Ascending Volcanic Fluids Portended By Spatiotemporal Variations Of The Earthquake Mechanisms In The Tatun Volcano Group In Northern Taiwan

To investigate the possible precursors of surface volcanism, we examined 2,473 earthquake focal mechanisms and the relative abundance of total sulfur (S-t) to carbon dioxide (CO2) in the Tatun Volcano Group in the northern Taiwan, where various reports have indicated ongoing volcanic activities. We analyzed three time-dependent observations: the occurrence rate of both shallower (0-2 km) reverse-type earthquakes and deeper (2-4 km) normal-type earthquakes, as well as the surface S-t/CO2 ratio. Among these observations, we found a series of similar variations, which progressed in a stepwise manner as the depth range of the observation decreased. To interpret the spatiotemporal variations of three observations, we construct a model involving the ascending volcanic fluids in the conduit and hydrothermal layer. The significant variations in deeper and shallower faulting behaviors portend a double warning of surface volcanism associated with the ascending fluids at similar to 4 and similar to 1 month(s) ago, respectively.Plain Language Summary The Tatun volcano group (TVG) is located at northern border of the metropolis Taipei, which is densely populated with more than seven million residents. Recent studies of both a young eruption record (similar to 6,000 years) and the existence of magma chamber indicate that the TVG is still active. The latent volcanism associated with the shallow pressure sources are a direct threat to the local residents. To investigate the possible precursors of surface volcanism, we examined both local behaviors of earthquakes' faulting mechanisms and the geochemical composition from fumarolic gases. We then found a series of similar variations, which were a step-by-step progression as the depth range of the observation decreased. These observations support us to construct a model involving the ascending volcanic fluids beneath the TVG. Practically, the significant variations of faulting behaviors provide a valuable warning of surface volcanism associated with the ascending fluids at several months ago.Key PointsWe demonstrate that ascending volcanic fluids were portended by spatiotemporal variations of earthquake mechanismsThese phenomena can be explained using a simple model involving the ascending volcanic fluid in the conduit and hydrothermal layerThe systemic spatiotemporal variation of earthquake mechanisms provides a double warning of surface volcanism