Yazar "Bektas, Ozcan" seçeneğine göre listele

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    3D MODELLING AND STRUCTURAL INVESTIGATION OF THE CENTRAL VOLCANICS IN SLOVAKIA USING MAGNETIC DATA
    (Carpathian Assoc Environment And Earth Sciences, 2013) Bektas, Ozcan; Buyuksarac, Aydin; Rozimant, Kamil
    The Central volcanics, located in central part of Slovakia, is characterized by intense andesitic volcanic activity that resulted in the formation of stratavolcanoes and dome complexes of Middle and Late Miocene age. The basement area has been affected tectonically resulting in the formation of horst and graben structures. The Central Slovakian Volcanic Field (CSVF) exhibits a very complex magnetic anomaly. A 3-km upward continued magnetic map indicates a deep-seated source for this magmatism. The pseudogravity transformation of the upward continued anomaly has also been constructed. This anomaly was modelled by a 3D-method. The anomalous body lies between the depths of 4.4 to 8.5 km beneath the surface of the CSVF. Volcanic structures and some lineaments are presented on the maxima of the horizontal gradient of the pseudogravity anomaly map. They are well correlated with the structural map of CSVF.
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    A Comparative Evaluation of Earthquake Code Change on Seismic Parameter and Structural Analysis; A case of Turkey
    (Springer Heidelberg, 2022) Buyuksarac, Aydin; Isik, Ercan; Bektas, Ozcan
    Turkey, which is one of the countries with high seismic risk, has made significant changes in both seismic risk maps and seismic design codes over time by adapting to these developments. Information about the important changes in the last two earthquake maps and provisions in Turkey was given and the effects of these changes on structural and seismic parameters were examined in this study. In order to make comparisons of seismic parameters, seven different settlements from seven different geographical regions in Turkey were taken into account which have the same seismic risk in the previous earthquake risk map. Seismic moments were also calculated separately for these locations to describe the intensity of future tectonic activity. With the current earthquake hazard map, geographical location-specific earthquake risk has been started to be used instead of regional risk. For the selected settlements with the same seismic risk in the previous map, the seismic risks were found high in some and low in some with the current hazard map. In addition, structural analyses were carried out for the sample reinforced-concrete building with the same structural characteristics in these seven different settlements in order to reveal the effect of the code and map change on the structural analysis. While the target displacements expected from the structures for the settlements with the same seismic risk take the same values, the target displacements are obtained differently for each, since the specific design spectrum is used for each location with the current map.
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    Crustal Structure of Turkey from Aeromagnetic, Gravity and Deep Seismic Reflection Data
    (Springer, 2012) Ates, Abdullah; Bilim, Funda; Buyuksarac, Aydin; Aydemir, Attila; Bektas, Ozcan; Aslan, Yasemin
    In this paper, aeromagnetic and gravity anomalies obtained from the General Directorate of Mineral Research and Exploration were subjected to upward continuation to 3 km from the ground surface to suppress shallow effects and to expose only regional, deep sources. Then, a reduction to pole (RTP) map of aeromagnetic anomalies was produced from the 3 km upward continued data. A sinuous boundary to the south of Turkey is observed in the RTP map that may indicate the suture zone between the Anatolides and African/Arabian Plates in the closure time of the Tethys Ocean. The sinuous boundary can be correlated with the recent palaeo-tectonic maps. The southern part of the sinuous boundary is quite different and less magnetic in comparison with the northern block. In addition, maxspots maps of the aeromagnetic and gravity anomalies were produced to find out and enhance the boundaries of tectonic units. Crustal thickness, recently calculated and mapped for the western Turkey, is also extended to the whole of Turkey, and the crustal thicknesses are correlated with the previous seismological findings and deep seismic sections. The average crustal thickness calculations using the gravity data are about 28 km along the coastal regions and increase up to 42 km through the Iranian border in the east of Turkey. Density and susceptibility values used as parameters for construction of two-dimensional (2D) gravity and magnetic models were compiled in a table from different localities of Turkey. 2D models indicate that all of the anomalous masses are located in the upper crust, and this could be well correlated with the earthquakes which occurred at shallow depths.
