MVO/VSG - Open Scientific Meeting
27 November 1996

Banded tremor at Montserrat, July-August 1996

Glenn Thompson

University of Leeds, UK.

After a long period of quiescence, activity at Soufriere Hills Volcano escalated on 20 July 1996. The first indications were VT swarms. Other earthquake types (LPs, hybrids and rockfalls) also increased in intensity significantly at this time. On 29 July several pyroclastic flows entered the sea, and similar episodes occurred on 31 July and 11 August. These events surpassed anything seen previously during the current eruption. Banded tremor was observed for the first time at this volcano on 23 July. Between 29 July and 7 August banded tremor saturated all seismic stations and appeared to be harmonic. Over the next few weeks the tremor decayed in amplitude and lengthened in period. Amplitude and period seemed to be interdependent. RSAM data shows the banded tremor clearly. Correlation of rockfall data with tremor bands demonstrates that banded tremor is linked to dome instability. Dome collapse had a large affect on tremor intensity which could have been due to decoupling caused by depressurization. Banded tremor has the potential to reveal a lot of information about the volcano and it is important that all data are analyzed in detail. There is still much work to do.

Montserrat Volcano Observatory