Application of Refraction Seismic On the Vulnerability of Underground Aquifers

Abstract

The multichannel seismic survey consists of a geophysical technique of indirect quantification, whose principles are based on the acoustic properties of the seismic waves produced locally. The current study deals with seismic refraction, whose main advantages are avoidance of any environmental impact during the exploration, low cost and a fast way to present the results. The objective of the technique is to show acoustic characteristics of the geological environment, such as the propagation velocity of the P wave allowing the estimation of the type of rock that constitutes the subsoil. The layers depths determination depends on velocities estimated in the data analysis. The information provided by the seismic survey is used to determine the degree of vulnerability of local groundwater reserves. The region of interest of this study is the central depression of the State of Rio Grande do Sul, Brazil. This region consists of one of the recharge areas of the Guarani Aquifer System. This system consists of a set of geological formations rich in sand and poor in clay, which results in a kind of compartmentalized sponge with potential to accumulate groundwater, covered by impermeable rock. Profiles analyzed, in the region of the municipality of Santa Cruz do Sul suggest the presence of basalt, argillite and sandstone at approximately 10 meters depth. These conditions indicate a vulnerability of the aquifer which varies laterally. Therefore, some regions showed to be less protected than others, requiring more attention on the possibility of propagation of some contaminant.