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

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Abstract

[1] 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.

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