Shear-Wave Velocity Tomography of the Lithosphere–Asthenosphere System beneath the Iranian Plateau.

We conducted a tomographic inversion of Rayleigh-wave dispersion to obtain 2D phase and group velocity tomographic images in 10–100 s period range and shear-wave velocity structures for the Iranian plateau. For this purpose, the fundamental mode of Rayleigh waves, recorded along 1586 paths by 29 broadband stations, was identified by applying the frequency time analysis (FTAN) to each epicenter–station path which, at the same time, satisfies the two-station method conditions. The fundamental modes identified by FTAN have been used to determine the path-average interstation phase and group velocities at selected periods. With this procedure, 243 group and phase velocity dispersion curves were processed to obtain tomographic maps by applying the Yanovskaya–Ditmar formulation for periods in the 10–100 s range. Averaged dispersion curves of phase and group velocities, which represent six rather homogeneous regions, are computed. Finally, we used a fully nonlinear inversion procedure to derive tomographic images of the elastic structure of the lithosphere and asthenosphere of the six main structural and seismotectonic features of the Iranian plateau. The dense path coverage in the Iranian plateau permits us to produce images that have substantially higher lateral resolution compared to images currently available from global and regional group velocity studies. Tomographic maps at high frequencies are well correlated with the upper crust structure, especially with sediment layers thickness. Estimated shear-wave velocity structures are well correlated with shield-like lithosphere structure in Zagros. No low-velocity zone (LVZ) is detected in Alborz and the South Caspian, which can imply the thrusting of oceanic crust of the southern Caspian Sea under the Alborz to the south. LVZs are derived for the region east of Iran, central Iran, and Kopeh Dagh.