High-resolution surface wave tomography beneath the Aegean-Anatolia region: constraints on upper-mantle structure

International audienceThis study provides new constraints on the upper-mantle structure from western Greece to central Anatolia using seismic data of permanent broad-band networks recently installed in Greece and Turkey and from a two-year temporary array (SIMBAAD experiment). We used ∼200 seismic events recorded at 146 broad-band stations with a typical interstation distance of 60–100 km across the study area. The high-resolution 3-D shear wave velocity model of the mantle is obtained by inversion of fundamental-mode Rayleigh wave phase velocity maps for periods between 20 and 195 s. The tomography is based on ray tracing in heterogeneous media taking into account external propagation effects. The horizontal resolution is approximately 100 km, however small heterogeneities may suffer from some horizontal smearing and damp- ing. The vertical resolution is approximately 100 km. The vertical smoothing is necessary to avoid unresolved spurious shear wave velocity oscillations in the upper mantle. The errors on shear wave velocities in our 3-D model (0.02–0.1km s−1) are significantly smaller than the amplitude of Vs variations (0.3–0.5 km s−1). In spite of the vertical and horizontal smoothing, our model shows details in the upper-mantle structure never reached at regional scale in the area. The overall structure is characterized by a low-velocity zone (80–200km depth) re- flecting a slow and warm asthenosphere underlying a thin lithosphere. The southwesternmost termination of the low-velocity anomaly corresponds to the northward dipping Hellenic slab. The detailed shear velocity structure of the upper mantle beneath Anatolia appears to be far more geometrically complex than revealed in previous tomographic studies of the area. At depths larger than or equal to 160 km, velocities are overall high beneath Anatolia, partly due to the presence of dipping high-velocity anomalies which we tentatively interpret as remnant slabs. The southernmost high-velocity anomaly beneath Anatolia is separated from the eastern edge of the Hellenic slab by a major low-velocity anomaly which we interpret as the trace of asthenospheric mantle material rising inside a vertical slab tear beneath southwestern Anatolia