HR: 17:15h
AN: V14B-06    [Abstracts]
TI: Source mechanisms of strong vulcanian explosions at Soufri\`{e}re Hills Volcano, Montserrat, B.W.I., from moment tensor inversions of very-long-period data
AU: * Hidayat, D
EM: hidayat@geosc.psu.edu
AF: Dept. of Geosciences, Penn State University, 334 Deike Bldg, University Park, PA 16802 United States
AU: Voight, B
EM: voight@ems.psu.edu
AF: Dept. of Geosciences, Penn State University, 334 Deike Bldg, University Park, PA 16802 United States
AU: Chouet, B
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Jolly, A
AF: Geology Dept., University of Hawaii, 200 W. Kawili St., Hilo, HI 96720 United States
AU: Bass, V
AF: Montserrat Volcano Observatory, Fleming, Salem, 664 Montserrat
AU: Williams, C
AF: Montserrat Volcano Observatory, Fleming, Salem, 664 Montserrat
AB: Seismic signals associated with explosions at Soufri\`{e}re Hills Volcano (SHV) as recorded by broadband seismic stations, were analyzed to better understand eruption dynamics and physical eruptive processes. We discuss recent data from July 2003. Several explosions in July followed conduit decompression associated with the 12-13 July 2003 lava dome collapse. The collapse/eruption in July and explosion events were preceded by long-period and hybrid seismicity. Waveforms of the explosions from an array of broadband seismometers also indicated VLP (8-30s period) signals. We explore the source mechanisms and locations of source centroids of the explosive events by using the linear inversion method of Ohminato et al. (1998) with a 3D mesh. Preliminary results suggest that the VLP waveforms are broadly consistent with a quasi-horizontal crack (sill) source, with residuals minimal at a depth of several km. Further analysis yields evidence of shallower initiation at depth of a few hundred m, also involving a flat subhorizontal source, followed by propagation of source to deeper level. We suspect that our data may be consistent with a "flat crack" that represents initiation and descent down-conduit of the fragmentation surface for the explosion. Although the seismic network is far from having ideal coverage for a robust estimate of source parameters, the data provide an interesting snapshot of explosion dynamics.
DE: 8414 Eruption mechanisms
DE: 8419 Eruption monitoring (7280)
DE: 7280 Volcano seismology (8419)
DE: 7215 Earthquake parameters
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting