Estructura de la corteza al oriente de la Sierra Madre Occidental, México, basada en la velocidad de grupo de las ondas de Rayleigh

Abstract

Dispersion of fundamental mode Rayleigh waves for two large nuclear explosions from Nevada, USA, recorded at UNM, seismological station in Mexico City, was used to estima te the shear wave velocity structure along a profile running mainly along the eastem flank of the Sierra Madre Occidental, Mexico. The observed group velocity dispersion data in the period range of 10 to 21 seconds can be explained by S homogeneous horizontal elastic layers over a half space. The average thickness of the crust is of the order of 40 km. The shear velocities and thicknesses obtained are as follows: Sediments, Vs1 = 1.5 km/s, h1 = 1.2 km; Granite, Vs2 = 2.90 km/s h2 = 2.2 km y Vs3 = 3.56 km/s, h 3 = 26 km; Basalt, Vs4= 4.10 km/s, h4= 10.0 km; Upper Mantle, Vs5 = 4.50 km/s, hs = 10.0 km; Mantle, Vs6=4.15 km/s, h6= ∞. A ratio of l. 78 is assumed for Vp/Vs. The velocity model suggests that the structure of the eastern flank of the Sierra Madre Occidental is transitional between the Alpine and the Basin and Range types. The model agrees satisfactorily with earlier results based on refraction studies of the crust in the surrounding regions, and supports the ideas about the Cenozoic tectonic evolution of the western North American Continent.