Analysis of seismic anisotropy across Central Anatolia by shear wave splitting

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2014

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Pamir, Dilekcan

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Central Anatolia plays a significant role to connect the theories on the ongoing tectonic escape, the African Plate subduction along Cyprus Arc and the collision of Arabian Plate along Bitlis Suture. On the other hand, the shear wave splitting measurements which characterize the seismic anisotropy are very sparse in the region. The seismic data recorded by national seismic networks with a denser coverage provides a unique opportunity to analyze the effect of present slab geometry (slab tears, slab break-off) on mantle deformation and test different models of anisotropy forming mechanisms. In this study, the anisotropic structure beneath the Central Anatolia is investigated via splitting of SKS and SKKS phases recorded at 46 broadband seismic stations. Our measurements yielded 1171 well-constrained splitting and 433 null results. Overall, the region displays NE-SW trending fast splitting directions and delay times on the order of 1 sec. However, a large number of stations which are spatially correlated with Cyprus Slab, Neogene volcanism and major tectonic structures present significant periodic back azimuthal variations on splitting parameters that cannot be explained by one-layered anisotropy with horizontal symmetry. Thus, we have modeled anisotropy for two-layered structures using a forward approach and identified NE-SW trending fast splitting directions with delay times close to 1 sec at the lower layer and NW-SE trending fast splitting with limited time delays (~0.3 sec) at the upper layer. Fast directions and delay times of the lower layer are similar to one-layered anisotropy and parallel or sub-parallel to the absolute plate motions which favors asthenospheric flow model associated to drag forces. In contrast, weak upper layer anisotropy is likely related to the internal deformation of Central Anatolian lithosphere.

Subject Keywords

Seismology, Anisotropy, Shear zones (Geology)., Lithosphere., Earth (Planet)

URI

http://etd.lib.metu.edu.tr/upload/12616797/index.pdf
https://hdl.handle.net/11511/23273

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Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats

D. Pamir, “Analysis of seismic anisotropy across Central Anatolia by shear wave splitting,” M.S. - Master of Science, Middle East Technical University, 2014.