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    Evaluation of Gravity and Aeromagnetic Anomalies for the Deep Structure and Possibility of Hydrocarbon Potential of the Region Surrounding Lake Van, Eastern Anatolia, Turkey
    (Springer, 2014) Aydemir, Attila; Ates, Abdullah; Bilim, Funda; Buyuksarac, Aydin; Bektas, Ozcan
    The North Anatolian Fault (NAF) is not observed on the surface beyond 40 km southeast of Karliova town toward the western shoreline of Lake Van. Various amplitudes of gravity and aeromagnetic anomalies are observed around the lake and surrounding region. In the gravity anomaly map, contour intensity is observed from the north of Mus city center toward Lake Van. There is a possibility that the NAF extends from here to the lake. Because there is no gravity data within the lake, the extension of the NAF is unknown and uncertain in the lake and to the east. Meanwhile, it is observed from the aeromagnetic anomalies that there are several positive and negative amplitude anomalies aligned around a slightly curved line in the east-west direction. The same curvature becomes much clearer in the analytic signal transformation map. The volcanic mountains of Nemrut and Suphan, and magnetic anomalies to the east of the Lake Van are all lined up and extended with this slightly curved line, provoking thoughts that a fault zone that was not previously mapped may exist. The epicenter of the major earthquake event that occurred on October 23, 2011 is located on this fault zone. The fault plane solution of this earthquake indicates a thrust fault in the east-west direction, consistent with the results of this study. Volcanic mountains in this zone are accepted as still being active because of gas seepages from their calderas, and magnetic anomalies are caused by buried causative bodies, probably magmatic intrusions. Because of its magmatic nature, this zone could be a good prospect for geothermal energy exploration. In this study, the basement of the Van Basin was also modelled three-dimensionally (3D) in order to investigate its hydrocarbon potential, because the first oil production in Anatolia was recorded around the Kurzot village in this basin. According to the 3D modelling results, the basin is composed of three different depressions aligned in the N-S direction and many prospective structures were observed between and around these depressions where the depocenter depths may reach down to 10 km.
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    Fault modeling around southern Anatolia using the aftershock sequence of the Kahramanmaras earthquakes (Mw=7.7 and Mw=7.6) and an interpretation of potential field data
    (Springer Int Publ Ag, 2024) Buyuksarac, Aydin; Bektas, Ozcan; Alkan, Hamdi
    On February 6, 2023, southeastern Turkiye experienced devastating doublet earthquakes (Mw = 7.7 and Mw = 7.6) with a series of aftershocks along the East Anatolian Fault Zone. The mainshocks were followed by similar to 15,000 aftershocks mainly distributed in the NNE-SSW direction, including similar to 400 events with an Mw >= 4.0 in the following 30 days. Although many moderate to large earthquakes have occurred in the historical and instrumental periods of this region, these double earthquakes and their aftershocks majorly impacted lives and released great seismic energy. In this study, we interpret the gravity-magnetic data and the epicenter and hypocenter distributions of the aftershocks to correlate the tectonic structures and the active fault zones. The results of potential field anomalies reveal that the rotational anomalies in the southwestward direction are associated with the tectonic structure of Anatolia. Results show that shallow aftershocks are associated with high-gravity anomalies, whereas deeper aftershocks are associated with low-gravity anomalies and they become shallower in places where gravity values increase. After the derivative transformations are applied to the magnetic anomalies, it is seen that the faults and regions of magnetic discontinuity are in good agreement. Consequently, the findings on gravity, magnetic anomalies and aftershock sequences demonstrate that the first mainshock occurred in the unbroken segment of the East Anatolian Fault Zone.
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    Geophysical Investigation of Mount Nemrut Stratovolcano (Bitlis, Eastern Turkey) Through Aeromagnetic Anomaly Analyses
    (Springer Basel Ag, 2020) Ekinci, Yunus Levent; Buyuksarac, Aydin; Bektas, Ozcan; Ertekin, Can
    Quaternary Mount Nemrut stratovolcano, having a spectacular summit caldera and associated lakes, is located north of the Bitlis-Zagros suture zone, Eastern Turkey. Although much attention has been paid to its geology, morphology, history and biology, a detailed geophysical investigation has not been performed in this special region. Thus, we attempted to characterize the stratovolcano and the surroundings using total field aeromagnetic anomalies. Potential field data processing techniques helped us to interpret geologic sources causing magnetic signatures. Resulting image maps obtained from some linear transformations and a derivative-based technique revealed general compatibility between the aeromagnetic anomalies and the near-surface geology of the study area. Some high amplitude magnetic anomalies observed north of the Nemrut caldera rim are associated with the latest bimodal volcanic activity marked by lava fountains and comenditic-basaltic flows occurred along the rift zone. After minimizing the high-frequency effects, a pseudogravity-based three-dimensional inversion scheme revealed that the shallowest deep-seated sources are located about 3.0 km below the ground surface. Two-dimensional normalized full gradient solutions also exposed the depths of these anomaly sources, in good agreement with the inversion results. This first geophysical study performed through aeromagnetic anomalies clearly gave insights into some main magnetized structures of the Mount Nemrut stratovolcano.
