the 

Eau Claire Formation, the calculated vertical displacement 

on fault A is about 120 m. Using a velocity of 6,000 m/s for 

strata faulted out, the calculated vertical displacement of the 

New Albany Shale is about 60 m, half of the apparent displacement of the Eau Claire Formation. Fault A probably 

cuts wells 1-2 0.3 km south and north of line 1 (fig. 2), where 

vertical fault displacements of 59 and 55 m are indicated by 

thicknesses of missing strata (table 5). The trace of fault A at 

the top of the Cypress Formation (fig. 2) is east of wells 1-2, 

and the trace of fault A at the bedrock surface is west of these 

wells.

In well 3, 0.1 km south of line 1 (fig. 2), the elevation 

of the top of the Upper Mississippian Cypress Formation is 

about the same as in wells 1-2 (table 5). Most of the vertical 

displacement in the Cypress Formation by the Wabash 

Island fault is east of well 3 and, therefore, east of fault A in 

line 1. In our survey area, except for anticline F (fig. 2), 

Cypress strata in the upthrown block of the Wabash Island 

fault define a west-dipping monocline. The dip on this mon-
O30 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

ocline exceeds the regional dip and may indicate rotation 

along the east-dipping Inman East fault. In line 1, displacement on fault A is apparently much less than in wells 1-2, 

and the fault may not reach the bedrock surface, although 

normal drag folding may be evidenced by an east-dipping 

reflection downthrown to fault A about 800 m below seismic 

datum at CDP location 475.

Part of the apparent upward decrease in displacement 

along fault A may be due to normal drag folding, as indicated 

by east dip of the New Albany reflection event downthrown 

to fault A, or due to ductile deformation in an elliptical 

region around the fault (Barnett and others, 1987), as may be 

indicated by apparent footwall uplift, or roll-under, of the 

Eau Claire Formation adjacent to fault A. Displacement may 

also decrease upward along fault A due to upward bifurcation of the fault. Steeper dipping fault branches are tentatively interpreted by dashed lines within the fault zone (fig. 

14). We designate these fault branches, from shallowest to 

deepest, as ABi-AB4. Faults A, B, and ABj-AB4 bound 

horses, or slices within the fault zone. We interpret that faults 

AB i-AB4 are tangential to faults A and B. In line 1, we interpret that fault branch ABj diverges from faults A and B 

about 1.2 and 0.3 km below seismic datum, respectively (fig. 

14). Faults within the fault zone may be more numerous and 

more complex than we have interpreted; however, some simplification may be justified because the faults are not clearly 

imaged through the Knox Group, which is nearly acoustically transparent.

Fault B apparently cuts well 3 above the Cypress Formation where 87 m of strata are faulted out about 300 m 

below seismic datum (table 5). Fault B extends downward 

from well 3 subparallel to fault A (figs. 13-14). The possible extension of fault B through the Knox Group and into 

basement rocks is dashed in the interpretation. The vertical 

displacement of the Eau Claire Formation by fault B is perhaps less than 30 m and may not be resolvable in the seismic data. We interpret that faults ABi~AB4 probably 

transferred displacement downward from the roof fault B to 

the floor fault A.

One effect of transferring displacement from one side 

of the quasi-planar fault zone to the other along faults such 

as AB i-AB4 may have been similar to that of a single listric 

fault with consequent rotation of strata in the downthrown 

block. Such rotational motion is generally associated with 

rollover, or reverse drag in the downthrown block, although, 

in consolidated rocks, normal drag folding may also occur 

(Hamblin, 1965). Normal drag folding is evidenced by the 

west limb of the hanging-wall syncline, I (fig. 2). Well 4 penetrates the Cypress Formation in syncline I about 14 m 

deeper than well 5 on the crest of anticline G (fig. 2, table 5). 

Reverse drag folding, or rollover, is evidenced by the east 

limb of syncline I and west limb of anticline G. Syncline I 

may narrow and die out with increasing depth and is perhaps

absent at the base of the Knox Group where the Mt. Vernon 

graben is only about 2.1 km wide (fig. 13). About 1.5 km 

south of line 1, well 11 intersects a fault 417m below seismic 

datum where 23 m of strata is faulted out (fig. 2, table 5). We 

interpret that this branch of the Wabash Island fault dies out 

northward into the west limb of the hanging-wall syncline I 

below line 1 (fig. 2). If faults ABj-AB4 or other faults within 

the fault zone are tangential to the floor and roof faults, then 

these steeper dipping fault surfaces must include both concave upward and convex upward surfaces. One effect of 

movement on a convex upward normal fault is normal drag 

folding of the hanging wall (Xiao and Suppe, 1992). Effects 

of both concave and convex upward fault surfaces may partially account for the divergence of dips of strata within the 

fault zone between faults A and B and in the hanging wall of 

the roof fault, B.

Line 3 is 2 mi (3.2 km) south of line 1. Figure 20 shows 

uninterpreted stack, and migrated time and depth sections. 

