Browsing by Author "Topal, Tamer"

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Empirical Correlations of Shear Wave Velocity (Vs) and Penetration Resistance (spt-N) for Different Soils in an Earthquake-Prone Area (erbaa-Turkey)
(Elsevier, 2011) Akin, Muge K.; Kramer, Steven L.; Topal, Tamer
The seismicity of the northern part of Turkey is mainly controlled by the North Anatolian Fault zone (NAFZ). The NAFZ is one of the world's most active seismic zones, and has produced destructive earthquakes and related hazards in the northern region of Turkey. Several earthquakes and earthquake-related hazards have occurred along different segments of this fault zone in the recent past. The study area, Erbaa town, is located along the eastern segment of North Anatolian Fault Zone (NAFZ) and is one of the largest towns of Tokat Province in the Middle Black Sea Region of Turkey. The center of Erbaa is located on the left embankment of the Kelkit River. After the disastrous 1942 (M-s=7.2) and 1943 (M-s=7.6) earthquakes, the settlement was shifted southwards. As a part of a seismic microzonation study of the Erbaa area, shear wave velocity (V-s) values of the geological units exposed in this area were required for site response analyses. The geological units in the study area consist mainly of alluvial and Pliocene units. These layers were evaluated on the basis of drilling, in-situ (SPT, SCPTU and SPT-based uphole) and laboratory testing. In this study, empirical correlations between shear wave velocity (V-s) and standard penetration test blow counts (SPT-N) were considered in order to define shear wave velocity profiles for the study area. The relationships between shear wave velocity, Standard Penetration Test (SPT) blow-counts and the soil properties were evaluated as functions of depth. SPT-based uphole tests were performed to measure shear wave velocity during drilling operations in some of the borings. The SPT-based V-s values were computed with different empirical formulas and compared with the measured SPT based uphole V-s measurements. The empirical correlations were found to require modification to provide the best correlation for this site. The depth factor was considered during the development of new empirical equations. Therefore, a site-specific formula was proposed in order to obtain V-s profiles for all layers in the study area. (C) 2011 Elsevier B.V. All rights reserved.
Evaluation of Liquefaction in Karasu River Floodplain After the October 23, 2011, Van (Turkey) Earthquake
(Springer, 2013) Akin, Mutluhan; Ozvan, Ali; Akin, Muge K.; Topal, Tamer
The eastern shore of Lake Van was shaken by a powerful earthquake (M (w) 7.2) on October 23, 2011. The epicenter of the earthquake was located at about 30 km north of the Van Province, which is one of the main cities in the Eastern Anatolia. The Van Province and particularly its largest district Ercis were adversely affected by the earthquake, and unfortunately, a total of 600 people lost their lives. Besides severe constructional damages and building collapses, ground deformations were widespread at many locations nearby the Lake Van and Karasu River floodplain. Numerous sand boils and lateral spreading cracks were observed at the left and right embankments of the Karasu River, which is one of the major streams in the region. In this study, field observations on liquefaction and lateral spreading features triggered by the M (w) 7.2 Van earthquake are initially presented. Then, the results of subsurface investigations including trial pits, drillings and geophysical surveys on specific large-scale sand boils are explained. Subsequently, liquefaction back-analysis is performed considering the gathered subsurface data. The analysis indicates that the liquefaction occurred in a shallow zone with approximately 4 m thickness in the investigated area. The Liquefaction Potential Index method reveals high liquefaction potential for the analyzed sand boil location. In addition, the effect of cap soil thickness on liquefaction is once more validated by this case.
Evaluation of the Physico-Mechanical Parameters Affecting the Deterioration Rate of Ahlat Ignimbrites (Bitlis, Turkey)
(Springer, 2017) Akin, Mutluhan; Ozvan, Ali; Dincer, Ismail; Topal, Tamer
The paper principally focuses on the durability assessment of various stratigraphic levels of Ahlat ignimbrites collected from the eastern region of Turkey. A total of four different ignimbrite types with dissimilar color, texture and particularly welding degree were tested in laboratory. The laboratory tests performed on the ignimbrite specimens indicate that the welding degree as well as the lithic material content mainly controls the strength and capillarity properties of the ignimbrites. In addition, the durability of highly porous ignimbrites strongly depends upon the degree of welding. The effect of several weathering agents on the ignimbrites was evaluated on the basis of decay constant parameter. Accordingly, salt and ice crystallization pressures are a couple of major destructive agents acting within the micropores of the ignimbrites. Conversely, the investigated specimens are relatively durable against cyclic wetting-drying. Statistical evaluations reveal that the pore diameter is the major controlling factor on the deterioration rate of the ignimbrites after specifically recurrent freeze-thaw cycles. Moreover, the dry unit weight of the ignimbrites is more significant than the uniaxial compressive strength considering the deterioration rates during wetting-drying and salt crystallization. A less significant relationship was obtained between pore diameter and salt crystallization decay constant.
