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Anisotropic Pn tomography of Turkey and adjacent regions



This study presents an analysis of Pn traveltimes to determine lateral variations of velocity, anisotropy of uppermost mantle and crustal thickness beneath Turkey and adjacent regions. From 1999 to 2010, more than 50 000 Pn arrivals are compiled from 700 regional earthquakes and 832 stations of permanent and temporary networks operated in the study area. We used a regularized least-squares inversion to estimate the uppermost mantle parameters. The results reveal features that correlate well with the geology and the active tectonics of the region. Overall, the Pn velocities show very fast (>8.4 km s–1) and very slow (<7.6 km s–1) anomalies indicating a heterogeneous lithospheric structure. Relatively uniform Pn velocities (7.9–8.1 km s–1) are observed in western Turkey. The lowest velocities coincide with the volcanics of the easternmost Anatolia and the Central Anatolian Volcanic Zone. High Pn velocities are observed at Mediterranean Basin (>8.3 km s–1), western Black Sea Basin (>8.3 km s–1), Adriatic Sea (>8.3 km s–1) and Zagros Suture (>8.3 km s–1). Pn anisotropy has maximum amplitude of ±0.6 km s–1 in the study area. The largest and coherent anisotropic anomalies are observed in the western Anatolia, Aegean Sea and Cyprian Arc. Pn anisotropy in western Anatolia, Aegean Sea and Greece correlate well with the present deformation of N–S regional extension. No clear correlation between anisotropy and the shear deformation along the North Anatolian Fault was observed. The majority of the stations in central Anatolia show small station residuals indicating the average crustal thickness of 35 ± 2 km. Western Anatolia and the Aegean Sea have crustal thicknesses between 28 ± 2 and 33 ± 2 km. In Greece, the crustal thicknesses are increasing from 33 ± 3 km from the western coast to a maximum of 48 ± 3 km beneath Dinarides-Hellenides. The large crustal thicknesses are also observed along southern coast of Anatolia (40–48 km).

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