Accession Number:

ADA053527

Title:

Observed Variation in the Spectral Ratio Discriminant from Short-Period P Waves

Descriptive Note:

Technical rept.

Corporate Author:

TELEDYNE GEOTECH ALEXANDRIA VA SEISMIC DATA ANALYSIS CENTER

Personal Author(s):

Report Date:

1977-09-19

Pagination or Media Count:

51.0

Abstract:

Short-period P-wave first arrivals recorded at the Large Aperture Seismic Array in Montana from a large number of teleseismic events were filtered in the bands of 0.4-3.0, 0.4-0.8, 1.4-1.8, and 1.8-4.0 Hz. Estimates of signal amplitude in each band were used to form spectral ratios similar to those which have been proposed as discriminants between earthquakes and underground nuclear explosions. Values for the ratios scattered over nearly two orders of magnitude and apparently did not depend on earthquake size or epicentral distance. Average logarithms of spectral ratios for 166 separate geographic regions ranged over one magnitude unit and showed some correlation with known patterns of lateral Q inhomogeneity in the earth, suggesting that attenuation causes much of the spectral ratio scatter. However, attempts to correct LASA m sub b on the basis of observed spectral ratios failed to reduce the scatter in an M sub s -m sub b plot. Variation in stress drops and other physical processes connected with the mechanism of earthquakes must cause as much variability in observed spectral discriminants as variations in attenuation.

Subject Categories:

  • Seismic Detection and Detectors

Distribution Statement:

APPROVED FOR PUBLIC RELEASE