Acceleration spectra at high frequencies were analyzed to make an estimation of the spectral decay parameter, κ, in the aftershock area of the 1978 Oaxaca earthquake. It was found that κ follows a linear behavior given by κ(r) = κ0 + αr, increasing with source-to-station distance, r, in the frequency band from 8 to 25 Hz. κ0 values range from 15.7 to 33.9 msec and do not show a strong variation from station to station on different types of crystalline terrain. Estimates of (r/dr do not indicate a strong lateral variation of the frequency-independent quality factor, Q, in the crust of the Oaxaca region. Apparent stresses were also calculated for a subset of aftershocks, and no clear scaling with seismic moment or κ0 is observed. Apparent stresses lie between 3.6 to 256 bars.

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