Cascading Ruptures of the 2022 Chihshang Earthquake Sequence Constrained by Seismic and InSAR Data
Foreshocks are closely linked to the mainshock’s rupture, and they can either accelerate or inhibit the nucleation of the mainshock. Resolving the source processes is therefore essential for understanding the trigger mechanisms during earthquake sequences. In September 2022, a strong earthquake sequence comprising an Mw 6.6 foreshock and an Mw 7.0 mainshock struck Taitung County, Taiwan, providing a valuable opportunity to study earthquake nucleation. We combine seismic waveforms and Interferometric Synthetic Aperture Radar (InSAR) deformation data to construct a three-fault model for this earthquake sequence. Using Pn/Pg and Rayleigh surface waves, we determine the relative hypocenter and centroid locations, respectively. The results, which integrate these two types of data, are verified by relative location measurements. In addition, other available geodetic data (InSAR and Global Navigation Satellite System) are used to validate our model, and the results reproduce the observations well. Finally, static Coulomb stress changes are calculated based on the three-fault model. The results show that subsequent subevents were triggered by preceding ones, indicating that the sequence ruptured in a cascading manner. According to the high historical seismicity in the region, special attention should be paid to the seismic risk in the stress-increased regions caused by the current earthquake.