A New Quantitative Welding Degree Classification for Ignimbrites
(Springer, 2023) Akin, Mutluhan; Topal, Tamer; Dincer, Ismail; Akin, Muge K.; Ozvan, Ali; Orhan, Ahmet; Orhan, Ayse
As a pyroclastic rock type, ignimbrites may reveal varying degrees of welding depending on the temperature (> 535 celcius) and overburden pressure conditions during its formation. The welding degree of ignimbrites increases as the formation temperature and the thickness of the overburden deposit in the depositional environment escalate, which are the most crucial factors controlling the rate of welding in ignimbrites. With the increasing temperature, plastic deformation is observed in ignimbrites and the glassy minerals are being welded. Furthermore, the thickness of the overburden causes the deformation of the ash matrix in ignimbrites at the lower sections and the pumice grains are flattened at different rates. An increase in the degree of welding of ignimbrites causes an improvement in the physical and mechanical properties of the rock material as well. Within the scope of this research, petrographical, mineralogical, and geochemical studies were carried out on a total of 16 different ignimbrite types, which have different color and texture properties, obtained from three different regions of Turkey (Kayseri, Nevsehir, Ahlat) where ignimbrites extensively crop out, and the physical and mechanical properties of these samples were revealed. Consequently, a new welding classification was developed for ignimbrites considering the uniaxial compressive strength and dry unit weight. The proposed welding classification consists of six classes ranging from non-welded to highly welded. When the welding degrees of the selected ignimbrites are evaluated, Kayseri ignimbrites mostly exhibit moderate welding characteristics. Nevsehir ignimbrites, on the other hand, have a low welding degree whereas the degree of welding in Ahlat ignimbrites may vary from low to high. Additionally, long and short axis lengths of pumice grains in the ignimbrite specimens were determined by measuring under the microscope, and shape ratios were determined by different shape parameter evaluation methods. As a result, it has been concluded that the pumice grains in Kayseri and Ahlat ignimbrites have a more lenticular structure than the pumice grains in Nevsehir ignimbrites. Eventually, the welding degree classes of ignimbrites and the classification developed by using threshold values of the oblateness ratio (OR) values of pumice grains at different welding degrees are quite compatible. The proposed welding degree classification is of great importance in the selection of ignimbrites widely used as dimension stone and in terms of engineering classification of this rock type as well as it will guide to the scientific studies to be performed on ignimbrites with varying physical and mechanical properties.
A Newly Developed Seismic Microzonation Model of Erbaa (Tokat, Turkey) Located on Seismically Active Eastern Segment of the North Anatolian Fault Zone (Nafz)
(Springer, 2013) Akin, Muge K.; Topal, Tamer; Kramer, Steven L.
A methodology to model seismic microzonation maps is required in the hazard mitigation decision plans of the earthquake prone areas. The stage of disaster preparedness for new residential places is of great importance for detailed seismic microzonation models. The effects of local geological and geotechnical site conditions were considered in order to establish site characterization as the initial stage of the models in this study. Dynamic soil properties based on the empirical correlations between shear wave velocity (V (s)) and standard penetration test blow counts were taken into account in order to define representative soil profiles extending down to the engineering bedrock. One-dimensional site response analyses were performed to analyze earthquake characteristics on the ground surface. The layers for soil classification, geology, depth to groundwater level, amplification, distance to fault, slope and aspect, and liquefaction-induced ground deformation potential of the study area were prepared in seismic microzonation models. The study area, Erbaa, is placed along the seismically active North Anatolian Fault Zone. Final seismic microzonation map of the study area was evaluated applying different GIS-based Multi-Criteria Decision Analysis (MCDA) techniques. Two of the MCDA techniques, simple additive weighting and analytical hierarchical process (AHP), are considered during the evaluation step of the final seismic microzonation map. The comparison is made in order to distinguish two different maps based on these MCDA techniques. Eventually, AHP-based seismic microzonation map is more preferable for the seismic design purposes in this study.
Seismic Microzonation of Erbaa, Tokat Province, Turkey, Based on Analytical Hierarchical Process
(Geological Soc Amer, inc, 2012) Akin, Muge K.; Topal, Tamer; Kramer, Steven L.
This study is to develop a seismic microzonation map using Analytical Hierarchical Process (AHP), one of the Multicriteria Decision Analysis methods based on Geographical Information Systems. The study area, Erbaa, is located along the eastern segment of the North Anatolian Fault Zone and is one of the largest towns and one of 12 districts within Tokat Province (population, similar to 176,000) in the Middle Black Sea Region of Turkey. Erbaa is located on the southwest bank of the Kelkit River. After the disastrous 1942 (M-s = 7.2) and 1943 (M-s = 7.6) earthquakes, the settlement was shifted southward. Erbaa is one of the most rapidly growing metropolitan areas of this province, with a population of similar to 96,000 people. Therefore, a microzonation study is needed for new settlement places. The data are classified as fundamental input data and derived input data, which are both considered in the AHP method. Fundamental input data include topographical, slope, aspect, lithology, and depth to groundwater table maps. The derived input data involve distance to fault, site classification based on shear wave velocity for the upper 30-m depth, amplification, and liquefaction-induced ground deformation maps, representing the seismic-based layers, produced from various analyses. Weight and rank values are assigned to different layers and to the corresponding classes of each layer. The resulting microzonation map reveals that the northern part requires detailed geotechnical investigation and that the southern part of the area is much more suitable for settlement.
Van Gölü Çevresindeki Kıyı Koruma Yapılarında Kullanılan Anroşmanların Duraylılığının ve Performansının Değerlendirilmesi
(2015) Bor, Mesut; Akin, Muge; Özvan, Ali; Topal, Tamer; Akın, Mutluhan