Jeodezi

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Browsing Jeodezi by Author "Bulut, Fatih."

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    Earthquake cycle of the North Anatolian Fault along the rupture zone of the August 17, 1668 Great Anatolian Earthquake
    (Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2021., 2021.) Yıldırım, Sevil Cansu.; Bulut, Fatih.
    We investigated the earthquake cycle along the 450-km rupture zone of the August 17, 1668 Great Anatolian Earthquake (M8.1) combining GPS and earthquake data. We elaborated on elastic rebound theory investigating creeping and locked stages of the individual fault segments. We simultaneously estimated segment-based slip rates and locking depths. Slip rates are used to estimate preliminary inter-seismic slip stor ages assuming fully locked fault segments right after the mainshocks. Misfits between co-seismic slips and preliminary inter-seismic slip storages indicate that the fault does not store slip for a while after major earthquakes. Our analysis shows a partitioning between creeping and locked stages. Only along one segment, the 1943 M7.7 rupture, creep played a minor role during the seismic cycle (0.1%). Along the 1939 M7.9, 1957 M7.0, 1967 M7.2, and 1999 M7.5 ruptures, creep played a considerable role (16.9%, 22.2%, 17.9% and 22.4%, respectively). Along the 1942 M7.1, 1944 M7.4, 1999 M7.1 rupture zones, creep played a substantial role, and covered almost half of the seismic cycle (54.4%, 44.0% and 48.3%, respectively). The segments host currently differ ent earthquake potentials as they have distinctive creeping/locking rates despite the fact that they are exposed to similar deformation rates (between 19.5±0.5 – 24.2±0.3 mm/y). Our results show that slip rates systematically accelerate from the east to the west. Failure of the NAFZ will probably end at the western segments within 239±3 years. The space-time pattern of the earthquakes during the last three complete and the current incomplete cycles confirms that the failure of the NAFZ starts from the east, and systematically migrate to the west deceleratingly.
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    Earthquake potential of the East Anatolian Fault
    (Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2020., 2020.) Uçan, Kaan Alper.; Bulut, Fatih.
    This study aims to forecast magnitude of future strong (6.0 M <7.0) and major (7.0 M <8.0) earthquakes along the East Anatolian Fault Zone (EAFZ hereafter), which is a seismically active plate boundary between Arabian and Anatolian plates. In this context, we investigated segmentation of the EAFZ reviewing previous studies on structural variation zone and historical earthquakes. We analysed the combined GPS velocity eld to obtain back-slips using steepest descent/gradient inversion method. The method projects GPS-derived back-slip rates onto the fault plane using Okada's quasi-in nite space model simulating elastic Green's functions to obtain on-fault slip de cit rates. Resulting slip de cit rates are used to estimate present-day slip budgets on each fault segment. We also analysed along-fault b-value distribution to verify if it can be used to di erentiate between locked and creeping patches. Our results show that the EAFZ currently have a 1.51 m average slip. We suggest that the EAFZ is split into eight fault segments generating strong/major earthquakes. The January 24, 2020 Elaz g earthquake (M 6.8) ruptured the Sivrice-Pütürge segment verifying our segmentation model and magnitude forecasts for future earthquakes. We found no slip de cit accumulation observed on the Hacılar segment. Remaining six segments are able to generate three strong, three major earthquakes. Currently Karlıova, Kaleönü-Beyhan, Palu-Sivrice, Taştepe, Çelikhan-Erkenek, Gölbaşı-Pazarcık segments can currently generate M 7.0, M 6.9, M 7.1, M 6.8, M 6.9, M 7.4 earthquakes, respectively. Karlıova, Palu-Sivrice, Taştepe, Gölbaşı-Pazarcık segments currently have the potential to generate previous strong/major earthquakes they hosted. We observed a reverse correlation between slip de cit rates and b-values verifying that b-value can be used to discriminate locked and creeping fault segments.
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    Evolution of earthquake hazards in İzmir response to M4+ earthquakes
    (Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2022., 2022) Yılmaz, Tolunay.; Bulut, Fatih.
