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Insights on structures, tectonic inversion and seismo-turbidite cyclicity of the Algerian margin


IPGP - Îlot Cuvier


Séminaires Géosciences Marines

Salle 310

Jacques Deverchère

IUEM, Brest

The neogene kinematics of the Algero-Balearic basin as well as seismic hazards along the Algerian coast remain key scientific issues in the Mediterranean realm. In this talk, I describe tectonic and sedimentary processes occurring over the Algerian marging which are evidenced thanks to several sea cruises led together with the C.R.A.A.G. and Sonatrach institutions in Algeria and French teams. Submarine slope morphology is characterised by deep canyons and efficient sediment transport by gravity processes, from the shelf break to the deep basin. Off west Algeria, at the contact with the Alboran domain, I show that WSW-directed extensional tectonic phase has shaped a stretched continental crust from Burdigalian to Tortonian times, which is assumed to result from the migration of the Alboran block driven by slab rollback, whereas tectonic reactivation of the deep western margin is limited. Imprints of the Plio-Quaternary fault activity in the central and eastern margins are much clearer, with imbricated thrusts, fault-propagation folds, perched basins, and ramp-flat trajectories interacting with the Messinian salt and seafloor currents. The sedimentary impact of the 2003 Mw 6.9 Boumerdes earthquake is huge, with cable breaks located at the outlets of submarine valleys and in areas of turbiditic levee overspilling, depicting the multi-source and multi-path character of the 2003 turbiditic event. Finally, I show that meaningful information of large earthquakes recurrence intervals may be obtained using turbidite record offshore Algeria, in a way similar to what is done off large subduction zones. The approach is tested on cores collected off the area shaken by the 1980 Ms7.3 El Asnam and 1954 M6.7 Orléansville earthquakes. Most events appear to correlate with the paleoseismic record of the El Asnam fault over the Holocene, providing clues on the calendar of great earthquakes and on seismicity clustering and synchrony.