HR: 1340h
AN: V53D-1595    [Abstracts]
TI: Extracting time domain Green's functions from ambient seismic noise recorded during the Mount St Helens 2004 eruption: A new tool for volcano monitoring ?
AU: * sabra, k
EM: ksabra@mpl.ucsd.edu
AF: Marine Physical Lab. Scripps Inst. Ocean. UCSD, 9500 Gilman Drive, La Jolla, 92093-0238
AU: Gerstoft, P
EM: gerstoft@ucsd.edu
AF: Marine Physical Lab. Scripps Inst. Ocean. UCSD, 9500 Gilman Drive, La Jolla, 92093-0238
AU: Roux, P
EM: proux@ucsd.edu
AF: Marine Physical Lab. Scripps Inst. Ocean. UCSD, 9500 Gilman Drive, La Jolla, 92093-0238
AU: Kuperman, W
EM: wak@mpl.ucsd.edu
AF: Marine Physical Lab. Scripps Inst. Ocean. UCSD, 9500 Gilman Drive, La Jolla, 92093-0238
AU: Fehler, M
EM: fehler@lanl.gov
AF: Los Alamos National Laboratory, P. O. Box 1663, MS D443 Bldg 1572 Room 108, Los Alamos, NM 87545
AB: It has been demonstrated experimentally that an estimate of the Green's tensor between two seismic stations can be obtained from the long-time average of the cross-correlation of ambient seismic noise at the two stations [Sabra et al, Geophys. Res. Lett., 32, 2005]. This result provides a means to find trace data that can be used to infer the local Earth structure without the use of active seismic sources or individual earthquakes events. Initially, the small coherent component of the noise field at each seismometer is buried in a spatially and temporally incoherent field produced by the distribution of random scattered noise sources. The coherent wavefronts emerge from a correlation process that accumulates contributions over time from noise sources whose propagation path passes through both seismometers. Cross-correlations have been computed from ambient noise recorded on 7 broadband seismic stations (receiver separation up to 19 km) of the UW-PNSN network located in the vicinity of Mount St Helens during the eruptive period from September to December 2004. At each station, the background seismicity level clearly increased during this period corresponding to the scattered seismic waves originating from the intense volcanic activity. The frequency content of these coherent signals varies as the eruption transitions from high frequency VT events to hybrid low-frequency LP events. A simple and straightforward processing yielded cross-correlation pairs, that clearly exhibits coherent waveforms. The potential use of this passive seismic imaging technique for eruptive volcanic systems monitoring is investigated across 1) the frequency band [0.8hz-10Hz], 2) the spatial distribution of the station pairs surrounding Mount St Helens (in range and azimuth), and 3) averaging time of a few hours to several days. Furthermore the temporal variations of the distinct arrivals for specific ambient noise cross-correlation functions are monitored and related to the chronology of events observed at Mount St Helens from September to December 2004 (explosions, lava dome growth).
DE: 8419 Volcano monitoring (7280)
DE: 8428 Explosive volcanism
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005