Stress evolution associated with the 1999 Chi-Chi, Taiwan, earthquake: Consequences for seismicity, postseismic slip and deformation

HR: 17:45h
AN: G44A-08 [Abstracts]
TI: Stress evolution associated with the 1999 Chi-Chi, Taiwan, earthquake: Consequences for seismicity, postseismic slip and deformation
AU: * Chan, C
EM: cchan@usgs.gov
AF: U. S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: * Chan, C
EM: cchan@usgs.gov
AF: Institute of Geophysics, National Central University, 300 Chung-Da Rd, Chung-Li, 320 Taiwan
AU: Stein, R S
EM: rstein@usgs.gov
AF: U. S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AB: We explore how Coulomb stress transfer might control aftershock distribution, long-term seismicity, and postseismic slip in a ramp-flat thrust fault system. The M_w=7.6 Chi-Chi shock, with a surface-cutting 30°-dipping ramp fault merging into a near-horizontal décollement, is representative of continental thrust systems throughout the world, and so inferences drawn from this uniquely well-recorded event may be widely applicable elsewhere. The 3D distribution of aftershocks and their focal mechanisms are consistent with the calculated spatial distribution of Coulomb stress changes. The coseismic and postseismic deformation is captured by an extensive GPS network, and so far, the postseismic time series have not been explained by viscoelastic rebound. Thus we consider whether the stresses imparted by the coseismic slip could have triggered postseismic slip on the fault. We find a fair correlation between the inferred postseismic slip (Yu et al., JGR, 2003) and regions of calculated stress increase on the ramp and décollement. The correlation of stress with slip is best if the fault friction is very high (μ'=0.8) along the uppermost 5 km of the ramp, and if friction is exceedingly low (μ'=0.0) along the décollement. Finally, we search for a change in aftershock distribution and rate caused by the postseismic décollement slip. We find a marked decrease in aftershocks with respect to Omori decay where the postseismic slip is calculated to further depress the Coulomb stress, and an increase of seismicity and the rate of M ≥ 5.0 earthquakes in the corresponding positively stressed zones.
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8108 Continental tectonics: compressional
DE: 8164 Stresses: crust and lithosphere
SC: Geodesy [G]
MN: Fall Meeting 2005