Finite fault modeling of the MW 5.5 2017 Pohang earthquake with multi-segmented fault system

Abstract:

Located near an enhanced geothermal system, the 15 November 2017 M_W 5.5 Pohang earthquake occurred at a city of Pohang, South Korea with a damaged buildings and injured people. The earthquake generated a measurable surface deformation, which gives an opportunity to quantify its source mechanism. In this study, we estimated a finite fault model for the Pohang mainshock via joint inversion of local seismograms and an InSAR observation. The constructed the fault model comprise of three segments inferred from its aftershock distribution. The initial rupture propagated to the southwest segment by 2 km and generated maximum peak slip up to ~30 cm. The rupture then sequentially propagated to the middle and northeast segment. Two largest aftershocks of M_L 4.3 and M_L 4.6 are located on the edge of the slip distribution, which may describe local asperities. Estimated rupture duration and fault dimension are 4 s and 40 km², respectively, suggesting relatively low stress drops. We propose that intersections between fault segments play a stress barrier, which controls rupture process. Observed complicated rupture process of the M_W 5.5 Pohang earthquake illustrates how rupture propagate in a multi fault system and reconciles the importance of seismic barriers that can control following aftershocks as well as fault dynamics.