HR: 1340h
AN: S33C-1472    [Abstracts]
TI: The Characteristics Of Intrinsic And Attenuative Dispersion Of Direct P-waves: Application In The Study Of Earthquake Precursory
AU: * Chen, C
EM: seichen@eq.ccu.edu.tw
AF: Institute of Seismology, National Chung Cheng University, No. 168, University Road, Min- Hsiung, Chia-Yi, 621, Taiwan
AU: Weng, C
EM: chiting.weng@msa.hinet.net
AF: Institute of Seismology, National Chung Cheng University, No. 168, University Road, Min- Hsiung, Chia-Yi, 621, Taiwan
AU: Chang, W
EM: wychang@nsc.gov.tw
AF: National Science Council, No. 106, HoPing E. Road, Sec. 2, Taipei, 10622, Taiwan
AB: The Morlet wavelet multiple-filter method is applied to measure relative group delays from first cycle P waves, from eight CWBSN stations located near the source of the 1999 Chi Chi, and Chia-Yi, Taiwan earthquakes. The data used in this study is from the year between 1998 and 2000. The epicentral distance is less than 30 km with depth less than 25 km and ML<e;3.0. Using continuous relaxation model, we can relates intrinsic dispersion to attenuation and by applying the genetic algorithm (GA), we are able to determine Qp, which allows us to investigate the temporal variations of Qp before and after the occurrence of a large earthquake. Our results indicate that the Qp is highly sensitive to crack density. Before the occurrence of a large earthquake, Qp increases significantly, which indicates that the pre-seismic stress accumulation may associate with fluid-filled higher density fractured rock in the source area and causes crack density to increase. One interesting phenomena that we find is that Qp decreases right before the occurrence of a large earthquake, not after the occurrence of an earthquake. This observation implies that t the temporal variation pattern of Qp can serve as an important indicator for stress level change before an earthquake occurs, which also provides another perspective to understand the siemogeneric process in the source area.
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Seismology [S]
MN: 2007 Fall Meeting