Seismic depth imaging of normal faulting in the
southern Death Valley basin
Sergio Chávez-Pérez, John N. Louie,
Seismological Laboratory/174 and Department of Geological Sciences, Mackay School of Mines,
University of Nevada, Reno, NV 89557-0141, USA,
and
Sathish K. Pullammanappallil
William Lettis & Associates, 1777 Botelho Avenue, Walnut Creek, CA 94596, USA.
[email protected], [email protected], [email protected]
http://www.seismo.unr.edu/
Paper submitted to GEOPHYSICS (Revised version, 28 Feb 1997; Accepted, 25 Apr
1997)
Click on any of the illustrations below for a high-resolution Adobe Acrobat PDF version.
ABSTRACT
Motivated by the need to image faults to test Cenozoic extension models for the Death Valley region of
the western Basin and Range province, an area of strong lateral velocity variations, we examine the
geometry of normal faulting in southern Death Valley by seismic depth imaging. We analyze COCORP
Death Valley Line 9 to attain an enhanced image of shallow fault structure to 2.5 km depth. Previous
workers used standard seismic processing to infer normal faults from bed truncations, displacement of
horizontal reflectors, and diffractions. We obtain a detailed velocity model by nonlinear optimization of
first-arrival times picked from shot gathers, examine the unprocessed data for fault reflections, and use a
Kirchhoff prestack depth imaging procedure to properly handle lateral velocity variations and arbitrary
dips. Fault-plane reflections reveal the listric true-depth geometry of the normal fault at the Black
Mountains range front in southern Death Valley. This is consistent with the concept of low-angle
extension in this region and strengthens its association with crustal-scale magmatic plumbing.
INTRODUCTION
Death Valley is a region of active extension and Quaternary volcanism. It is located in eastern California
between the Panamint Mountains on the west and the Black Mountains on the east, within the
southwestern portion of the Basin and Range province (Fig. 1). Death Valley is a pull-apart basin
developed in a releasing bend of a dextral strike-slip fault system. The northeastern boundary of the
basin is controlled by the Northern Death Valley-Furnace Creek fault zone and the southwestern
boundary is controlled by the southern Death Valley fault zone. The central part of the basin is
characterized by normal faulting. The western slopes of the Black Mountains are essentially an exhumed
west-dipping normal fault that transfers motion between the two strike-slip faults (e.g., Topping, 1993).
Death Valley is therefore an asymmetric half-graben basin.
Fig. 1. Map of the southern Death Valley region showing topographic contours and Quaternary faults
(thin black lines and a shaded region along the Death Valley fault zone) from a modified version of the
map of Jennings (1994), locations of COCORP Lines 9 and 11 (thick, solid black lines), the velocity
profile used for depth imaging (thick, dashed black line) and a faulted cinder cone of Quaternary age
(star). Diagonal dashed lines indicate the possible extent of the Death Valley bright spot (de Voogd et
al., 1986).
The data collected by Consortium for Continental Reflection Profiling (COCORP) in this region may
have imaged, perhaps for the first time, crustal-scale plumbing associated with a deep magma chamber
beneath a pull-apart basin (de Voogd et al., 1986; 1988). Line 9 traverses roughly east-west, subparallel
to the direction of extension, while Line 11 runs almost perpendicular to the dominant extensional
direction (Fig. 1). A dipping event in the time sections of both lines extends from above a prominent
midcrustal reflection (identified by de Voogd et al., 1986, as the ‘‘Death Valley bright spot’’; Fig. 1) at
about 6 s two-way time to near the surface, at a faulted cinder cone of Quaternary age. de Voogd et al.
(1986) suggested this event is a reflection from a magma conduit or feeder dike that has now solidified.
Shallow-dipping events to 2 s on Line 9 define a half-graben that appears to be bounded by a listric fault
(Serpa et al., 1988).
