HR: 0800h
AN: S41B-0984    [Abstracts]
TI: The gouge structure in the San Jacinto fault zone, southern California
AU: * Hong, T
EM: tkhong@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Menke, W
EM: menke@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AB: The seismic properties of gouge in fault zone have been limitedly investigated due to its narrow width which makes conventional tomographic approaches inapplicable. In particular, the depth extent of the low-velocity gouge remains uncertain, which is very important information for inference of fault properties, e.g., rheology, brittle-ductile transition, pore pressure, and rupture energy. The spatial reciprocity allows us to use natural seismicity to mimic the situation in which seismic arrays are placed deep in fault zone. This experimental geometry is very difficult to achieve in practice. Under the reciprocity theorem, a seismic record at event location for synchronized impulses on the surrounding stations can be constructed. The travel time between given two event locations is estimated using a waveform cross-correlation technique. As events in fault zone are normally clustered on the rupture plane, the estimated velocities directly reflect the structure of the gouge. The technique is applied to 157 events of 1998 to 2004 around the San Jacinto and Elsinore fault zones, southern California. The low-velocity gouge in the San Jacinto fault zone is persistently observed up to the depth of brittle-ductile transition zone (~16 km). On the other hand, the low-velocity gouge in the Elsinore fault zone is only visible in the northwestern portion at shallow depth. The shear velocity in the gouge at the San Jacinto fault zone is slower by about 20 to 35 % than those in the wall-rock.
DE: 7200 SEISMOLOGY
DE: 7203 Body waves
DE: 7205 Continental crust (1219)
DE: 7270 Tomography (6982, 8180)
SC: Seismology [S]
MN: Fall Meeting 2005