NNE-SSW left-lateral active faults in the Motril-Djibouti marginal plateau, Northern margin of the Alboran Sea (Western Mediterranean)

Abstract

Seafloor of the Alboran Sea is characterized by a penetrative system of tectonic structures that are well defined both by displacement and folding of Quaternary sedimentary units and formation of several marked morphological features related to contemporary faulting activity. These structures are evidenced in multibeam bathymetry mosaics and subsurface parametric and high resolution seismic (airgun, sparker) profiles, which allow to analyze their strong deformation. The pattern of seismic epicentres distribution has also a good correlation with these structures. The group of Quaternary structures is constituted by three families of strike-slip faults that they work as a conjugated system. The first one has a WNW-ESE to NW-SE trend and right-lateral shear movement, and the other two have respectively NE-SW and NNE-SSW geometry and a left-lateral shear displacement. The activity of NNE-SSW family is recent than the NE-SW one since they displace them. Likewise it has been recognized the presence of N-S trending normal faults and NE-SW anticline folds. The Motril-Djibouti marginal plateau (northern margin of Alboran Sea) on the southwestward prolongation of the Eastern Betic Shear Zone, is crossed by at least eight active fault zones of NNE-SSW direction. They are characterized on the seafloor by corridors of fault escarpments and tectonic depressions, both grabens and halfgrabens, as minor pull -apart basins. The corridors length 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. The main fault zones currently are responsible of a large part of the regional seismicity. The eastern fault zone corresponds to the northern prolongation of the Al Idrissi fault