CHARACTERIZING RESPONSE AND RECOVERY OF GROUNDWATER SYSTEM FOLLOWING AN EARTHQUAKE

Environmental tracer data were utilized to analyze the hydrogeochemical signatures of deep fluids within fault zones in southeastern part of South Korea. Following the M_W 5.5 Pohang Earthquake in November 2017, groundwater samples from around the epicenter were monitored for hydrogeochemical changes using environmental tracer data from 2017 to 2021. The southeastern region of South Korea exhibits distinct NNE-directed geomorphological features, including several strike-slip fault systems and a NNW-SSE trending reverse fault. The epicenter is situated in an active fault zone around KW4 displaying the highest ³He/⁴He values among the measured samples in the study area. Following the earthquake, there was a slight increase in ³He/⁴He in most groundwater samples from monitoring wells, while ³He/⁴He decreased in some groundwater samples from wells around the Ulsan fault. Additionally, concentrations of Na, Ca, SO₄, and HCO₃ decreased around wells within the Ulsan Fault area after the earthquake. Hydrological and geochemical data were compared to monitor the recovery of an aquifer system around strike-slip, reverse faults, and active fault zones after earthquakes. Most of environmental tracer recovered the concentration before earthquake in the aquifer system three to five years after the earthquake. Our results indicate that further research is recommended to delineate the potential of seismic precursor signals even though the 5-year hydrological and geochemical data is useful to evaluate the response and recovery of groundwater systems after earthquakes.

This study was supported by the National Research Foundation of Korea (2022R1A5A1085103).