Results from the broadband seismic network on Montserrat

Abstract

A digital broadband seismic network has been installed around Soufriere Hills Volcano on Montserrat. While several distinctive types of seismic events with frequencies ranging from 0.5 Hz to 30Hz could be idnetified, the emphasis is on two types of low-frequency events which indicate the involvement of a fluid phase in the source mechanism: the so-called long-period events and the hydbrid events. The latter occur in swarms with distinct periodicities of four to 12 hours and preceed major dome collapses and explosions. The swarms correlate very well with the tilt observed at the flanks of the volcanic edifice and, hence, can be linked to the pressurization of the magmatic system. Occasionally, separate hybrid events merge and form harmonic tremor, which sometimes has a shifting spectral content. This revels temporary changes in the source parametrs. Low-frequency seismic signals on Montserrat are considered to be key parameters for the monitoring of the internal dynamics of the volcano.