abstract

Aftershocks of the MS = 6.0 Pocatello Valley, Idaho, earthquake of March 27, 1975 (UTC) provided data for characterizing the seismic attenuation in northern Utah. Ground-motion records were recorded on a linear array of L-7 velocity seismographs deployed over an epicentral distance range of 12 to 150 km from the source area. Frequency-dependent distance attenuation exponents derived from pseudo-relative velocity response (PSRV) spectra show that the high-frequency (5 to 20 Hz) spectral components attenuate with epicentral distance (R) approximately as R-1.8 and the low-frequency (0.2 to 1.0 Hz) components attenuate approximately as R-1.0. Comparison of the attenuation data derived from the Pocatello Valley, Idaho aftershocks with corresponding data obtained from analysis of earthquake and nuclear explosion records recorded in portions of Nevada, California, Colorado, and New Mexico reveals distinct regional similarities and differences in seismic attenuation. The distance attenuation exponents derived from the northern Utah and Colorado data are very similar in the 1 to 10 Hz range, but they indicate a more rapid attenuation rate than the exponents derived for southern Nevada and California which are very similar across the entire frequency spectrum.

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