Seismic discontinuities in the Mediterranean mantle

Layering in the upper and lower mantle across the Mediterranean has been determined using P-to-S converted phases identified through receiver function analysis. Conversion of the receiver function’s time axis to depth was based on local 1D S-velocity models. The 1D velocity model for each station was extracted from a three-dimensional S-velocity model for the Mediterranean region (EAV03), enhanced with crustal structure derived from receiver function analysis. Under the Mediterranean region we observed a mantle transition zone thickness of 261 ± 10  km, on average, which agrees with a dominance of high velocities imaged in tomographic models at these depths. A thick mantle transition zone ( > 270 km) was observed in regions with ongoing or past subduction: eastern Spain, southern Italy, southern Greece and the north-western African coast. Conversions from the 410 km and 660 km discontinuities were clearly observed for most stations. Amplitudes of both discontinuities are anomalously large throughout the Mediterranean region, 4.9% and 5.7%, respectively. We observed significant conversions from the 520 km discontinuity. The lower mantle showed strong lateral variations resulting in spatially incoherent converted phases from discontinuities near 860 km, between 900 km and 1200 km, and 1320 km depth.