Examination of Seismoelectric Observations at the Test Site Schillerslage and Laboratory

Within the development of a new test-site in Schillerslage near Hannover with typical north-german geology of shallow sandy aquifers alternating with till deposits, we used the opportunity of having a well-defined site, already investigated by various geophysical methods and boreholes, to test the observability of the seismoelectric signals. The electrical signals related to seismic excitation are caused by an electrokinetic coupling occurring at the grain-fluid interface and can be of two kinds: First, a coseismic electromagnetic signal highly similar to the compression wave and travelling with it, and second a converted electromagnetic signal originating from interfaces with discontinuities in hydraulic properties as in porosity, hydraulic conductivity, fluid salinity and further parameters. The field data at Schillerslage displays both types of seismoelectric signals. Analysing the amplitude distribution of the converted signal, the depth of an interface could be detected at 2.1 ± 0.3 m, implying a P-wave velocity around 240 m/s in the upper layer. Laboratory experiments, which are in the initial stage, allow to study the dependence of both coseismic and converted signals on various hydraulic parameters more thoroughly.