Crustal Velocity Structure of Turkey from Ambient Noise Tomography

In eastern Turkey, the ongoing convergence of the Arabian and African plates with Eurasia has resulted in the westward extrusion of the Anatolian plate. To better understand the current state and the tectonic history of this region, we image crust and uppermost mantle structure with ambient noise tomography. Our study area extends from longitudes of 32°-44°E. We use continuous data from two temporary seismic deployments, our 2006-2008 North Anatolian Fault Seismic Experiment and the 1999-2001 Eastern Turkey Seismic Experiment, as well as from additional seismic stations in the region. We compute daily cross-correlations of noise records between all station pairs and stack them over the entire time period for which they are available, as well as in seasonal subsets, to obtain interstation empirical Green's functions. After selecting interstation cross-correlations with high signal-to-noise ratios and measuring interstation phase velocities, we compute phase velocity maps at periods ranging from 8-40 s. At all periods, the phase velocity maps are similar for winter and summer subsets of the data, indicating that seasonal variations in noise sources do not bias our results. Across the study area, we invert the phase velocity estimates for shear velocity as a function of depth. The shear velocity model, which extends to 50 km depth, highlights tectonic features apparent at the surface: the Eastern Anatolian Volcanic Province is a prominent low-velocity anomaly whereas the Kirsehir Block has relatively fast velocities. In addition, in the southeastern part of our study area, we image a high velocity region below 20 km depth which may be the northern tip of the underthrusting Arabian plate. There are velocity jumps across the Central and East Anatolian Fault Zones. The North Anatolian Fault Zone appears as a fast anomaly in the upper crust.