Polarization Anisotropy Along the Anatolian African Plate Boundary

This study focuses on mantle flow beneath and around the Anatolian plate using measurements of seismic anisotropy. Observations of shear wave splitting across the Anatolian plate have a NE-SW fast direction and lag time similar to that observed from temporary broadband stations within the plate, indicating that the anisotropic fabric may be relatively uniform throughout the upper mantle beneath the Anatolian plate. The extensive young basaltic volcanism, regional travel time tomography, and regional phase attenuation tomography all indicate that the lithospheric mantle beneath most of the Anatolian plate has largely been removed or is very thin. Unless exceptionally high anisotropy exists in the thinned lithosphere, the main contribution to the observed delay times (of order 1 s) must therefore be asthenospheric and thus reflect recent asthenospheric flow patterns. One exception appears to be a change in the fast direction across a region of concentrated extension in western Anatolia. We observe a change in the orientation of the splitting that is consistent with the direction of crustal extension. The African-Anatolian plate boundary is made up of two very different convergent margins: the Hellenic arc to the west and the Cyprian arc to the east. There is substantial evidence that the Hellenic arc is retreating and the Cyprian arc is relatively stationary. Furthermore, both earthquake hypocenters and tomographic models indicate that the Cyprian angle of subduction is much less steep than the subduction occurring along the Hellenic arc. This substantial geometric difference implies that there is a tear or gap in the subduction of African oceanic lithosphere beneath the Anatolian plate along what is called the Isparta Angle. We are investigating mantle dynamics and mantle flow around and through this possible tear in the lithosphere. We will use a combination of seismic tomographic methods (surface wave, body wave, and attenuation) as well as neotectonics studies to help constrain the extent, timing and amount of deformation in and around the Isparta angle. We have initiated this study by deploying another array of seismometers across the western Cyprean arc and extending to the easternmost Hellenic arc and the Burdur fault zone. We will combine these stations with a number of newly established permanent stations in the region to map the asthenospheric flow through this possible stab tear.