HR: 0830h
AN: S11D-0330    [PDF]
TI: Colluvial Wedge Study at the Provo Segment of the Wasatch Fault Zone
AU: * Buddensiek, M L
EM: maikeb@geophys.utah.edu
AF: University of Utah, Department of Geology and Geophysics, 135 South 1460 East Room 719, Salt Lake City, UT 84112 United States
AU: Olig, S S
EM: susan_olig@urscorp.com
AF: Seismic Hazards Group URS Corporation, 500 12th Street, Suite 200, Oakland, CA 94607 United States
AU: Mattson, A
EM: amattson@mines.utah.edu
AF: University of Utah, Department of Geology and Geophysics, 135 South 1460 East Room 719, Salt Lake City, UT 84112 United States
AU: Bruhn, R L
EM: rlbruhn@mines.utah.edu
AF: University of Utah, Department of Geology and Geophysics, 135 South 1460 East Room 719, Salt Lake City, UT 84112 United States
AU: Schuster, G T
EM: schuster@mines.utah.edu
AF: University of Utah, Department of Geology and Geophysics, 135 South 1460 East Room 719, Salt Lake City, UT 84112 United States
AB: Measuring the size and depth of colluvial wedges by paleoseismic trenching is valuable in estimating the past history of a fault. Unfortunately, trenching is very costly, time consuming and causes environmental damage. A complementary investigation method is seismic trenching, i.e. inverting traveltime data from refraction experiments to produce trench-scale tomograms. Here, we show the preliminary results for inverting three seismic lines collected next to the Mapleton Megatrench, which crosses the Provo Segment of the Wasatch Fault Zone, Utah. The seismic data were collected along an 83.5 m high-resolution line along a USGS trench site and two 595 m long low-resolution lines parallel and perpendicular to the high-resolution line. The low-resolution lines were used to image the Lake Bonneville sediment horizon (LBS) in order to establish an upper LBS datum on the tomograms; and the high-resolution data were used to find colluvial wedges. The LBS horizon interpreted from the tomograms agreed with the actual location determined from three sediment cores. The pending results of the trench, that intersected the high-resolution line, show that the faulting is more complex than seen in the smoothed tomograms. However, some of the faults and three possible colluvial wedges were interpreted in the tomogram. It is also clear that some important geologic features seen in the trench are too finely detailed to be resolved in the tomogram. Due to the complexity of the fault geometry encountered in the paleoseismic trench, we see a need to increase the resolution of the geophysical method to a scale of 0.5 meter.
DE: 7221 Paleoseismology
SC: Seismology [S]
MN: 2003 Fall Meeting