Interest in fault reflections spans several decades (e.g., Swartz and Lindsey, 1942; Deacon, 1943;
Robinson, 1945; Bortfeld and Hurtgen, 1960; Allenby, 1962; Hole et al., 1996). They are of
fundamental value for the correct positioning in space of the fault planes and optimum stacking of depth
migrated shot gathers. There have been very few attempts, however, to directly image steeply-dipping
faults in deep crustal data (Louie et al., 1988; Louie and Qin, 1991; Pullammanappallil and Louie,
1993). This is mostly due to strong lateral velocity variations and the lack of reliable velocity models.
Current debates about the listric (concave upwards) versus planar geometry of normal faults in
extensional terranes are partly due to the lack of reliable depth images from seismic reflection data. A
recent example of this controversy has arisen concerning the geometry and nature of the Sevier Desert
normal fault in west-central Utah (Von Tish et al., 1985; Anders and Christie-Blick, 1994). The presence
of shallow-dipping normal faults is one of the most important criteria for recognizing extensional
regimes (e.g., Shelton, 1984). In fact, substantial extension can only be accomplished by initially
shallow faults or by faults that rapidly rotate toward shallower dips as extension proceeds (Wernicke and
Burchfiel, 1982).
There has been controversy on the accomodation of crustal extension in the southern Death Valley basin
(e.g., Wright and Troxel, 1973; Wernicke, 1981; King and Ellis, 1990). Faults on seismic sections
collected in this region have been inferred from sedimentary bed truncations (Serpa et al., 1988), and not
directly imaged; thus, a depth-imaged view of this fault zone is needed. The geometry of the fault plane
can only be obtained by depth imaging of the fault reflections.
The bulk of the research using seismic reflection data to investigate basement-involved extensional
tectonics is based on time imaging, where lateral velocity variations are not considered. This is due to
the fact that depth imaging requires reliable velocity models to migrate reflected refractions and straddle
reflections (de Bazelaire and Viallix, 1994) from steep fault planes into their true position. Motivation
for this study comes from the need to directly image fault geometries that cannot be constrained using
conventional time sections, and to help lessen the ongoing controversy of how crustal extension is
accommodated at depth. Standard time imaging techniques, like the one used by Serpa et al. (1988),
provide a good starting point for subsequent depth imaging processing. Defining fault plane geometries
demands, however, a reliable velocity model and detailed prestack imaging including nonhyperbolic
fault reflections exhibiting reverse moveout on record sections.
DEPTH IMAGING METHOD
New approaches to prestack depth imaging of land data with complex topography (e.g., Rajasekaran and
McMechan, 1995a, b) require only preprocessing, velocity analysis and depth migration. We analyze the
COCORP data by following an equivalent processing scheme. We use minimum preprocessing (editing,
muting and trace balancing), a well-constrained velocity model for shallow depths, and Kirchhoff-sum
prestack depth migration to image fault plane reflections. Traveltime computation for the imaging
process can thus rely on a very accurate velocity structure to enhance the final migrated product.
Velocity model
We modify the velocity profile of Line 9 developed by Pullammanappallil and Louie (1994) by using a
simulated-annealing optimization scheme for inversion of first-arrival times. The scheme employs a fast
finite-difference solution to the eikonal equation (Vidale, 1988) to compute traveltimes, and it produces
a suite of final models with comparable least-square error. This enables us to select and average together
the models most likely to represent the geology of the region. This scheme is independent of the starting
model and it has the ability to find the global minimum, unlike commonly used linearized inversion
techniques.
Pullammanappallil and Louie (1994) analyzed ray coverage through their velocity model and used the
standard deviation of a suite of final models having similar error to find out which parts of the model are
well-resolved. They used 6213 picks from 281 shot gathers and projected the line geometry onto a
straight line, maintaining the source-receiver offsets of the actual survey (Fig. 2). We refined this
well-constrained velocity model (to 2.5 km depth) by decreasing the grid spacing during optimization to
improve resolution. Optimization with a grid spacing of 25 m took about 12 CPU hours on a Sun
Sparc10 computer.
