Streaks of seismicity are lineations of earthquakes found on a fault. These
lineations are typically found to subparallel to the direction of slip in the
region, which implies that they are created by a slip related process. Their
simple geometry makes them an attractive targe to study the mechanics of faulting
as they effectively represent one-dimensional seismicity.
I have computed relocations of medium magnitude seismicity on streaks on the
Calaveras Fault. To relocate these events I use a novel location technique based
upon source array analysis. First, I treat a catalog of relocated microseismicity
as a source array and compute optimal propagation parameters for P, S,
and coda waves independently. Using these propagation paramters, I then search
for the optimal locations for medium magnitude earthquakes. While this is a
complicated method to locate earthquakes, a high percentage of clipped waveforms
prevents us from using more standard earthquake relocation methods (e.g., double-difference
based methods, like HYPODD) on this data set.
The results of this
method suggest that medium magnitude earthquakes nucleate on the streak but
rupture into a region relatively devoid of seismicity. This suggests that
streaks represent a rheological boundary between regions of a fault that are
slipping aseismically (i.e., in creep) and regions that accomodate their slip
budget through earthquakes.
Rubinstein, J.L. and G.C. Beroza (2007), Full Waveform Earthquake Location: Application to Seismic Streaks on the Calaveras Fault, California , Journal of Geophysical Research, v. 112, B05303, doi: 10.1029/2006JB004463.
