HR: 14:55h
AN: S53C-06    [Abstracts]
TI: Regional-scale Seismic Event Relocation in Northern California
AU: * Waldhauser, F
EM: felixw@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, 61 Rt 9W, Palisades, NY 10964 United States
AU: Schaff, D P
EM: dschaff@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, 61 Rt 9W, Palisades, NY 10964 United States
AB: We present results from relocating the hypocenter catalog of the Northern California Seismic Network (NCSN), using a recently computed comprehensive data base of cross-correlation differential times for earthquakes between 1984-2003. The correlation data base includes approximately 3 billion P- and S-wave differential times that are calculated from pairs of waveforms recorded at common stations with cross correlation coefficients (CC) of 0.6 or greater, for events separated by less than 5 km. Approximately 90% of the seismicity includes events that have CC > 0.7, with at least one other event recorded at four or more stations. Comparison with a subset of independently measured differential times using different correlation techniques and parameters reveal that 96% of the measurements agree within 10 msec, which translates into relative location errors of less than several tens of meters. To first order, the areas of highly correlated events correspond to areas of dense seismicity, such as the Long Valley Caldera and Geysers Geothermal Field. The cross-correlation data is combined with differential times formed from NCSN phase picks to relocate the entire NCSN catalog with the double-difference algorithm. 1-D layered velocity models used by the NCSN for routine location and 3-D model information where available are used to predict partial derivatives and differential times. Well located larger events and explosions are used to constrain absolute locations. Preliminary relocations indicate a much sharper image across most of the seismically active regions. Relocations of about 80,000 earthquakes along the San Andreas Fault System from north of San Francisco to Parkfield, for example, indicate that the degree of resolution obtained in recent, small scale relocation studies along strike slip faults can also be obtained for large areas and across complex tectonic structures.
DE: 7205 Continental crust (1219)
DE: 7219 Seismic monitoring and test-ban treaty verification
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7294 Seismic instruments and networks (0935, 3025)
SC: Seismology [S]
MN: Fall Meeting 2005