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Öğe 3D Modeling and Tectonic Interpretation of the Erzincan Basin (Turkey) using Potential Field Data(UNIV NACIONAL DE COLOMBIA, 2019) Aydin, Omer L.; Bektas, Ozcan; Buyuksarac, Aydin; Yilmaz, HuseyinErzincan Basin was investigated using gravity data within the scope of this study. It is also aimed to reveal the discontinuities in the work area as well as the buried discontinuities. Boundary determination filters and analysis of the structure of the data and its connection are revealed and clear information is obtained. Gravity anomalies were applied with an upward continuation method for 0.25, 0.50, 0.75 and 1 km levels. Total Horizontal Derivative (THD) filter, Analytical Signal (AS) filter, Tilt Angle Derivative (Tilt) filter, Total Horizontal Derivative (THDR) filter, Theta Angle Derivative (Cos theta) filter, Hyperbolic Tilt Angle Derivative (HTAD) were applied to upward continued data. The discontinuities in the region and the boundaries of the geological structure were revealed. Tilt and Theta Angle derivatives yield the best results from the applied derivative based filters. The obtained data were compared with the existing surface geology and the compatibility between the formations was checked. New discontinuities were found in addition to the discontinuities determined from surface observations in the light of the obtained results. Erzincan Basin was modeled in three dimensions using gravity data of the study area. As a result of modeling, Erzincan Basin has been determined to have an average thickness of 7 km.Öğe 3D MODELLING AND STRUCTURAL INVESTIGATION OF THE CENTRAL VOLCANICS IN SLOVAKIA USING MAGNETIC DATA(NORTH UNIV BAIA MARE, 2013) Bektas, Ozcan; Buyuksarac, Aydin; Rozimant, KamilThe 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.Öğe Achieving Intensity Distributions of 6 February 2023 Kahramanmaraş (Türkiye) Earthquakes from Peak Ground Acceleration Records(Mdpi, 2024) Buyuksarac, Aydin; Isik, Ercan; Bektas, Ozcan; Avcil, FatihOn 6 February 2023, two large earthquakes struck southern Turkiye on the same day, resulting in a considerable loss of life and property damage over a large region that included 11 cities. After these disasters, there was a requirement to define the soil-related intensity distribution, aside from manufacturing defects caused by buildings. The modified Mercalli intensity (MMI) scale results in the same intensity value (XI) when decimal values are not mathematically considered, even though the fundamental data in the AFAD and USGS sources differ. In this study, an equation based on the MMI-PGA relationship was obtained and tested with ten previously developed equations to calculate the earthquake intensity. Seven of these selected equations, depending on the earthquake magnitude, were calculated comparatively. The equation most compatible with the earthquakes that occurred on 6 February 2023 was obtained in this study. In addition, it was decided that three similar equations could also be used. Intensity distribution maps were created according to the calculated MMI values. In this way, it has been observed that different earthquake intensity values are more sensitive, reliable, objective, and sustainable.Öğe Bedrock Depth Calculation of ?anakkale (Turkey) Basin Using Rayleigh Ellipticity and Microgravity Survey(Inst Geophysics Unam, 2023) Buyuksarac, Aydin; Eyisuren, Onur; Bektas, Ozcan; Karaca, OznurIt is a well-known fact that the local ground effect plays an important role in the damage to structures during earthquakes. In order to define the soil-structure interaction correctly, the geometry of the tight and loose soil layers in the soil should be well known. In addition, the impedance contrast due to local ground effects can be deeper than the first 30 m, which is accepted as the engineering depth, and in this case, the Vs,30 parameter is disabled. For this reason, the location of engineering bedrock and seismic bedrock gains importance. The variation of shear wave velocity with depth is a key parameter for seismic field effect estimation. In addition, the separation of low-density layers close to the surface and higher-density bedrock can be easily done by the gravity method. Bedrock/seismic foundation levels were determined by using these two methods together for canakkale soils, which are known to have thick alluvial thickness and liquefaction problems. Microgravity measurements