Volcano-hydrothermal inflation revealed through spatial variation in stress field in Tatun Volcano Group, Northern Taiwan

Abstract

To investigate the inflation characteristics of subsurface volcano-hydrothermal activity, we examine the spatial variability of the stress field in the Tatun Volcano Group (TVG) of Northern Taiwan using 1016 earthquake focal mechanisms at depths shallower than 5 km from 2012 to 2017. We determine these focal mechanisms using the data from a dense seismic network composed of 40 seismic stations in an area of approximately 10 × 10 km2 in the TVG. We find that this area is subject to the northwest–southeast trended extension and subvertical compression. The stress magnitude ratios (∅) near the Dayoukeng area are significantly lower than that in the other areas. This feature is likely related to an inflating source buried underneath the Dayoukeng area. Our model shows good agreement between the observed and predicted ∅ values when the inflating pressure source located at a depth of approximately 2 km and with the average potency ranging from 1.4 × 105 to 7 × 105 m3 near the Dayoukeng area. We suggest that this inflation is associated with the local volcano-hydrothermal activity. This inflation is the principal pressure source in the shallow crust (≤5 km at depth) in the TVG and may persist for at least a decade.