Monitoring earthquake-induced pore pressure changes in the creeping fault system triggered by the 2022 Chihshang earthquake sequence

Abstract

Our goal is to comprehend fluid circulation within fault zones and its impact by monitoring hydrochemical and hydrophysical aspects across multiple dimensions. We also monitor nearby micro-seismicity and surface deformation. MAGIC (Multidimensional Active fault of Geo-Inclusive observation Center) is located at the Chihshang creeping fault, situated at the boundary of tectonic plates in eastern Taiwan. This fault exhibits aseismic creep at a rate of 2 cm per year, alongside high seismic activity. The earthquake sequence of 2022 began with a magnitude 6.4 event on September 17 (local time), followed by a magnitude 6.8 earthquake the next day. The epicenters were within the Central Range fault system, positioned to the west of our monitoring network. This presents a significant opportunity to observe co-seismic changes in pore pressure within the footwall and fault zone. The findings revealed that after the initial earthquake in the adjacent fault system, the pore pressure within the footwall swiftly decreased by nearly 100 cm within 15 hours. Simultaneously, the pore pressure within the fault zone increased by approximately 25 cm during the same period. Subsequently, the footwall's pore pressure continued to decrease with the second earthquake and then slowly recovered. These alterations in pore pressure suggest that fractures underwent both opening and closure during stress migration.