Evaluating groundwater responses to earthquakes using hydrological and environmental tracer data

<p>Environmental tracer data were applied to assess chemical signatures of deep fluid in the fault zones in the southeastern part of South Korea. After <em>M_W</em>5.5 Pohang Earthquake in November 2017, hydrogeochemical and environmental tracer data from groundwater samples around epicenter were monitored from 2017 to 2021. Monitoring wells significantly responded to the earthquakes were selected to evaluate temporal variations of environmental tracer data in the groundwater system. The southeastern part of South Korea shows a distinctive NNE-directed geomorphological feature with several strike-slip fault systems and two wells are closely located to this fault. One monitoring station, KW5, is closely located to the Ulsan Fault, which is a reverse. ³He/⁴He was slightly increased in most of groundwater samples from monitoring wells after <em>M_W</em>5.5 Pohang&#160;Earthquake, while ³He/⁴He decreased in some groundwater samples from wells around reverse fault (Ulsan fault). Especially, ³He/⁴He in the wells of KW5 station closely located to the Ulsan Fault considerably decreased after the earthquake. However, the concentrations of Na, Ca, SO₄ and HCO₃ increased around wells in Ulsan Fault after the earthquake. In this study, the response of aquifer system after earthquakes was compared to assess the differences in chemical changes of fluid around strike-slip and reverse faults using hydrogeochemical and environmental tracer data.</p> <p>This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2022R1A5A1085103).</p>