Syscal, Promis
In weathered crystalline context, the general high clay content results in low permeability. In this case, the groundwater extraction can only be performed in the unweathered rock at larger depth. In order to be able to extract water, people have to find high permeability areas generally located in fault zones areas.
Different geophysical methods measuring the soil electrical resistivity can be used to detect these targets. The profiling simply consists in moving a ABMN quadripole of fixed dimension. The spacing between electrodes is adapted to the depth of the target. The Syscal instrument range is well adapted to locate shallow to deep fault or dyke (Syscal Junior / Syscal R1 / Syscal R2 / Syscal Pro). With its high power, the VIP range transmitter (up to 10 kW) associated to the Elrec or Fullwave range receivers can be used to increase the electrode spacing, to locate deeper targets.
This methodology allows to highlight lateral resistivity variation along a profile, but not to locate the depth and vertical extension of the fault. Therefore it can be completed by an electrical resistivity tomography (ERT) on the location of the previous anomaly. The Syscal Switch range of equipment can also be used to perform shallow to deep electrical resistivity tomographies (Syscal Junior Switch / Syscal R1 Switch / Syscal Pro Switch). Our equipments allow to image length, depth and dip angle of the fault to identify the best drilling location.
The Promis 10 slingram type EM profiler or the T-VLF can also be useful to detect faults that are generally filled with clay (conductive) or not (resistive).
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