Geodetic Finite-Fault Rupture Model of the 4 February 2018 Mw 6.2 Hualien Earthquake (Taiwan) and Its Potential Impact on the Occurrence of the 6 February Mw 6.4 Event

Abstract The 4 February 2018 Mw 6.2 earthquake struck the Hsincheng Ridge, offshore Hualien, in eastern Taiwan. Using a kinematic inversion of Global Navigation Satellite System (GNSS) time series combined with a forward calculation of dilatation static offsets, we infer that the earthquake has ruptured an asperity located at a depth of 10–15 km on a 25 km × 15 km northeast (NE)-dipping subhorizontal fault plane with a dominant right-lateral strike-slip mechanism. The total rupture duration inferred from simulations of dilatation time series is about 15 s, which corresponds to a rupture velocity of approximately 1.7 km·s−1. The aftershock sequence occurring within the first 2 days following the mainshock is characterized by abundant seismicity (1138 events with ML≥1.7) comprising two clusters located on both sides of the mainshock hypocenter at midcrustal depth (about 7–13 km). The seismicity in the NE cluster is likely controlled by afterslip, whereas aftershocks in the southwest cluster likely represent time-dependent failures in response to coseismic static stress excess. Furthermore, we find that the 4 February 2018 event has generated maximum static and dynamic Coulomb stress excess of 0.1 MPa in the hypocenter region of the 6 February 2018 Mw 6.4 mainshock, which suggests that the earthquake could have possibly advanced the occurrence of the 6 February earthquake. Finally, we report preliminary observations of a possible small-scale interplay between seismic and aseismic deformation (afterslip) in the vicinity of the hypocenter of the 6 February earthquake. The investigation of the precursory phase, if any, would require further high-precision geodetic and seismological measurements.