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

Abstract : 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.