Analysis and forward modeling of seismic anisotropy during the ongoing eruption of the Soufrière Hills Volcano, Montserrat, 1996-2007

Abstract

Volcanic stress field analysis has been lauded as a potentially powerful tool for midterm to long-term eruption forecasting. However, because tectonic processes can also produce localized stress field reorientations, evidence for a direct causal link between observed stress field reorientations and magmatic activity is of critical importance. In this study, we show that local stress field reorientations preceding changes in volcanic activity at the Soufrire Hills Volcano, Montserrat, are observable using two independent measures of crustal stress (local (volcano-tectonic) earthquake fault plane solutions and measurements of shear wave splitting in regional earthquakes). We further demonstrate that the local stress field orientation during a 6 month period preceding the onset of eruptive activity at Soufrire Hills in 1999 is highly localized and spatiotemporally variable and that the spatial pattern of precursory local stress orientations is consistent with numerically modeled patterns of stress resulting from pressurization of a vertical dike. These observations provide compelling evidence for a direct causal link between pressurization of midlevel volcanic conduit systems by ascending magma and precursory local stress field reorientations and demonstrate that seismological analysis can be used to detect subtle local changes in stress that herald eruptive activity. Copyright 2011 by the American Geophysical Union.