The Slab Puzzle of the Alpine-Mediterranean Region: Insights from Surface Wave Tomography

Mediterranean tectonics is driven since the Lower Cretaceous by a multi-phase subduction and collision history with highly-variable plate configurations. The presence, as well as the geometry of the slabs, remain however enigmatic in many regions due to the small size of the slabs and their strong tearing and fragmentation. Only in some cases, the geometry of the slabs can be inferred from intermediate deep seismicity. The existence of Eurasian, Adriatic, and African slab segments down to 300 km depth is discussed using a shear-wave velocity model (MeRE2020) obtained by Rayleigh-wave tomography. 14 slab segments varying in lateral length along-strike between about 200 km and 800 km are identified. We distinguish three categories of subducted slabs: attached slabs reaching down to the model bottom, shallow slabs of shorter length in down-dip direction, and detached slab segments. There is an intricate relationship between slab fragmentation and the relatively small and highly curved subduction zones and collisional orogens characteristic for the Mediterranean. In addition, challenges to reveal seismic properties of the lithosphere-asthenosphere system in the Mediterranean to understand plate deformation in the area are presented.