The North Anatolian Fault Zone (NAFZ) in Turkey is a major continental strike-slip fault, 1200 km long and with a current slip rate of 25 mm/yr. Historical records show that the NAFZ is capable of producing high-magnitude earthquakes, activating different segments of the fault in a westward progression. Currently, the NAFZ poses a major seismic hazard for the city of Istanbul, which is situated close to one of the two strands into which the fault splays in northwestern Turkey. Understanding of fault zone structure and properties at depth is essential to constrain where deformation occurs within the lithosphere and how strain localises with depth. In fact, geodynamic models explaining surface deformation require knowledge of the width and depth extent of the fault zone in both the crust and upper mantle. In this framework, this thesis aims to provide better constraints on fault zone geometry within the lithosphere. To achieve this objective P and S wave teleseismic tomography have been applied to the data recorded by a dense array of broadband seismic stations (DANA, Dense Array for Northern Anatolia); through teleseismic tomography it was possible to image the NAFZ structure in both the crust and uppermost mantle. In addition, joint inversion i of P-wave teleseismic data and local earthquake data collected using the same array provided a greatly improved resolution within the upper 20 km of the crust. Results from this work highlighted the presence of a shear zone associated to the northern branch of the NAFZ in the study area. The fault zone appears to be 15 km wide within the upper crust and narrows to < 10 km within the lower crust and to Moho depth. In the uppermost mantle its width is constrained to be 30 to 50 km.

This study aims to determine the chemical (anion-cation) and isotopic compositions (&amp / #948 / 18O-&amp / #948 / D-3H) of the geothermal waters along the North Anatolian Fault Zone (NAFZ) and highlight any possible seismicity-induced temporal variations during the course of two years (2002-2003) monitoring programme. The geothermal sites are alligned along a 800 km transect of the NAFZ and are, from west to east, Yalova, Efteni, Bolu, Mudurnu, Seben, KurSunlu, Hamam&ouml / z&uuml / , G&ouml / zlek and ReSadiye. The thermal waters of NAFZ are dominantly Na-HCO3, whereas the cold waters are dominantly Ca-HCO3 in character. The highest temperature (72.3&amp / #61616 / C) is recorded in Seben. The hot waters are slightly acidic to alkaline in character with pH values ranging between 5.92-7.97, while the cold waters are comparatively more alkaline with pH values between 6.50-8.83. Both hot and the cold waters are meteoric in origin. The hot waters have lower &amp / #948 / 18O-&amp / #948 / D and tritium values suggesting higher recharge altitudes for aquifers and longer residence times for waters, respectively, in the geothermal system (compared to the cold waters). Temporal variations are detected in both ionic and isotopic compositions of the cold and the hot waters, and these reflect seasonal variations for cold and seismicity-induced variations for hot waters. Although no major earthquakes (M&gt / 5) occurred along the NAFZ during the monitoring period, temporal variations recorded in Cl and 3H, and to a lesser extent in Ca and SO4 contents seem to correlate with seismicity along the NAFZ. In this respect, Yalova field deserves the particular attention since seismicity induced variations were better recorded in this field.

Over the past century, a series of large (> 6.5) magnitude earthquakes have struck along the North Anatolian Fault Zone (NAFZ) in Turkey in a roughly East to West progression. The progression of this earthquake sequence began in 1939 with the Ms 8.0 earthquake near the town of Erzincan and continued westward, with two of the most recent ruptures occurring near the Sea of Marmara in 1999. The sequential nature of ruptures along this fault zone implies that there is a connection between the location of the previous rupture and that of the future rupture zones. This study focuses on understanding how previous rupture events and tectonic influences affect the stress regime of the NAFZ and how these stress changes affect the probability of future rupture along any unbroken segments of the fault zone using a two dimensional finite element modeling program. In this study, stress changes due to an earthquake are estimated using the slip history of the event, estimations of rock and fault properties along the fault zone (elastic parameters), and the far-field tectonic influence due to plate motions. Stress changes are not measured directly. The stress regime is then used to calculate the probability of rupture along another segment of the fault zone. This study found that when improper estimates of rock properties are utilized, the stress changes may be under- or over- estimated by as much as 350% or more. Because these calculated stress changes are used in probability calculations, the estimates of probability can be off by as much as 20%. A two dimensional model was built to reflect the interpreted geophysical and geological variations in elastic parameters and the 1939 through 1999 rupture sequence was modeled. The far-field tectonic influence due to plate motions contributed between 1 and 4 bars of stress to the unbroken segments of the fault zone while earthquake events transferred up to 50 bars of stress to the adjacent portions of the fault zone. The 1999 rupture events near Izmit and Düzce have increased the probability of rupture during the next ten years along faults in the Marmara Sea to 38% while decreasing the probability of rupture along the faults near the city of Bursa by ~6%. Large amounts of strain accumulation are interpreted along faults in the Marmara Sea, further compounding the case for a large rupture event occurring in that area in the future. / Ph. D.

