Source parameters of the 2022 ML 6.6 Guanshan (Taiwan) earthquake determined through teleseismic P-wave inversion and rupture directivity analysis

Two closely timed moderate-sized earthquakes (e.g., the ML 6.6 Guanshan and ML 6.8 Chihshang earthquakes) occurred in eastern Taiwan on 17–18 September 2002. To understand the rupture relationship between the two earthquakes, we used a teleseismic P-wave inversion and rupture directivity analysis to investigate the source parameters of the ML 6.6 Guanshan earthquake. The teleseismic P-wave inversion method assumed earthquake rupture to be a single source to determine the focal mechanism, seismic moment, and azimuth-dependent source duration for the Guanshan earthquake. The rupture directivity analysis using the azimuth-dependent source duration showed that the Guanshan earthquake unilaterally ruptured along a west-dipping fault plane (Central Range fault) with a rupture velocity (Vr) of approximately 2.8 km/s from the hypocenter toward the deeper part of the fault. Furthermore, through time-domain deconvolution, the source time function of the Guanshan earthquake approximated an isosceles triangle, which also indicated that the earthquake rupture was relatively simple. Here, we propose a fault-based relationship between the ML 6.6 Guanshan and ML 6.8 Chihshang earthquakes. After the ML 6.6 Guanshan earthquake, the source area was relocked, preventing the Chihshang earthquake from rupturing southward. Instead, it ruptured the fault from south to north.