HR: 1340h
AN: V53C-1415    [Abstracts]
TI: Multiplets and Detection of Seismic Velocity Changes During the 1998-99 Seismic Series at Deception Island Volcano, Antarctica
AU: Carmona, E
EM: ecarmona@iag.ugr.es
AF: Instituto Andaluz de Geofisica, Universidad de Granada, Campus de Cartuja s/n, Granada, 18071, Spain
AU: * Martini, F
EM: Francesca.Martini@ucd.ie
AF: Seismology and Computational Rock Physics Lab., School of Geological Sciences, University College Dublin, Belfield, Dublin, 4, Ireland
AU: Ibanez, J M
EM: jibanez@ugr.es
AF: Instituto Andaluz de Geofisica, Universidad de Granada, Campus de Cartuja s/n, Granada, 18071, Spain
AU: Bean, C J
EM: Chris.Bean@ucd.ie
AF: Seismology and Computational Rock Physics Lab., School of Geological Sciences, University College Dublin, Belfield, Dublin, 4, Ireland
AB: During the 1998-1999 Antarctic summer, the pattern of seismicity at Deception Island Volcano changed significantly with respect to previous years. This was characterized by the occurrence of an intense swarm of local earthquakes. More than 2000 local earthquakes were recorded in the period January-February 1999. The average moment magnitude was around 0.5, with the exception of two earthquakes of magnitude 2.3 and 3.4; array analysis was used to establish the hypocentral distribution of the earthquakes. A regional origin of the seismicity, or direct involvement of magmatic fluids, was demonstrated to be unlikely. Most earthquakes in the series were found to be related to small (<0.4 bar) stress changes on small faults which can be explained by lubrication by pressurized fluids (Ibanez et al. 2003). The presence of fluids in the source area could explain the fracturing process and is supported by the observation of hybrid events in the same source region. The study of the spatial distribution of the first motion of the P waves suggests that different source mechanisms acted in a very small volume, and often at the same time. Many distinct families of events with very similar waveforms were identified. When recorded at the same station, the similarity of repeating earthquakes indicates that source and wavepath are the same, and therefore any observed difference in waveforms is related to a change in the medium. Employing Coda Wave Interferometry (Snieder et al., 2002), the families of events identified in the series show a drop in the velocity over a short time period around the two events with bigger magnitudes. These variations may be related to cracking and/or fluid influx. After the seismic crisis, a change in the composition of the fumarolic gases was observed with the appearance of sulfur deposits around the fumaroles, and a clear uplift and inflation of a few centimeters was detected (Garcia et al., 2001). The seismic characteristics and the spatial and temporal behavior of the series, associated with other geochemical, bathymetric and geodetic observations, favor the hypothesis that the seismic series was caused by the stress generated by uplift of the source area due to magmatic injection in depth (Ibanez et al., 2003). The correlation between the observed velocity variations, and their timing with seismological, geochemical and geodetical evidence, supports the influx hypothesis as a causative mechanism.
DE: 7280 Volcano seismology (8419)
DE: 8045 Role of fluids
DE: 8419 Volcano monitoring (7280)
DE: 8434 Magma migration and fragmentation
DE: 9310 Antarctica (4207)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting