Shear wave velocities beneath the eastern part of Brazil

Abstract

Rayleigh wave dispersion curves from seventeen earthquakes which occurred in the North Atlantic Ocean area are used to obtam the shear wave velocity structure of the eastern part of the Brazilian territory. The dispersion curves were divided into three groups of paths (A, B, and C) according to geographical position of the epicenters, and a dispersion curve representative of each path was computed. The inversion results of these dispersion curves show that the crustal structure is composed basically of three layers with S-wave velocities varying from 3.30-3.57 km/s, 3.52-3.66 km/s and 3.86-3.92 km/s, respectively. The sub-Moho layer is chll{acterized by shear wave velocities varying from 4.41 to 4.43 km/s. Path C exhibits a sub-Moho thickness thinner than the other two paths. Below the sub-Moho layer, shear wave velocities of 4.27 km/s and 4.22 km/s are found in both paths A and C, but it has been clearly resolved only in path C where the S-wave ,velocity was assumed to be 4.22 km/s. A comparative analysis between the models obtained in the present study and those representative of other shield areas reveals a strong similarity between the models of eastern Brazil and those of eastern South America (Hwang and Mitchell, 1987) and Antarctica (Dewart and Toksoz, 1965; Singh, 1994). This is probably related to the past existence of Gondwanaland.