Mapping Karst Conditions Using 2D And 3D Resistivity Imaging Methods

Authors of this document have performed several geophysical investigations within the eastern<br>United States. Most of this experience has involved subsurface investigations in carbonate rock units.<br>As compared with different geophysical techniques including micro gravity, electromagnetics, ground<br>penetrating radar, spontaneous potential, and other methods, the best results in characterizing subsurface<br>conditions in karst terrain were accomplished using surface resistivity imaging.<br>The following discussion is based on two case studies, both involving two-dimensional and theedimensional<br>surface resistivity surveys performed over Paleozoic age carbonate rocks in northern<br>Virginia and West Virginia. The purpose of this document is to show the benefits and pitfalls of twodimensional<br>and three-dimensional resistivity imaging used to characterize subsurface conditions in the<br>karst terrain. Both methods are compared based on different site geologies, array geometries, and target<br>size and depth. A short discussion of dipole-dipole method commonly used in two-dimensional arrays,<br>versus pole-pole used in three-dimensional arrays is presented to indicate differences in expected data<br>resolution.<br>The intention of this document was also to highlight the importance of volumetric visualization<br>of three-dimensional data sets for analysis and interpretations. Creating volumetric three-dimensional<br>models of resistivity is useful in evaluating the location, orientation and character of potential fracture<br>systems within relatively uniform rock masses.