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 (δ) of 42.5°, slip (λ) of 80°, strike (φ) of 202°, and seismic moment of 2.5 × 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 × 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.

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