Electrical Techniques
Electrokinetic Sounding (EKS)
Detail
EKS provides a measure of the variation in the hydraulic conductivity of saturated subsurface layers with depth by measuring the seismically induced time varying electromagnetic response from saturated aquifers. Readings can be taken using two pairs of electrodes aligned symmetrically about the seismic source. This normally consists of a mechanical weight drop or simple hammer and plate. The vertical resolution of a particular sounding is a function of the frequency of the seismic energy that can be generated and propagated as well as the permeability contrast between different regions within a saturated aquifer.
In most situations a hammer source is sufficient and azimuthal soundings are carried out at each measurement station to monitor anisotropy. In order to relate hydraulic conductivities to depth additional information on the seismic velocity of subsurface layers and their conductivities is required. These properties are independently derived elsewhere, for example by calibration against boreholes, from TDEM soundings and shallow seismic refraction surveys.
The EKS method as discussed above is somewhat controversial with some researchers claiming seismically induced Raleigh-wave signal as the main source of so-called EKS signal.
