[S-CG40] Science of slow-to-fast earthquakes

[SCG40-37] Improvment of Seismic Hazard Assessment Through the Reevaluation of Crustal Deformation along Active Faults: A Case study of the Hengchun Fault in Southern Taiwan

*Shih-Han HSIAO¹, Kuo-En CHING¹, Jack GILETYCZ², Wu-Lung CHANG², Ryosuke ANDO³, Chien-Liang CHEN⁴ (1.National Cheng Kung University, 2.National Central University, 3.University of Tokyo, 4.Geological Survey and Mining Management Agency, MOEA)

Keywords:slow-slip events, Hengchun fault, 2006 Pingtung earthquake doublet, slip deficit rate

The geological data have been long served as a fundamental source for estimating the fault geometry and slip rates in the seismic hazard assessment. Nevertheless, owing to the limited geographic coverage of fault slips in seismic hazard assessment, recent efforts to improve seismic hazard models in various countries involve the integration of geodetic data to enhance the characterization of fault geometry and slip rates. Crustal deformation discovered by the geodetic network provides the dense and time varying information along the active faults, the characteristics of the gedetic data is helpful for capturing the contemporary behavior of fault systems. In this study, we adopted the Hengchun fault (HCNF) in southern Taiwan as an example, which has been proposed to accumulate strain and have a potential to generate an Mw larger than 6.8 earthquake. However, based on the analysis of geodetic data from 9 continuous GNSS stations, 37 campaign-mode GNSS stations, and 3 precise leveling routes spanning from 2002 to 2022 along the HCNF, its earthquake potential was suggested to be reevaluate. Based on the spatial distribution of surface velocity field, a velocity discontinuity is revealed along the HCNF, implying that the fault trace might be located at approximately 1-2 km east of the currently proposed fault trace. The distinct time-varying surface velocity patterns indicate that there is a triggered trasient event on the fault following the 2006 M_L 7.0 Pingtung offshore earthquake.The slip deficit rate and slip rate distributions of the HCNF were assessed using the baseline inversion and coseismic source models, respectively. The modeling results indicate that the energy accumulated on the HCNF, mainly distributing on the middle and shallower area. The energy release on its southern and northern segments has progressively propagated from south to north since the 2006 earthquake. Geological investigations confirm surface ruptures along the HCNF until 2017, which also verifies the presence of surface fault creep. Based on these findings, the occurrence of a triggered slow slip event (SSE) on the inland HCNF following the 2006 earthquake in Taiwan is proposed, and the SSE continues to release partial energy. Consequently, due to the relocation of the fault trace, the renewed fault geomtery and the energy released by the SSE on the HCNF, we suggested that the earthquake potential of the HCNF is supposed to be partially decreased. Furthermore, the quasi-dynamic model will be adopted in the future to delve into the mechnism of the inland SSE.