Crustal structure south of the Mexican volcanic belt, base don group velocity dispersion

Abstract

An average shear-wave velocity structure of the crust has been estimated for paths between the Guerrero-Michoacan coast, along the Mexican subduction zone, and Mexico City. This structure is obtained from inversion of group velocity dispersion data, estimated from broadband seismograms of regional events recorded in the city. For a better defmition of the dispersion curve we have used a new stacking technique of the period-group velocity amplitude distributions of individual records. The mid-crustal structure (5 to 30 km depth) is well defmed but both the shallow and the deep structures are not well resolved due to limited period range of the dispersion data. A clear boundary between the upper and lower crust is found between 15 and 20 km. Synthetic seismograms computed for the model compare well with the observed ones, giving us confidence in the results and in the possible use of this model in routine determination of moment tensor solutions. The thick low-velocity superficial layer found in the Oaxaca region is not present beneath the region studied here.