Imaging Anatolian Lithospheric Structures using High-Resolution Double-Beamforming Ambient Noise Surface-Wave Tomography

Abstract

The Anatolian Plateau is one of the most heterogeneous and seismically active segments of the Alpine–Himalayan orogenic belt. It was formed through the amalgamation of several microplates with the Eurasian Plate following the multi-episodic opening and closure of the Tethyan oceans. These complex tectonic processes have produced a highly heterogeneous lithospheric structure across Anatolia. Despite numerous local and regional scale tectonic and geophysical studies, a comprehensive and high-resolution image of the Anatolian lithosphere remains incomplete. To address this, we conducted ambient noise tomography to image the crust and upper mantle beneath the Anatolian Plateau using 2.5 years of continuous vertical-component seismic recordings from 135 broadband stations. By applying the double-beamforming method to cross-correlations, we extracted Rayleigh-wave phase velocities over periods of 8–120 s and group velocities over periods of 6–100s. Two-dimensional phase and group velocity maps are constructed using the Fast-Marching Surface Tomography (FMST) . To obtain a high-resolution three-dimensional shear-wave velocity model, a nonlinear Bayesian Markov Chain Monte Carlo (MCMC) approach was applied. The resulting Vs model reveals several key features. A low-velocity layer at depths of 10–30 km likely reflects partial melting or thermally weakened crust. A high-velocity layer at depths of 50–80 km, interpreted as evidence for a thin and laterally variable mantle lithosphere, with lithospheric thickness in eastern and central Anatolia ranging from 60 to 70 km, while the thickest lithosphere (~120 km) is observed beneath western Anatolia and the eastern Taurus Mountains. . A pronounced upper-mantle low-velocity anomaly beneath eastern to central Anatolia is interpreted as asthenospheric upwelling or lateral flow. Finally, two deep high-velocity anomalies beneath the southern margin of Anatolia are attributed to the subducting African lithosphere along the Hellenic and Cyprus trenches.