SUMMARY This 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 damping. 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 (0.02–0.1 km 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 (80–200 km depth) reflecting 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.

International audienceConstraining mantle deformation beneath plate boundaries where plates interact with each other, such as beneath active or halted mountain belts, is a particularly important objective of "mantle tectonics" that may bring a depth extent to the Earth's surface observation. Such mantle deformation can be mapped at scale lengths of several tens of kilometers through the analysis of seismological data and particularly by mapping seismic anisotropy from the splitting analysis of vertically-propagating SKS waves that largely reflect the strain-induced crystal preferred orientations of the rock-forming minerals within the upper mantle. In the present study, we analyse data from approximately 50 broadband seismic stations covering the Western Alps and we provide a coherent picture of upper mantle anisotropy beneath the belt. The large-scale anisotropy pattern is characterized by fast split directions that closely follow the trend of the belt. Moreover, the maximum anisotropy magnitude is not located beneath the internal zones of the belt but instead beneath external units. All suggests that the anisotropy is likely dominated by sublithospheric mantle deformation. We propose that the observed anisotropy pattern can be explained by recent or active mantle flow around the Eurasian slab presently plunging beneath the inner parts of the Alps

Ambient seismic noise correlations are widely used for high-resolution surface-wave imaging of Earth's lithosphere. Similar observations of the seismic body waves that propagate through the interior of Earth would provide a window into the deep Earth. We report the observation of the mantle transition zone through noise correlations of P waves as they are reflected by the discontinuities associated with the top [410 kliometers (km)] and the bottom (660 km) of this zone. Our data demonstrate that high-resolution mapping of the mantle transition zone is possible without using earthquake sources.