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Imaging the upper mantle beneath Turkey and surrounding regions
This study includes two interdependent sections. The first section presents an analysis of Pn travel times to determine Pn velocity, Pn anisotropy and crustal thickness variations beneath Turkey and surroundings. Between 1999 and 2010, more than 50 000 Pn arrivals are compiled from 700 regional earthquakes by 832 stations of permanent and temporary networks operated in the study area. A regularized least squares inversion method is used to estimate crustal thickness variations and image velocity perturbations in the uppermost mantle. The results reveal features that correlate well with the surface geology and the active tectonics of the region.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. The average velocity of 8.0 km s-1 is determined from a linear fit to Pn travel times. Relatively uniform Pn velocities (7.9-8.1 km s-1) are observed in the western Turkey. Large velocity contrasts are located at subduction and suture zones. A sharp transition in the central Anatolia is apparent from the uniform Pn velocities in the west to lowest velocities (< 7.6 km s-1) in the east. The lowest velocities coincide with the volcanics of the easternmost Anatolia and the Central Anatolian Volcanic Zone. Beneath the Dead Sea Fault Zone and Dinarides-Hellenides, the upper mantle velocities are also low (< 7.8 km s-1). High Pn velocities are observed beneath oceanic lithosphere such as 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 zone (> 8.3 km s-1). Large velocity contrasts are observed at subduction, suture zones and across the North Anatolian Fault.Pn anisotropy has maximum amplitude of ±0.8 km s-1 in the study area corresponding to 10% anisotropy. The coherent and largest anisotropic anomalies are observed in the western Anatolia, Aegean Sea, and Cyprian Arc. A significant anisotropic pattern is observed in the Cyprian arc region. Pn anisotropy in western Anatolia, Aegean Sea and Greece correlate well with the present state of tectonic deformation and GPS velocities. The Dinarides-Hellenides exhibit arc-parallel anisotropy. In western Anatolia, anisotropy is aligned in N-S direction along the major principal strain orientation. Along the North Anatolian Fault, the anisotropy directions are E-W, aligned with the fault geometry in the western part while no correlation is observed on the central and eastern parts of the fault. Anisotropy in eastern Anatolia is complex and the directions are varying strongly in the region of low Pn velocities. The absence of anisotropy is apparent in an area dominated by the neogene volcanism. Low Pn velocities and absence of clear anisotropic pattern beneath eastern Anatolia may have resulted from thermal anomalies in the uppermost mantle possibly due to delamination processes.Large positive station delays are observed along the southern coast of Anatolia, eastern Anatolia and beneath Dinarides-Hellenides while large negative station delays are observed in western Anatolia and the Marmara region. 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 (40-48 km) are also observed along southern coast of Anatolia. In eastern and southern Anatolia the average crustal thicknesses are 40 km and 36 km, respectively.In the second section of this study, shear wave splitting on records of core-refracted (SKS) phases are obtained. Waveform data from 850 teleseismic earthquakes occurred between 1999-2010 at epicentral distances greater than 84? and less than 130? with magnitudes greater than 6.0 are analyzed. A total number of 4163 splitting measurements are obtained from 217 broadband seismic stations located in and around Turkey.The anisotropy parameters measured from SKS are consistent with the results of similar studies conducted in North-Central Anatolia, eastern Anatolia and Aegean. Fast direction polarizations are dominantly in NE-SW direction in the eastern Anatolia. In the Marmara region, fast polarization directions are in NNE-SSW direction with greater lag times. There is a relatively sharp change in the fast polarization directions form NE-SW to NW-SE at the Antalya Bay, Isparta Angle region (~30oE). SKS measurements are non-uniform in central and northern Greece. There are progressive changes in the fast splitting directions as well as delay times from eastern Turkey to the Aegean. The change in the fast splitting directions from NNE-SSW in the eastern Anatolia to N-S in the Aegean may be the result of the retreat of the Hellenic slab. Through the North Anatolian Fault, shear wave splitting directions are aligned NE-SW.
