HR: 09:30h
AN: S31D-07    [Abstracts]
TI: The Possible Asperities on the Xianshuihe-Anninghe-Zemuhe Fault Zone: Evidence From Microseismicity
AU: * Zhu, A
EM: alzhu2007@hotmail.com
AF: Earthquake Administration of Shanghai Municipality, 87 Lanxi Road, Shanghai, 200062, China
AU: Xu, X
EM: xiweixu@vip.sina.com
AF: Institute of Geology, CEA, Chaoyang District, Beijing, 100029, China
AB: The Xianshuihe-Anninghe-Zemuhe fault zone, which forms the eastern margin of the Tibetan plateau, is a 700km long, left-lateral seismically active fault zone in western Sichuan, China. We mapped b value and local recurrence time TL along this fault zone using the relocated microseismicity that projected on the cross section to identify the possible locations of the asperities. Strong variations in b values are observed along the fault zone, which are consistent in geometry with the surface faulting segmentation. The anomalously short local recurrence time TL and low b value appear on the Luhuo-Daofu segment of the Xianshuihe fault zone, Shimian-Mianning segment of the Anninghe fault zone, and Xichang-Puge segment of the Zemuhe fault zone, indicating that these segments are the relatively active parts that produce more large microearthquakes than average. With the hypothesis of b value being in inverse proportion to the stress and the method of mapping asperities by using TL proposed by Wiemer and Wyss (1997), we interpret these segments as the asperities of the fault zone which have accumulated high stress and locked. The Luhuo-Daofu segment, which has generated 4 historic earthquakes greater than Ms6.0 since 1900, is structurally simple to be the most active segment amongst the whole fault zone with the slip rate up to 14mm/yr, while the Shimian-Mianning segment is well known for void of historic earthquakes. They are all easy to accumulate stress and become locked. The anomalously high b value and long TL estimates as well as high seismicity rate of a value in the southeastern segment of the Xianshuihe fault zone along Qianning-Kangding-Shimian suggest that this segment is creeping at present and not likely to produce a major earthquake, although both the historic earthquakes and microseismicity are active there.
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8111 Continental tectonics: strike-slip and transform
DE: 8123 Dynamics: seismotectonics
SC: Seismology [S]
MN: 2007 Fall Meeting