HR: 13:40h
AN: NS23A-01    [Abstracts]
TI: Near-Surface Seismic Reflection and GPR Imaging of the Active Emigrant Peak Fault, Fish Lake Valley, NV
AU: * Black, R A
EM: black@ku.edu
AF: University of Kansas, Dept. of Geology 1475 Jayhawk Blvd. 120 Lindley Hall, Lawrence, KS 66045,
AU: Christie, M W
EM: mc1983@ku.edu
AF: University of Kansas, Dept. of Geology 1475 Jayhawk Blvd. 120 Lindley Hall, Lawrence, KS 66045,
AU: Tsoflias, G P
EM: tsoflias@ku.edu
AF: University of Kansas, Dept. of Geology 1475 Jayhawk Blvd. 120 Lindley Hall, Lawrence, KS 66045,
AU: Stockli, D F
EM: stockli@ku.edu
AF: University of Kansas, Dept. of Geology 1475 Jayhawk Blvd. 120 Lindley Hall, Lawrence, KS 66045,
AB: Multifaceted near-surface geophysical studies of active faulting in the Eastern California Shear Zone are being conducted at the University of Kansas. During the summer of 2006 shallow seismic reflection and GPR data sets were acquired across the active Emigrant Peak fault on the east side of Fish Lake Valley, Nevada. This fault is a normal fault that aids in the transfer of regional right-lateral deformation associated with the Death Valley/Fish Lake Valley fault zone. Locally a 20 m high scarp marks the trace of the main fault across a large, active alluvial fan. The GPR experiment produced a pseudo-3D image approximately 500m by 115m in size with a bin size of 1m by 5m. Depth penetration was dependent on antenna frequency, but reached approximately 25m in the dry alluvial fan sediments. Two 2-D seismic lines were acquired with a depth penetration of approximately 200m using a 30.06 caliber rifle source. The main line was over 400m in length and the cross line over 150m in length. CMP bins were 0.25m in size. Both data types were processed to migrated images and imported into an industry-standard reflection interpretation package. Analysis of the GPR volume allowed the interpretation of numerous normal faults parallel to the main Emigrant fault both near the main scarp and as ‘off-fault' deformation. Some are down-to-the-basin ‘growth faults' and some are antithetic in nature. Faults were only mapped if they were continuous across many x-lines. The migrated seismic images contain numerous reflections, grouped in packages of short reflectors of different amplitudes and dip orientations. The GPR fault planes were transferred onto the seismic data and correlated with obvious breaks in dip and amplitude between the reflection packages. After basic interpretation of the faults the stratigraphic changes across the fault planes were analyzed on the seismic data to estimate offsets at different depths for each fault. Currently, we are working to estimate a quantitative cumulative depth/throw history for each fault using both data sets. The seismic data allows us to quantify cumulative fault throw vs. depth at scales of meters to tens of meters. The GPR is more limited. The GPR data is, however, absolutely necessary to confidently identify the faults. The two data types are thus complimentary, especially in areas of complex ‘off-fault' deformation and active sedimentation.
DE: 1219 Gravity anomalies and Earth structure (0920, 7205, 7240)
DE: 6982 Tomography and imaging (7270, 8180)
DE: 7200 SEISMOLOGY
DE: 8175 Tectonics and landscape evolution
SC: Near-Surface Geophysics [NS]
MN: 2007 Fall Meeting