Browsing by Author "Akkaya, Ismail"

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The Application of Hvsr Microtremor Survey Method in Yuksekova (Hakkari) Region, Eastern Turkey
(Pergamon-elsevier Science Ltd, 2015) Akkaya, Ismail
The horizontal to vertical spectral ratios of microtremor (HVSR) analysis of Yuksekova and its surroundings is carried out using the results of field investigations, local soil conditions and seismotectonic features of the region. Soil-structure interaction is one of the most important reason for building damage ratio. The effects of soil conditions on probably damaged building units were determined, by conducting HVSR microtremor measurements. In this study data collection is handled during 30 min using three component seismograph measurements at 40 points in the Yuksekova region. HVSR peak period map shows that the fundamental period range between 0.4 and 1.6 s in the soft sediments units. Rock sites of the northern coast of Yuksekova period range between 0.1 and 0.2s. HVSR peak amplitude values are in the interval 1.5-6.0. (C) 2015 Elsevier Ltd. All rights reserved.
An Approach for Determining the Relationship Between the Parameters of Pressuremeter and Spt in Different Consistency Clays in Eastern Turkey
(Springer Heidelberg, 2018) Ozvan, Ali; Akkaya, Ismail; Tapan, Mucip
The pressuremeter test is one of the borehole loading tests that determines the deformation characteristics of subsurface soil. The main idea of the pressuremeter test is to inflate the cylindrical hole drilled in order to measure the pressure-deformation relations of the soil. Another in situ test by which soil properties are determined is the well-known standard penetration test (SPT). The consistency and firmness of soils can be determined using the test results of these in situ tests. In order to determine the relationship between the results of these two tests in clayey soils with low and high plasticity characteristics, a total of 20 boreholes with 1.5-4.5 m depths were drilled, and both tests were performed at varying depths. Following the pressuremeter test, pure limit pressure (P (L)) values and pressuremeter deformation modulus (E (M)) were calculated for 31 different levels, respectively. These values were compared to SPT (N (60)) values, and high determination coefficients (R (2)) were attained. Therefore, for clayey soils, it is possible to determine E (M) and P (L) values from SPT results, and consequently SPT test results can be used to calculate settlement and bearing capacity as well as the undrained shear strength values (c (u)) of low and high plasticity clayey soils.
Availability of Seismic Vulnerability Index (Kg) in the Assessment of Building Damage in Van, Eastern Turkey
(Springer, 2020) Akkaya, Ismail
The seismic vulnerability index (K-g) is a parameter that depends on the dynamic properties of soil. With this parameter, it is possible to evaluate the vulnerability of a point-based site under strong ground motion. Since it is related to the natural vibration period and amplification factor, the parameter can be calculated for both soil and structure. In this study, HVSR microtremor measurements are recorded at more than 200 points in the Van region to generate a seismic vulnerability index map. After generating the map, it is determined that the hazard potential and seismic vulnerability index is high at the sites close to Van Lake and at the densely populated city center. Damage information of the buildings investigated after the 2011 Van earthquakes (M-w = 7.1) are placed on the seismic vulnerability index map and it is realized that there may be a correlation between the damage and the seismic vulnerability index. There is a high correlation, approximately 80 percent, between the damage rate map based on the damaged building data and the K-g values. In addition, vulnerability indexes of buildings are calculated and the eff ect of local soil conditions and building properties on the damage levels are determined. From the results of this study and the site observations after the 2011 Van earthquakes, it is found that structural damage is not only structure-dependent but is also related to the dynamic behavior of soil layers and local soil conditions.
Comparison of Spt and Vs-Based Liquefaction Analyses: a Case Study in Ercis (Van, Turkey)
(Springer international Publishing Ag, 2018) Akkaya, Ismail; Ozvan, Ali; Akin, Mutluhan; Akin, Muge K.; Ovun, Ugur
Liquefaction which is one of the most destructive ground deformations occurs during an earthquake in saturated or partially saturated silty and sandy soils, which may cause serious damages such as settlement and tilting of structures due to shear strength loss of soils. Standard (SPT) and cone (CPT) penetration tests as well as the shear wave velocity (V-s)-based methods are commonly used for the determination of liquefaction potential. In this research, it was aimed to compare the SPT and V-s-based liquefaction analysis methods by generating different earthquake scenarios. Accordingly, the Ercis residential area, which was mostly affected by the 2011 Van earthquake (M-w = 7.1), was chosen as the model site. Ercis (Van, Turkey) and its surroundings settle on an alluvial plain which consists of silty and sandy layers with shallow groundwater level. Moreover, Caldiran, Ercis-Kocapinar and Van Fault Zones are the major seismic sources of the region which have a significant potential of producing large magnitude earthquakes. After liquefaction assessments, the liquefaction potential in the western part of the region and in the coastal regions nearby the Lake Van is found to be higher than the other locations. Thus, it can be stated that the soil tightness and groundwater level dominantly control the liquefaction potential. In addition, the lateral spreading and sand boiling spots observed after the 23rd October 2011 Van earthquake overlap the scenario boundaries predicted in this study. Eventually, the use of V-s-based liquefaction analysis in collaboration with the SPT results is quite advantageous to assess the rate of liquefaction in a specific area.
