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Waveform modeling of two earthquakes (M 1.1) of July 1983 from the Miramichi aftershock zone

DEPARTMENT OF EARTH AND ATMOSPHERIC SCIENCES SAINT LOUIS UNIVERSITY, P.O. BOX 8099, LACLEDE STATION, SAINT LOUIS, MISSOURI 63156

Abstract

The earth model proposed earlier (Saikia and Herrmann, 1985a) is tested by modeling the short-distance waveforms from the earthquakes of 15 July 1983 (UTC 14h 46m 02.97s) and 18 July 1983 (UTC 05h 20m 01.08s) recorded at hard-rock sites in the Miramichi aftershock zone. Before comparing the waveforms, the admissible focal mechanisms are isolated by maximizing the vector dot product between both the observed and synthetic P- and S-wave amplitudes as well as the dot product of their amplitude ratios. The minimum value for the vector dot product is specified as 0.80. A focal-mechanism solution with the following parameters—a dip () of 42.5°, slip () of 80°, strike () of 202°, and seismic moment of 2.5 x 10¹⁷ dyne-cm—shows the best waveform fit for the earthquake of 15 July 1983. Several focal mechanisms are possible for the earthquake of 18 July 1983, but a mechanism with a dip of 44°, slip of 110°, strike of 25°, and seismic moment of 3.9 x 10¹⁷ dyne-cm, which produces wave shapes and amplitudes in agreement with the observed data, is preferred. Spectral domain seismic moments are comparable to those of time domain seismic moments.