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Single-Station Backazimuth Estimation from P- and Rg-Waves at Regional Distance in the Central Appalachians
Final rept. 28 Mar-28 Sep 1993
VIRGINIA POLYTECHNIC INST AND STATE UNIV BLACKSBURG DEPT OF GEOSCIENCES
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The study examines the accuracy of single-station backazimuth measurements from polarization analysis of near regional P- and Rg-wave arrivals. The data set consists of 37 signals from mining explosions in the distance range 100 to 300 km, recorded at station BLA, Blacksburg, Virginia. The station-source backazimuth estimates derived from the three component station are compared with results derived from independent information, primarily from regional network epicenter locations. For P-wave signalnoise ratios in excess of 2.0, the mean backazimuth error of the single-station estimate is 6 degrees for sources in the northwest quadrant and the standard deviation is 21 degrees. Generally, only the initial 1 second or less portion of the P-wave arrival is polarized in the source station azimuth. Off-azimuth arrivals consisting of converted and scattered energy appear early in the P coda. Emergent P-wave arrivals from the delay fired explosions, combined with steep apparent angles of incidence averaging 22 degrees complicate the single station, three component location problem. A subset of 27 signals featuring recognizable Rg arrivals was analyzed using a phase difference criterion. On average, the resulting backazimuth estimates are almost as reliable as those derived from the P-wave motion. Source-receiver backazimuth measurement, P-Wave polarization, Rg-Wave polarization.
APPROVED FOR PUBLIC RELEASE