HR: 0800h
AN: S51A-0131    [Abstracts]
TI: Seismic Investigation of Recent Events in the Mendocino Triple Junction Region: Stress Release and Orientation within the Gorda Plate and along the Mendocino Fault
AU: * Theiner, T R
EM: theiner@geo.utep.edu
AF: University of Texas at El Paso, Geological Sciences , El Paso, TX 79968 United States
AU: Velasco, A A
EM: velasco@geo.utep.edu
AF: University of Texas at El Paso, Geological Sciences , El Paso, TX 79968 United States
AU: Doser, D I
EM: doser@geo.utep.edu
AF: University of Texas at El Paso, Geological Sciences , El Paso, TX 79968 United States
AB: The Mendocino Triple Junction (MTJ) is the intersection of the San Andreas fault zone, Mendocino fault, and Cascadia subduction zone. This region has a history of strong earthquakes of magnitude 6.5 or greater, with much of the seismicity within the Gorda plate. We investigate recent and historic earthquakes in the MTJ region. Data for this study has been collected as digital data downloaded from the North California Earthquake Data Center (NCEDC) for the Berkeley Digital Seismic Network (BDSN) for years 1992 to 2002. We modeled each event for focal mechanism and total moment. Our results have been compiled with larger events with known focal mechanisms and moment from the Harvard Centroid Moment Tensor (CMT) and NCEDC catalogs to reveal the overall state of stress for the region. We divide our events by magnitude and class of focal mechanism (thrust, strike slip, transpressive and normal) and plot the direction of moment as a function of the P-axis. We find that the larger strike-slip events in the Gorda plate align with a P-axis that might be expected for the San Andreas fault, smaller events align with an expected Mendocino fault orientation, and very few events have an orientation related to the Cascadia subduction zone. These results suggest that Gorda plate deformation is not relieving stresses associated with the Cascadia subduction zone, and that the state of stress release for the entire region is dominated by the Mendocino fault.
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
DE: 7215 Earthquake parameters
SC: Seismology [S]
MN: 2004 AGU Fall Meeting