Fig. 2. Velocity profile (top) for COCORP Line 9 (Pullammanappallil and Louie, 1994). At an expanded
scale, indicated by the gray shading, is our refined velocity model (bottom), including rapid lateral
variations, that we use to compute the traveltimes needed for Kirchhoff prestack depth migration. Note
the changes in topography. Datum depth (0) corresponds to 1 km above sea level. Vertical exaggeration
is 2.5 (top) and 2 (bottom).
Line 9 runs from the Panamint Range in the west to the Greenwater Valley in the east (Fig. 2). The
prominent low-velocity region (1.8 to 2.4 km/s) in the optimization result corresponds to the southern
Death Valley sedimentary basin. Beneath the basin, velocity increases to 4.5 km/s at 2.5 km depth (with
respect to the datum at 1 km elevation). Below this depth velocity increases to 5.5 km/s. The
optimization scheme reconstructs higher velocities (4 km/s) at the Black and Panamint mountains, which
we correlate to igneous or metamorphic rocks observed at the surface. The velocities and depths of the
basin in this section are within 10\% of those obtained by Geist and Brocher (1987) with iterative
forward modeling using ray tracing and least-squares inversion. Velocity error increases to 0.5 km/s at 2
km depth below the mountains, but remains good down to 4 km beneath Death Valley.
Kirchhoff prestack depth migration
Data preprocessing before migration includes surgical muting to remove refracted arrivals and retain all
other events, and trace equalization. We equalize using the first 4 s of the 16 s correlated traces. True
amplitudes are normalized so that the mean-squared amplitude over the 4 s is the same for all traces.
A practical approach to image steeply-dipping reflectors in this area of strong lateral velocity variations
and crooked acquisition geometry is Kirchhoff migration. This is mainly due to its speed and flexibility
in handling 3-D source-receiver geometry as compared with other techniques (e.g., reverse time and
least-squares migration). The Kirchhoff prestack depth migration method we use is similar to that of
Louie et al. (1988) and of Louie and Qin (1991). The migration is a backprojection of assumed primary
reflection amplitudes into a depth section. It has been identified by Le Bras and Clayton (1988) as the
tomographic inverse of the acoustic wave equation under the Born approximation in the far field,
utilizing WKBJ rays for downward continuation and two-way reflection traveltime for the imaging
condition.
Because the backprojection requires knowledge of the source wavelet for crosscorrelation with each
seismic trace, we roughly approximate this by crosscorrelating with a boxcar function 0.4 s long, close
to the central period of the reflection arrivals. The net effect of this is to smooth the migration, center the
reflection pulses, and avoid aliasing (Lumley et al., 1994). We compute first-arrival traveltimes with
Vidale’s (1988) finite-difference solution to the eikonal equation, as the migration algorithm is similar to
the two-eikonal method described by Reshef and Kosloff (1986). Each image is obtained by summing
the data at traveltimes computed through the detailed velocity model, and the final result is obtained by
stacking the migrated partial images for each gather. The final migrated image might be improved by
velocity smoothing trials to further stabilize the travel times needed by Kirchhoff migration, by
including an operator anti-aliasing criterion, by obtaining a reliable estimate of the source wavelet, or by
low-pass filtering after migration (to remove artifacts).
To illustrate our reconstruction of fault plane reflections, Fig. 3 shows observed and synthetic shot
gathers (computed with the fourth-order finite-difference solution of the full-wave acoustic wave
equation described by Vidale, 1990) for VPs 531 and 554. Note that the fault reflection exhibits reverse
moveout. Fig. 4 shows the corresponding depth migrations of the observed and synthetic shot gathers of
Fig. 3. The fault plane reflections are labeled. Stronger reflections, like those of the fault plane, migrate
more coherently than weaker ones.
Fig. 3. (Left) Shot gathers for sources at VP531 and VP554 showing a fault plane reflection event with
reversed moveout. (Right) Full-wave acoustic forward modeling of shot gathers assuming the source is
located at VP531 and VP554 and using the velocity model of Fig. 2 (without density contrasts).
Synthetic arrivals are late because model receivers do not follow deep valley topography.
