Lateral variation of Lg wave propagation in southern Mexico

Abstract

In this study we investigated lateral variation of Lg wave propagation in southern Mexico from recordings of 92 crustal earthquakes along 591 travel paths. The efficiency of Lg propagation was measured in terms of Lgto Pn spectral ratio. It was found that Lgpropagation is inefficient for travel paths through the Gulf of Mexico coastal plains and the Gulf of Tehuantepec, areas with thick layers of sediments. An average Lg quality factor, QLg, as a function of frequency for southern Mexico was estimated for the efficient Lg travel paths. The relation obtained for QLg in the frequency range 1.6–8 Hz is QLg(f) = 204 f0.85. The lateral variation of QLg−1was solved as a mixed‐determined inverse tomography problem, separately for each frequency, in which a spatial smoothness constraint was imposed and a priori information was added in poorly covered regions. The spatial resolution obtained was about 200 km. It was found that the Trans‐Mexican Volcanic Belt, the Gulf of Mexico coastal plains, and the area east of 94°W are characterized by lower than average QLgvalues, i.e., higher attenuation. High QLg values were obtained for the Mixteco‐Oaxaca terranes, while for the Guerrero terrane, values similar to the average were obtained. The results show a correlation between QLg and crustal structure and provide valuable information on lateral variation of QLg, which is needed for reliable prediction of ground motion during future earthquakes.