<p>Magnetic surveys are one of the principal geophysical methods employed to map the structure of basement rocks deeply buried below cover strata. In resource studies, aeromagnetic surveys are commonly acquired at regional scales (100-1000’s km2) while very few studies have attempted to resolve basement structures at site-scale (<10 >km2). In this study, high-resolution lake-based magnetic survey methods were evaluated for mapping of deeply-buried basement faults (Küçükçekmece Lagoon, Turkey; 6 km2) and a suspected meteorite impact crater (Charity Shoal, Lake Ontario; 9 km2). Total magnetic intensity (TMI) surveys were acquired using a single Overhauser magnetometer with 50-150 m line spacing. Interpretation of the magnetic data was aided by forward modelling of TMI data and depth to basement estimates using Euler and analytic signal methods. Total magnetic intensity (TMI) maps of Küçükçekmece Lagoon identify several north-northwest trending (340-350°) magnetic lineaments that are aligned with strike-slip faults mapped from offshore seismic data. The pattern of magnetic anomalies in the lagoon is consistent with extensional normal faulting of bedrock and lake sediments. Magnetic results from Charity Shoal reveal a large (>1400 nT) parabolic-shaped magnetic anomaly centered over the crater basin and an annular magnetic high (40-50 nT) corresponding with the basin rim. Modelling results exclude the origin of the CSS as a shallow glacial erosional or karst sinkhole feature and are most consistent with a pre-Paleozoic meteorite impact in the Precambrian basement.</p> / Master of Science (MSc)

Turkey is one of the most earthquake prone countries in the world. The study area, Erbaa, is located in a seismically active fault zone known as North Anatolian Fault Zone (NAFZ). Erbaa is one of the towns of Tokat located in the Middle Black Sea Region. According to the Earthquake zoning map of Turkey, the study area is in the First Degree Earthquake Zone. The city center of Erbaa (Tokat) was previously settled on the left embankment of Kelkit River. After the disastrous 1942 Niksar-Erbaa earthquake (Mw = 7.2), the settlement was moved southwards. From the period of 1900s, several earthquakes occurred in this region and around Erbaa. The 1942 earthquake is the most destructive earthquake in the center of Erbaa settlement. In this study, the geological and geotechnical properties of the study area were investigated by detailed site investigations. The Erbaa settlement is located on alluvial and Pliocene deposits. The Pliocene clay, silt, sand, and gravel layers exist in the southern part of Erbaa. Alluvium in Erbaa region consists of gravelly, sandy, silty, and clayey layers. The alluvial deposits are composed of stratified materials of heterogeneous grain sizes, derived from various geological units in the vicinity. The main objective of this study is to prepare a seismic microzonation map of the study area for urban planning purposes since it is getting more essential to plan new settlements considering safe development strategies after the disastrous earthquakes. In this respect, seismic hazard analyses were performed to deterministically assess the seismic hazard of the study area. Afterwards, the essential ground motions were predicted regarding near fault effects as the study area is settled on an active fault zone. 1-D equivalent linear site response analyses were carried out to evaluate the site effects in the study area. Amplification values obtained from site response analyses reveal that the soil layers in the study area is quite rigid. Furthermore, liquefaction potential and post liquefaction effects including lateral spreading and vertical settlement were also delineated for the study area. The above-mentioned parameters were taken into account in order to prepare a final seismic microzonation map of the study area. The layers were evaluated on the basis of overlay methodologies including Multi-Criteria Decision Analysis (MCDA). Two different MCDA techniques, Simple Additive Weighting (SAW) and Analytical Hierarchical Process (AHP), were carried out in GIS environment. The seismic microzonation maps prepared by SAW and AHP methods are compared to obtain a final seismic microzonation map. Finally, the map derived from the AHP method is proposed to be the final seismic microzonation map of Erbaa. As an overall conclusion, the northwestern part of the study area where the loose alluvial units exist is found to be vulnerable to earthquake-induced deformations. On the other hand, the Pliocene units in the southern and alluvial units in the northeastern part are quite resistant to earthquake effects. In addition, the proposed final seismic microzonation map should be considered by urban planners and policy makers during urban planning projects in Erbaa.