Enerex offers innovative methods for measuring and interpreting magnetic data particularly suited to studying high-resolution structural geology. Indeed, using a measurement system with a compact drone makes it possible to cover large areas quickly and with better resolution than traditional surveys by plane or helicopter.
Villards d’Héria site case-study
Villards-d’Héria is a French town located in the Jura department in Eastern France. Drone magnetic surveys were carried out to improve the understanding of the geological and structural limits around two Roman sanctuaries between which underground water circulation is proven.
The survey was carried out using a lightweight system mounted on a drone (900g DJI Mavik Pro), 35 m from the ground (just above the canopy). After acquisition, data processing, and removal of anthropogenic effects, we obtain a high-resolution map of the magnetic anomaly linked to lithological and/or structural contacts in the underground.
On this magnetic anomaly map, the color variations correspond to different geological limits: changes in rocks’ nature, faults, etc. We can then notice different types of elements.
Limits consistent with elements of the geological map.
Within the best-marked limits, we can observe the ancient banks of a lake whose current level has been artificially raised. We can also see the main depth boundaries between different geological layers. The latter do not correspond exactly to the limits observed on the surface and reported on the geological map because they indicate contacts at depths that are not vertical.
High-resolution elements about certain topographical elements.
In addition to the main limits, we can note an alternation of fine contacts with a predominantly N010°E and N145°E orientation in correlation with certain topographic elements visible on the LIDAR data. These contacts suggest small-scale structural or lithological limits. These directions are known in the sector, with a coherent relationship with a known fault system, probably linked to the Vuache fault further south.
The magnetic surveys on the Villards-d’Héria site therefore made it possible to make various observations and preliminary interpretations, revealing great potential for geological interpretations. These elements of local and high-resolution geology will allow us to better understand the articulation between archaeological sites, the possible impact of seismicity on their history and abandonment, and in general the structural geology and seismic potential of the region which are still poorly known.
This study was carried out within the framework of the PCR “Territory occupancy, continuity, evolution” (coord. R. Grebot), for which we thank all the participants who allowed us to present the results, particularly the Onno Archéo association, project coordinator.
