TRANSVERSE ISOTROPIC CRUST STRUCTURE BENEATH THE NORTHWEST AND CENTRAL NORTH ANATOLIA REVEALED BY SEISMIC SURFACE WAVES PROPAGATION

Abstract

The Anatolian crust, which is abnormally hot, is widely deformed by subduction related volcanism. Suture zones, transform faults, thrusts and folds and metamorphic core complexes add to the geological complexity. Volcanic provinces such as Western, Central and Eastern Anatolia and Galatea are recognized as distinct features in the region. The middle-to-lower crust depths appear to be intruded by horizontal sills and the upper crust by vertical dykes. Both horizontal sills and vertical dykes leave anisotropic signs detected as Vertical Transverse Isotropy (VTI) that is explored by Love and Rayleigh surface wave inversions, i.e., Love-Rayleigh wave discrepancy which arises because the dykes and sills act differently against the Love and Rayleigh surface waves. The current study gives emphasis to the Northwest and Central North Anatolia utilizing both single-station and two-station tomography techniques to recover the two-dimensional group and phase speed charts from which one-dimensional dispersion inversions are implemented. The one-dimensional inversions are joined to construct the three-dimensional crust of the studied region. The shear-wave anisotropy is used to locate the anisotropy in the crust. The vertical dykes in the upper crust fit into negative VTI around -10% while the horizontal sills in the middle-to-lower crust yield positive VTI around 12%. The vertical magma flows within the vertical dykes and the horizontal magma flows within the horizontal sills contribute constructively to the anisotropy created by the special shape orientations of sills and dykes. The earthquakes hypocenter distribution and high and low speeds alongside the VTI provide significant clues to differentiate between diverse geological districts.