Regional centroid moment tensors for earthquakes in the 2016 South Alboran seismic crisis

Data files and modelling results of regional centroid moment tensors obtained for earthquakes in the 2016 South Alboran seismic crisis, and presented in the article "Earthquake crisis reveals the development of an embryonic continental fault system”, by Eulàlia Gràcia et al. Large continental faults extend for thousands of kilometres to form boundaries between rigid tectonic blocks. These faults are often associated with prominent topographic features, and they can produce large earthquakes. Here we present first evidence of such a major tectonic structure in its initial growing stage, the Al-Idrissi Fault System (AIFS), in the Alboran Sea. Until now, this fault system had always been described as a complex diffuse boundary between Eurasia and Nubia plates. However, combining newly acquired high-resolution bathymetric and seismic reflection data, together with seismological analyses of the 2016 Mw 6.4 earthquake offshore Morocco – the largest event ever recorded in the area – we unveil a 3D geometry for the AIFS, which definitively correspond to a crustal-scale boundary. We report evidence of left-lateral strike-slip displacement, characterize fault segmentation and demonstrate that the AIFS is the source of the 2016 events. The occurrence of the Mw 6.4 earthquake together with historical and instrumental events supports that the AIFS is currently growing through propagation and linkage of its segments. Thus, the AIFS provides a unique model for inception and growth of a young continental fault system.