Triggered slip on multifaults after the 2018 Mw 6.4 Hualien earthquake by continuous GPS and InSAR measurements

Abstract

On 6 February 2018 at 23:50 local time, a Mw 6.4 earthquake struck eastern Taiwan. We characterize the instantaneous surface ground motion and the permanent displacement induced by this event from continuous GPS data and SAR images within a short time after the mainshock. We use high-rate GPS positioning techniques to obtain epoch-by-epoch positions peak ground displacement to assess potential seismic damage. The maximum coseismic GPS horizontal displacement of about 450 mm trending to the northeast is observed at the station HUAL located on the hanging wall of the Milun fault. The PEPU located on the footwall of the Milun fault shows a coseismic horizontal displacement of 280 mm trending to the southwest and a coseismic uplift of about 70 mm. Moreover, ascending and descending tracks of ALOS-2 and Sentinel-1 SAR images are processed to estimate coseismic surface deformation along the line-of-sight (LOS) toward the satellite. Then, wide coverage from east-west and uplift components of surface deformation is fulfilled by combining the LOS displacement from ascending and descending interferograms. The main deformation area revealed by both GPS results and D-InSAR interferograms is concentrated around the Milun and Lingding faults. Significant uplift on the footwall of the northern Lingding Fault implies that the Milun fault and an unknown westdipping fault close to the Lingding fault were triggered. Both the two nodal planes of the Mw 6.4 Hualien event could be different with the kinematic behavior of the Milun fault and Lingding fault. Thus we suggest that slip on multiple faults was triggered during the 0206 event.