Fig. 4. Depth migration of the observed and synthetic shot gathers of Fig. 3. (Left) Shot gathers for
source at VP531 and VP554. (Right) Depth migration of the synthetic shot gathers assuming the source
is located at VP531 and VP554. Note that some of the artifacts seen in the migration of the observed
gathers are also observed in the migration of the synthetic gathers. Ellipses depict approximate locations
where the fault plane geometry and basin bottom are defined. Vertical exaggeration is 2.
RESULTS
Two aspects of the interpretation of Line 9 by Serpa et al. (1988) have been criticized by Smithson and
Johnson (1989). First, the west-dipping listric fault they depicted is not imaged in their seismic section
(Fig. 5a); second, its surface projection, which coincides with the approximate trace of the Death Valley
fault zone and a faulted cinder cone (Fig. 1, 5b), may be pure coincidence. Our prestack migration result
did not reveal the details of basin stratigraphy typically seen in conventional time or poststack depth
imaging. Neither did it reproduce the shallow layered structure interpreted as a late Cenozoic basin
deposit. It directly images in true depth (Fig. 6a), however, the fault plane inferred by Serpa et al.
(1988).
Fig. 5. a) Stacked section and b) time to depth conversion and interpretation by Serpa et al. (1988). A, B,
and C denote important dipping reflections. Solid black lines show the trend of the basin-fill reflectors,
PC-PZ indicates the location of inferred Precambrian and Paleozoic sedimentary rocks faulted against
the bottom of the basin. AL indicates the area of late Cenozoic basin deposits and QB indicates the
surface position of the faulted 690,000-yr-old basaltic cinder cone. Note the nonlinear depth scale.
Fig. 6. a) Our enhanced depth image and b) depth interpretation of the basin and the fault plane. QB
indicates the surface position of the faulted 690,000-yr-old basaltic cinder cone. Note the changes in
topography. Vertical exaggeration is 2.
Apart from the fault plane geometry, Fig. 6a also shows an enhanced depth image of the basin bottom.
Strong, positive reflectivity spots (black arrows) clearly depict the bottom of this half-graben. Note how
stronger reflections, like those of the fault plane, migrate more coherently than weaker ones. This
influences the overall quality of the migrated image. Artifacts appear as elliptical trajectories that
degrade image quality and resolution, mostly beneath the basin bottom. This is due to sparse receiver
(near offset 500 m, station spacing 100 m) and source coverage in this deep crustal data designed for
much deeper targets.
Fig. 7. a) Migration result, b) migration artifacts from incoherent prestack data, c) focusing, and d)
focused migration displaying the principal events from coherent data. Note the improved fault plane
image despite loss of clarity in the basin bottom. Vertical exaggeration is 2.
Common-offset migration is a commonly used, intuitive and physically-oriented validation test for
migrated images in the context of migration velocity analysis. In our case, we have found, based on
previous work with similar crustal scale data (e.g., Louie and Qin, 1991), that the Bayesian statistical
method of Harlan et al. (1984) is a good indicator of the validity of the migrated images. Our validity
check is to use Harlan’s entropic measure of non-Gaussianity from amplitude histograms of transformed
data and of transformed ‘‘noise’’ (artificially incoherent data) to determine which migrated structures
are real and which are artifacts (Fig. 7a). This is done by remigrating the data after destroying coherence
by randomly flipping the signs of data traces.
We obtain an image that displays migration artifacts from incoherent prestack data (Fig. 7b). Then, we
scale the raw migration by Harlan’s focusing measure at each image point (Fig. 7c) to give a section that
displays the principal events from coherent data. Following this procedure, the focused migration shows
that the fault plane is not an imaging artifact (Figure 7d), nor is an unknown structure below the basin,
despite the loss of definition of the basin geometry.
DISCUSSION
The aim of our depth imaging methodology is to determine the geometry and the location of fault planes
not shown but inferred by conventional time sections. We have achieved this in our images. However,
our prestack migration result did not bring out all the details of basin strata seen in conventional time or
poststack depth imaging, and it did not reproduce all the shallow layered structure interpreted as a late
Cenozoic basin deposit (Fig. 5b). This is mainly due to masking of the signal by migration artifacts,
sideswipe reflections, and lateral smearing of a complex 3-D velocity model, simplified into a complex
2-D velocity model.
