Seismic expression of magma‐induced crustal strains and localized fluid pressures during initial eruptive stages, Soufrière Hills Volcano, Montserrat

Abstract

We explore volcanotectonic earthquake activity during the early stages of volcanic activity (1995–96) at Soufrière Hills volcano. We focus on several zones of temporally‐confined seismic activity that comprise assemblages of small scale structural elements, >2–4 km distant from the volcano, at depths 2–4 km below sea level, and consider seismicity in relation to regional tectonics and heterogeneity of stiffness and strength as revealed by the SEA‐CALIPSO tomography experiment. The clustered seismicity and relatively aseismic zones are interpreted to reflect a broad weakened tectonic zone of ESE trend that crosses Montserrat, and the ascent of a magmatic dike of NNE trend, which altered the stress distribution to promote localized fault movements and caused localized dilatation with changes in pore‐fluid pressures, to either weaken or strengthen the rock mass depending on the local polarity of strain.