HR: 1340h
AN: S43A-1060    [Abstracts]
TI: Using Near-Field Seismogras to Estimate the Slip Weakening Distance
AU: * Mori, J
EM: mori@eqh.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Insitute, Kyoto University, Gokasho, Uji, Kyoto, 611-0011 Japan
AB: Accurate estimates of the slip weakening distance, Dc, are usually difficult to make because a reliable determination of the slip time history is needed. Usually these time histories are obtained for numerous subfaults from the inversion of local seismograms. Instead of using the model results of finite fault inversion, I make measurements directly on near-field seismograms that are located very close to the fault. Recently, there are have been several large earthquakes with good recordings within a few kilometers of shallow faults, such as the 1999 Chi-Chi, Taiwan earthquake. I assume for stations that are located very close to the fault, the waveforms are dominated by the near-field terms from the portion of the fault closest to the station, if that portion has significant slip. The slip weakening distance is identified as the slip corresponding to the maximum slip velocity on the fault. Results from the Chi-Chi earthquake for stations in the north where the slip was large, show that the peak velocity is reached within about 2 seconds of the beginning of slip, and corresponds to a slip of about 230 cm. This estimate of the slip weakening distance is significantly less than some previous determinations using results from the model slip functions. For stations in the south, where there was considerable less slip on the fault, the slip weakening distance was about 100 cm. For cases where near-field data is recorded very close to faults with large amounts of slip, this method may provide a reliable way to measure the slip weakening distance.
DE: 7209 Earthquake dynamics (1242)
DE: 7215 Earthquake source observations (1240)
SC: Seismology [S]
MN: Fall Meeting 2005