High-Precision Relative Event Location with Cross-Spectral Analysis
Semiannual rept. 23 Aug 1991-4 Apr 1992
TELEDYNE GEOTECH ALEXANDRIA VA ALEXANDRIA LABS
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Location relative to a reference event is often more useful and precise than absolute event location. The use of relative location accounts for most of the errors arising from path effects. Such location requires relative times for pairs of events observed at a common station, which can be obtained with high precision for similar events by waveform cross-correlation. The precision can be further boosted by applying the cross-spectral analysis method, which can obtain relative delay times with resolution up to an order magnitude better than the seismogram sampling interval. During this report period, records of a large number of explosions with precisely known locations were assembled. Software for determining the delay time between two waveforms was developed and tested on real data. Preliminary analysis of data from six closely-located Yucca Flat explosions recorded at the four broadband digital stations, ELK, KNB, LAC, and MNV provided encouraging results. The mean location error was found to be only about 1 km an impressive result if one considers the large epicentral distances about 200 km to 320 km and the complex geology of the Nevada Test Site. Relative Location, Cross-spectral Analysis, Waveform Cross-correlation.