Desenvolvimento de um método para determinar o grau de vulnerabilidade local de aquíferos subterrâneos livres usando sísmica de refração

Abstract

A multichannel refraction seismic survey is a geophysical technique of indirect quantification, whose principles are based on the detection of acoustic properties of locally produced seismic waves. The present study seeks to present a method to estimate the degree of intrinsic vulnerability of free aquifers based on the physical properties of geological structures using seismic waves. The used technique presents as main advantages: the absence of environmental impacts during acquisitions, low cost and agility in the presentation of the results. In addition, it also provides data with potential to elaborate large resolution studies of the vulnerability longitudinal variation. Seismic surveys show the acoustic characteristics of the geological environment, such as the propagation velocity of the longitudinal wave, allowing the estimation of the rock type which constitutes the subsurface. The determination of the depths of the strata is based upon knowledge of the wave speeds and transit times in the geological layers. The proposed method was applied as case studies in the municipalities of Santa Cruz do Sul, Candelaria, Alegrete and some of others in the Quarta Colônia in the state of Rio Grande do Sul. This region is exploited by agriculture of various crops and livestock, in addition, it constitutes one of the various recharge areas of and outcropping of the Guarani Aquifer System-SAG. The interest in assessing the degree of vulnerability of aquaculture formations stems fundamentally on the need to provide the competent authorities with an instrument that is useful in planning and making decisions aimed at preserving underground water reservoirs. The developed method allowed to estimate the local variability of vulnerability based on geological characteristics.