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    Geophysical Variations During the Total Solar Eclipse in 2006 in Turkey
    (Tubitak Scientific & Technological Research Council Turkey, 2011) Ates, Abdullah; Buyuksarac, Aydin; Bektas, Ozcan
    It has been observed that some geophysical parameters could be changed during a solar eclipse. We have therefore measured gravity and magnetic fields during solar eclipses. We also measured the gravity field during the previous eclipse on the 11(th) of August, 1999. Gravity measurements on the 29(th) of March, 2006 are compared with previous gravity measurements at the same location during the eclipse on the 11(th) of August, 1999. Both showed the same behaviour during the eclipses. Gravity measurements showed fluctuations during both eclipses. A decrease in the intensity of the magnetic field was observed. Low-pass filtered magnetic data show peculiarity during the eclipse which can be correlated with the fluctuations in the gravity fields.
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    Preliminary seismic microzonation of Sivas city (Turkey) using microtremor and refraction microtremor (ReMi) measurements
    (Springer, 2013) Buyuksarac, Aydin; Bektas, Ozcan; Yilmaz, Huseyin; Arisoy, M. Ozgu
    Sivas city, located in the inner east part of Anatolia (Turkey), is far from seismic sources. However, the city is under risk owing to strong earthquakes occurring around the area, and different soil conditions that can produce variation in the ground motion amplification. Microzonation of cities provides a basis for site-specific hazard analysis in urban settlements. In particular, seismic microzonation can be achieved by means of detailed seismic assessment of the area, including earthquake recordings and geological studies. In this paper, we propose a preliminary microzonation map for the city of Sivas, based on the variation in the dominant periods of the sediments covering the area. The periods are retrieved from microtremor measurements conducted at 114 sites, using the horizontal-to-vertical spectral ratio technique. The results of microtremor analysis were compared with those obtained from refraction microtremor measurements at two profiles crossing the studied area. According to the classification of dominant periods, Sivas area can be divided into four zones, probably prone to different levels of seismic hazard. However, specific studies including analysis of weak earthquakes are required in the future to validate our microzonation map.
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    Statistical and seismotectonic analyses of the Marmara region under existing stress regime in the west of the NAFZ
    (Springer Int Publ Ag, 2024) Alkan, Hamdi; Ozturk, Serkan; Bektas, Ozcan; Buyuksarac, Aydin
    The Marmara Region is an active tectonic region in northwestern T & uuml;rkiye, which comprises some important strike-slip active fault mechanisms and important tectonic units, located near the western part of the North Anatolian Fault Zone. In the historical and instrumental period, the Marmara Region experienced large/devastating earthquakes. Considering this continuous activity, in this study, we investigate the tectonic structure and performed future seismic hazard estimation of the region based on some seismotectonic parameters. For this evaluation, we plot the Coulomb stress change maps of 1912 M & uuml;refte-& Scedil;ark & ouml;y, 1953 Yenice-G & ouml;nen and 1999 & Idot;zmit mainshocks with the earthquakes (MW >= 4.5) that occurred in the study region after 2003. For the estimation of b-value, occurrence probabilities and return periods of earthquakes, we used a homogenous local seismicity catalogue consisting of 119.029 events for the period between 1912 and 2023. In the findings of this study, the lower b-values and increasing Coulomb stress changes which are trigger stress failure compatible are observed in the west and northwest of the Marmara Sea. In contrast, the higher/moderate b-values and decreasing Coulomb stress values are observed in the east and southeast of the Marmara Sea. The results of probability assessments show that an earthquake with Mw = 6.5 may occur with a probability of 98% in the west of the Marmara Sea after 2025. As a remarkable fact, a comprehensive assessment of these types of variables will supply important findings for earthquake hazard and potential in the study region.