Figure 21 shows the interpreted migrated time and depth sections. These data image part of the Wabash Island fault at 

depths less than 1.5 km. The apparent dip of the quasi-planar 

fault is about 74° to the east. For a strike of N. 22° E. (fig. 2), 

the calculated true dip is 75° east-southeast. Wells 12-13 are 

0.7 km south and north of line 3. In these wells, 113 and 94 

m of strata are faulted out 109 and 224 m below seismic 

datum, respectively (table 5). These wells probably cut the 

westernmost fault branch of the Wabash Island fault. The 

vertical displacement of the fault imaged in line 3 is probably 

about 100 m, as in wells 12-13 and other nearby wells 

on-trend with the interpreted fault, but this can not be confirmed with certainty by correlation of events across the 

fault, perhaps because the seismic data are affected by less 

CDP coverage (lower stacking fold) in the taper on the east 

end of line 3.

A stream crossing line 3 near CDP location 76 flows 

from a narrow marshy slough that extends 1.4 km to the 

north-northeast, subparallel to the Wabash Island fault. Oil 

wells penetrate the bedrock surface at a depth of about 40 m 

in this area. The interpreted trace of the westernmost branch 

of the Wabash Island fault at the bedrock surface extends 

northeastward from the vicinity of location 72 in line 3. This 

interpreted trace roughly coincides with the east edge of the 

marshy slough defined approximately by the 360-ft (110-m) 

contour of ground-surface elevation above sea level. This 

spatial coincidence is probably without significant causal 

connections because there are several other sloughs in the 

area trending north-northeast. It is possible, however, that 

development of this particular slough was influenced by (1) 

bedrock surface topography associated with fault-related 

folds or differential erosion of bedrock on either side of the 

fault or in the fault zone, (2) movement of fluids along the 

fault, or (3) fault reactivation by regional compressive forces 

in Quaternary time. Reactivation of the fault surface imaged 

in line 3 might have been favored because the fault has a
REFLECTION SEISMIC PROFILING OF THE WABASH VALLEY FAULT SYSTEM IN THE ILLINOIS BASIN O31

large displacement, which probably continues to basement, 

and the fault may have less curvature than branches of the 

Wabash Island fault further east.

HOVEY LAKE FAULT

The Hovey Lake fault cuts the New Albany Shale near 

the intersection of seismic lines 1 and 2. About 0.4 km southeast of this intersection, 94 m of strata are faulted out by four 

faults at depths of 362-640 m in well 8 (table 5, fig. 2). 

About 80 m of section is faulted out by three faults in nearby 

well 9. In Mississippian and Pennsylvanian strata below 

seismic line 1, the Mt. Vernon graben appears to be roughly 

symmetric, with about equal displacement on the Wabash 

Island and Hovey Lake faults. Wells 5-7 (table 5) penetrate 

the Cypress Formation near line 1, at the crest of anticline G, 

in the hanging-wall syncline J, and in the footwall anticline 

H, respectively (fig. 2). The vertical displacement of the 

Cypress Formation across the Hovey Lake fault is 78 m 

between wells 5 and 7, and 89 m between wells 6 and 7. The 

interpreted depth sections of line 1 show that the Hovey Lake 

fault steepens upward as it bifurcates into two or more faults 

in a listric fan at shallow depths (figs. 13, 15). At depths 

greater than 1.8 km, the fault has an apparent west dip of 

about 69°. The fault strikes about N. 21° E. and the true dip 

is about 70° west-northwest. Near the surface, the faults dip 

about 70°-80° to the west-northwest.

In line 1, the Hovey Lake fault displaces the New 

Albany, Knox, and Eau Claire events by about 38,25, and 14 

ms, respectively. Assuming a velocity of 6,000 m/s for the 

strata faulted out, the computed vertical displacements of the 

New Albany Shale and the top of the Knox Group are about 

114 and 75 m, respectively. Using a velocity of 7,000 m/s for 

the Knox strata faulted out at the footwall cut of the Eau 

Claire Formation, the calculated vertical displacement is 

about 49 m. The decrease in vertical displacements with 

increasing depth along the Hovey Lake fault may be related 

to a decrease with increasing depth of rotation of strata and 

folding associated with the Wabash Island fault. The Hovey 

Lake fault apparently intersects the Wabash Island fault 

within the basement rocks. If the roof fault B of the Wabash 

Island fault continues through basement rocks, then it apparently intersects the Hovey Lake fault about 5.7 km below 

seismic datum. If the Hovey Lake fault extends below this 

depth, however, it may intersect the floor fault A of the 

Wabash Island fault about 6.0 km below seismic datum (5.9 

km below sea level). We interpret that the Hovey Lake fault 

is a subsidiary antithetic fault to the Wabash Island fault. It 

may result in part from rotation of strata due to curvature on 

the Wabash Island fault within basement rocks near the 

apparent intersection of the Wabash Island and Hovey Lake 

faults. Such curvature is not clearly resolvable, however, by 

the reflection seismic data of line 1. The east limb of anticline G probably developed by reverse drag folding or rotation of strata due to movements on the listric Hovey Lake 

fault. The east limb of the hanging-wall syncline J is probably due to normal drag folding associated with that fault.

