Open Access

Viktor Peter Nawa

• In this thesis the Quadrupole Electrical Resistivity Tomography (QERT) method is presented as a new measurement concept for profile-based geoelectric field measurements. The concept is based on a tensorial formulation of the apparent resistivity in order to make three-dimensional statements about the underground conductivity structure. For a simple application of the method a number of similarities to the classical dipole-dipole method were made, such as the presentation of the measurement data in a pseudo-section. The added value of the method compared to the classical profile-based methods is especially the differentiation of lateral structures. Anomalies, which are located laterally to the profile, can be detected with respect to their position (left-right) as well as their conductivity contrast. For the practical implementation of the concept a measuring device was developed and constructed, the CR Device. The device uses 64 channels for simultaneous signal recording of voltage and current time series with up to 1 kHz sampling rate. The current injection is freely programmable and allows any survey design. The measurement of the voltages is performed against a common reference (CR) electrode and thus allows the reconstruction of any dipole voltage by difference formation. A complementary, Matlab-based software package completes the measuring system. An evaluation module allows the raw data of the CR device to be read in, processed and displayed in a suitable form. An inversion module allows the inversion of measurement data into a three-dimensional subsurface model. With a modeling module, measurements over any subsurface situation can be simulated and subsequently analysed. A field measurement on a volcanic maar in the Eifel region, Germany, demonstrates the benefits of the method. A QERT profile was set-up tangentially to a conductive anomaly in the centre of the maar. The measurement data were successfully inverted into a geologically coherent 3D resistivity model.