Reply to comment on ‘Correlation of vertical electrical sounding and electrical borehole log data for groundwater exploration’ by G.K. Hodlur and Ratnakar Dhakate, Geophysical Prospecting doi:10.1111/j.1365–2478.2009.00831.x

Abstract

We are thankful to Dr P.C. Chandra for his comments and for the interest he has shown in our article. To begin with, the doubt concerning equivalence and suppression are explained. By following the principle of equivalence, certainly at a single site of investigation, various subsurface geophysical models can give the same sounding curves. However, while deciding the final model, the model that fits with the subsurface geological conditions in the field around or at the site of investigation is to be given importance. Hence, in any study area few parametric soundings are carried out near existing borewells whose lithologs are available, in order to assess the resistivities and thicknesses of the subsurface geological formations. This knowledge is used as calibration to interpret the vertical electrical soundings carried out around the parametric soundings. When compared with the parametric sounding, the interpreted results of the soundings located around the region of parametric sounding should generally show a similar subsurface geophysical structure, namely in the number of subsurface layers and patterns of resistivity changes of the interpreted geoelectric layers. Variations in resistivities and thicknesses of different geoelectric layers will have to occur as the vertical electric soundings (VES) are located at different sites and hence the subsurface geometry, degree of compaction and saturation of the geoelectric layer changes in space. However, the trends should match satisfactorily. Such an exercise facilitates in choosing the right interpretation from the various subsurface models created by interpretation of any sounding curve. This is the method to tackle the problems of principle of equivalence. For example, in this article at the Ramanu-