A Study of the Local Magnitude Scale in the Basin of Mexico: Mutually Consistent Estimates of log A0 and Ground-Motion Scaling

Abstract

A study of the local magnitude scale in the Basin of Mexico is presented using about 1810 synthetic Wood-Anderson peak amplitudes at 13 stations from the Valley of Mexico seismic network (rsvm). Data from all available rsvm earthquakes located in central Mexico were used, and the events within the Basin of Mexico were relocated. Parametric and nonparametric expressions for the log A ( r ) curve were determined and corrected to Richter’s reference level, which was obtained after the linear separation of source, site, and distance terms. The parametric attenuation function is best expressed as log A ( r ) = −0.48 log ( r /100) − 0.0018 ( r − 100) − 3. The results of the attenuation curve are consistent with ground-motion scaling studies (geometrical spreading, Qs , and stochastic simulations): the Basin of Mexico is characterized by a complex attenuation model at short distances, but the general trend is that of a highly attenuative region. We observe that the coda magnitude has been underestimating the excitation levels of local events in the Basin of Mexico and may require station corrections to improve its accuracy. Our study will provide local magnitudes to the seismicity catalog in the Basin of Mexico, thus contributing to more successful earthquake hazard analyses in the most important and heavily populated region of Mexico.