Multifault complex rupture and afterslip associated with the 2018 Mw 6.4 Hualien earthquake in northeastern Taiwan

We investigate the coseismic and post-seismic deformation due to the 6 February 2018 M-w 6.4 Hualien earthquake to gain improved insights into the fault geometries and complex regional tectonics in this structural transition zone. We generate coseismic deformation fields using ascending and descending Sentinel-1A/B InSAR data and GPS data. Analysis of the aftershocks and InSAR measurements reveal complex multifault rupture during this event. We compare two fault model joint inversions of SAR, GPS and teleseismic body waves data to illuminate the involved seismogenic faults, coseismic slip distributions and rupture processes. Our preferred fault model suggests that both well-known active faults, the dominantly left-lateral Milun and Lingding faults, and previously unrecognized oblique-reverse west-dipping and north-dipping detachment faults, ruptured during this event. The maximum slip of similar to 1.6 m occurred on the Milun fault at a depth of similar to 2-5 km. We compute post-seismic displacement time series using the persistent scatterer method. The post-seismic range-change fields reveal large surface displacements mainly in the near-field of the Milun fault. Kinematic inversions constrained by cumulative InSAR displacements along two tracks indicate that the afterslip occurred on the Milun and Lingding faults and the west-dipping fault just to the east. The maximum cumulative afterslip of 0.4-0.6 m occurred along the Milun fault within similar to 7 months of the main shock. The main shock-induced static Coulomb stress changes may have played an important role in driving the afterslip adjacent to coseismic high-slip zones on the Milun, Lingding and west-dipping faults.

Automated summary

Our study investigates the coseismic and post-seismic deformation of the 6 February 2018 Hualien earthquake, revealing complex multifault ruptures in this transition zone. By analyzing aftershocks and InSAR data, we identify the involvement of both well-known active faults and previously unrecognized ones in the event. Kinematic inversions suggest that afterslip occurred on the Milun and Lingding faults, as well as a west-dipping fault, with maximum cumulative afterslip of 0.4-0.6m along the Milun fault within around 7 months of the main shock. The study also indicates that static Coulomb stress changes from the main shock may have influenced the afterslip on adjacent faults.