10:00 〜 10:15
[MIS04-05] Soil gas degassing and hydrogeological changes before and after the 2022 M6.8 Chihshang Earthquake in eastern Taiwan
★Invited Papers
キーワード：Soil gas, Chihshang Fault, CO2 degassing, precursory changes
A magnitude 6.6 earthquake occurred on September 17, 2022, followed by a magnitude-6.8 mainshock struck approximately 17 hours later on September 18, 2022, along the southern Longitudinal Valley in east Taiwan, the boundary between the Eurasian and Philippine Sea plates, causing serious damages of buildings and the surface. Soil gas surveys (gas species and CO2 degassing) were performed to investigate the gas-bearing properties of local seismogenic faults together with multi-parameters hydrogeological monitoring of the fault zone in the borehole around the Chihshang Fault (CSF) before/after these earthquakes. Recorded soil radon and hydrogeological data (e.g., pH, groundwater temperature, Chloride) showed precursor signals that preceded around one month the major earthquake. A higher value of CO2 flux in the area was found after the earthquake, which can be interpreted as an extra contribution of the gas sources from depth, or the increased permeability of the fault system. The findings of this study reported the precursory changes from deep to surface, caused by the mixture between the different chemical concentrations/fluid reservoirs from groundwater and surrounding formations through water-rock interaction, which may be associated with pre-seismically induced changes of permeability or opening of preexisting micro-fractures along the fault zones.