Significant advances in quantitative understanding of seismoelectric effects of electrokinetic origin have been made since they were first observed, but field data needed to validate theoretical models and associated numerical simulations have remained scarce.
The high quality field data presented in this work serve to verify conceptual and quantitative models. Clear seismoelectric signals with amplitudes on the order of 1 microvolt per metre provide a unique opportunity to study amplitude and phase characteristics of seismoelectric signals measured on surface and in boreholes. Complementary geological and geophysical data are used to determine the characteristics of sediments and interfaces that have made these aquifers and aquitards amenable to seismoelectric investigation.
The results of vertical profiling experiments in glaciogenic sediments at Fredericton, Canada, represent the first field measurements to confirm that the co-seismic fields predicted by a quasi-static model are consistent with field measurements. The amplitudes of the co-seismic field are influenced by the resistivity and porosity of the sediments where the measurements are made. Further experiments, in a sandy unconfined aquifer near Perth, Australia, demonstrated that it is possible to measure interfacial seismoelectric signals in boreholes. Measurements of signal amplitude versus depth, and polarity reversals, observed for the first time in a borehole, have confirmed the strong bipolar character of the interfacial seismoelectric conversion in the near field. The conductivity of sediments around the interface was found to have a significant influence on the amplitude of the signal and the field distribution.
A surface-based seismoelectric imaging experiment over the same aquifer succesfully imaged both the base of the vadose zone and a shallower water retentive layer. The seismoelectric shot records presented in this work are the first example of such clear interfacial signals measured from hydrogeological interfaces deeper than 10 m. The amplitude distribution of the dominant interfacial signal was found to agree, to a first-order approximation, with that of a short electric dipole.
Results from these experiments suggest that hydrogeological targets exhibiting significant contrasts in water saturation, electrical conductivity and acoustic impedance, due to cementation, are amongst the best candidates to be imaged using seismoelectric conversions.
Several organizations made it possible for me to conduct my research and present my results at conferences by providing funding. I would like to acknowledge the contributions of the Natural Science and Engineering Research Council (NSERC), the John S. Little travel fellowship, the Water Corporation, the Atlantic Innovation Fund, the Commonwealth Research Centre of Landscapes, Environment, and Mineral Exploration, the Canadian Geophysical Union, the European Association of Geoscientists and Engineers, Geometrics and the University of New Brunswick.