Reassessment of the Carboneras Fault 3D geometry based on new bathymetric and high-resolution multi-channel seismic reflection data

The NE-SW Carboneras Fault is one of the main active structures in the Alborán Sea and, together with the Al-Idrisi Fault, forms the Trans-Alborán Shear Zone, which connects the Betic and Rif Cordilleras. The accurate representation of the offshore 3D geometry and seismogenic characteristics (e.g., slip rate or maximum magnitude) of this large left-lateral strike-slip fault system is essential for assessing the seismic potential in a slow-deforming region, such as the Alborán Sea. Here, we combine the interpretation of multibeam bathymetric and high-resolution multi-channel seismic reflection (HR-MCS) data to reassess the offshore extent of the Carboneras Fault and the adjacent morphostructural elements. Topographic attributes were applied to the bathymetric data to enhance the visualization of the fault trace at the seafloor. Our findings suggest that the offshore Carboneras Fault extends for 110.3 km, exceeding previous estimates. We identified twenty fault segments along the Carboneras Fault trace, with individual lengths up to 46 km and azimuths varying from N40º to N238º. Geomorphic features typically associated with strike-slip systems such as deflected drainage systems, shutter and pressure ridges, and horsetail splays were also identified. Structural seismic attributes applied to the HR-MCS profiles highlight major subsurface discontinuities, allowing detailed mapping of the fault geometry at depth. Seismic interpretation also accounted with the identification of seven horizons offset by the Carboneras Fault, comprising the Paleozoic-Triassic basement, the Messinian unconformity and Early Pliocene to Late Quaternary seismic units. Based on this information, we constructed fault and horizon surfaces to develop the first 3D model of the Carboneras Fault. This model provides key constraints on crustal architecture and offers new insights into fault growth mechanisms, thereby reducing uncertainties and improving the assessment of the seismogenic potential of this major offshore fault system.