HR: 1340h
AN: S43B-1001    [Abstracts]
TI: Anomalous Pn waves observed in the eastern Taiwan: indication of a thin crust beneath the Longitudinal Valley
AU: * Liang, W
EM: wtl@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, Taiwan, P.O.Box 1-55, Nankang1, Taipei, 115 Taiwan
AU: Chiu, J
EM: jerchiu@memphis.edu
AF: Department of Earth Sciences, University of Memphis, Johnson Hall Room 107, Memphis, 38152 United States
AB: We have found significant Pn waves for raypaths traveling along the Longitudinal Valley of eastern Taiwan with epicentral distances less than 200 km, where is supposed to be the suture zone of the arc-continent collision between Eurasia and Philippine sea plates. The waveforms analyzed in this study are generated from recent earthquake that occurred around 20 km depth at both ends of the Longitudinal Valley. This azimuth dependent Pn waves are characterized with its low amplitude wavetrain and the earlier arrival times. As revealed in the travel-time curve plot, the apparent velocity for this series of Pn arrivals is $\sim$7.9 km/s that is comparable with the crust-mantle boundary P wave velocity. Considering the focal depths and associated epicentral distances, on possible explanation of this observation is that the moho depth beneath the Longitudinal Valley is somehow shallower than elsewhere on land of Taiwan. This result is consistent with the latest tomographic image of Taiwan by Kim and Chiu (2004).
DE: 7218 Lithosphere and upper mantle
DE: 7230 Seismicity and seismotectonics
DE: 8110 Continental tectonics--general (0905)
DE: 8123 Dynamics, seismotectonics
DE: 7205 Continental crust (1242)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting