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Öğe 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, 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 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, OzcanTurkey, 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.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 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 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 Geophysical Variations During the Total Solar Eclipse in 2006 in Turkey(Tubitak Scientific & Technological Research Council Turkey, 2011) Ates, Abdullah; Buyuksarac, Aydin; Bektas, OzcanIt 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.Öğe Geothermal gradients and seismicity correlations in the Biga Peninsula (NW Türkiye) based on Curie point depths(Inst Geology & Geography, 2025) Bektas, Ozcan; Buyuksarac, Aydin; Pamuk, Eren; Canbaz, OktayThe Biga Peninsula has hot springs with geothermal temperatures varying between 40oC and 175oC. In this study, we investigate the regional temperature distribution and change in radiogenic heat production in the Biga Peninsula. We use EMAG2 magnetic data to estimate the Curie point depth (CPD). Our findings show that the CPD in the region varies between 9 km and 17 km. We also calculated the geothermal gradient and heat flow values based on the CPD data. which range between 92.9 and 141.6 mWm-2. Additionally, we also obtained values for zo, zt, and zbfrom the power spectrum and calculated 1D geothermal gradient change for examined blocks. The resulting equations are: zt= z80 degrees C, zo= z350 degrees C, and zb= z580 degrees C. These equations enabled us to propose a new formula to calculate the CPD. We also obtained the Conrad discontinuity depth (zc = z680 degrees C) in the Biga Peninsula. Furthermore, we prepared 2D heat flow and temperature profiles along three sections to investigate the relationship between heat changes and earthquake focal distributions. The results indicate that seismicity is high in the southwest of the Biga Peninsula, which has a high CPD, high heat flow value, and shallow Conrad discontinuity.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 Shear-wave velocity model of the Sivas City (inner eastern, Türkiye) using Rayleigh wave ellipticity inversion controlled by 2D microgravity modeling(Springer Int Publ Ag, 2025) Bektas, Ozcan; Buyuksarac, Aydin; Saritepe, Halil Erdim; Onal, Kemal Mert; Canbaz, Oktay; Eyisuren, Onur; Pamuk, ErenThe change in duration, amplitude, and frequency content of the earthquake ground motion as it passes through the rock and ground environment is referred to as the local ground effect. Impedance differences between bedrock and soil, as well as the dynamic behavior of soils, can amplify this effect. The geometry of both dense and loose soil layers must be known to accurately define soil-structure interaction and properly assess how soil behavior affects a structure during an earthquake. Local ground effects are known to play a significant role in structural damage during earthquakes. In basin-like environments, however, studies based on foundation and sub-base depth often lack sufficient information, making it difficult to identify problems associated with basin effects. It is not appropriate to provide construction-related information, especially in environments with a basin structure like Sivas, without determining the bedrock or solid ground conditions. This study aimed at determining the bedrock/seismic foundation depth for the central settlement of Sivas and defining the basin structure, involved large-scale microgravity measurements. The study area was modeled in three dimensions using the gravity data obtained. Long-term microtremor measurements were also conducted, and one-dimensional depth-shear-wave (Vs) velocity models were generated using the Rayleigh ellipticity method. The bedrock/seismic foundation structure of the study area was defined using two different methods, and these definitions were combined into two-dimensional sections. A depth map of the study area was created, revealing that the thickness of the loose basin unit is approximately 90 m. Ambient noise was recorded at 35 points with a velocity seismometer, and S velocity (Vs) profiles were obtained from joint inversion of Rayleigh ellipticity data and dispersion curves from MASW and ReMi data. Furthermore, the Vs-depth structure of the basin was defined along the profiles cutting the basin in NW-SE and S-N directions, based on the Vs velocities in the 2D gravity model. The frequency range along these profiles was found to be 0.6 Hz in the deep parts of the basin and 2.5 Hz in the shallow parts.Öğe Three dimensional shear wave velocity (Vs) structure and dynamic soil properties of Adiyaman-Golbasi basin using HVSR and SPAC methods(Elsevier Sci Ltd, 2026) Pamuk, Eren; Firat, Seyhan; Buyuksarac, Aydin; Cretin, Kemal Onder; Bektas, Ozcan; Isik, Nihat Sinan; Saritepe, Halil ErdimOn February 6, 2023, two devastating earthquakes (M-w 7.8 and M-w 7.6) struck southeastern T & uuml;rkiye, two of the most destructive seismic events in the country's history. This study investigates the structural damage and seismic vulnerability in the G & ouml;lbasi Basin, located in Adiyaman Province-one of the regions most severely affected by these events. Geophysical techniques, the HVSR (Nakamura) and spatial autocorrelation (SPAC) methods, were employed to develop shear wave velocity (Vs) profiles and evaluate the dynamic soil properties of the basin. Shear wave velocities within the G & ouml;lbasi Basin, down to a depth of 300 m, range from 211 to 923 m/s, with the lowest values observed near the lake, indicating weak and loose soil conditions. Natural site periods vary between 0.1 s and 2.86 s, with the longest periods (T > 2.5 s) also concentrated in the vicinity of the lake. In areas where the engineering bedrock (Vs > 760 m/s) lies deeper than 250 m, natural periods frequently exceed 1.5 s. These findings suggest that zones with thick alluvial deposits and low Vs values are particularly susceptible to seismic hazards. Structural damage was most severe in areas where Vs is below 350 m/s, site periods exceed 1 s, and the engineering bedrock lies deeper than 50 m. Notably, low-rise industrial buildings and low-rise structures with basement floors remained intact despite poor soil conditions. In contrast, in areas with more competent ground conditions, structural collapses were more likely caused by deficiencies in engineering design or construction quality.
