Seismic source parameters from the Guerrero subduction zone

Abstract

Abstract A method to systematically determine seismic moment and corner frequency from shear-wave spectra has been applied to strong-motion data recorded in Guerrero, Mexico. The method determines a model spectrum that minimizes the misfit from the observed spectrum, after a correction for frequency-dependent site response has been applied. The calculated moments for larger events in Guerrero are consistent with moments determined from teleseismic body waves adjusted for differences in focal depth and consequent assumed differences in the velocity and density structure in the source region. The average stress drop for the 82 earthquakes with magnitudes from 3 to 7 is 150 bars. The spatial distribution of the stress drops shows a distinctive pattern. At the northwest end of the Guerrero gap, adjacent to the aftershock zones of large earthquakes in 1979 and 1985, there is a mix of low- and high-stress-drop events. At the southeast end of the Guerrero gap, where the most recent large earthquake occurred in 1957, there are predominantly high-stress-drop events. This pattern might be caused by the different relative positions of these two active regions in the earthquake cycle, although several other explanations cannot be ruled out.