S-WAVE CODA Q FROM 3-HZ TO 20-HZ AND P-WAVE Q FOR FORESHOCKS AND AFTERSHOCKS OF THE PETATLAN EARTHQUAKE

In order to understand better the variations of mechanical properties close to the source and the failure process in the upper portion of the crust in a geologically very young subduction zone, the seismic S wave coda Qc from 3 to 20 Hz and P wave half pulse width Qp from 6 to 12 Hz were determined for selected foreshocks and aftershocks of the 1979 Petatlan, Mexico, Ms = 7.6 earthquake. Observations indicate that Qc, and perhaps the frequency dependence n, are sensitive to the physical property changes in the source region and might be useful as predictors of large earthquakes in a shallow subduction zone environment. -from Authors