Tomographic investigation of the wear along the San Jacinto fault, southern California

The seismic properties of the wear along the San Jacinto fault are investigated using local seismic records for clustered fault-zone earthquakes. Spatial reciprocity allows us to use the seismicity along fault plane to mimic the situation where receiver arrays are placed at depth on the fault plane. A seismic record at the event location is constructed by stacking the original station records. Waveform cross-correlations is then used to calculate the traveltimes of shear waves traveling between the pair of events. We analyze 157 small earthquakes occurring between 1998 and 2004 on the San Jacinto and Elsinore fault zones. Low shear velocities in the San Jacinto fault zone related to wear and gouge are persistently observed up to the depth of brittle-ductile transition zone (∼16 km). On the other hand, low velocities in the Elsinore fault zone are only visible in the northwestern portion at shallow depth. The wear structures in the San Jacinto fault zone display lower shear velocities by 6-8% than those of the wall-rock.