Multiple-event analysis of the 2018 M-L 6.2 Hualien earthquake using source time functions

Abstract

Through forward multiple-event analysis of teleseismic P-waves using source time functions (STFs), derived by non-negative time-domain deconvolution, we inferred the rupture features of the 2018 Hualien earthquake. At least six sub-events composed the Hualien earthquake, with the largest one (corresponding to M-w = 6.3) occurring 4.8 s later than the initiation of rupture. The total seismic moment (M-0) of 6.48 x 10(18) Nm (M-w = 6.5) and radiated seismic energy (E-S) of 1.76 x 10(14) Nm led to the E-S/M-0 ratio similar to 2.72 x 10(-5). A static stress drop (Delta sigma(S)) of 5.03 MPa was also derived for the earthquake. On average, the rupture parameters of the 2018 Hualien earthquake from this study were similar to globally average values. From M-0 and source duration (10.9 s), this implied an average rupture velocity (Vr) less than 2.0 km s(-1). The forward multiple-event modeling showed that Delta sigma(S) varied with the sub-events and increased with E-S/M-0 to imply the frictional strength being heterogeneous along the fault. From the highest STF peak (6.9 s after the initiation) near the land-sea interface, we suggested that the Hualien earthquake be divided into two rupture processes. One with low Delta sigma(S), low E-S/M-0, and high Vr occurred at sea; the other with high Delta sigma(S), high E-S/M-0, and low Vr occurred on land. Both seawater and local velocity structures probably played crucial factors behind these rupture discrepancies during the 2018 Hualien earthquake.