We carefully reprocessed the records to corroborate Serpa et al.’s (1988) stacked section and found no
clear evidence of some of the dipping events they used for their interpretation. For instance, their
dipping event ‘‘A’’ (Fig. 5a) resembles the case where muting is not properly done, or not done at all, to
reject refracted arrivals from complex areas near faults. Our reprocessed stacked section (not shown)
only defines basin strata and basin-bottom geometry.
Abundant crustal time sections in the Basin and Range province have allowed researchers to delineate
planar steeply-dipping, listric, and subhorizontal low-angle normal fault geometries exhibiting several
styles of extension (e.g., Wernicke and Burchfiel, 1982; Anderson et al., 1983; Cheadle et al., 1985,
1986; Okaya and Thompson, 1985; Von Tish et al., 1985; Thompson et al., 1989). Faulting has usually
been inferred from the correlation of reflectors with mapped faults, and from bed truncations and
displacement of horizontal reflectors and diffractions. Our results are unique in the sense that, to the best
of our knowledge, this is the first time fault plane geometry has been directly defined in the western
Basin and Range province, accounting for lateral velocity variations and reverse-moveout fault
reflections.
The non-planar geometry of the fault (Fig. 6a) is consistent with the concept of low-angle extension in
the region and strengthens de Voogd et al.’s (1986) association of listric normal faulting with a proposed
magma conduit traced to the surface location of a cinder cone. The fault clearly dips west, but our
west-east section shows somewhat of an apparent dip for this north-northwest striking fault. The section
may be exhibiting many subsidiary faults quite obliquely, with the possibility that we are looking at
apparent dip of out-of-plane reflections. de Voogd et al. (1986) proposed, in addition, that the fault may
dip down to the north to meet a midcrustal reflection bright spot, at a depth of approximately 15 km. The
imaged fault (Fig. 6b) dips at about 70 degrees near the surface and flattens to less than 40 degrees with
depth. Its trend implies it would be roughly subhorizontal at about midcrustal depths (10-15 km), as to
define a deep detachment (Wright and Troxel, 1973).
Our work underscores the need for a combined depth imaging approach that utilizes the strengths of
each method to enhance image quality. For instance, we could obtain a ballpark estimate of extension
and depth to detachment by using poststack depth migration to image basin stratigraphy, complement
the prestack results, and validate the geological plausibility of the depth images. This would allow us, in
principle, to determine the angular relationship between shallow basin stratigraphy and the fault plane,
and to construct the fault profile using hanging-wall rollover geometry (Rowan and Kligfield, 1989;
Dula, 1991) with the aid of simple structural balancing techniques.
CONCLUSIONS
Our analysis demonstrates a two-step methodology (tomography and prestack depth imaging) for true
depth processing of fault reflections to define fault plane geometry and depth in a complex land data set.
Depth imaging of structures in the southern Death Valley basin from COCORP Line 9 shows a
west-dipping basin-bounding listric normal fault (Black Mountains range-front fault) and a well-defined
half-graben basin bottom (Death Valley). This is the first true-depth image of a listric normal fault plane
in the western Basin and Range province that accounts for strong lateral velocity variations. Its geometry
is consistent with the concept of low-angle extension in the region and strengthens the association of
listric normal faulting with a proposed magma conduit traced to the surface location of a cinder cone.
ACKNOWLEDGMENTS
The first author acknowledges financial support by CONACYT, Mexico’s National Council for Science
and Technology. This work was also funded in part by US National Science Foundation grant
EAR-9405534. Glenn Biasi, Raymon L. Brown, Mark Stirling, and Serdar Özalaybey provided useful
criticism and suggestions. Ernie Hauser kindly provided COCORP field records and locations from
Death Valley. We also thank Julián Cabrera, William S. Harlan, and Reinaldo J. Michelena for their
helpful reviews.
REFERENCES
Allenby, R.J., 1962, The importance of reflected refractions in seismic interpreting: Geophysics, 27,
966-980.
