Seafloor features in the northern margin of the Alboran Sea (Western Mediterranean) related to Quaternary active tectonics

Workshop. Alboran Domain and Gibraltar Arc: Geological Research and Natural Hazards - El dominio de Alborán y el Arco de Gibraltar: Investigación geológica y riesgos naturales - Le Domaine Alboran et l'Arch de Gibraltar: Recherche géologique et risques naturels, 16-18 octubre 2019, Granada..-- 2 pages

Seafloor of the Alboran Sea is characterized by several minor and major features related to tectonic activity. Minor features are basically alignments of tectonic scarps, longitudinal and rhombic depressions, longitudinal ridges and smooth elongated bulges. These morphotectonic features are generated by a penetrative system of faults and folds that have been active along the Quaternary deforming and displacing the seabed. These structures have been evidenced by means of multibeam bathymetry mosaics and subsurface very high resolution parametric and high resolution seismic (airgun, sparker) profiles, which allow to analyze their morphologic characteristics and the related deformation. The active Quaternary structures are constituted by three families of strike-slip faults that work as a conjugated system. The first one has a WNW-ESE to NW-SE trend and right-lateral shear movement with extensional secondary component; this group correspond to structures as the Yussuf Fault that bounds the Alboran ridge to the east, the Averroes Fault that displaced the Adra ridge, and several structures in the northern Alboran Basin margin as the Adra and Balanegra faults. The other two have respectively NE-SW and NNE-SSW geometry and a left-lateral shear displacement, the first family corresponds basically to the La Serrata-Carboneras Fault that has also push and swell segments related to reverse secondary component, and the second group is constituted by several fault zones extended from close the Alhoceima region in northern Africa through the Alboran Ridge to nearby the Adra region in the south of the Iberian Peninsula. The NNE-SSW system is so marked at the Motril-Djibouti marginal plateau where this family is constituted at least by five left-lateral fault zones that are characterized on the seafloor by corridors of fault escarpments and tectonic depressions, both grabens and halfgrabens, featured as minor pull-apart basins. The corridors lengths vary between 18 and 48 km and their widths between 0.2 and 3.9 km. A dense secondary N-S normal faulting is related to the strike-slip movement of the main faults, and several intermediate normal fault zones are located between them. These fault systems are extended south-westwards of the Motril-Djibouti marginal plateau, between the Banks of Djibouti and the Ibn-Batouta seamount, where these faults have a splay configuration on the seafloor, except the eastern one, that corresponds to boundary fault of this fault system. The eastern fault zone of the NNE-SSW family is the Al Idrissi fault prolongation, and is strongly marked by development of longitudinal ridges features, generated by push and swell structures, to the west of the Alboran ridge that appoint to a reverse secondary component of this fault in this area. Likewise, to the north of the Motril-Djibouti marginal plateau, it has been recognized the presence of N-S trending normal faults and NE-SW anticline folds affecting the seabed. The northern margin of the Alboran Sea is located to the south-west of the Eastern Betics Seismic Zone. The distribution pattern of seismicity epicentres in this area has a good correlation with the describe NNE-SSW left lateral strike slip faults. These active fault zones are currently responsible of a large part of the regional seismicity