Analysis of the risk of karst collapse in Lapão, Bahia, Brazil

Abstract

On October 2008, the large extent of dissolution of limestone in the Irecê Basin resulted in the occurrence of minor ground shakes and the enhancement of fractures along the surface of the ground and on the walls of buildings in the urban and periurban area of the city of Lapão. After preliminary geological and geotechnical studies to analyse the danger of collapse of underground caves, we have carried out gravity and electro-resistivity profiles in order to map the concealed caves and to help the determination of the level of groundwater within them. The interpretation of the results provided useful information both for the immediate safety of the population and for subsequent hydrological and geotechnical work. We have defined five risk areas based on the variations of the Bouguer and of the electrical resistivity data, by correlating the distribution of gravity lows with the presence of caves and the less resistive zones with the presence of brine water underground.