US Geological Survey


Date of this Version



Published in GEOPHYSICAL RESEARCH LETTERS, VOL. 36, L01303, doi:10.1029/2008GL036367, 2009


We examine a 24-hour period of active San Andreas Fault (SAF) tremor and show that this tremor is largely composed of repeated similar events. Utilizing this similarity, we locate the subset of the tremor with waveforms similar to an identified low frequency earthquake (LFE) ‘‘master template,’’ located using P and S wave arrivals to be ~26 km deep. To compensate for low signal-to-noise, we estimate event-pair differential times at ‘‘clusters’’ of nearby stations rather than at single stations. We find that the locations form a near-linear structure in map view, striking parallel to the SAF and near the surface trace. Therefore, we suggest that at least a portion of the tremor occurs on the deep extension of the fault, likely reflecting shear slip, similar to subduction zone tremor. If so, the SAF may extend to the base of the crust, ~10 km below the deepest regular earthquakes on the fault.