The trigger mechanism of low-frequency earthquakes on Montserrat

• Published in: Journal of volcanology and geothermal research 2006-05, Vol.153 (1), p.37-50
• Main Authors: Neuberg, J.W., Tuffen, H., Collier, L., Green, D., Powell, T., Dingwell, D.
• Format: Article
• Language: English
• Subjects: conduit resonance; low-frequency events; Montserrat; seismic trigger; soufrière Hills
• ISSN: 0377-0273; 1872-6097
• DOI: 10.1016/j.jvolgeores.2005.08.008

A careful analysis of low-frequency seismic events on Soufrièere Hills volcano, Montserrat, points to a source mechanism that is non-destructive, repetitive, and has a stationary source location. By combining these seismological clues with new field evidence and numerical magma flow modelling, we propose a seismic trigger model which is based on brittle failure of magma in the glass transition. Loss of heat and gas from the magma results in a strong viscosity gradient across a dyke or conduit. This leads to a build-up of shear stress near the conduit wall where magma can rupture in a brittle manner, as field evidence from a rhyolitic dyke demonstrates. This brittle failure provides seismic energy, the majority of which is trapped in the conduit or dyke forming the low-frequency coda of the observed seismic signal. The trigger source location marks the transition from ductile conduit flow to friction-controlled magma ascent. As the trigger mechanism is governed by the depth-dependent magma parameters, the source location remains fixed at a depth where the conditions allow brittle failure. This is reflected in the fixed seismic source locations.