[S-GC37] Volatiles in the Earth - from Surface to Deep Mantle

[SGC37-07] Persistent crustal CO₂ emissions following the 2022 M6.8 Chihshang earthquake sequence in eastern Taiwan

★Invited Papers

*Ching-Chou FU¹、Kuo-Hang Chen¹、Kuo-Wei Wu¹、Pei-Ling Wang²、Li-Hung Lin³、Hao Kuo-Chen³、Chung-Hsiang Mu¹、Vivek Walia⁴ (1.Institute of Earth Sciences, Academia Sinica, Taiwan、2.Institute of Oceanography, National Taiwan University, Taiwan、3.Department of Geosciences, National Taiwan University, Taiwan、4.National Center for Research on Earthquake Engineering, NARL, Taiwan)

キーワード：2022 M6.8 Chihshang Earthquak, CO2 degassing, Chihshang Fault

On September 17, 2022, a magnitude 6.6 earthquake occurred, followed by a magnitude 6.8 mainshock in Chihshang approximately 17 hours later, along the southern Longitudinal Valley in eastern Taiwan, where the Eurasian and Philippine Sea plates meet. This seismic event caused significant damage to buildings and the surface. In order to investigate the gas-bearing properties of the Chihshang Fault (CSF) zone and gain a better understanding of the degassing behavior, soil gas surveys were conducted to examine gas species and CO₂ degassing. Our findings indicate that the observed increase in CO₂ flux at the surface after the CS earthquake could be attributed to the release of gases from both deep and shallow sources, with the enhanced permeability of the fault system playing a role in this process. The presence of a heavier ¹³C isotopic composition provides evidence of an additional contribution of CO₂ gas migrating from depth to the surface, a phenomenon that persisted for at least three months after the earthquake. These observations suggest that the CSF system acts as a conduit connecting deep and surface gas reservoirs, with CO₂ emissions linked to significant seismic activity. The earthquake-induced microfractures may gradually heal and return to their original state. Based on our estimates, the total natural CO₂ degassing around the entire CSF zone is approximately 1200 t/d before the Chihshang earthquake and 2200 t/d after the earthquake. These findings shed light on the dynamic behavior of gas emissions associated with seismic events and provide valuable insights into the degassing processes within the study area.