Observational test for wave propagation effects in local earthquake seismograms

Strong motion data for aftershocks of the 1982 Miramichi earthquake are analyzed to determine site effects on recorded waveforms. Although aftershocks vary in source mechanism, the complicated vector particle motion of P and S arrivals are often coherent between events recorded at the same station. This suggests that near-surface receiver structure has a significant effect on the recorded waveforms. Resonance features dominate the wavetrains with P reverberations existing on the vertical components and S reverberations prominent on the radial components indicating near vertical incidence. These reverberations take the form of peaks in the amplitude spectra which may complicate corner frequency interpretation. A careful analysis of three component waveform data in earthquake aftershock data sets such as the one considered here may be useful in determining local site conditions independent of assumed source models. -from Author