Continental lithosphere can undergo pervasive internal deformation, often distributed over broad zones near plate boundaries. Because of the paucity of observational constraints on three-dimensional movement at depth, patterns of flow within the lithosphere remain uncertain. End-member models for lithospheric flow invoke deformation localized on faults or deep shear zones or, alternatively, diffuse, viscous-fluid-like flow. Here we determine seismic Rayleigh-wave anisotropy in the crust and mantle of the Aegean region, an archetypal example of continental deformation. Our data reveal a complex, depth-dependent flow pattern within the extending lithosphere. Beneath the northern Aegean Sea, fast shear-wave propagation is in a North–South direction within the mantle lithosphere, parallel to the extensional component of the current strain rate field. In the south-central Aegean, where deformation is weak at present, anisotropic fabric in the lower crust runs parallel to the direction of palaeo-extension in the Miocene. The close match of orientations of regional-scale anisotropic fabric and the directions of extension during the last significant episodes of deformation implies that at least a large part of the extension in the Aegean has been taken up by distributed viscous flow in the lower crust and lithospheric mantle.

Acknoweldgements: This work was funded by the German Research Foundation within Collaborative Research Centre SFB 526 `Rheology of the Earth' and by Science Foundation Ireland (grant 08/RFP/GE01704). Earthquake data were provided by NOA, Greece (thanks to G. Stavrakakis), and GEOFON, GFZ Potsdam. GIPP, GFZ Potsdam, supplied seismic acquisition systems for CYCNET.

For further reading: Endrun, B., S. Lebedev, T. Meier, C. Tirel, and W. Friederich (2011), Complex layered deformation within the Aegean crust and mantle revealed by seismic anisotropy, Nat. Geosci., 4, 203–207. doi: 10.1038/ngeo1065

Keywords: anisotropy, continental_deformation