Evaluation of geoelectric parameters to delineate the subsurface fractures for groundwater exploration around coastal Maharashtra, India

Abstract

Modelling of electrical resistivity data especially from coastal area assumes an explicit significance for groundwater prospecting studies. Direct current (DC) Vertical electrical sounding (VES) data were acquired from 84 locations around Aronda-Redi-Vengurla-Malvan region, Sindhudurg district, Maharashtra, India, with an objective to decipher the structural trend for identifying groundwater potential zones of the area using geophysical indicators. The VES curves obtained were primarily of 3-5 geoelectric layers. One-dimensional inversion results divulge that the top layer is predominantly comprised of laterites/fractured laterites followed by an assortment of clay/clayey sand and granulites/fractured granulites as basement rocks. Several NNE-SSW and NW-SE oriented major lineaments and its criss-crosses have been reported in this region and the source of groundwater appears to be contained in weathered/semi-weathered layer of laterite/clayey sand at depth of 10-12 m from the surface. Geoelectric parameters for interpretation included curve type, anisotropy coefficient, fracture porosity, and reflection coefficient. The electrical anisotropy varied from 1 to 3.95, while the reflection coefficients ranged from 0.1 to 0.99 in the study area. It is seen that stations with low reflection coefficient revealed higher electrical anisotropy, suggesting an inverse correlation between these two parameters. The northeastern, southern and northwestern part of the study area revealed higher values of fracture porosities, wherein a positive relationship with the high and low values of electrical anisotropy was observed. These results would be helpful for interpreting the geological signatures like fractures, joints and lineaments for identifying groundwater prospective zones in the coastal area.