Figures 18-19 show interpreted time and depth sections 

of line 2. In these data we interpret that the Hovey Lake fault 

bifurcates upward into fault branches D and E about 1 km 

below seismic datum. The easternmost branch, fault E (fig. 

19), is apparently intersected by well 10 about 0.1 km west 

of line 2, where 24 m of strata are faulted out 212m below 

the seismic datum (fig. 2, table 5). Fault E has an apparent 

north dip of about 45° along line 2. For a strike of about N. 

21° E., the true dip of the fault is calculated to be about 70° 

west-northwest. In well 10, about 0.1 km west of line 2, fault 

D intersects the bedrock surface in line 3 about 200 m north 

of fault E. The apparent dip on fault D near the bedrock surface is about 52° north. Assuming a strike of N. 21° E., the 

true dip is therefore about 79° west-northwest. The vertical 

displacement on fault D is probably about 70 m. Normal 

drag folding is apparently imaged by dipping reflections 

downthrown to fault D. About 4 km south of line 1 the vertical displacement of the Cypress Formation by the Hovey 

Lake fault is about 40 m. The southwest flank of anticline H 

may indicate normal drag folding on the upthrown block of 

the Hovey Lake fault, or it may have resulted from displacements associated with underlying blind fault branches of the 

Hovey Lake fault.

SUMMARY AND DISCUSSION

Our objective in shooting common-depth-point minihole reflection seismic lines 1-3 in southwestern Indiana 

was to image and interpret deep structure of the Wabash Valley fault system. We interpret that, northeast of Hovey Lake 

in seismic line 1, the Wabash Island fault is confined to a 

fault zone about 200 m wide that dips about 65° east-southeast. Hanging-wall deformation associated with this fault 

apparently extends across the Mt. Vernon graben and 

includes the Hovey Lake fault, which we interpret to be a 

subsidiary antithetic fault even though the graben appears 

roughly symmetrical at the level of Mississippian and Pennsylvanian strata. The Hovey Lake and Wabash Island faults 

apparently intersect at a depth of about 6 km beneath line 1 

within Precambrian basement rocks. Hanging-wall deformation associated with both faults includes normal and reverse 

drag folding. In seismic line 1, the vertical displacement on 

the Hovey Lake fault and roof fault of the Wabash Island 

fault apparently decreases with increasing depth, whereas 

the displacement on the floor fault of the Wabash Island fault 

apparently increases with increasing depth. In lines 1-2, the 

Hovey Lake fault is apparently listric and bifurcates upward 

above the New Albany Shale. The Wabash Island fault probably includes both listric and convex-upward fault surfaces 

bounding horses within the fault zone. In seismic line 1, the 

roof and floor faults of the fault zone are apparently
O32 INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE

quasi-planar through most of the Paleozoic strata. East of 

Hovey Lake in seismic line 3, the Wabash Island fault may 

be more complex and the floor fault apparently dips more 

steeply, about 75° east-southeast.

We see no evidence of pre-Mount Simon rift-fill associated with large-displacement basement faults that might 

have been reactivated. The basement is poorly reflective 

compared to the top of the Eau Claire Formation where a 

low-velocity layer of about 200 m in thickness may delimit 

the upper part of that formation. The precise onset of the 

acoustic basement event is indeterminate, but the seismic 

data are consistent with an Eau Claire thickness of about 360 

m for an interval velocity of 5,800 m/s and a Mount Simon 

Sandstone thickness of 300 m for an interval velocity of 

about 5,450 m/s. This is consistent with the existence of a 

Mount Simon Sandstone basin extending into southwestern 

Indiana on trend with the Reelfoot rift, although the sandstone may not thicken to 600 m in southwestern Indiana as 

originally postulated by Schwalb (1982). Impetus for additional seismic profiling may come from exploration for deep 

reservoirs of oil or gas. Seismic methods should be effective 

in exploration and development of any deep hydrocarbon 

deposits that might be trapped by the faults and associated 

folding. The method of minihole pattern shooting in this 

region is effective with close spacing of traces in stacked 

sections.

REFERENCES CITED

Ault, C.H., and Sullivan, D.M., 1982, Faulting in southwest Indiana: U.S. Nuclear Regulatory Commission Report 

NUREG/CR-2908 RA, 50 p.

Barnett, J.A.M., Mortimer, J., Rippon, J.H., Walsh, J.J., and Watterson, J., 1987, Displacement geometry in the volume containing 

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Published in the Central Region, Denver, Colorado 

Manuscript approved for publication July 6, 1994 

Edited by Richard W. Scott, Jr. 

Graphics prepared by Indiana Geological Survey 

Photocomposition by Norma J. Macs

a U.S. GOVERNMENT PRINTING OFFICE: 1995-673-046/86098