were made at 100 points and the anomalies obtained were modelled in three dimensions. In light of the data obtained from this study, it has been determined that the thickness of the loose basin unit in the study area is in the range of about 50-300 m. Ambient vibration was recorded with the help of a velocity seismometer at 146 points, and S velocity (Vs) profiles were obtained by using the inversion of the observed ellipticity curve. In addition, the velocity-depth change rate structure of the basin is defined depending on the Vs velocities on the 2D gravity model made along the two profiles that cut the basin in N-S and E-W directions. Along these profiles, the frequency range has been determined as 0.8-1.3 Hz in the deep parts of the Basin and 1.5-11.0 Hz in the shallow parts.Öğe 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, YaseminIn 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.Öğe Effects of the Karacadag Volcanic Complex on the thermal structure and geothermal potential of southeast Anatolia(SPRINGER, 2018) Bilim, Funda; Aydemir, Attila; Kosaroglu, Sinan; Bektas, OzcanThe Karacadag Volcanic Complex (KVC) is the largest volcanic unit in SE Turkey. It is also defined as a shield volcano on the northernmost part of the Arabian Plate. The main goal of this study is to investigate the geothermal potential of this region associated with the magnetic signature of this volcanic complex and surrounding area. Besides this primary objective, the possibility of there being volcanic intrusion into the buried fault zones under the volcanic cover are also investigated to determine the interrelations between the active tectonics and heat flow in the area. A spectral analysis method is applied to the magnetic anomalies of the volcanic rocks to identify the Curie point depth (CPD) and geothermal gradient, as well as to estimate heat flow and radiogenic heat production of radioactive minerals in the complex. A tilt angle map is also presented, in correlation with instrumentally recorded earthquake magnitudes, to indicate tectonic trends that are consistent with the maps of the thermal parameters in this study. In contrast with expectations for the KVC area, the region around Akcakale and Suruc Grabens is the most prolific zone for geothermal potential, despite them not showing strong magnetic anomalies. Curie point depths are shallow, down to 18 km. around the Akcakale Graben, and deeper, down to 22 km, around the Bitlis-Zagros Suture Zone where the geothermal gradients increase from 26 to 32 degrees C km(-1) through the graben area. Heat flows in this zone are in the range from 75 to 90 mW m(-2) depending on the thermal conductivity coefficient (2.3, 2.5, 2.7, and 3.0 W m(-1) K-1) used. Radiogenic heat production values also indicate slightly changing spectra in the range 0.19 to 0.25 mu W m(-3)). None of these parameters are focused around Mt. Karacadag. However, the earthquake epicenters (generally M <= 4) are aligned with the boundary faults of the Akcakale Graben where the CPD, geothermal gradient, and heat flow maps indicate relatively high potential. We thus suggest that this graben area would be good for future geothermal exploration. On the contrary, considering the low geothermal gradient and heat flow values, Mt. Karacadag can be accepted as being an extinct volcano, despite its apparent, high, magnetic anomalies.Öğe Estimating shear wave velocity using acceleration data in Antakya (Turkey)(UNIV NACIONAL DE COLOMBIA, 2014) Buyuksarac, Aydin; Over, Semir; Genes, M. Cemal; Bikce, Murat; Kacin, Selcuk; Bektas, OzcanThis manuscript presents a site response analysis and an estimation of S-wave velocity that are dependent on acceleration data. First, existing data, such as density, seismic wave velocity, and soil cross-sections, are obtained from previous seismic microzonation studies and used to prepare input data for a suite of MATLAB routines, which are referred to as SUA software. Acceleration data are obtained from four free-field strong-motion stations of the SERAMAR project, which was conducted between 2006 and 2009 in conjunction with a Turkish-German joint research project, and inputted into the software as basic data. The results include a 1D velocity cross-section versus depth and an amplification model of the site. Three different depth levels can be determined for the ranges of 0-5 m, 5-15 m and 15-25 m. The seismic velocities vary between 380 and 470 m s-1 for the first 5 m; 320 and 480 m s-1 for 5-15 m; and 470 and 750 m s-1 for 15-25 m. These results are comparable with the amplification values from the microtremor data from previous studies. The 1D velocity models are appropriate for the soil conditions.