The present day stress states in the Marmara region
In this study, for the analysis of high quality fault plane solutions, data from stations of KOERI and the TURDEP project in the Marmara Region was merged. Data from a total of 105 stations, including 5 continuous SBO stations of KOERI was used. The earthquakes were selected with the following criteria; minimum local magnitude of 2.0, number of minimum P-wave first motion polarity of 10 and toleration of maximum misfit of 1. During the study 85, 75, 73, 102, and 63 source mechanisms were determined in Ganos Offshore, Tekirdağ Basin, Çınarcık Basin, Yalova Region and Gemlik Region, respectively. Through the determination of 9226 high quality P-wave first motion polarities for the selected 398 earthquakes, the number of average polarity per earthquake was 23. Average error depth, latitude, longitude, and GAP values were also obtained as 2.75 km, 0.98 km, 1.25 km and 63?, respectively. Furthermore, using the algorithm of Horiuchi et al., (1995), simultaneous focal mechanism solutions of individual earthquakes and recent stress regimes along with R-values have been determined for the five clusters. As a result, it was found out that NW-SE trending trans-tensional stress structures leading mostly normal and oblique faulting systems are predominant in Tekirdağ Basin, Çınarcık Basin, Yalova and Gemlik clusters. Nevertheless, Ganos Cluster was presented as a dextral strike-slip deformation system through the transition from normal to reverse faulting system. Vertically oriented Sigma-2 axis was obtained for the Ganos Offshore cluster, whereas in all other regions Sigma-1 axis was vertical.
Imaging fluid-rich zones by magnetotelluric method at South Marmara
Magnetotelluric data at sixteen sounding locations along two parallel profiles at south Marmara region were collected to improve the understanding of the crustal electrical conductivity structure. The PW (~40 km) and PE (~35 km) profiles yield data in the frequency range 320-0.0005 Hz. Remote reference technique (Gamble et al., 1979) was used to enhance the data quality. The effects of near surface inhomogenities (galvanic distortions) were removed from the data utilizing Groom and Bailey (1989) decomposition. Following the decomposition, the geoelectric strikes of N102°E and N72°E were calculated for the PW and PE profiles, respectively. The data were rotated using these strike directions. Following this step, they were modeled in two dimensions using the inversion code developed by Ogawa and Uchida (Ogawa and Uchida, 1996), with error floors of 10 per cent for apparent resistivity and 2.86° for phase of both TE (transverse electric) and TM (transverse magnetic) modes. Resulting models suggest that the South Marmara fault possibly corresponds to a lateral resistive boundary between Manyas-Karacabey basin and Bandırma-Karadağ uplift on the PW and Uluabat uplift and Mudanya uplift on the PE profile. The features characterized in geoelectric models also correlate with known faults in the study area. While the conductive zones beneath the northern ends of the profiles at depths greater than 13 km are attributed to partially melting in the crust or the existence of deep crustal fluids below the impermeable layers, the highly resistive zones are associated with low fluid condition and high rigidity.
BRTR (PS-43) diziniminin sismik arka plan gürültü analizi
The seismic background noise variation of BRTR array, composed of two sub arrays located in Ankara and in Kırıkkale-Keskin, has been investigated by calculating Power Spectral Density and Probability Density Functions for seasonal and diurnal noise variations between 2005 and 2011. PSDs were computed within the frequency range of 100 s ? 10 Hz. The results show us a little change in noise conditions in terms of time and location. Especially, noise level changes were observed at 3-5 Hz in diurnal variations at Keskin array and there is a 5-7 dB difference in day and night time in cultural noise band (1-10 Hz). On the other hand, noise levels of medium period array are high in 1-2 Hz frequency range. High noise levels were observed in daily working times when we compared to night-time in cultural noise band. The seasonal background noise variation at both sites also shows very similar properties to each other. Since both arrays consist of borehole instruments and away from the coasts, we saw a small change in noise levels caused by microseism. Comparison between Keskin short period array and Ankara medium period array show us Keskin array is quiter than Ankara array. Finally, to analyze contribution of BRTR array to IMS network for detection capabilities, six-year long event bulletin data were retrieved between 2005 and 2011 to create annual seismic detection threshold maps for BRTR. These results also depend on the changes in IMS network configuration and IMS network stations data availability.