A Debris Avalanche at Suphan Stratovolcano (Turkey) and Implications for Hazard Evaluation
(Springer, 2016) Ozdemir, Yavuz; Akkaya, Ismail; Oyan, Vural; Kelfoun, Karim
The Quaternary Suphan debris avalanche deposit is located in Eastern Anatolia, Turkey. The avalanche formed by the sector collapse of a major stratovolcano towards the north, possibly during a single catastrophic event. The deposit has an estimated volume of 4 km(3) and ran out over 25 km to cover an area of approximately 200 km(2). Products of the collapse are overlain by younger eruptive units from the Suphan volcano. We have tested the numerical code VolcFlow to first reproduce the emplacement of the Quaternary Suphan debris avalanche and then to develop a hazard assessment for potential future sector collapses and subsequent emplacement of debris avalanches and associated tsunami. The numerical model captures the main features of the propagation process, including travel distance, lateral spread, and run up. The best fit obtained for the existing flow has a constant retarding stress of 50 kPa and a collapse scar volume of 4 km(3). Analysis of potential future collapse scenarios reveals that northern sector debris avalanches (up to 6 km(3)) could affect several towns. In the case of a sector collapse towards the south, a tsunami will reach the city of Van and several of the biggest towns on the southern shoreline of Lake Van. Cities most affected by the larger amplitude waves would be Van, Edremit, Gevas, Tatvan, and, to a lesser extent, Ercis, with wave amplitudes (first waves after the onset of the collapse) between 8 and 10 m.
Deformation Patterns in the Van Region (Eastern Turkey) and Their Significance for the Tectonic Framework
(Slovak Acad Sciences Geological inst, 2019) Sengul, M. Alper; Gurboga, Sule; Akkaya, Ismail; Ozvan, Ali
The area of investigation is located on the south-eastern shore of Lake Van in Eastern Turkey where a destructive earthquake took place on 23rd October. 2011 (Mw =7.1). Following the earthquake, different source mechanisms, deformations, and types of faulting have been suggested by different scientists. In this research, Edremit district and vicinities located on the southern side of Van have been investigated to understand the deformation pattern in a travertine (400 ka) formation on the surface, and its structural and stratigraphic relationships with the main faults under the surface by using two-dimensional (2D) Electrical Resistivity Tomography (ERT) profiles. The results were used to document the deformation pattern of rocks with the Miocene and the Holocene (400 ka travertine) in ages. By means of the investigations, deformation patterns implying the tectonic regimes during the Oligocene-Miocene-Pliocene, and Quaternary time have been determined. According to detailed field work, the local principal stress direction has been defined as approximately N35 degrees W. This is also supported by the joint set and slip-plane data. Moreover, Oligocene-Miocene units provide a similar principal stress direction. Our data suggest that the southern part of the Elmalik fault is characteristic of reverse faults rather than of the normal fault system that has been previously reported. In addition, the Gurpinar fault controlling the deformation patterns of the region is a reverse fault with dextral component.
Determination of the Shear Wave Velocity Structure of Substations by the Hvsr Inversion Method Using Broadband and Strong Ground Motion Earthquake Data in the Lake Van Region, Eastern Türkiye. Baltica
(inst Geology & Geography, 2024) Akkaya, Ismail; Alkan, Hamdi
In this research, the horizontal -to -vertical spectral ratio analysis and the Monte -Carlo inversion algorithm are applied to calculate the substations shear wave velocity structure beneath the Lake Van region. To discover the variation of shear wave velocity, the local earthquakes recorded on 15 strong ground motions and 14 broadband stations, located on dissimilar geological units, are used. The most important aim of this investigation is to reveal the geological structure and bedrock depths beneath each station. For this purpose, two-dimensional cross -sections are generated from velocity models in different directions. The average bedrock depth variation is determined at 10 m and 250 m as a result of the horizontal -to -vertical spectral ratio inversions at the earthquake stations in the region. The deepest bedrock depths are calculated at the earthquake stations close to the settlements in the study area. These depth variations are interpreted as the local site effects of possible destructive and big earthquakes that may be a factor increasing the damage ratio in these regions.
