Differential geomagnetic sounding in the Rhinegraben

The method of differential geomagnetic sounding has been used to study the geomagnetic anomaly of the Rhinegraben. The measurements, performed along three profiles involving 18 stations, have allowed us to point out very particular properties of the anomalous transient magnetic field and of the telluric field; at each station on the anomaly, these two fields are linearly polarized according to two perpendicular directions. Moreover, these fields have exactly the same time dependence at all the stations on the anomaly. These properties lead us to conclude that the anomalous currents are not locally induced but instead are more probably concentrated and channelled in the shallow sediments of the graben.