Electrokinetic geophysics for groundwater assessment and complex near-surface characterization

We present and discuss two electrokinetic geophysical methods and their value for groundwater assessment and complex near-surface characterization: self-potential (SP), and coupled seismo-electromagnetics (seismoelectrics). The scope of this work can be broadly divided into two parts: we present and discuss the results of a self-potential study carried out in a Karst environment in Tampa, Florida, we present a novel seismoelectric (SE) methodology that uses surface wave signals, thereby mitigating the major present-day practical limitation for the seismo-electric method: the relatively low converted signal strengths. For the SP campaign, we collected 555 data points. After reference and closure corrections, a map of the study site displaying SP anomalies was produced. We compare the map with an SP profile along a known sinkhole in the study area, and can clearly observe a strong, negative SP anomaly that is most likely related to preferential downward infiltration/flow of groundwater at the location of the sinkhole. The novel concept for seismoelectric signals makes use of surface waves, as compared to the relatively weak seismoelectric body wave responses (in particular the so-called interface response fields) that traditionally have been used for seismo-electric lateral and depth characterization. We show that we can identify information at depth about, for instance, subsur-face contrasts in the SE coupling coefficient (or other porous medium parameters of interest), using the novel approach of Dispersive Relative Spectral Amplitudes (DRSA). Building on the established successes of seismic surface wave studies, this novel methodology has the potential to change the way we think about seismoelectric data acquisition and applications.