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

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 Mw = 6.3) occurring 4.8 s later than the initiation of rupture. The total seismic moment (M0) of 6.48 × 1018 Nm (Mw = 6.5) and radiated seismic energy (ES) of 1.76 × 1014 Nm led to the ES/M0 ratio ~2.72 × 10-5. A static stress drop (ΔσS) 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 M0 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 ΔσS varied with the sub-events and increased with ES/M0 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 ΔσS, low ES/M0, and high Vr occurred at sea; the other with high ΔσS, high ES/M0, 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.