Determination of strain accumulation along Tuzla fault
Aegean Region is one of the most deforming parts of Alpine-Himalayan belt which isbounded by the Hellenic trench, mainland Greece and western Turkey. Anatolian plate isplaced between the Eurasian and African plates. The Anatolian plate moves counter-clockwise and it is observed that the velocity of this movement grows through west. AegeanRegion is an important place for geoscientists as it is a seismically active region whichincludes normal and lateral faults. In addition, the third biggest city in Turkey, İzmir is alsosettled in the region with nearly 4 million population.This study is carried out on the Tuzla Fault which is a right lateral strike slip fault,begins from Gaziemir district and dives under the sea from the Doganbey Cape. Historicalevidence shows that catastrophic earthquakes occurred on the Tuzla Fault. The Tuzla Faulthas created moderate earthquakes in the past two decades and still has the potential to createlarge earthquakes.The main objective of this study is to determine strain accumulation along the fault byusing the results of the GPS campaigns carried out in the study area. Analysis of GPS datashow that velocities reach up to 28.54 mm/yr ?1.90 mm/yr. and are consistent with thepresent-day tectonic deformation of the region. Principal components of crustal strain alongthe Tuzla Fault reach up to 140 nanostrain/yr. The strain rates are in accord with seismicityand the directions of the calculated strain rates reflect the expected behavior of NE - SWextension of the Aegean Region.
Numerical modelling of Amasra and Fatsa tsunamis in the Black Sea
Two historical tsunamis in the Black Sea have been investigated in this study, employing models obtained from the studies of each event: the Fatsa Tsunami, triggered by the Erzincan Earthquake (Ms=8.0, on 26 December 1939); and the Amasra Tsunami, triggered by the Bartın Earthquake (Ms=6.6, on 3 September 1968). Seismic source parameters of Erzincan and Bartın Earthquakes were investigated on the based of literature and data available for tsunami modeling purposes. In the study, tsunami models from two earthquakes occurred in sea and on land were generated by the NAMIDANCE Tsunami Simulation and Visualization code, using the seismic source parameters. In the Black Sea region, tsunami impact areas were presented by calculating tsunami arriving time, generation of wave, wave propagation and height of wave based on numerical simulation.
Investigation of post seismic deformatoin in Karliova (Turkey) inferred from Insar anaysis
Interferometric Synthetic Aperture Radar is a new technique used in investigating the deformations occurring on the earth surface. By its capability of providing much broader domain coverage as compared to any other available techniques, geologists are using the interferometric synthetic aperture radar technique in many areas of their research and primarily crustal deformation. The purpose of this study is to observe the post-seismic impacts using the interferometry technique. In line with this purpose, the effects of deformations resulting from post-seismic impacts of earthquakes have been analyzed with the interferometric synthetic aperture radar technique. The region Karlıova was chosen as the study area. Karlıova-Bingöl-Erzincan triangle is located in the junction of the two most important transform faults: the North Anatolian Fault (NAF) and the East Anatolian Fault (EAF). The area between that two transform faults is a place where KDGB and KB-GD trending cross-fault systems is developed. Therefore, it is the region of the highest concentrations of the active faults in Turkey. The earthquakes that occurred in this region between 2005-2008 were examined in detail. With this study using the InSAR technique, for two separate earthquakes (10.12.2005 Mw=5.2 Depth:18 km and 26.08.2007 Mw=5.1 Depth:5km), a deformation in the direction of the satellite view of 56 mm during 2005-2006 and 140 mm during 2006-2008 has been determined respectively. In the interferograms generated by using the radar images in the C-band, one fringe theoretically corresponds to a deformation of half the radar wavelength. Therefore, deformations less than 28 mm in the area cannot be determined by the InSAR technique. The SAR data differ from the GPS data in time. During this time range, 17 earthquakes of moderate magnitude have also occurred in the area. The results differ from each other significantly since InSAR measurements contain post-seismic deformation while GPS observations do not. The spatial density of GPS sites is limited. Moreover, noisy interferograms due to atmospheric signal, and phase unwrapping errors affects the accuracy assessment and interpretation of the results.
