HR: 0800h
AN: V21C-0622    [Abstracts]
TI: Changes in the Orientation of Local Stresses Prior to and During Magmatic Activity at the Soufriere Hills Volcano, Montserrat
AU: * Roman, D C
EM: droman@earth.leeds.ac.uk
AF: School of Earth and Environment, University of Leeds, Leeds, LS2 9JT United Kingdom
AU: Neuberg, J
EM: locko@earth.leeds.ac.uk
AF: School of Earth and Environment, University of Leeds, Leeds, LS2 9JT United Kingdom
AU: Luckett, R R
EM: rrl@bgs.ac.uk
AF: Montserrat Volcano Observatory, British Geological Survey, Fleming's, 000 Montserrat
AU: White, R A
EM: rwhite@usgs.gov
AF: United States Geological Survey, 345 Middlefield Road MS 977, Menlo Park, Ca 94035 United States
AB: Systematic changes in the orientation of double-couple fault-plane solutions (FPS) for volcanotectonic (VT) earthquakes have been linked to stress changes induced by the dilation of the magmatic conduit system and may precede the onset of eruption by weeks to months, potentially providing advance warning of an impending eruption. To determine whether analysis of FPS for VT earthquakes recorded during the ongoing eruption of the Soufriere Hills Volcano, Montserrat, could be used to detect the arrival of magma in the mid-level conduit system, we produced a large catalog of high-quality FPS that spanned several phases of the eruption, and then analyzed this catalog to determine whether a temporal correlation exists between eruptive activity and FPS orientation. We repicked VT earthquakes recorded on the Montserrat Volcano Observatory analog and digital seismic networks from the beginning of the eruption in 1995 to May 2005 and relocated them using a 1D velocity model. We then determined well-constrained FPS for the relocated earthquakes. Well-contrained FPS for 607 VT earthquakes indicate primarily oblique strike-slip faulting. In August 1995 (prior to the onset of lava extrusion in September 1995), October 1996-June 1997 (during a period of dome-building), May-November 1999 (prior to the restart of the eruption in November 1999 following a year-long pause), and April-May 2005 (prior to the restart of the eruption in June-August 2005 following a two year pause), FPS pressure (p-) axes are oriented approximately perpendicular to the inferred direction of regional maximum compressive stress around Montserrat. In contrast, FPS p-axes for earthquakes accompanying a pause in the eruption in 1998-1999, and from December 1999-March 2005 are oriented approximately parallel to regional maximum compression. VT earthquakes with FPS p-axes oriented perpendicular to regional maximum compression are thought to reflect local stresses induced by the inflation of a dike-like magmatic conduit system beneath Soufriere Hills prior to and during episodes of eruption.
DE: 7280 Volcano seismology (8419)
DE: 8164 Stresses: crust and lithosphere
DE: 8419 Volcano monitoring (7280)
DE: 8488 Volcanic hazards and risks
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005