Crustal S-wave structure around the Lake Van region (eastern Turkey) from interstation Rayleigh wave phase velocity analyses

This study focuses on the average crustal and the upper mantle structure throughout the Lake Van region of eastern Turkey.The study aimed to investigate the structure with the fundamental mode interstation Rayleigh wave phase velocities from the localand the regional earthquakes recorded by Kandilli Observatory and Earthquake Research Institute stations. Considering back azimuthdifferences of each source and station path, six different broadband station pairs and 27 earthquakes were selected to determine the1-D shear-wave velocity structures throughout the region by using an interstation method (slant stacking technique). The linearizedleast squares algorithm was used to obtain the 1-D shear-velocity model that best fit the observed phase velocity dispersion curve. Thenormalized statistical resolution matrix was calculated to measure the reliability of the solution. Inversion results revealed that thesolution quality of the upper crust is weak due to the high resolution lengths. The average shear-wave velocities in the lower crust scaledown to approximately 3.5 km/s. It was inferred that this low-velocity zone shown in the lower crust may be associated with widespreadvolcanism. Final 2-D S-wave velocity models obtained from the inversion revealed that the crust-mantle boundary is ~42 km, and shearvelocities vary from 3.6 to 4.2 km/s. Furthermore, the upper mantle (~45 70 km) velocities are slower than globally suggested models(e.g., IASP91), and this is possibly related to shallow hot asthenospheric material.

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