2.5. Geophysical prospection results

After the selection of the presumed active faults, it is necessary to confirm the presence of a real discontinuity affecting the quaternary level. Geophysical prospecting was carried out on different selected targets.

At fisrt, some rapid methods have been tested in order to improve the methodology of investigation. Electromagnetic mesurements have been perfomed (EM31 and VLF). These two methods allow to measure conductivity (or resistivity) of the ground down to a few meters (EM31) and a few tenths of meters (VLF). One 200 m long profile can be performed in about 30 minutes. Theses methods are classically used in crystallines basement and not in a sedimentary context.

Left : EM31 measurements at Riedseltz quarry - right : VLF at Mundolsheim slope

Results of these investigations are encouraging and have been confirmed by electrical tomography performed by Liège university. Sharp and aligned anomalies have been identified on the Mundolsheim scarp.

Ground Penetrating Radar (Left) and electrical tomography (right) at Mundolsheim slope.

Example of Mundolsheim scarp : EM31 - VLF - and DGPS correlations