HR: 0800h
AN: G51B-0821    [Abstracts]
TI: Postseismic Slip Following the 1999 Chi-Chi, Taiwan, Earthquake
AU: * Yu, S
EM: yusb@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, 128 Academia Road, Sec.2, Nanakng, Taipei, TW 115 Taiwan
AU: Tsai, Y
EM: u9145100@cc.ncu.edu.tw
AF: Institute of Geophysics, 300 Jongda Road, Chungli, TW 320 Taiwan
AU: Hsu, Y
EM: yaru@earth.sinica.edu.tw
AF: Seismological Lab, Caltech, 252-21 Caltech , Pasadena, CA 91125 United States
AU: Chen, H
EM: chenhy@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, 128 Academia Road, Sec.2, Nanakng, Taipei, TW 115 Taiwan
AU: Kuo, L
EM: kuo@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, 128 Academia Road, Sec.2, Nanakng, Taipei, TW 115 Taiwan
AB: GPS measurements have been carried out frequently in the epicentral region after the devastating 1999 Chi-Chi, Taiwan, earthquake (Mw 7.6). Furthermore, seven continuous GPS stations were put into operation in the same area mostly within three weeks after the main shock. As part of a national earthquake research program, additional 20 continuous stations were set up in 2001. GPS data from these continuous and campaign sites are utilized to study the postseismic deformation following the Chi-Chi earthquake. Postseismic transients mainly occurred on the hanging wall with east over west thrusting, similar to the coseismic displacement field. A major part of the postseismic deformation is aseismic and afterslip seems to be the dominant mechanism for the first 15-month period after the main shock. Inverting the postseismic GPS data to infer the deeper fault geometry and afterslip distribution, we obtain an optimal model with a sub-horizontal decollement at a depth of 10.4 km. The maximum afterslip occurs in the hypocentral region and in the northern part of the decollement. After removing the postseismic exponential decay transients, coseismic or instrumental offsets, and periodic motions, the position time series of continuous GPS sites show a quite linear trend. However, the contraction rates in central Taiwan from 2002 to 2005 are about two times of the pre-earthquake rates derived from 1993-1999 GPS data. The impact of viscoelastic relaxation on lower crust or upper mantle during the 6-year postseismic period will be investigated by finite element modeling.
DE: 0545 Modeling (4255)
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 1243 Space geodetic surveys
DE: 3270 Time series analysis (1872, 4277, 4475)
SC: Geodesy [G]
MN: Fall Meeting 2005