Öğe 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, OzcanThe 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.Öğe Failure mechanism by wrench faulting in Central Anatolia(Pergamon-Elsevier Science Ltd, 2024) Buyuksarac, Aydin; Gundogdu, Erdem; Bektas, Ozcan; Isik, ErcanThe study area, where volcanism and tectonism are active at the same time, consists of the Cappadocia Volcanic Complex (CVC) in the middle, Tuzgol & uuml; on the west side, and Ecemis, fault systems on the east side. Remote sensing image processing method and derivation to aeromagnetic data were applied to identify the structural lineations that tectonically control the study area within the scope of the study. As a result of the lineation analysis performed in the west of the study area, 167 lineaments in the west, most of which are NW oriented, and 316 lineaments, most of which are NE oriented, were determined in the east. These findings are in agreement with the known fault orientations in the area. It is known that earthquakes greater than M > 4 occurred in these known faults during the neotectonics period, and they also have the potential to produce M > 6 earthquakes. In addition, the Tuzgol & uuml; and Ecemis, Faults' shearing effect relative to each other is an indication that a wrench tectonics mechanism has developed in the study area. With the remote sensing study and following the existing surface traces, two fault systems in opposite directions, the Tuzgol & uuml; Fault (-30 degrees) dipping counterclockwise and the Ecemis, Fault, clockwise (60 degrees) dipping, were determined. The orientation and locations of the faults could be determined by tilt transformation applied to the magnetic anomaly map of the study area. In particular, the effects of wrenching in the study area can be clearly observed in magnetic anomalies.Öğe 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, HamdiOn 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.Öğe 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, CanQuaternary 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.Öğe Investigation of earthquake sequence and stress transfer in the Eastern Anatolia Fault Zone by Coulomb stress analysis(Tubitak Scientific & Technological Research Council Turkey, 2024) Alkan, Hamdi; Buyuksarac, Aydin; Bektas, OzcanA devastating earthquake with a magnitude of (M-w = 7.7) occurred on February 06, 2023, in the Pazarcik segment of the Eastern Anatolian Fault Zone, which has not shown major earthquake activity for a long time. On the same day, another earthquake with a magnitude of (M-w = 7.6) occurred in Ekinozu-Elbistan (Kahramanmaras) in the northwest. Three more earthquakes with magnitudes of M-w = 6.6, M-w = 5.9, and ML = 5.7 occurred on the same day, and significant damage, loss of life, and property occurred in 11 provinces and districts. A sixth earthquake occurred with M-w = 6.4 magnitude in Defne-Hatay on February 20, 2023. In addition, more than 32,000 aftershocks were recorded while this study was in progress. The interconnection of these earthquakes was investigated by Coulomb stress analysis. It showed compatibility with the distribution of both these six earthquakes and small aftershocks, in which earthquakes transfer stress to each other during their formation phases. By calculating Coulomb stress changes, mainshock ruptures have played an important role in transferring stresses between Elazig and Malatya in the northeast, Kahramanmaras-Goksun in the west, and Hatay and Syria in the south. Also, our calculations showed that shallow depths in and around source zones received positive stress changes (similar to 1.0 bar) due to the focal depths of mainshocks with their aftershocks. Finally, it has been better understood with these earthquakes that the stress transfer time of high-energy earthquakes can be shortened considerably.