Using Cone Penetration Test Information to Constrain Marine ERT Inversion

Sharp resistivity contrasts are generally smoothed out in conventional L2 inversions of Electrical Resistivity Tomography data. We adjusted the L2 inversion to include several L1-type sharp transitions. On the lake Markermeer, the Netherlands, archaeologists need to know the position and elevation of the buried Pleistocene surface. We collected marine ERT data and cone penetration tests (CPT’s) over a future sand pit location. The top of the Pleistocene sequence is represented by a sharp contrast in resistivity. This was apparent from combining the information from four resistivity cone penetration tests and 50 normal CPTs. The CPT information was first interpreted in terms of stratigraphic units and was subsequently used to steer the ERT inversion. The top of the Pleistocene was defined as the 8 Ohm.m isosurface in the final resistivity model. The ERT-based Pleistocene surface showed much more detail than the surface obtained from interpolation of CPT point observations and improved our interpretation considerably.