Sondeos magnetotelúricos de banda ancha (BMT) para el estudio del acuífero transfronterizo de Zarumilla, Ecuador-Perú

Abstract

This paper focuses on the cross - border aquifer of Zarumilla. The characteristics of this coastal aquifer with very high conductivity in the surface strata due to its ma- rine sediment content, considerably limit the exploration depth of the controlled source geophysical techniques used in the past (VES and TDEM) to study the strat- igraphic distribution and hydrological bed of the aquifer. A proposal was made to apply the magnetotelluric method which has the advantage of not depending on the dimension of an array, the electrodic configuration nor the power supplied by a motor generator. All that is required is a small scale surface to conduct the sound- ing process with the possibility of reaching the depth of the bed in spite of the pres- ence of superficial conductor layers. 

The objective of this paper is to establish a model of the cross- border aquifer of Zarumilla based on the interpretation of broadband magnetotellurics (BMT). To this end, the resistivities and phases of the invariance of the impedance for each sound- ing were estimated and they were subsequently both inverted using a smoothed layer algorithm and another discrete layer algorithm to obtain the corresponding depth models. Simultaneously, an analysis was undertaken of the frequencies at which the maximum tipper values occurred, which is a measure of lateral disconti- nuities of the site, in order to analyze said variations in terms of possible structural limits. Lastly, three representative profiles were selected for interpretation in terms of geology, using the results of the inverted two-dimensional TE and TM modes and integrating information available from previous studies. A block model was also made based on the interpolation of the layer models obtained to have a general idea of the subsoil in the area of interest. This geological model is the starting point for the creation of a robust, reliable hydrological model for the sustainable use of the hydrological resources in the zone.