Multiscale fracture analysis along the French chalk coastline for investigating erosion by cliff collapse

Albert Genter (1) , Anne Duperret (2) , A. Martinez (2) , R.N. Mortimore (3) , J.-L. Vila (1)

1 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)
2 LOMC - Laboratoire Ondes et Milieux Complexes
3 Applied Geology Research Unit

Coastal cliffs of Upper Normandy and Picardy are eroded by cliff collapses of various sizes. This paper presents a multi-scale analysis of the pre-existing fractures embedded within the Cretaceous chalk. About 20 representative sites equally spaced along the 120-km long coastal section were analyzed and compared to a continuous structural analysis of the coast derived from aerial photographs taken in 1986. Ancient collapses interpreted on the aerial photos were compared to the pre-existing fracture content. Regional faults, pre-1986 collapse location and fracture density are spatially correlated. However, recent collapses observed on the field between 1998 and 2001 did not systematically correlate to the pre-existing fracture occurrence and therefore, there is no clear link between recent collapse and the regional faults.

Mots clés: Coastal cliff erosion; Fracture network; Cretaceous chalk; Upper Normandy; France; Coastal cliff erosion

Domaines: Géomorphologie

Albert Genter, Anne Duperret, A. Martinez, R.N. Mortimore, J.-L. Vila. Multiscale fracture analysis along the French chalk coastline for investigating erosion by cliff collapse. Geological Society of London. Coastal Chalk Cliff Instability, Geological Society of London, pp.57-74, 2004, Engineering Geology Special Publications 20, ⟨10.1144/GSL.ENG.2004.020.01.04⟩. ⟨insu-00800017⟩