Short-Term Deep Postseismic Slips Following Large Earthquakes in Southern Taiwan

Abstract

Deep postseismic slips that reflect the rheology and the deformation of the seismogenic fault after large earthquakes are usually investigated less than shallow slips because of the difficulty of obtaining direct observations. In this study, we used the seismicity of repeating aftershock sequences (RASs) to improve our understanding of the deep postseismic slips after three large earthquakes in southern Taiwan. To more precisely characterize the evolution of the RASs, we applied a template-matching technique to continuous waveform data for 90 days before and after the mainshocks. We identified 28 RASs that mainly occurred in regions near the mainshock hypocenters with relatively high VP/VS ratios. The deep fault slips estimated from the RASs show that the postseismic slip rates decreased logarithmically with increasing duration time, suggesting that the faults were creeping according to the velocity-strengthening friction law. We inferred that the high hydraulic pressure environment contributed to the fault creep, but the dynamic stress perturbation may have been the main factor affecting the fault creep. The results of this study improve our understanding of the behavior of deep faults and may aid in future seismic hazard assessments in Taiwan.