Abstract

Regional seismograms from four historical earthquakes of M 5.8 to 7.3 that occurred in southeastern Canada in the first half of this century were digitized. Instrument-corrected Fourier spectra of the shear-wave portion of the signal were computed for the frequency range from approximately 0.05 to 2 Hz. These spectra were corrected for the effects of regional attenuation to obtain apparent source spectra for each of the four events. The apparent source spectra for all events strongly support the empirical source model of Atkinson (1993a) and show that the Brune point-source model, as applied in most eastern ground motion prediction relations, grossly overpredicts intermediate-frequency spectral amplitudes.

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