    In this study, we investigated the evolution of earthquake hazards in İzmir (Turkey), the city accommodating the third highest population in Turkey in response to M4+ size earthquakes analyzing Coulomb stress change on all potential receiver faults in the target region. The city is located in western Turkey, which falls under Aegean tectonics, which leads to very high earthquake activity in the region. Fault segments with increasing Coulomb stress host high earthquake activity verifying that M4+ earthquakes prepone the generation processes of some earthquakes. In contrast, fault segments with decreasing Coulomb stress host earthquake silence verifying that M4+ earthquakes postpone the generation processes of some earthquakes. Hence, M4+ earthquakes played a critical role in the occurrence of the 2021 Samos Earthquake (M 6.92) as they increased the Coulomb stress above 0.1 bars along its rupture plane. To sum up, our results show that Coulomb stress change generated by M4+ earthquakes plays a critical role in earthquake activity in the vicinity of İzmir, Turkey.
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    Seismo-geodetic characterization of the Tuzla Fault (İzmir/Turkey) : |its kinematics and earthquake potential
    (Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2020., 2020.) Gelin, Bengisu.; Bulut, Fatih.
    Izmir, the third largest city of Turkey, located in western coast of the country is seismically super active due to Hellenic subduction zone and extensional back-arc basin under the Aegean Sea. This tectonic environment has attened the cities in the region again and again as reported in the historical records. Hence, investigating the seismically active faults in the region is crucial to elaborate on earthquake hazard for the cities along the Western Turkey. In this context, we jointly analyzed geodetic, geological and seismological data to investigate latest failure, present day deformation, slip accumulation and fault kinematics along the Tuzla Fault. Historical and recent earthquakes were investigated to determine the latest failure of the Fault and result reveals that there is no evidence of a large earthquake failing the Fault entirely since 1688. Six epochs GPS measurements of fteen stations were analyzed for the time period of 2009-2017 to obtain horizontal tectonic slip rates along the Tuzla Fault. As a result, overall southwest movements change between 26.67 1.03 mm/yr and 28.96 1.00 mm/yr with respect to Eurasia. Di erential slip rates range between 1.00 to 2.00 mm/yr. Magnitude calculations were done for Tuzla Fault and its segments seperately. Tuzla Fault has currently a potential to generate a strong earthquake up to M6.2-M6.8. Strain analysis results show that the Çatalca Segment and northern Orhanlı Segment, accumulates high shear strain and therefore accommodate higher potential for co-seismic slip. According to fault plane solutions and maximum shear strain values and planes, Cumalı Segment has dextral characteristic, however, maximum shear strain planes indicates sinistral structure in Çatalca Segment.
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    Slip and strain partitioning across subparallel strands of the north Anatolian fault in the Marmara Region
    (Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2021., 2021.) Okur, Yağızalp.; Bulut, Fatih.
    Marmara Region hosts a substantial part of the inhabitants in Turkey, more than 30% of the total population in the cities of Istanbul, Bursa, and Kocaeli. This region has experienced a number of large earthquakes in the past and still under threat of de structive earthquakes in the future. There, subparallel strands of the North Anatolian Fault (NAF) expand into the region distributing the earthquake hazards across the whole region. In this context, it is a key issue to investigate how the tectonic process is distributed between these sub-parallel strands in order to discriminate their indi vidual earthquake hazards. In this context, we jointly used historical earthquakes and GPS slip rates to quantify the slip and strain partitioning of the subparallel strands of the fault system. In addition to all available slip rates, we analyzed 50 new GPS sites (38 continuous and 12 campaign-based) to intensify the GPS network in the re gion. Historical earthquake records since 100 AD shows that 76.4% of the total slip is stored on the northern strand. The rest of the slip is partitioned between middle and southern strands as 11.8% and 11.8% respectively. These ratios are almost confirmed by GPS observations with 76.8%, 12.7%, and 10.5% slip ratios for northern, middle, and southern strands respectively. In conclusion, the northern strand of the NAF is the most active compared to the middle and southern strands and therefore accommo dates the highest earthquake hazards in the Marmara region. As middle and southern strands deform at substantially slower slip rates, they accommodate relatively much lower earthquake hazards.