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This study aims to reveal upper-crustal velocity structure of Inner part of Izmir Gulf by using ambient noise tomography. One-year noise data have been used from 17 stations belong to IzmirNET. Rayleigh wave group velocities which present good signal/noise ratio have been obtained from dispersion curves by using multiple filter technique. Results have been mapped for 2, 4 and 6 s period intervals. Then, shear wave velocities have been obtained from the inversion of group velocity by using local dispersion curves belongs to same periods. Low velocity areas representing alluvial deposits beneath Inner part of Izmir Gulf, have been precisely observed down to 3 km on group and shear wave maps. Added to this, it is also detected not only the existence of low velocities but also high values in the depth slices of inner part of the Gulf. This method may provide precise and high resolution images of crustal structure and upper mantle by using ambient noise tomography without seismic events. It can be applied in the future to the Aegean Region, Turkey or neighbouring countries by using broad-band data set. [ABSTRACT FROM AUTHOR]

It has been two decades since the publication of the 5-degree global crustal model CRUST5.1in 1998. More recently, the 1-degree model CRUST1.0 was released for wide use in 2013.The more recent model was based on a comprehensive, updated database of crustal structureinformation from active source experiments as well as receiver function studies, Moho depthmaps from regional seismic tomography and, in some instances, results from gravity studies.A change in strategy to compile CRUST1.0 also was an iterative model validation andsubsequent update to fit global surface wave dispersion data. Yet, in an attempt to updateCRUST1.0 to the final version, some discrepancies with surface wave constraints remained.This project zooms in on the Mediterranean Sea and compares model predictions withobservations. CRUST1.0 subsequently was used as a starting model to compile a global model of theentire lithosphere, LITHO1.0 that was released in 2014. This model is based on surfacewave data alone, with an updated and larger database that includes proprietarydata in the Eastern Mediterranean/Asia Minor area. While intermediate-period(40 – 29 s) Rayleigh wave phase velocity is well-explained by CRUST1.0, groupvelocities are underpredicted in the western Mediterranean and overpredicted inthe eastern Mediterranean, by up to nearly 10%. Both CRUST1.0 and LITHO1.0fail to model Love wave group velocities adequately, even at long periods (T> 50s). Recently, new surface wave constraints collected around the Mediterranean area allowtomographic imaging to unprecedented detail. The extension to shorter periods than what isavailable on global scale allows assessment of structure not only on the crust in general butalso in areas with thick sediment cover, such as the Nile Delta in the eastern Mediterranean.At this level, we validate the 1997 Laske and Masters global sediment model that wasadopted into CRUST1.0. [ABSTRACT FROM AUTHOR]

Turkey poses a complex crustal structure as a result of the convergence of the Arabian and African plates. The North Anatolian Fault Zone (NAFZ) represents 1600 km long active right-lateral strike-slip fault system of the country that has caused several destructive earthquakes. Location of historical earthquakes indicates that the activity on the fault tends to migrate westward. In the western part of NAFZ, there is a seismic gap inside the Sea of Marmara. Reliable knowledge of physical properties of the crustal structure of the unruptured segment within the Sea of Marmara is crucial for proper seismic hazard assessments considering that the megacity Istanbul with its millions of habitants, is closely located to this seismic gap. In this study, ambient seismic noise tomography, for the first time, has been applied to obtain a high-resolution image of the crustal structure of northwestern Turkey. For forward estimation of traveltimes, we employed the Fast Marching Method. A Bayesian framework was utilized to invert traveltime residuals extracted from Green's functions for the Rayleigh wave group velocity models at various frequencies. Besides the Transdimensional Bayesian tomography imaging, we also applied a rather simple and computationally fast 2-D nonlinear tomography scheme on the same data-set to gain a rough idea on group velocity variation in the regions. Our high-resolution tomographic images included group velocities of Rayleigh waves resolved between 1 and 20 s. Lateral variation of group velocities successfully revealed the basin structures such as Çınarcık, Tekirdağ, and Adapazarı Basins between periods 1 and 10 s that are characterized by typically low group velocities with low uncertainties. The low-velocity zones appear to mark well weakness zones along the NAFZ in the crust and the complex structure due to the active tectonics of the Anatolia. Finally, different tectonic units, in particular, to the east were identified from each other as our maps highlight Istanbul-Zonguldak Zone from Armutlu-Almacik Block with a sharp high to low-velocity change in N-S direction. [ABSTRACT FROM AUTHOR]