Modelo Preliminar de Velocidades Sísmicas da Crosta através de Explosões Locais Registradas pela Rede Sismográfica de Sobradinho - BA

Abstract

Seismograms Of explosions from local mines and quarries registered by the Seismographic Network of Sobradinho (Bahia) during the period from 1979 to 1983 have been analysed. A preliminary model of seismic velocities for the crust and upper mantle in the adjacent regions of the Reservoir of Sobradinho (8o-10.5oS and 40o-42oW) is proposed on the basis of the seismic record sections. An experimental S-P/distance curve up to distances of about 200 km is also presented. It gives smaller S-P times than the Jeffreys-Bullen model and suggests a single layer Crustal model without the Conrad discontinuity and a   depth to the Moho discontinuity of more than 33 km. The velocity values and Vp/Vs ratios seems to show a difference in the structure and composition of the crust to the south and to the north of the Reservoir of Sobradinho. The depth to the Moho discontinuity (~ 40 km) suggested in this work agrees with the results of previous gravimetric   measurements taken in the region. The upper mantle P-wave velocity is about 8.2 km/s.