Ph.D. Theses
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Browsing Ph.D. Theses by Subject "Geology, Structural -- Turkey."
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Item Crust and upper-mantle imaging by using P and S receiver functions in different tectonic regimes(Thesis (Ph.D.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2015., 2015.) Kahraman, Metin.; Türkelli, Niyazi.P and S receiver functions (RF) are effective tools to solve crustal and upper-mantle velocity contrasts. In this respect, RFs are utilized to image three different tectonic regimes of Anatolia. Firstly, western segment of the North Anatolian Fault Zone (NAFZ) is inspected by data from a dense broadband network (Dense Array for North-Anatolia - DANA) of 71 seismic stations with a nominal station spacing of 7 km in the vicinity of the 1999 Izmit earthquake. High resolved 2-D cross-section images reveal previously unkown small-scale structures and fault geometries in the crust and upper-mantle. Secondly, N-S extension dominated Western Anatolia (WA) is observed by 47 permanent broad-band stations. Totally, 3563 high signals to noise ratio P wave RFs with cut-off frequency of ~1 Hz are obtained among 43146 teleseismic earthquakes. Crustal differences, sharp Moho changes and low velocity zones are defined by 2-D cross-sections in the region. Lastly, Isparta Angle (IA) is imaged by data from a temporary and permanent broad-band seismic network that is composed 42 seismic stations. 4501 P wave RFs are used to resolve upper crustal and Moho depths and 946 S wave RFs are operated to figure out lithosphericasthenospheric boundary (LAB). Migrated P wave RFs cross-sections present Moho anomalies and African slab in the crust of IA. On the other hand, migrated S wave RFs cross-sections show variation of LAB boundary between ~50 to ~90 km depth range.Item Interseismic behavior along the North Anatolian fault in the Marmara region using 3D structure(Thesis (Ph.D.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2022., 2022) Yılmaz, Zeynep.; Konca, Ali Özgün.A series of earthquakes occurred along the North Anatolian Fault (NAF) during the 20th century, primarily migrating from east to west. The only part of the NAF that has not broken is under the Marmara Sea. The Main Marmara Fault (MMF), the NAF’s northern branch, is the most active one, with the highest slip rate amongst the several branches of the NAF. Since the seismic gap of ~150 km is beneath the sea, the geodetic data is not sufficient to constrain the full fault coupling, particularly in the Central Marmara. Nevertheless, the current data does imply that the GNSS vectors along the northern coast of the Marmara Sea are smaller than expected. One interpretation is that the MMF has heterogeneous interseismic coupling with creeping and locked segments. Another explanation is that the fault is locked, but the strain is asymmetrically localized around the MMF as a result of the deep basins. In this study, the competing effects of weak interseismic locking of the MMF and deep basins around the fault are studied by developing a 3-D finite element model for the Marmara Region, which includes a realistic topography, the 3-D geometry of the main fault, and basins, and using the geodetic data as a constraint. Our findings show that the deep basins confine the interseismic strain in the fault vicinity, and using a homogeneous half-space model leads to a slight underestimation of the locking depth. Our 3-D model shows that while the basins have some effects on strain localization, the heterogeneity of interseismic coupling is necessary to explain the observed GNSS data. We infer a change in the locking depth at the Ganos Bend between the strongly coupled Ganos and the weakly coupled Western Marmara. Seismic studies also indicate that these two segments vary considerably in background seismicity. The 50 km creeping segment coincides well with repeating earthquakes and higher rates of diffuse seismicity. Variations in regional stresses and earthquake focal mechanisms, including the 2019 Silivri earthquake sequence, are compatible with the dilatational quadrants in the region due to the loading caused by the interseismic creep of the Western Marmara.Item Lithospheric structure of the western Turkey and aegean region(Thesis (Ph.D.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2019., 2019.) Afacan Ergün, Tuğçe.; Karabulut, Hayrullah.Aegean-Anatolia region undergoes an intense internal deformation as evidenced by the existence of major active faults, intense seismic activity and the marked thinning of the crust. It makes the region center of attraction to the study the interaction between the deep structure with the surface deformation. The aim of this study is to provide constraints on the crustal and uppermost mantle structure by using seismic data of permanent broad-band network of Kandilli Observatory and Earthquake Research Institute (KOERI-RETMC), and a temporary array of Seismic Imaging beneath Aegean-Anatolia Domain (SIMBAAD) experiment. Seismic stations of Republic of Turkey Prime Ministry Disaster and Emergency Management Presidency (AFAD), Incorporated Research Institutions for Seismology (IRIS) and previous experiment called Western Anatolia Seismic Recording Experiment (WASRE) were used to complement the network. In this regard we present two high resolution lithospheric images along a ~650 km transect crossing western Anatolia at 28°E longitude from the Black Sea to the Mediterranean and a ~550 km transect crossing central Anatolia at 30.5°E longitude. A total of 5250 receiver functions are computed from the records of teleseismic earthquakes at 40 broadband seismic stations for each of the profiles with an average spacing of ~ 15 km. Lateral variations of crustal thickness, Vp/Vs are inferred from both H-K, and common conversion point stacks (CCP). In order to have a better idea on the accuracy of the estimated crustal parameters we also performed a search scheme based on the Neigboorhood Algorithm. The receiver functions are inverted for a 1-D layered medium to determine the layer thicknesses, Vs and Vp/Vs. The CCP images reveals a longwavelength variations of Moho depth from ~31 km in the Thrace basin to ~25 km beneath the Marmara Sea, ~25 km beneath the Menderes Massif and ~20 km on the coast of the Mediterranean on the western Anatolia transcent. On the eastern transect, a smooth Moho topography is observed with a sharp discontinuity at depths ranging from 34 km beneath the Black Sea coast, ~35 km beneath the Sakarya Zone with mafic composition to 43 km beneath the Antalya Bay on the central Anatolia profile. The Moho of the subducted African lithosphere is imprinted between ~40 and ~60 km depth at the southern end of the western Anatolia profile, dipping northward where the subducted Cyprus lithosphere is observed dipping northward with an angle of 40◦ between ~40 and ~100 km depths beneath the Antalya Bay on the central Anatolia transect.