Preseismic, coseismic and postseismic deformation of the 1999 Chi-Chi earthquake
Speaker: Chi-Hsien Tang Adviser: Ya-Ju Hsu, Wu-Lung Chang
Abstract
On September 21, 1999, the Mw 7.6 Chi-Chi earthquake ruptured the Chelungpu fault in central Taiwan and generated large coseismic slip (>10 m) and significant postseismic deformation recorded by the GPS network in Taiwan. Previous studies used preseismic (1993-1999.7), coseismic and postseismic (1999.7-2001) GPS data of the Chi-Chi earthquake to infer the fault slip behavior during, and after the earthquake. The geodetic data show that the coseismic slip occurred within a locked patch on the fault, and the afterslip, which was driven by the main shock stress change, occurred dominantly downdip from the rupture area. Several researches had concluded that the time evolution of the early postseismic deformation is consistent with afterslip being governed by velocity-strengthening frictional sliding. Comparing with the distribution of temperature on the fault derived from thermokinematic model also shows that aseismic slip becomes dominant where temperature is estimated to exceed 200°C at depth. This is approximately consistent with the temperature induced transition from velocity-weakening to velocity-strengthening behavior on quartzo-feldspathic rocks (250 - 350°C) that is observed in laboratory experiments. The area with the increase of coseismic Coulomb stress on the décollement is consistent with the dominant afterslip area, conforming to the assumption that afterslip is dominantly driven by stress change on the fault. The observed results and the temporal evolution of afterslip are also compared well to the theoretical model of seismic cycle.
References
Hsu, Y. J., Avouac, J. P., Yu, S. B., Chang, C. H., Wu Y. M., and Woessner, J., 2009. Spatio-temporal slip, and stress level on the faults within the Western Foothills of Taiwan: implications for fault frictional properties, Pure Appl. Geophys., 166, 1853-1884.
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Hsu, Y. J., Segall, P., Yu, S. B., Kuo, L. C., and William, C. A., 2007. Temporal and spatial variations of postseismic deformation following the 1999 Chi-Chi, Taiwan earthquake, Geophys. J. Int., 169, 367–379.