ALBERT

Description: Highlights • Crust and mantle lithospheric structures beneath the eastern Mediterranean Sea are resolved from the joint inversion of surface wave measurements and wide-angle refraction seismics. • Vp/Vs and Poisson's ration estimates point to the presence of serpentinized oceanic crust beneath the Ionian Basin and thinned continental crust beneath the Levant Basin. • Oceanic lithosphere in the eastern Mediterranean Sea consists of three different domains: a) 180 km thick, Triassic Ionian lithosphere, b) 200 km thick, Permo-Carboniferous lithosphere beneath the Central Eastern Mediterranean and c) 180 km thick lithosphere beneath the eastern Herodotus Basin. • Thin continental lithosphere (75 km thick) beneath the Levant Basin underlain by the shallow Middle East Asthenosphere. • The spatial correlation between the shallow Middle East Asthenosphere and the Dead Sea Fault reveals focusing of lithospheric deformation in an area of thinned lithosphere. Abstract The tectonic plate under the eastern Mediterranean Sea shows a remarkable variability as it comprises Earth's oldest oceanic lithosphere as well as the transition towards continental lithosphere beneath the Levant Basin. Its thickness and other properties offer essential information on the lithospheric evolution but have been difficult to determine seismically due to the high heterogeneity of the region and its complex crustal structure. Here, we combine a large, new surface wave dataset with published wide-angle data in order to determine lithospheric properties in the eastern Mediterranean. Our stochastic inversions of broad-band, phase-velocity dispersion measurements resolve the crust-mantle structural trade-offs and yield robust, 1-D shear-wave velocity models down to 300 km depth beneath the Ionian and Levant Basins. The thickness of the crust beneath the two locations is 16.4 ± 3 km and 22.3 ± 2 km, respectively. The Poisson's ratio (σ) of 0.32 and Vp/Vs of 1.93 in the crystalline crust confirm the presence of serpentinized oceanic crust beneath the Ionian Basin. Beneath the Levant Basin, low crustal Vp/Vs (∼ 1.7) and Poisson's (∼ 0.24) ratios indicate continental crust. Beneath the Ionian Basin, the lithosphere is about 180 km thick. By contrast, thin, 75 km thick lithosphere is found beneath the Levant Basin. S-velocity tomography based on surface wave data also shows thick, spatially variable oceanic mantle lithosphere beneath the eastern Mediterranean. Thickness of the oceanic lithosphere increases eastwards from the Triassic Ionian towards the Permo-Carboniferous lithosphere in the Central Eastern Mediterranean. These results demonstrate that oceanic lithosphere can thicken by cooling substantially beyond the limits suggested by the plate cooling model. Beneath the eastern Herodotus oceanic Basin, lithospheric thickness is decreasing to about 180 km. Thin continental lithosphere and shallow asthenosphere are present beneath the Dead Sea Fault, demonstrating that the localization of the lithospheric deformation and crustal seismicity along the fault correlates spatially with the thinning of the underlying continental lithosphere.