Tectonic geomorphology along an active strike-slip fault: the Yusuf fault system (Alboran Sea; Westernmost Mediterranean)

Abstract

The NW-SE convergence (4-5 mm/yr) between the African and Eurasian plates controls the present-day crustal deformation in the Alboran Sea (westernmost Mediterranean). Although instrumental seismicity is characterized by low to moderate magnitude events, large earthquakes (I > IX and M > 6.0) have occurred in this region (i.e., 1522 Almeria, 1790 Oran, 1910 Adra, or 2016 Al-Idrissi earthquakes). The dextral strike-slip Yusuf Fault System (YFS) is one of the largest active faults in the Alboran Sea and its seismogenic and tsunamigenic hazard needs to be characterized. The fault system trends WNW-ESE and has a length of ~150 km. Using multi-scale bathymetric data and different morphological analysis tools (i.e., slope or relief image maps), we have characterize the changes in the morphology of the seafloor along the YFS related to its Plio-Quaternary activity. The tectonic evolution of the fault system has resulted in the formation of a large pull-apart basin, which is deeper than the surrounding areas, a topographic ridge, an elongated depression and morphologic lineaments following its trend. The dataset also images several submarine landslides scars, mainly on the steeper slopes surrounding the pull-apart basin. In addition, the analysis of ultra-high resolution bathymetry acquired with AUV has revealed the presence of a series of en-echelon scarps with heights ranging from few centimeters to less than 10 meter. Seismic profiles across these scarps show that they are related to different fault strands of the YFS that are offsetting the seafloor, possibly because of an earthquake occurred in historical times