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Figure 1. Map of Dixie Valley, Nevada. Gray areas are mountainous, white areas are basins.
Dashed box is area of Figure 2. WC is Wood Canyon, CC is Coyote Canyon, DVGF is the
Dixie Valley geothermal field.
Figure 2.
Map showing our geophysical transects.
The two transects are oriented
approximately perpendicular to and parallel to the 1954 ruptures. Medium-resolution seismic
line along Cattle Road terminated at the white star. High-resolution seismic line along Cattle
Road terminated 150 m east of rangefront. Area corresponds to dashed box in Figure 1.
Figure 3. Balanced geological cross-sections of the rangefront graben at East Job Canyon from
Caskey et al. [1996], see for complete discussion. (a) Current graben configuration at East Job
Canyon (Figure 3). Hachured area corresponds to area down-dropped during rupture. Eastfacing and west-facing scarps were measured to dip 50 and 70, respectively. (b) is the
prerupture configuration. (c) thru (e) show configurations of fault dip change below the graben.
Hachured areas in (c) thru (e) are equal to hachured area in (a). The models show that graben
collapse is most reasonable for =25 or =20, resulting in a fault dipping 25to 30below
15 m depth.
Figure 4. Complete Bouguer gravity map of Dixie Valley after Schaefer [1983]. Gravity
contours are 2 mGal. Hachures are on down side. Evidence from fault mapping for low-angle
Dixie Valley fault dip is between Wood and Coyote Canyons. Local gravity high between these
two latitudes may represent elevated basement rocks.
Figure 5. CDP stack of our high-resolution Cattle Road profile. Section is one-to-one at 3000
m/s. Superimposed line-drawing is from Figure 3d.
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Figure 6. Raw shot-gather from our medium-resolution seismic reflection line. Highlighted,
simultaneous refraction arrival can be used to limit the range of fault dip, given velocity
information. The smooth nature of the arrival suggests that the fault plane is planar down to 1.5
km depth. The 48 receivers are within 730 m of rangefront scarp on Cattle Road. Source is at
SP101 on Figure 2.
Figure 7. Velocity model obtained by first arrival optimization of the medium-resolution data.
The one-to-one velocity model reveals deepening of low velocities towards the center of the
profile (east, towards the valley) and shallowing of high velocities towards the rangefront.
White line is the deepest penetration of refracted first arrivals. After testing several resolution
settings, an 8 m grid spacing resulted in the most robust model. The model is extended down to
2 km for use in migration (note broken depth axis).
Figure 8. Stolt-migrated stack of our medium-resolution seismic reflection profile. Migration
velocity was 2 km/s. Darker lines trace the most prominent reflectors. See text for description.
Figure 9. Kirchhoff pre-stack migration of our medium-resolution seismic reflection profile,
with interpreted section below. See text for description.
Figure 10. 2.5-D gravity model of Dixie Valley at Cattle Road (Figure 2). Circles are observed
gravity, dashed line is model misfit. Fault dips to east at 26No vertical exaggeration.
Figure 11.
No-vertical-exaggeration combination of seismic and gravity results.