HR: 1340h
AN: H43E-1676    [Abstracts]
TI: Damage asymmetry from hydro-geomorphic signals along the trifurcation area of the San- Jacinto Fault
AU: * Wechsler, N
EM: wechsler@usc.edu
AF: University of Southern California, Earth Science Dept. 3651 Trousdale Parkway, Los Angeles, CA 90089, United States
AU: Rockwell, T K
EM: trockwell@geology.sdsu.edu
AF: San Diego State University, Dept. Geological Sciences 5500 Campanile Dr., San Diego, CA 92182, United States
AU: Ben-Zion, Y
EM: benzion@terra.usc.edu
AF: University of Southern California, Earth Science Dept. 3651 Trousdale Parkway, Los Angeles, CA 90089, United States
AB: An important earthquake research topic is the question of whether there are geological controls on rupture propagation direction. A persistent preferred propagation direction should produce asymmetric damage structure that is recorded in the volume of rock surrounding a fault, and there may be geomorphic manifestations on active faults that can be recognized and analyzed in a quantitative fashion. The San-Jacinto Fault (SJF) is one of the most active faults in southern California, with well expressed geomorphology, a fast geologic slip rate, and a strong GPS strain signal. We use standard morphometric analysis to detect the damage asymmetry across a part of the SJF in the trifurcation area where the Clark, Coyote-Creek and Buck-Ridge segments meet. The analysis is done at two scales: 1. Small scale DEM with 30m per pixel resolution derived from SRTM data. 2. Large scale DEM with 1m per pixel resolution derived from LIDAR data, covering the fault at ~1 km width. The geomorphic analysis is done using the GIS software ArcMap and the TauDEM tool box. We compare several morphometric parameters (drainage density, stream frequency, texture ratio, bifurcation ratio, ruggedness number, hypsometric integral) for drainages on both sides of the fault. North of the trifurcation point, the north-east side of the fault is more damaged, in agreement with Dor el at (2006) and Lewis et al (2005), but south of the trifurcation the situation is reversed. A number of factors can affect the results of the morphometric analysis, including the proximity of several fault strands, a restraining bend on the main strand, and different lithologies on the two sides of the fault. The current results are not conclusive since the morphometric analysis depends on various additional factors, such as different slopes, rates of erosion, vegetation, etc., that were only partially accounted for. Nevertheless, these preliminary results on reversed damage asymmetry suggest that large earthquakes on the SJF tend to nucleate in the trifurcation area and propagate from there to the NW and SE.
DE: 1815 Erosion
DE: 1819 Geographic Information Systems (GIS)
DE: 1825 Geomorphology: fluvial (1625)
DE: 7250 Transform faults
DE: 8118 Dynamics and mechanics of faulting (8004)
SC: Hydrology [H]
MN: 2007 Fall Meeting