Geology and knowledge of the subsurface

Highlights

New: educational maps of the subsurface

In order to make the subsurface more easily understandable for the general public, BRGM has developed a new mapping concept with an innovative key format explaining the type of rock and the chronological sequence of the main events that have taken place at the site. The first maps cover the cities of Paris and Lyon as well as Sancerre/Pouilly-sur-Loire. In this area, the map shows the subtle relationships between the land, the vineyards and the subsoil.

New: educational maps of the subsurface. © BRGM

CarHab mainland France: mapping to support biodiversity objectives

The CarHab project was set up by the Ministry for Ecological Transition to develop a national map of natural and semi-natural habitats. The role of BRGM is to draw up maps showing the potential distribution of vegetation and natural habitats on a scale of 1:50,000 based on the (chemical) nature of the rocks, prior to the modelling stage, which is rendered on a scale of 1:25,000. This predictive mapping is a real decision-support tool for spatial planning and environmental protection. Following on from the maps of mainland France, completed in 2021, BRGM will work on French overseas territories and the coastal fringe of French Guiana in 2022 and 2023.

Geodiversity-biodiversity links: translation of geological formations into lithology and then into codes compatible with ecological data, for the prediction of biotopes. © BRGM

Unified declaration for underground works (Duplos): a new online service

The Mining Code requires the declaration of any non-geothermal drilling to a depth of over 10 metres. This declaration can now be completed on the Duplos portal (duplos.brgm.fr). The information is sent to government departments, and primarily the DREAL, which generates a BSS code for each borehole. This unique identifier is then fed into the BSS (subsurface) database. To submit the end-of-drilling report, the drilling company can use either Duplos or DiaLog, an app for the technical description of boreholes, supported by the portal. This remote service was rolled out in 2021 in eight regions of mainland France, before being deployed across all French territories in 2022. In late 2021, over 300 accounts had already been created and 900 declarations filed.

AEROVERGNE: a helicopter-borne geophysical campaign with conclusive results

In an area of 215 km² to the north of the Puys mountain chain in Auvergne, for the first time in mainland France, simultaneous testing was carried out using three methods of acquiring helicopter-borne geophysical data (magnetism, electromagnetism, gamma-spectrometry) in the specific geological context of bedrock under a cover of volcanic soil. Financed by ERDF funds for the Auvergne and by BRGM, the Aérovergne project highlighted the value of these surveys in improving knowledge of the subsurface of this region. This topic was the subject of a thesis in late 2021, financed by BRGM, Clermont Auvergne Métropole and the Volvic mineral water company.

Aérovergne helicopter-borne geophysics campaign in Auvergne. This project involves a survey drawing upon three geophysical methods to try to unravel the mysteries of the subsurface of this region. © BRGM - A. Raingeard

The SISMAORE oceanographic campaign revealing the seabed north of the Mozambique Channel

The SISMAORE campaign led by BRGM has enabled the acquisition of new geophysical and geological data around the Comoros volcanic archipelago.
This survey revealed the existence of two large recent tecto-volcanic fields and recent volcanic events all along the archipelago, as well as showing the architecture of the new volcano located east of Mayotte and its substratum. It also provided information on sediment evolution and major landslides. Data from SISMAORE are being analysed as part of the ANR Coyotes project, in order to gain a clearer picture of the geodynamic context of the archipelago for better risk management.

Volcanic edifice on the seabed of the abyssal plain of the western Somali basin (north of Mayotte, Mozambique Channel). Extract from the SISMAORE bathymetric map. © BRGM

Martinique: mapping of surface geological formations for ground movements

Following on from the work in Reunion Island and Mayotte, the surface geology of Martinique has now been mapped on a scale of 1:25,000, covering over 60% of its territory. The methodology implemented by BRGM combines field acquisitions with helicopter-borne electromagnetic data. This has made it possible to precisely map regolith formations, with a database of 5,767 outcrops and over 18,000 photos. These documents will be used in particular to produce new hazard maps of ground movements.

Cigéo: a new scientific programme for the storage centre project

BRGM is assisting Andra in developing its scientific programme for the characterisation and multi-scale modelling of karstic aquifers of Barrois limestone in eastern France. This surface area of the Cigéo site is set to house the surface installations of the future centre for the geological storage of radioactive waste. A thesis co-supervised by the University of Lorraine, Andra and BRGM is now under way. At the same time, a multidisciplinary R&D programme has been designed by BRGM and Andra and will be carried out over the coming years by various contributors.