dc.description.abstract | On September 17th and 18th, 2022, two strong earthquakes with moment magnitudes Mw 6.5 (referred to as the Guanshan earthquake) and Mw 7.0 (referred to as the Chishang earthquake) struck the Longitudinal Valley (LV), where the arc-continent collision occurs between the Eurasian plate (EP) and the Philippine Sea plate (PSP) sutures. Two intriguing phenomena were observed from the Central Weather Bureau (CWB) reports and the distribution of their aftershocks.Firstly, the Guanshan earthquake and Chishang earthquake had a close spatial and temporal relationship, occurring only within 24 hours apart and several kilometers away from each other. Secondly, the aftershock distributions suggested that both events ruptured on the west-dipping Central Range Fault (CRF), which is considered to have smaller earthquake production compared to the Longitudinal Valley Fault (Bruce et al., 2006).To understand the rupture behavior of the CRF, we first determined the finite fault models of both events using a joint inversion approach that considered teleseismic waveforms (P, SH, Rayleigh, Love), strong-motion records, static, and high-rate GNSS data. Then, the Coulomb stress change is calculated to examine the triggering effect between the two earthquakes. The results showed that the Guanshan earthquake and Chishang earthquake exhibited different rupture characteristics. The Guanshan earthquake mainly ruptured in the down-dip direction, with a slight extension towards the shallow part and to the south, reaching a maximum slip of approximately 1.9 meters. On the other hand, the Chishang earthquake′s rupture primarily propagated northward and was closer to the surface, with a maximum slip of about 5 meters. Additionally, the interesting observation related to velocity pulse produced by Chishang earthquake is also investigated. Our forward simulation suggested that the velocity pulse observed in Yuli township may have resulted from the rupture of two different fault systems. One could be due to the combination of the near-fault directivity of the Yuli Fault and the amplification effect of shallow low-velocity layers, while the other could be caused by the rupture of the Longitudinal Valley Fault. We also discussed some issues related to the interaction between the Guanshan earthquake and Chishang earthquake, both statically and dynamically. Firstly, based on the inverted finite fault model, the Coulomb stress change increased on the Chishang mainshock, indicating that the Guanshan earthquake statically triggered the subsequent Chishang earthquake. Secondly, the inverted lower rupture velocity (ranging from 1.0 to 1.5 km/s) near the source region of the Chishang earthquake may provide evidence of the existence of a barrier that prevented the Guanshan earthquake from rupturing northward dynamically. | en_US |