The Algerian margin is located at the slow-rate convergent boundary between African and Eurasian plates and experienced several strong earthquakes in the last centuries. Among them, the 2003 Mw 6.8 Boumerdès event has triggered large turbidity currents in the slightly concave canyons of the slope and numerous cable breaks in the abyssal plain. In this study, we explore where, how and when the tectonic inversion of the margin off Boumerdès has left witnesses in the seafloor morphology and whether the observed deformation correlates with the 2003 coseismic rupture zone and with the Plio-Quaternary sedimentation. We have performed a careful analysis of the seafloor morphology and subsurface seismic reflectors at the landscape scale and along/between canyons by combining classical GIS-based methods and Virtual Reality techniques. From the mid-slope to the deep basin off the ∼60 km long Boumerdès-Dellys coast, we evidence large knickpoints corresponding to the development of four main cumulative fault scarps and two perched basins which are deeply incised by steep canyons and gullies. We interpret these structures to result from frontal propagation of two main south-dipping thrusts by upper crustal décollement ramping, evidencing an incipient sub-thrust imbrication in a stage of initiation of an accretionary wedge. The flat-ramp thrust geometry and their along-strike segmentation explain the development and shape of the perched basins in the backlimb of fault-related folds. The onset of growth strata is dated at 1.5 ± .5 Ma on the slope and .9 ± .3 Ma in the deep basin. The length, position, strike and segmentation of the older, southern thrust ramp are consistent with the coseismic characteristics of the Mw 6.8 2003 earthquake. The cumulative vertical scarp throw exceeds 1 km, supporting Quaternary shortening rates of 1.6 ± .7 mm/yr, in agreement with geodetic strain rates across the western Mediterranean basin. Virtual Reality offers powerful and promising means to correlate seismic imagery and seafloor morphology and is of great help to improve the robustness of tectonostratigraphic interpretation.
International audienceThe evolution of coastal sites such as beach/barrier/marsh systems is known to be strongly forced by sea level rise and controlled by storms, sediment input and human impacts. The relative weight of each may vary in time. However, it is difficult to determine the relative importance of these forcing controls and, therefore, how coastal systems evolve through time. In order to study this evolution we have selected the case study of Trunvel marsh, western Brittany, France, which is directly exposed to the most violent storms and has been extensively depleted of sediment during and since WW2. The relative balance of anthropogenic and meteorological controls and relative sea level rise is compared. Sediment cores have been obtained from within the marsh, cross sections of the barrier have been studied and air photos and old maps have been analysed. From 4000 BP to recent times the system has behaved in a simple way: the beach and the barrier accumulated sand and gravel, seeming to migrate inland with relative sea level rise and the marsh was alternatively eroded by the local river or fed by aeolian drifted sands. Very occasional storms may have breached the barrier and temporarily invaded (flooded) the marsh. Conversely, large events of river discharge may have breached the barrier, although there appears to be some natural resilience and the barrier rebuilds itself after each storm and the marsh is, once again isolated from the sea. At the beginning of the Roman period land use change appears to have modified the river discharge, following which the marsh seems to have been in its natural condition again until WW2, although some dykes were built and channels excavated. During WW2 the gravel was almost totally removed and used for concrete to build fortifications along the coast. After WW2, the system was totally controlled by management practices, the aim of which was to recreate a “natural” environment so that today this is a “human made natural landscape” and is now classified as a nature reserve. The barrier is no longer able to withstand storms and the river discharge does not always reach the sea. Therefore human management of water level in the marsh is today the main morpho-dynamic control for the whole system
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.