Electrical Resistivity Imaging (ERI) using Multielectrodes for Studying Sub?surface Formations in Cauvery Plains

Among all geophysical methods, resistivity methods are most widely used in ground water, mineral and oil exploration. The multi electrode electrical resistivity imaging (ERI) play a very significant role in the resistivity/IP prospecting, for detecting sub-surface formations and for studying sub-surface geological strata architecture. In this type of surveys, a number of electrodes are planted on the ground surface maintaining an equal inter-electrode separation. The number of electrodes may be 12, 24, 48, 72 or 96?..depending upon type of the measuring system. Electrical Resistivity imaging (ERI) survey is carried out at two identified locations of Cauvery plains viz., kottuchery and kadalangudi. The site selection is done on the basis of local geology, geomorphology etc. The resistivity images with Dipole-Dipole at kadalangudi location showed up to 22 m depth whereas Wenner-Schlumberger, the scanned depth is 60m. Thus the resistivity image with Wenner-Schlumberger arrays has shown greater depth of investigation. Also it is observed that high resistivity layer is almost embedded between two low resistivity formations. The bore hole thus recommended based on ERI conformed a good corroboration between the geo-electrical image and lithology. A similar finding with the ERI at Kottuchery near karaikal indicated a good corroboration between the top image with the Dipole array and the bottom image with the Wenner-Schlumberger array. Hence, the Electrical Resistivity Imaging (ERI) being a non-invasive method is a significant tool in investigating sub-surface formations with precision, accuracy and reasonable resolution.