HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) References Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by MANCHEE, E. B. Articles by WEICHERT, D. H. Search for Related Content GeoRef GeoRef Citation

Epicentral uncertainties and detection probabilities from the Yellowknife seismic array data

SEISMOLOGY DIVISION OBSERVATORIES BRANCH DEPARTMENT OF ENERGY, MINES, AND RESOURCES, OTTAWA, Canada

Abstract

Analog recording tapes from the Yellowknife seismic array have been processed diqitally in Canada for over a year, with concentration on the automatic detection and epicenter location of events between 26° and 90° distance, using short period P-wave arrivals.

For the purpose of detection, signals from the individual seismometers in the two arms of the cross array are analog band-pass filtered, digitized at 20 samples/s, multiplexed into a digital computer, velocity and azimuth filtered and correlated, using an exponentially weighted integration over time with an equivalent width of 1.6 s. The correlograms for up to 168 phased beams are scanned for values exceeding a preset trigger level and an event is recorded when the level is passed consistently a number of times. In late 1966, during a seismically quiet period and with the array fully operational, the 50 per cent automatic detection level achieved by this method for events in the Third Zone to Yellowknife was m4.0 ± 0.1, slightly better than the level of an analog trigger operated at the station which uses the correlogram method for a single unphased beam only. The 50 per cent detection level of the Yellowknife standard station is about m4.4 and thus the array-computer automatic detection method gives about m0.4 improvement, which is expected from the processing method used if the noise is largely uncorrelated. No significant variations in the detection level with azimuth have yet been observed.

Approximate epicenter locations are determined from the best apparent arrival vector. The best vector is assumed to be given by the maxima of parabolas at constant azimuth and wave number interpolated between the highest values of the correlograms.

USCGS P.D.E. information is used in conjunction with the J-B tables to calculate an expected apparent arrival vector. The difference between the expected and best interpolated arrival vectors has an average deviation of about 6 ms/km. Their distribution does not suggest a simple crustal or upper mantle cause under the array station.

This article has been cited by other articles:

				I. Bondar, R. G. North, and G. Beall Teleseismic slowness-azimuth station corrections for the International Monitoring System Seismic Network Bulletin of the Seismological Society of America, August 1, 1999; 89(4): 989 - 1003. [Abstract] [PDF]

				D. H. WEICHERT and M. HENGER The Canadian seismic array monitor processing system (cansam) Bulletin of the Seismological Society of America, August 1, 1976; 66(4): 1381 - 1403. [Abstract] [PDF]

				J. CAPON Characterization of crust and upper mantle structure under LASA as a random medium Bulletin of the Seismological Society of America, February 1, 1974; 64(1): 235 - 266. [Abstract] [PDF]

				C. WRIGHT Array studies of seismic waves arriving between P and PP in the distance range 90{degrees} to 115{degrees} Bulletin of the Seismological Society of America, February 1, 1972; 62(1): 385 - 400. [Abstract] [PDF]

				F. M. ANGLIN Detection capabilities of the Yellowknife seismic array and regional seismicity Bulletin of the Seismological Society of America, August 1, 1971; 61(4): 993 - 1008. [Abstract] [PDF]