000008125 001__ 8125
000008125 005__ 20260611182940.0
000008125 037__ $$aCTALK-2026-0119
000008125 100__ $$aVan Noten, Koen
000008125 245__ $$aEstimation of Carboniferous Bedrock Depth Using Borehole-Calibrated H/V Spectral Ratios for Geothermal Assessment in Lille Metropolitan Area, France
000008125 260__ $$c2026
000008125 269__ $$c2026-06-10
000008125 520__ $$aThe geothermal potential of the Lille Metropolitan Area (France), specifically for open-loop applications, strongly depends on the geometry and depth of the Carboniferous limestone basement, which forms the main regional target reservoir in northern France. Understanding the structural continuity, the presence of basement faults, and the thickness of the overlying sediments is essential for designing geothermal systems, preparing drilling strategies, and assessing risks linked to deep karstic or tectonic structures. The region exhibits a pronounced geological heterogeneity, with Meso-Cenozoic sediment thickness varying laterally from a few to 200 meters over short distances due to the influence of the Variscan basement structural network, the Meso-Cenozoic transgression and depocenter location, and later the Cenozoic tectonic reactivation phase. To address the scarcity of borehole information and to provide a systematic, spatially continuous estimation of the depth to the Carboniferous bedrock, a large-scale passive seismic survey was conducted across the Mélantois and Pévèle areas in Northern France. The applied method is the Horizontal-to-Vertical Spectral Ratio (HVSR) analysis of recorded ambient seismic noise. HVSR exploits the contrast in seismic impedance between the sedimentary cover and the underlying bedrock to extract the fundamental resonance frequency which is empirically linked to sediment thickness. Combining HVSR analysis with bedrock depth information from boreholes hence allows developing resonance-to-depth relations. These relations are subsequently used to construct “virtual boreholes” from ambient noise measurements, enabling bedrock depth estimations at locations where no direct geological information exists. This extended abstract presents the results of the depth conversion of 459 HVSR measurements, calibrated on 63 boreholes reaching the Carboniferous, providing a high-resolution view of the bedrock paleorelief and its implications for geothermal development in the Lille Metropolitan Area.
000008125 594__ $$aNO
000008125 6531_ $$aH/V Spectral Ratio Method
000008125 6531_ $$aAmbient Seismic Noise
000008125 6531_ $$aGeothermal Exploration
000008125 6531_ $$aBoreholes
000008125 700__ $$aGraveleau, Fabien
000008125 700__ $$aChanier, Frank
000008125 700__ $$aBouka Biona, Tchianik
000008125 700__ $$aBossennec, Claire
000008125 700__ $$aWatremez, Louise
000008125 700__ $$aLecocq, Thomas
000008125 773__ $$tWorld Geothermal Congress, Calgary, Canada
000008125 8560_ $$fkoen.vannoten@ksb-orb.be
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000008125 906__ $$aContributed
000008125 980__ $$aCTALKCONT