Improving the Gravity Anomaly Map of French-Belgian Hainaut using Multi-Scale Fusion of New Gravity Acquisitions and Legacy Data in an Adaptive and Open-Source Gravimetric Processing Workflow

Abstract. In Wallonia, the centre of Hainaut (SW Belgium) is considered the main area where deep geothermal resources are proven. In this region bordering France, the geothermal resource is located within the reservoir formed by the Carboniferous limestones. Productive levels are associated with karst resulting from the dissolution of interbedded massive anhydrites.

To improve current knowledge of deep geological structures and to better delineate the geothermal targets, a new detailed regional gravity anomaly map has been produced. This has involved the integration and harmonisation of legacy and new cross-border gravity data, combined with homogeneous reprocessing of the effect of topography and interpolation using the equivalent source method. The legacy data come from the Belgian and French databases published by the ROB (Belgium) and BRGM (France) respectively, to which unpublished data from the Battaille 1967 campaign have been added. The new gravity data come from the recent MoreGeo 2019–2022 gravity acquisition campaign. This campaign covers an area of 820 km² with 3,400 gravity stations distributed along densely sampled profiles and displays a mean square error of 39.61 µgal. The multi-scale fusion of non-standardised data was achieved by developing a gravimetric processing workflow based on open-source Python libraries. It includes an advanced drift correction and a terrain correction up to 167 km in extent.

The resulting map is consistent with previous maps, in particular the strong correlation between the anomaly and the thickness of the Meso-Cenozoic deposits. It also shows new anomalies that may be due to deep-seated structures. It will be used as a basis for modelling the geothermal reservoir, provided that the effect of the Meso-Cenozoic deposits is removed.