Source scaling telationships of microearthquakes at Parkfield, CA, determined using the SAFOD pilot hole seismic array

Weestimate thesourceparametersof34microearthquakes at Parkfield,CA,ranginginsizefromM-0.2 toM2.1, byanalyzingseismogramsrecorded bythe32-level, 3-componentseismic arrayinstalled in theSAFODPilotHole. Wesucceeded in obtainingstablespectral ratios by stacking theratioscalculatedfromthemovingwindowstakenalongtherecordfollowingthedirectwaves.Thesespectral ratios were modeledtodetermine seismicmoments andcornerfrequenciesassuming an omega-squared model. Static stress dropsand apparent stresses ofmicroearthquakes at Parkfielddisplay moment-independent scaling in agreementwith scaling lawsreported for moderate and large earthquakes. It is likely that thedynamics of microearthquakes at Parkfieldis macroscopicallysimilar to that oflarger tectonic earthquakes.