Anders, M.H., and Christie-Blick N., 1994, Is the Sevier Desert reflection of west-central Utah a normal
fault?: Geology, 22, 771-774.
Anderson, R.E., Zoback, M.L., and Thompson, G.A., 1983, Implications of selected subsurface data on
the structural form and evolution of some basins in the northern Basin and Range province, Nevada and
Utah: Geol. Soc. Am. Bull, 94, 1055-1072.
Bortfeld, R. and Hürtgen, H., 1960, On the identification and construction of reflected refractions:
Geophys. Prosp., 8, 12-24.
Cheadle, M.J., Czuchra, B.L., Ando, C.J., Byrne, T., Brown, L.D., Oliver, J.E., and Kaufman, S., 1985,
Geometries of deep crustal faults: evidence from the COCORP Mojave survey, in Barazangi, M., and
Brown, L., Eds., Reflection seismology: the continental crust: Geodynamics series, 14, Am. Geophys.
Union, 305-312.
Cheadle, M.J., Czuchra, B.L., Byrne, T., Ando, C.J., Oliver, J.E., Brown, L.D., Kaufman, S., Malin,
P.E., and Phinney, R. A., 1986, The deep crustal structure of the Mojave Desert, California, from
COCORP seismic reflection data: Tectonics, 5, 293-320.
Deacon, L.E., 1943, An analysis of abnormal reflexions: Geophysics, 8, 3-13.
de Bazelaire, E., and Viallix, J.R., 1994, How faults express themselves on seismic data: 56th Meeting
and Technical Exhibition, Euro. Assoc. Expl. Geophys., Expanded Abstracts of Papers, P099.
de Voogd, B., Serpa, L., Brown, L., Hauser, E., Kaufman, S., Oliver, J., Troxel, B.W., Willemin, J., and
Wright, L.A., 1986, Death Valley bright spot: A midcrustal magma body in the southern Great Basin,
California?: Geology, 14, 64-67.
de Voogd, B., Serpa, L., and Brown, L., 1988, Crustal extension and magmatic processes: COCORP
profiles from Death Valley and the Rio Grande rift: Geol. Soc. Am. Bull., 100, 1550-1567.
Dula, Jr., W.F., 1991, Geometric models of listric normal faults and rollover folds: Am. Assoc. Petr.
Geol. Bull., 75, 1609-1625.
Geist, E.L., and Brocher, T.M., 1987, Geometry and subsurface lithology of southern Death Valley
basin, California, based on refraction analysis of multichannel seismic data: Geology, 15, 1159-1162.
Harlan, W., Claerbout, J., and Rocca, F., 1984, Signal/noise separation and velocity estimation:
Geophysics, 49, 1869-1880.
Hole, J.A., Thybo, H., and Klemperer, S.L., 1996, Seismic reflections from the near-vertical San
Andreas fault: Geophys. Res. Lett., 23, 237-240.
Jennings, C.W., 1994, Fault activity map of California and adjacent areas: Geologic Data Map No. 6,
Faults, Locations of Recent Volcanic Eruptions, scale 1:750,000, Calif. Div. of Mines and Geol.,
Sacramento, CA.
King, G., and Ellis, M., 1990, The origin of large local uplift in extensional regions: Nature, 348,
689-693.
Le Bras, R.J., and Clayton, R.W., 1988, An iterative inversion of backscattered acoustic waves:
Geophysics, 53, 501-508.
Louie, J.N., and Qin, J., 1991, Subsurface imaging of the Garlock fault, Cantil Valley, California: J.
Geophys. Res., 96, 14461-14479.
Louie, J.N., Clayton, R.W., and Le Bras, R.J., 1988, 3-d imaging of steeply dipping structure near the
San Andreas fault, Parkfield, California: Geophysics, 53, 176-185.
Lumley, D.E., Claerbout, J.F., and Bevc, D., 1994, Anti-aliased Kirchhoff 3-D migration: 64th Ann.
Internat. Mtg., Soc. Explr. Geophys., Expanded Abstracts, 1282-1285.
