Complex Rupture Features and Triggering during the 2022 Chishang Earthquake Sequence in Eastern Taiwan Estimated by InSAR, GPS, Strong Motion, and Teleseismic Waveform Evidence

The most recent 2022 Chishang earthquake sequence broke a long-time seismic quiescence on the Central Range fault (CRF), attracting lots of attention to the seismic behaviors and fault interactions of the Longitudinal Valley zone (LVZ), eastern Taiwan orogeny. However, detailed rupture features of both the foreshock and mainshock are still scarce. Here, available static displacements (i.e., Interferometric Synthetic Aperture Radar [InSAR], Global Positioning System [GPS], and strong motion [SM]) and kinematic waveform evidence (i.e., high-frequency GPS, strong motion, and teleseismic data) are used to delineate the rupture behaviors of both the foreshock and mainshock in this sequence. Our results indicate that the static displacements derived from strong-motion sites rival the high precision of GPS observations, replenishing the near-field constraints on the hanging wall together with InSAR and GPS. The optimal uniform slip models exhibit that both the foreshock and mainshock generally ruptured the west-dipping CRF along the south-southwest-striking direction with a steep dip angle > 65 degrees. The slip distribution models revealed that the rupture of foreshock and mainshock nearly ruptured a total length of CRF within 65 km from the Guanshan to Ruisui at a depth of above 14 km, and their slips are concentrated within one asperity and two asperities, respectively. The spatial evolution of this sequence's ruptures exhibits a discontinued and separated pattern, and is well consistent with the local seismicity. Considering that the mainshock was initialed in a weak slip and negative static Coulomb stress region caused by the foreshock, the 2022 sequence occurrence is in favor of a preslip triggering mechanism. The rupture region of the 2022 sequence filled the "seismic gap" along the western flank of the LVZ and will promote the potential seismic hazard in this region.