3-D P wave velocity structure of Marmara region using local earthquake tomography
The 3D P wave velocity model of upper and lower crust of the Marmara Region between 40.20 - 41.20 N and 26.50 - 30.50 E is obtained by tomographic inversion (Simulps) of 47034 P wave arrivals of local earthquakes recorded at 90 land stations, 30 OBO stations and 14162 shot arrivals recorded at 35 OBO stations (Seismarmara Survey, 2001) between October 2009 and December 2012. We first obtained a 1D minimum model with Velest code in order to use it as an initial model for 3D inversion with 648 well located earthquakes located within the study area. We first developed a 1D model by VELEST code then used it as an initial model for 3D tomography. After trial 3D inversions we decided to create a more adequate initial model for 3D inversion. Choosing the initial model we estimated the 3D P wave velocity model representing the whole region both for land and sea. The results are tested by making Checkerboard Test, Restoring Resolution Test and Characteristic Test, and the reliable areas of the resulting model is defined in terms of RDE, DWS, SF and Hit count distributions. By taking cross sections from the resulting model we observed the vertical velocity change along profiles crossing both land and sea. All the profiles crossing the basins showed that the high velocities of lower crust make extensions towards the basin area which looks like the force that gives a shape to the basins. Under the north of the Central Basin and Çınarcık Basin high velocity zones appeared which look like resisting walls holding the north of the basins between 5 km and 15 km. The same is also observed under the southern Tekirdağ Basin between 5 km and 15 km. These extensions of lower crust towards the basins appeared with an average velocity of 6.3 km/s. These extensions might be the result of the deformation due the shear in the region and it is also interpreted that the development of these high velocities coincides with the development of the basins. Thus, both the basins and the high velocity zones around them might be resulted from the entrance of the NAF into the Marmara Sea when also a shear regime is dominated due to the resistance of the northern Marmara Region (Yılmaz, 2010). The seismicity is observed between 5 km and 15 km after the 3D location of the earthquakes. The locations of the earthquakes improved and the seismogenic zone is determined well, between 5 km and 15 km. The depths of the pre-kinematic basement and crystalline basement showed great differences under the sea. It is observed that the velocity under sea becomes compatible with land after 8 km.
Collapse risk estimation of reinforced concrete buildings
In this study, collapse risks of five-storey RC frame buildings are estimated analytically using advance mathematical model. The concentration of this study is on advanced nonlinear analysis of the building including nonlinear modeling of columns and beams with their shear capacities. Collapse fragility curves are obtained in terms of spectral acceleration corresponding to dominant natural period of the building. The collapse risk of the building is obtained through integration of collapse fragility curves of models and corresponding hazard curve. In the first chapter of this study, the scope of the work and literature survey have been given. In the second chapter, the methodology of estimating collapse risk in an analytical way has been introduced. The steps of the proposed methodology for collapse risk estimation have been explained briefly. In the third chapter, mathematical modeling of the buildings has been given in details in terms of non-linear material properties, lump and distributed plasticity approach for structural members. In the fourth chapter, objectives of the analysis, the strong ground motion records and hazard curves used in the analysis phase have been presented. In the fifth chapter, fragility curves are obtained and the collapse risk has been calculated for each building under consideration. In the last chapter, the conclusions are presented.
1-D local crustal structures from seismological data in the Cyprus Subduction zone and Antalya Bay
The eastern Mediterranean is a tectonically complex region, where long-term subduction and accretion processes have shaped the overall evolution. Recently, many seismic tomography studies have shown subducted slabs of the Neo-Tethyan lithosphere, continuing its subduction in the Hellenic trench, stalled in the Cyprus trench and being torn near the intersection between them. Antalya bay is a key region located on the western flank of the Cyprus Subduction Zone (CSZ), close to the junction between the Hellenic and Cyprus Arcs. Here deep earthquakes are nucleated, which otherwise cannot be seen anywhere else along the CSZ. For this reason, we focus our attention specifically to the Antalya Bay area but also the remaining parts of the CSZ. Several regional studies have been carried out to define the velocity structure beneath the region but none have been able to locate the CSZ. One of the main reasons for this was the lack of incorporation of a wide seismic network in those regional studies. We compile a large catalog of seismicity and relocate earthquakes to infer 1D local crustal structure using the clusters of seismicity. We used seismic data between 2005 ? 2011 which are recorded at more than 250 seismic stations operated by several agencies and portable deployments. The data-set is composed of over 10,000 events and earthquakes can be grouped in several distinct clus-ters. We defined five of these clusters, where the total number of events is more than 4500, among which we selected over 2000 events with the highest data quality. 1-D local P-wave velocity models are developed using this high quality data-set and the earthquakes are relocated using the local velocity models. The compiled and reanalyzed data will contribute to perform local earthquake to-mography. Moreover, obtained local velocity models represent a fundamental step towards an improved seismic tomography studies in a very crucial region in the eastern Mediterranean.