The association between volcanic fluid variations and seismic events in the Tatun Volcano Group, northern Taiwan

International audienceTaiwan is located at the western edge of the circum-Pacific volcanic belt. Hydrothermal activity is still common inthe Tatun Volcano Group, and it is one of the major geothermal areas in Taiwan. Before developing the geothermalresources, monitoring volcanic activities and further evaluating volcanic hazards are essential measures. Geochemistryplays an important role in investigating geothermal reservoirs. In the past decade, researchers in Taiwanhave accomplished several studies in this area. Our group collected volcanic gas and water samples to analyzetheir chemical compositions and isotopic ratios.Integrating our observations with seismic and gravity data, we can associate fluid variations with two mechanisms.Firstly, the variations of fluid concentration, seismic events and gravity fluctuations occurred in a time series.SO2/H2S ratios from Da-you-keng varied from 0 to 3 since 2005 to 2007. Meanwhile, HCl concentrations alsoincreased dramatically. Then large gravity variations and volcanic earthquake swarms took place subsequently.Same process happened again in 2010. We infer that magma chamber disturbance and/or deep fluid transportationmight be the major cause. The other case, unlike the former one having multiple proxy variations, we only observedHCl concentration increasing rapidly after big earthquakes. The variations are reckoned as the consequenceof hydrothermal reservoir disturbed by earthquakes, and the responding time is short and rapi