HR: 0830h
AN: S41C-0093    [PDF]
TI: Stress Interaction and Triggering of Aftershocks Associated With the 1999 Chi-Chi, Taiwan, Earthquake
AU: * Ma, K
EM: fong@earth.ncu.edu.tw
AF: Institute of Geophysics, National Central Univ., 300 Jungda Rd., Institute of Geophysics, National Central Univ., Chung-Li, Twn 32054 Taiwan
AU: Chang, C
EM:
AF: Institute of Geophysics, National Central Univ., 300 Jungda Rd., Institute of Geophysics, National Central Univ., Chung-Li, Twn 32054 Taiwan
AU: Stein, R
EM:
AF: US Geological Survey, Menlo Park, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AB: We employed the models of Coulomb stress changes to investigate the features of the 1999 Chi-Chi earthquake on fault interactions and earthquake triggering. The seismicity examined by Z-map shows a butterfly shape of increased of seismicity consistent with the pattern for Coulomb stress changed associated with a thrust event. Due to the surface-cutting thrust fault, the Coulomb stress change show relief of stress near the surface of the fault, consistent with less amount of the aftershocks along the fault surface. The correlation of the aftershocks occurrence is significant at deeper depth ($>$12 km), especially in the off-source region. The lobe with positive Coulomb stress change tends to be broader at deeper depths. It explains the occurrence of large amount of aftershocks at deeper depth. Most of the aftershocks occurred in the positive Coulomb stress changes region. The six large aftershocks, which occurred within a week of the mainshock, located near the boundary of the positive and negative Coulomb stress changes in off source region. The positive stress changes associated with these events are of about 2-7 bars, suggesting that only little change of the Coulomb stress could yield the triggering of large aftershocks. The examination on stress interaction shows that at deeper depths ($>$6 km) significant increases of Coulomb stress changes were found beneath the Chelungpu nearby active faults, namely Shuangtung and Shuilikeng faults, suggesting the activation of the faults after the Chi-Chi earthquake. The Chunghua fault, to the west of the Chelungpu fault, as the frontal thrust of the Taiwan fold and thrust belts the Coulomb stress change beneath it shows significant increase of stress up to 50 MPa. Long term monitoring of the stress flow might be necessary to investigate the future behavior of the Chunghua fault. In additions, our study shows that variable of slips in dip direction has significant influence on the pattern of Coulomb stress change. It suggests the importance of accurate fault slip model in both strike and dip direction toward stress triggering study.
DE: 7209 Earthquake dynamics and mechanics
DE: 7230 Seismicity and seismotectonics
SC: Seismology [S]
MN: 2003 Fall Meeting