HR: 14:40h
AN: S13F-05    [Abstracts]
TI: Seismicity and Tectonics of the Northeast Caribbean from a Passive Ocean Bottom Seismograph Study
AU: * Pulliam, J
EM: jay@ig.utexas.edu
AF: UT Institute for Geophysics, Jackson School of Geosciences J.J. Pickle Research Campus University of Texas at Austin 10100 Burnet Road, Building 196, Austin, TX 78758-4445, United States
AU: ten Brink, U
EM: utenbrink@usgs.gov
AF: U.S. Geological Survey, Woods Hole Field Center Quissett Campus 384 Woods Hole Road, Woods Hole, MA 02543-1598, United States
AU: Lopez-Venegas, A
EM: alopez@usgs.gov
AF: U.S. Geological Survey, Woods Hole Field Center Quissett Campus 384 Woods Hole Road, Woods Hole, MA 02543-1598, United States
AU: Huerfano, V
EM: victor@rmsismo.uprm.edu
AF: Puerto Rico Seismic Network Puerto Rico Seismic Network Puerto Rico Seismic Network Puerto Rico Seismic Network, Box 9017 University of Puerto Rico, Mayaguez, Mayaguez, PR 00681-9017, United States
AU: von Hillebrandt-Andrade, C
EM: christa@midas.uprm.edu
AF: Puerto Rico Seismic Network Puerto Rico Seismic Network Puerto Rico Seismic Network Puerto Rico Seismic Network, Box 9017 University of Puerto Rico, Mayaguez, Mayaguez, PR 00681-9017, United States
AB: The Northeast Caribbean Plate boundary is prone to tsunamis due to the occurrence of a) subduction zone earthquakes along the Lesser Antilles and the Hispaniola and Puerto Rico trenches, b) other large earthquakes due to more local tectonic activity, such as in the Mona Passage (1918 tsunami) and in the Virgin Islands basin (1867 tsunami), and c) moderate earthquakes that destabilize steep underwater slopes and cause a tsunamigenic landslide. Recent seismicity has been concentrated to the north and west of the British Virgin Islands, in the region sometimes referred to as the Sombrero Seismic Zone (SSZ). In the combined seismicity catalog maintained by the Puerto Rico Seismic Network (PRSN), several hundred small to moderate magnitude events can be found in the SSZ prior to 2006. However, beginning in 2006 and continuing to the present, the rate of seismicity suddenly increased, and a new locus of activity developed to the east of the previous location. Ocean bottom seismographs (OBSs) were deployed in the Northeast Caribbean for three months in 2005 and for six months in 2007 to record earthquakes in the SSZ in an effort to better constrain earthquake locations, to identify crustal features, including a possible rupture in the subducting North American Plate, that could cause tsunamigenic events and to clarify the tectonics that lead to larger earthquakes and tsunamis. Data were analyzed jointly with records from permanent stations of the Puerto Rico Seismic Network (PRSN), whose stations are located on islands to the south of the Sombrero zone and are therefore biased and incomplete without offshore complements. Our goal was to identify, locate, and estimate focal mechanisms for small- magnitude seismic events in this corner of the Caribbean. In the 2005 data set, consisting of recordings by nine OBSs and the ten closest PRSN stations, we identified and analyzed thirty-five events on at least four OBSs and one or more PRSN stations and an additional fifteen events that were observed on four or more OBSs only. Upon relocation, the jointly recorded events revealed tighter clustering and clear biases with respect to original PRSN locations. Changes in epicenters were greatest in the northeastern limit of activity, while there was a consistent progression toward deeper focal depths for events closer to the island of Puerto Rico. The average change in focal depth for the cluster of five events closest to Puerto Rico was 35 km. Events located solely with OBSs were consistent with the relocated events. Most of the relocated events are consistent with the depth and dip of the subducted North American plate in this region and may therefore be associated with active subduction, rather than the shallow tectonics suggested by original locations. Events recorded during the longer 2007 OBS deployment are being analyzed to explore this association and its implications for tearing of the North American Plate lithosphere during subduction.
DE: 7220 Oceanic crust
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Seismology [S]
MN: 2007 Fall Meeting