HR: 0800h
AN: S11B-1026    [Abstracts]
TI: Comparison of Waveform Cross Correlation Performance Across Different Broad Area Seismic Source Regions
AU: * Schaff, D P
EM: dschaff@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964 United States
AU: Kim, W
EM: wykim@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964 United States
AU: Waldhauser, F
EM: felixw@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964 United States
AU: Richards, P G
EM: richards@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964 United States
AB: We are evaluating a method of locating seismic sources (earthquakes, explosions) based on the large-scale use of waveform cross-correlation (WCC) measurements instead of the conventional measurements of seismic wave arrival time (phase picks). WCC measurements have been demonstrated to be 10 to 100 times more accurate, where they can be obtained. The principal issue we are exploring is the extent to which a significant fraction of seismicity can be located using WCC measurements. We are studying the Charlevoix region in eastern Canada, the New Madrid seismic zone in the central United States, and northern California. In the first two regions the datasets have been assembled from scratch working in conjunction with regional network operators. For Charlevoix, courtesy of the Geological Survey of Canada, we now have 2,470 events with corresponding catalog, phase, and waveform data. For New Madrid, two datasets have been acquired. The first is from the PANDA deployment between 1989 and 1992, which consists of 884 events with bulletin and waveform information. The second is from the Center for Earthquake Research and Information (CERI) network, operated by University of Memphis, from which we currently have waveform data for 1995-2003, with extensive catalog and phase data. Preliminary WCC results of the PANDA network indicate that 68% (597 out of 884 events) correlate with cross-correlation coefficients (CC) above 0.7 at four or more stations. Four stations are the minimum required to obtain a location estimate. Both P- and S-waves are correlated on all three components. The window lengths are 1 s and the lags searched over are also 1 s. It appears in a few examples that similar correlations are possible over 1 to 10 kilometer inter-event separation distances due to a site resonance from soft sediments underneath certain stations. In the Charlevoix seismic zone there are only 10% of the events that meet the criteria of CC $>$ 0.7 at four or more stations. To explain this low fraction of similar seismicity we find that both earthquake density and station density are important for applying waveform cross correlation. A final comparison can be made with all of northern California where both earthquake density and station density are high. A recently completed project performing 26 billion correlation measurements for 225,000 events demonstrated that a remarkable 90% of the events in northern California have CC $>$ 0.7 with at least one other event at four or more stations. Subsequent work in California is using this data to relocate all the seismicity and look for repeating events which have high CC and differential times close to zero. Initial results indicate that repeating events appear across a variety of tectonic settings.
DE: 7230 Seismicity and seismotectonics
DE: 7294 Instruments and techniques
SC: Seismology [S]
MN: 2004 AGU Fall Meeting