HR: 0800h
AN: S21B-0277    [Abstracts]
TI: Earthquake Triggering and Fault Interaction in a Thrust Fault System: the 1999 Chi-Chi, Taiwan, Earthquake
AU: * Chan, C
EM: han@eqkc.earth.ncu.edu.tw
AU: Ma, K
EM: fong@earth.ncu.edu.tw
AU: Stein, R S
EM: rstein@usgs.gov
AB: To understand earthquake triggering and possible fault interaction in a thrust fault system, we calculate the changes in seismicity rate associated with the 1999 Chi-Chi, Taiwan, earthquake, and the Coulomb stress change caused by the earthquake. The Coulomb stress change for the ruptured Chelungpu fault shows large stress changes near the fault, and broad lobes of stress increase and decrease off the fault. The pattern of the aftershock distribution show similar feature to the Coulomb stress change calculated for a simple slip model, suggesting its strong association. More than 70% of the aftershocks in strike-slip and thrust faulting mechanisms can be explained by the increased Coulomb stress changes. Most of the calculated zones of Coulomb stress increase, often by less than 1 bar, correspond to sites of aftershocks. Although the Chi-Chi earthquake is a thrust event, many of the triggered aftershocks show strike-slip mechanisms, particularly to the 2 south and southeast of the southern tip of the thrust fault. The calculated Coulomb stress change on the likely rupture planes of the M>6 aftershocks is also generally positive, with values of 2-5 bars. This suggests that the large aftershocks do not necessarily occur where the Coulomb stress change is most positive. The feature for stress shadow is also observed to the further west of the fault, but less significant to the observation for stress triggering. Thrust faults to the east of the ruptured Chelungpu fault lie in calculated Coulomb stress shadows, whereas the Changhua and Chuko faults, to the west and south of the Chelungpu fault, are subject to stress increases. Comparison with historical events since 1600, the calculated Coulomb stress change shows strong correlation of the occurrences of the earthquake on the Chelungpu fault to the events on Changhua and Chuko faults in the 19th century. This seems to suggest the possible predictive power of the static stress calculation in estimating occurrences of future large earthquakes.
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
DE: 2722 Forecasting
SC: Seismology [S]
MN: 2004 AGU Fall Meeting