Assessing the Yuli surface deformation from the 20220918 Chishang earthquake: an integrated RTK GNSS network approach

Abstract

The 20220918 Chishang earthquake impacted the Yuli area in the Longitudinal Valley of eastern Taiwan. Longitudinal Valley is situated near the boundary of the Philippine Plate and Eurasian Plate boundary with frequent seismicity and historical earthquakes. This study uses RTK GNSS measurements to characterize the 0918 seismic effects, revealing different coseismic displacement patterns in the Central Range, Coastal Range, and Longitudinal Valley blocks. Ruptures were mainly in the Longitudinal Valley, extending into downtown Yuli township. The influence on these geological formations highlights the complex interactions between the structures and underlying tectonic forces. Our investigations show that the Central Range block experienced a 1.17 m SW horizontal displacement and 1.1 m vertical uplift, while the Coastal Range block displayed a 1.18 m NW horizontal displacement and 0.65 m subsidence. The Longitudinal Valley block was divided by recent ruptures, with its western part impacted by the Central Range block, experiencing a 0.79 m SW displacement and 0.63 m uplift, and its eastern part influenced by the Coastal Range block, experiencing a 1.02 m NW displacement and 0.13 m subsidence. Our data indicates that different blocks were all affected differently, reflecting complex relationships between the subsurface faults to the surface fault traces. The result suggests the Central Range Fault have triggered the Yuli Fault for west-side up motion and possess a westward dip connected to the Central Range Fault. The post-seismic surveys reveal complex interactions between the Central Range and Longitudinal Valley Faults, vital for advancing earthquake mitigation strategies.