Association of Five Moderate-Large Earthquakes to the Faults in Taiwan

Abstract

Five moderate-large earthquake sequences were relocated using the double-difference earthquake location algorithm called hypoDD to study their association to the faults in Taiwan. The relocation after hypoDD shows better clusters of aftershock seismicity by using the concept of multiple events. Our results show that the rupture of 1993 Da-Pu earthquake resulted from a northeast-southwestern strike, western dipping fault. Geologically, there is no clear and direct geological feature that is consistent with this feature in this area. Thus , the 1993 Da-Pu earthquake might be attributed to a blind thrust. The rupture of the 1995 Nan-Ao earthquake shows a clear east-west strike, southern dipping fault. It might be related to the Lupihsi fault. The rupture of 1997 Ruey-Li earthquake strike is NE-SW, estrern dipping. The fault associated with this earthquake was either Tachienshan fault or Chukou fault. The rupture of Chia-Yi earthquake had the strike in N-S, western dipping. No clear geological structure in this region is associated with this feature. We infer that the Chia-Ui mainshock might have also resulted from a blind thrust. The aftershock distribution of the 1999 Chi-Chi earthquake shows clear involvement of nearby active faults. This implies the triggering of nearby active faults. This implies the triggering of nearby active faults after the mainshock. On the Chelungpu fault ruptured plane, most of the aftershocks occurred in the region with less slippage during main shock. This suggests the almost total release of the stress along the Chelungpu fault during the rupture. The possible involvement of blind thrust in southwestern Taiwan suggests the importance of understanding the possibility of a blind thrust structure beneath Taiwan.

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