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

[SGC37-P16] Evolving Volcanic Unrest in the Tatun Volcano Group: Linking Microseismic Activity and Geochemical Signals in Northern Taiwan

*AITI CHEN¹, Hsiao-Fen Lee², Yuji Sano³, Takanori Kagoshima⁴, Naoto Takahata⁵, Cheng-Horng Lin⁶, Ching-Hua Lo¹ (1.Department of Geosciences, National Taiwan University, 2.National Center for Research on Earthquake Engineering, National Applied Research Laboratories, 3.Marine Core Research Institute, Kochi University, 4.Graduate School of Science and Engineering, University of Toyama, 5.Atmosphere and Ocean Research Institute, University of Tokyo, 6.Institute of Earth Sciences, Academia Sinica)

Keywords:helium, hot spring, volcanic gases, disaster prevention

Taiwan is located at the boundary between the Eurasian Plate and the Philippine Sea Plate, where complex tectonic interactions have resulted in significant volcanic and seismic activity. The Tatun Volcano Group (TVG), a Quaternary active volcanic system in northern Taiwan, lies adjacent to the Taipei metropolitan area, making it crucial for volcanic monitoring and disaster risk assessment. This study integrates microseismic and geochemical monitoring to investigate the relationship between deep magmatic activity and the hydrothermal system in TVG. Our results indicate a transition from a relatively quiescent phase (2017-2018) to a increaseing phase of volcanic activities since 2019. Seismic monitoring recorded a surge in microseismicity, with 4,550 events detected in 2020, nearly twice the background level of 2,000-2,500 events per year, including several earthquakes with magnitudes exceeding 3.0. A vertically concentrated microseismic cluster was identified beneath Da-you-keng (DYK(, likely linked to the migration of magmatic or hydrothermal fluids. Coinciding with the seismic increase, fumarolic gas compositions exhibited notable changes, particularly in helium isotopic ratios (³He/⁴He), which showed a rising trend in the DYK region from 2020 to 2021. These observations suggest deep magmatic degassing and stress variations within the volcanic system. Additionally, geochemical monitoring of hot springs and groundwater from 2019 to 2024 reveals fluctuations in CO₂, H₂S, and SO₂ concentrations, which correlate with regional fault structures and groundwater recharge conditions. The CO₂/³He ratio variations align with seismic trends, further supporting the link between magmatic activity and gas release. The observed correlations between microseismicity, hydrothermal anomalies, and magmatic degassing highlight the dynamic nature of the volcanic system, providing insights into the sources and transport mechanisms of volcanic gases, enhancing hazard assessment and eruption forecasting efforts in northern Taiwan.