HR: 16:00h
AN: T54A-01    [Abstracts]
TI: Calico Fault Structure Determined Using Traveltime Data from Seismicity and Explosions
AU: * Cochran, E S
EM: cochran@ucr.edu
AF: University of California, Riverside, Department of Earth Sciences, Riverside, CA 92521, United States
AU: Li, Y
EM: ygli@usc.edu
AF: University of Southern California, Department of Earth Sciences, Los Angeles, CA 90089, United States
AU: Shearer, P M
EM: pshearer@ucsd.edu
AF: University of California, San Diego, Institute of Geophysics and Planetary Physics, Scripps, La Jolla, CA 92093, United States
AU: Vidale, J E
EM: seismoguy@mac.com
AF: University of Washington, Department of Earth and Space Sciences, Seattle, WA 98195, United States
AU: Fialko, Y
EM: yfialko@ucsd.edu
AF: University of California, San Diego, Institute of Geophysics and Planetary Physics, Scripps, La Jolla, CA 92093, United States
AB: A dense array of 100 seismometers deployed near the Calico Fault, located in the eastern California shear zone, recorded explosions and seismicity between June and December, 2006. Seismic velocity reductions associated with the fault damage zone are mapped in detail along and across strike; in addition, the depth extent of the velocity reduction is investigated. Three shots exploded in and out of the fault zone reveal seismic velocities in the very shallow crust. The first shot was located within the array, a second in the fault approximately 6 km from the array, and a third outside of the fault, also about 6 km away. In addition, we use local, regional, and teleseismic earthquake body waves to measure the width of the low-velocity zone and investigate variations in that width along strike and with depth. We use the SCEC velocity model as a starting point and then perturb the velocity model in a finite zone along the Calico fault to find a match to the observed travel times. Results suggest a 1 to 2 km wide low-velocity zone, in good agreement with the InSAR-derived compliant zone. Our measurements are in accord with InSAR observations showing that the Calico fault suffered twice the strain of the surrounding bedrock during the Hector Mine and Landers earthquakes, confirming a zone of reduced shear modulus around the fault. These findings indicate that faults can affect rock properties at significant distances from the primary fault slip surfaces, a result with implications for the portion of energy expended during rupture to drive the cracking and yielding of rock.
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 7203 Body waves
DE: 7218 Lithosphere (1236)
DE: 7270 Tomography (6982, 8180)
DE: 8159 Rheology: crust and lithosphere (8031)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting