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Temporal and spatial variations of post-seismic deformation following the 1999 Chi-Chi, Taiwan earthquake

Hsu, Ya-Ju and Segall, Paul and Yu, Shui-Beih and Kuo, Long-Chen and Williams, Charles A. (2007) Temporal and spatial variations of post-seismic deformation following the 1999 Chi-Chi, Taiwan earthquake. Geophysical Journal International, 169 (2). pp. 367-379. ISSN 0956-540X.

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We use GPS displacements collected in the 15 months after the 1999 Chi-Chi, Taiwan earthquake (Mw 7.6) to evaluate whether post-seismic deformation is better explained by afterslip or viscoelastic relaxation of the lower crust and upper mantle. We find that all viscoelastic models tested fail to fit the general features in the post-seismic GPS displacements, in contrast to the satisfactory fit obtained with afterslip models. We conclude that afterslip is the dominant mechanism in the 15-month period, and invert for the space–time distribution of afterslip, using the Extended Network Inversion Filter. Our results show high slip rates surrounding the region of greatest coseismic slip. The slip-rate distribution remains roughly stationary over the 15-month period. In contrast to the limited coseismic slip on the décollement, afterslip is prominent there. Maximum afterslip of 0.57 m occurs downdip and to the east of the hypocentral region. Afterslip at hypocentral depths is limited to the southern part of the main shock rupture, with little or no slip on the northern section where coseismic slip was greatest. Whether this results from along strike variations in frictional properties or dynamic conditions that locally favour stable sliding is not clear. In general, afterslip surrounds the area of greatest coseismic slip, consistent with post-seismic slip driven by the main shock stress change. The total accumulated geodetic afterslip moment is 3.8 × 10^19 N m, significantly more than the seismic moment released by aftershocks, 6.6 × 10^18 N m. Afterslip and aftershocks appear to have different temporal evolutions and some spatial correlations, suggesting that aftershock rates may not be completely controlled by the rate of afterslip.

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Additional Information:© 2007 The Authors. Accepted 2006 November 2. Received 2006 October 30; in original form 2006 June 16. We are grateful to many colleagues at the Institute of Earth Sciences, Academia Sinica and the Land Survey Bureau, Ministry of Interior who have participated in collecting GPS data. We thank Mark Simons and Jean-Philippe Avouac for permission to use FEM modelling results obtained byY.J. Hsu at Caltech as part of a research project funded by EAR-0537625. We are grateful for constructive comments from Dr John Beavan and two anonymous reviewers, as well as to Shinichi Miyazaki, Jessica Murray, and Eric A. Hetland. This study was supported by the Institute of Earth Sciences, Academia Sinica, the National Science Council of the Republic of China grant NSC 94-2119-M001-008, the National Science Foundation grant EAR-0106695 to Stanford University, the National Science Foundation grant EAR-0537625 to Caltech and the Gordon and Betty Moore Foundation. This is a contribution of the Institute of Earth Sciences, Academia Sinica, IESAS1143, Caltech Seismological Laboratory contribution number 9161 and Caltech Tectonics Observatory contribution number 58.
Subject Keywords:afterslip; Chi-Chi earthquake; postseismic deformation; viscoelastic relaxation.
Issue or Number:2
Record Number:CaltechAUTHORS:HSIgji07
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Official Citation:Ya-Ju Hsu, Paul Segall, Shui-Beih Yu, Long-Chen Kuo, Charles A. Williams (2007) Temporal and spatial variations of post-seismic deformation following the 1999 Chi-Chi, Taiwan earthquake Geophysical Journal International 169 (2), 367–379. doi:10.1111/j.1365-246X.2006.03310.x
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9191
Deposited By: Kristin Buxton
Deposited On:05 Dec 2007
Last Modified:02 Oct 2019 23:58

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