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 M_L 6.6 Guanshan and M_L 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 M_L 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 M_L 6.6 Guanshan and M_L 6.8 Chihshang earthquakes. After the M_L 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.