Öğe Investigation of magnetic surveying data of buried grave jars in Harmanoren Necropolis (Turkey) using linear transformations and analytic signal(ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, 2006) Buyuksarac, Aydin; Bilim, Funda; Ates, Abdullah; Bektas, OzcanHarmanoren Necropolis is the third biggest excavated necropolis in southwest Anatolia, dating back to 2500 B.C. The individual burials are composed of ceramic jars. The dead bodies were placed in the fetal position in buried grave jars which were elongated eastwards. Buried burnt ceramics can be located by their own magnetic field directions. Thus, magnetic surveying was used in the Harmanoren Necropolis in three different areas to locate buried grave jars ahead of archaeological excavation. Magnetic anomalies present some results, but to identify these as buried grave jars, advanced spectral methods were applied to the magnetic anomalies. Polarity orientations of magnetic anomalies are different from a north-south direction due to remnant magnetization. 'Reduction to the pole' transformation could not entirely remove disoriented polarities arising from the effect of remnant magnetization. 'Analytic signal' transformation minimizes the disorientation caused by the effect of remanence. Magnetic susceptibility measurements of samples from the excavated jars indicate that the observed magnetic anomalies could be caused by them. A good correlation was observed between the processed magnetic anomalies and excavation results. (c) 2005 Elsevier Ltd. All rights reserved.Öğe Mineralization characteristics of Lead-Zinc-Copper deposits in Akdagmadeni Region (Northern Central Anatolia, Türkiye): Integration of field study, geochemical, isotope, and geophysical data(Elsevier Gmbh, 2024) Gokce, Ahmet; Canbaz, Oktay; Cakir, Esra Unal; Bozkaya, Gulcan; Bektas, Ozcan; Basdelioglu, OrbayThe Akdagmadeni region is one of the important Pb-Zn-Cu metallogenic provinces in T & uuml;rkiye. Most of the Pb-ZnCu deposits in the region are located near granitoid intrusions within metamorphic rocks, and they are typically classified as skarn-type ores associated with granitoids. However, no relationship has been determined between the Bas,& ccedil;atak prospect and any granitoid outcrop. This raises the question of whether the Pb-Zn-Cu mineralization in the region is related to granitoids or if magmatic processes remobilized pre-existing mineralization. Observations from field studies suggest that mineralization in the Bas,& ccedil;atak prospect is a stratiform type, metamorphosed occurrence that might have occurred earlier than the granitic intrusions. The geochemical data indicated that the granitoids have low-grade, subeconomic Cu potential and no Zn productivity potential, supporting these observations. Geophysical data also show that there is no intrusive body beneath this prospect. Granitoid-related deposits (Karapir- Ortakoy and Ak & ccedil;ak & imath;s,la) exhibit two distinct occurrences around the contact between the granite and the surrounding metamorphic rocks. The first type of occurrence (O-1) is formed at the contact and contains magnetite, pyrrhotite, and chalcopyrite. The second type of occurrence (O-2) is located outside the contact and is rich in sphalerite and galena. Both O-1 and O-2 contain skarn minerals along with ore minerals. The delta 34 S values of sulfide minerals from the deposits range from-0,7 to 7,5 parts per thousand (V-CDT). These values overlap with those of both magmatic sulfur and reduced sulfur from seawater-dissolved sulfate, making it difficult to suggest a sulfur source without additional data. Lead isotope compositions of the galenas from all deposits plot above the average crustal growth curve, suggesting an upper crustal and orogenic source similar to Western Mediterranean and T & uuml;rkiye type materials described in the literature for the lead, source in different time intervals. Furthermore, Pb isotope geochemistry suggests a contemporaneous age with the host metamorphic rocks (Carboniferous - Lower Permian) for the Bas,& ccedil;atak prospect. These results support observations indicating a syn-genetic formation for the Bas,& ccedil;atak prospect. The age range of granite-related deposits forms two sub-groups:105-77 Ma and 61-50 Ma corresponding to the Upper Cretaceous and Paleocene transition. These data indicate that that the galenas were formed in two different stages in these mineralizations. Stratiform mineralization in the Bas,& ccedil;atak prospect likely formed either through exhalative sedimentary processes by hydrothermal fluids or through chemical sedimentary processes under reductive conditions in a marine environment during metamorphism. O-1 appears to have been formed by hydrothermal fluids developed during granitic magmatism. A plausible formation process for O-2 involves the leaching of sulfur, lead and other metals from Bas,& ccedil;atak type enrichments in metamorphics, with transportation and deposition within the epidotized calc-schist and marbles outside the granitoid contacts. The uplift of granitic intrusions prepared the channels and depositional environment for O-2 and caused heating of the hydrothermal fluids during this mineralization period.