HR: 1340h
AN: S43C-1028    [Abstracts]
TI: A Ground Penetrating Radar Experiment along the Warm Springs Valley Fault System, Western Nevada
AU: * dePolo, C M
EM: cdepolo@unr.edu
AF: Nevada Bureau of Mines and Geology, University of Nevada, Reno, Reno, NV 98557
AU: O'Neal, M L
EM: moneal@loyola.edu
AF: Science Education, Loyola College in Maryland, Baltimore, MD 21210
AB: We conducted a ground penetrating radar (GPR) survey of several fault traces from the Warm Springs Valley fault system in western Nevada. Several trenches have been excavated along the southern part of the fault system, in an ideal setting to experiment with GPR. Our survey was conducted with a pulseEKKO 100 GPR system, using a 1000v transmitter, at an antenna frequency of 200 MHz, with an antenna separation of 0.5 m and a step spacing of 0.1 m. With a wavelength of 0.5 m, this frequency of energy penetrated up to 6 m into the sediments we explored, with the potential to resolve the upper and lower surfaces of stratigraphic units that were 12.5 cm or thicker. We used a limited two-way travel time window of 150-200 ns, to allow imaging of our desired target depth with minimal unwanted reflections (recording instrument, truck, wire fences, etc.). We ran surveys immediately adjacent to two fault trenches (Trenches WSVFS T1 and WSVFS T3) to compare them with established trench logs, and additional surveys over other parts of the fault (WSVFS T2) with a 30 m setback to avoid the noise effects from trenches (trench walls, bottoms, fencing, etc.). The latter survey was run as a series of seven trench-parallel lines, with two perpendicular tie lines to evaluate profile-to-profile features. The results from the approximately 400 meters of radar data collected in this experiment are encouraging. Nearly all mapped faults had fault-type signatures on the radar profiles, and the general stratigraphic features of the upper 1 to 3 m of sediments were imaged fairly well. Major faults were easily recognized as offset reflections, abrupt lateral changes in amplitudes of reflections and overall unit characteristics, and offset groundwater barriers. Numerous secondary faults were also recognizably imaged, although they were more difficult to discern from natural variations in the sediments (textural and structural), and from noise inherent in the GPR method. Liquefied units were found to correspond to chaotic radar reflections. Further research will include experimentation with varying antenna frequencies and orientation, step spacing, and more closely spaced 3-D grid data collection.
DE: 7221 Paleoseismology
DE: 7223 Seismic hazard assessment and prediction
DE: 6964 Radio wave propagation
DE: 0994 Instruments and techniques
SC: Seismology [S]
MN: 2004 AGU Fall Meeting