Okaya, D.A., and G.A. Thompson, 1985, Geometry of Cenozoic extensional faulting: Dixie Valley,
Nevada: Tectonics, 4, 107-125.
Pullammanappallil, S.K., and Louie, J.N., 1993, Inversion of seismic reflection traveltimes using a
nonlinear optimization scheme: Geophysics, 58, 1607-1620.
Pullammanappallil, S.K., and Louie, J.N., 1994, A generalized simulated-annealing optimization for
inversion of first-arrival times: Bull. Seism. Soc. Am., 84, 1397-1409.
Rajasekaran, S., and McMechan, G.A., 1995a, A new approach to pre-stack seismic processing:
Geophys. J. Int., 121, 255-266.
Rajasekaran, S., and McMechan, G.A., 1995b, Prestack processing of land data with complex
topography: Geophysics, 60, 1875-1886.
Reshef, M., and Kosloff, D., 1986, Migration of common-shot gathers: Geophysics, 51, 324-331.
Robinson, W.B., 1945, Refraction waves reflected from a fault zone: Geophysics, 10, 535-545.
Rowan, M.G., and Kligfield R., 1989, Cross section restoration and balancing as aid to seismic
interpretation in extensional terranes: Am. Assoc. Petr. Geol. Bull., 73, 955-966.
Serpa, L., de Voogd, B., Wright, L., Willemin, J., Oliver, J., Hauser, E., and Troxel, B., 1988, Structure
of the central Death Valley pull-apart basin and vicinity from COCORP profiles in the southern Great
Basin: Geol. Soc. Am. Bull., 100, 1437-1450.
Shelton, J.W., 1984, Listric normal faults: An illustrated summary: Am. Assoc. Petr. Geol. Bull., 68,
801-815.
Smithson, S.B., and Johnson, R.A., 1989, Crustal structure of the western U.S. based on reflection
seismology, in Pakiser, L.C. and Mooney, W.D., Eds., Geophysical framework of the continental United
States: Geol. Soc. Am. Memoir, 172, 577-612, Boulder, CO.
Swartz, C.A., and Lindsey, R.W., 1942, Reflected refractions: Geophysics, 7, 78-81.
Thompson, G.A., Catchings, R., Goodwin, E., Holbrook, S., Jarchow, C., Mann, C., McCarthy, J., and
Okaya, D., 1989, Geophysics of the western Basin and Range province, in Pakiser, L.C. and Mooney,
W.D., Eds., Geophysical framework of the continental United States: Geol. Soc. Am. Memoir 172,
177-203, Boulder, CO.
Topping, D.J., 1993, Paleogeographic reconstruction of the Death Valley extended region: Evidence
from Miocene large rock-avalanche deposits ib the Amargosa Chaos Basin, California: Geol. Soc. Am.
Bull., 105, 1190-1213.
Vidale, J.E., 1988, Finite-difference calculation of traveltimes: Bull. Seism. Soc. Am., 78, 2062-2076.
Vidale, J.E., 1990, Comment on ‘‘A comparison of finite-difference and Fourier method calculations of
synthetic seismograms’’ by Daudt, C.R. et al.: Bull. Seism. Soc. Am., 80, 493-495.
Von Tish, D.B., Allmendinguer, R.W., and Sharp, J.W., 1985, History of Cenozoic extension in central
Sevier desert, west-central Utah, from COCORP seismic reflection data: Am. Assoc. Petr. Geol. Bull.,
69, 1077-1087.
Wernicke, B., 1981, Low-angle normal faults in the Basin and Range province: nappe tectonics in an
extending orogen: Nature, 291, 645-648.
Wernicke, B., and Burchfiel, B.C., 1982, Modes of extensional tectonics: J. Struct. Geol., 4, 105-115.
Wright, L.A., and Troxel, B.W., 1973, Shallow fault interpretation of Basin and Range structure,
southwestern Great Basin, in De Jong, K.A., and Scholten, R., Eds., Gravity and Tectonics, 397-407,
Wiley, New York.