Öğe A new automatic method for estimation of magnetization and density contrast by using three-dimensional (3D) magnetic and gravity anomalies(ELSEVIER SCIENCE BV, 2012) Bektas, Ozcan; Ates, Abdullah; Aydemir, AttilaIn this paper, a new method estimating the ratio of magnetic intensity to density contrast of a body that creates magnetic and gravity anomalies is presented. Although magnetic intensity and density of an anomalous body can be measured in the laboratory from the surface samples, the proposed new method is developed to determine the magnetic intensity and density contrast from the magnetic and gravity anomalies when the surface samples are not available. In this method, density contrast diagrams of a synthetic model are produced and these diagrams are prepared as graphics where the magnetic intensity W is given in the vertical axis and Psg (pseudogravity)/Grv (gravity) values in horizontal axis. The density contrast diagrams can be prepared as three sub-diagrams to show the low, middle and high ranges allowing obtain density contrast of body. The proposed method is successfully tested on the synthetic models with and without error. In order to verify the results of the method, an alternative method known as root-mean-square (RMS) is also applied onto the same models to determine the density contrast. In this manner, maximum correlation between the observed gravity and calculated gravity anomalies is searched and confirmation of the results is supported with the RMS method. In order to check the reliability of the new method on the field data, the proposed method is applied to the Tetbury (England) and Hanobasi (Central Turkey) magnetic and gravity anomalies. Field models are correlated with available geological, seismic and borehole data. The results are found consistent and reliable for estimating the magnetic intensity and density contrast of the causative bodies. (C) 2012 Elsevier B.V. All rights reserved.Öğe Preliminary seismic microzonation of Sivas city (Turkey) using microtremor and refraction microtremor (ReMi) measurements(SPRINGER, 2013) Buyuksarac, Aydin; Bektas, Ozcan; Yilmaz, Huseyin; Arisoy, M. OzguSivas 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.Öğe 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, AydinThe 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.Öğe Thermal structure of the crust in Inner East Anatolia from aeromagnetic and gravity data(ELSEVIER SCIENCE BV, 2013) Bektas, OzcanInner East Anatolia has many hot spring outcomes. In this study, the relationship between the thermal structure and hot spring outcomes is investigated. The residual aeromagnetic and gravity anomalies of the Inner East Anatolia, surveyed by the Mineral Research and Exploration (MTA) of Turkey, show complexities. The magnetic data were analyzed to produce Curie point depth estimates. The depth of magnetic dipole was calculated by azimuthally averaged power spectrum method for the whole area. The Curie point depth (CPD) map covering the Inner East Anatolia has been produced. The Curie point depths of the region between Sivas and Malatya vary from 16.5 to 18.7 km. Values of heat flow were calculated according to continental geotherm from the model. The heat flow values vary between 89 and 99 mW m(-2). Heat flow values are incorporated with surface heat flow values. Gravity anomalies were modeled by means of a three-dimensional method. The deepest part of the basin (12-14 km), determined from the 3D model, are located below the settlement of Hafik and to the south of Zara towns. Two-dimensional cross sections produced from the basin depths, Curie values and MOHO depths. Based on the analysis of magnetic, gravity anomalies, thermal structures and geology, it seems likely that the hot springs are not related to rising asthenosphere, in the regions of shallow CPDs (similar to 16.5 km), and mostly hot springs are related to faulting systems in Inner East Anatolia. (C) 2013 Elsevier B.V. All rights reserved.