Determining the Site Effects of 23 October 2011 Earthquake (Van Province, Turkey) on the Rural Areas Using Hvsr Microtremor Method
(indian Acad Sciences, 2015) Akkaya, Ismail; Ozvan, Ali; Tapan, Mucip; Sengul, M. Alper
A magnitude of 7.1 Mw earthquake struck Van city on October 23, 2011. Although, construction practices of all rural housing units are similar in the region, the earthquake caused massive damage to villages located on soft soils in northern region of the city. In this study, the effects of soil conditions on damaged housing units were determined by conducting horizontal to vertical spectral ratios of microtremor (HVSR) measurements. The level of damage in the villages that are settled on lacustrine and stream sediments has verified that the damage correlates well with comparatively high HVSR peak period and HVSR peak amplitude values in the range of 0.2-1.6 s and 4-10, respectively. The HVSR peak period and HVSR peak amplitude levels on rock units are in the range of 0.1-0.2 s and 1.5-2, respectively. It is important to note that hillside effect is found to be another key factor that increased the level of damage to the housing units in some villages.
Effects of Structural Parameters on Seismic Behaviour of Historical Masonry Minaret
(Budapest Univ Technology Economics, 2018) Erdil, Baris; Tapan, Mucip; Akkaya, Ismail; Korkut, Fuat
The October 23, 2011 (M-w = 7.2) and November 9, 2011 (M-w = 5.6) earthquakes increased the damage in the minaret of Van Ulu Mosque, an important historical masonry structure built with solid bricks in Eastern Turkey, resulting in significant shear cracks. It was found that since the door and window openings are not symmetrically placed, they result in unsymmetrical stiffness distribution. The contribution of staircase and the core on stiffness is ignorable but its effect on the mass is significant. The pulpit with chamfered corner results in unsymmetrical transverse displacements. Brace wall improves the stiffness however contributes to the unsymmetrical behaviour considerably. The reason for the diagonal cracks can be attributed to the unsymmetrical brace wall and the chamfered pulpit but the effect of brace wall is more pronounced. After introducing the cracks, a new model was created and calibrated according to the results of Operational Modal Analysis. Diagonal cracks were found to be likely to develop under earthquake loading. Drifts are observed to increase significantly upon the introduction of the cracks.
Impact of Jet-Grouting Pressure on the Strength and Deformation Characteristics of Sandy and Clayey Soils in the Compression Zone
(Korean Society of Civil Engineers-ksce, 2019) Akin, Mutluhan; Akkaya, Ismail; Akin, Muge K.; Ozvan, Ali; Ak, Yusuf
Jet-grouting as a soil improvement method is extensively preferred in today's civil engineering practice. High-modulus grout columns constructed by extremely high jetting pressures displace the surrounding soil causing a densification in soil particles. Accordingly, the strength as well as the deformation characteristics of subsurface soils are relatively improved across the compression zone which is under the influence of high jetting pressure. In this study, the modification of soil properties in compression zone after jet-grouting in sandy and clayey soils is investigated by standard penetration tests (SPT) and multi-channel analysis of surface waves (MASW) performed at a couple of construction sites along established jet-grout column rows. The in-situ test results point out significant improvement of the measured parameters compared to initial values. The rate of enhancement in the compression zone is higher in sandy strata than that of clayey deposits. The strengthening of soil due to jetting pressure is validated by finite element analyses as well. Furthermore, very low shear strain values are obtained in clayey soils with respect to the improved characteristics of compression zone representing extremely low shear deformation under foundation.
Investigation of Site Effect of Lake Van Region (Eastern Turkey) by Using Strong Ground Motion Records
(Elsevier, 2023) Akkaya, Ismail
The site effect plays a very important role in determining the structural damage that may occur in a possible major earthquake. In this study, seventy-nine strong ground-motion records (M > 4.5) from past earthquake events in the Lake Van region, recorded by 14 accelerometer stations located on dissimilar geological units, were analyzed for local soil properties using horizontal-to-vertical spectral ratio (EHVSR) method. In addition, EHVSR results were compared with Standard Spectral Ratio (SSR) results, which is another method used to determine soil amplification. The obtained predominant period, amplification factor, seismic vulnerability index (Kg) and bedrock depth values were examined. The EHVSR results show that the predominant frequencies of the sites and the amplification factor values were estimated as 0.58-5.77 Hz and 1.84-7.5, respectively. The seismic vulnerability index (Kg) values, which are crucial parameter in hazard assessment, change from 1.6 to 30. The bedrock depths range between 11 and 186 m for the study area. From the results of this study it is found that the damage may be high after a possible destructive earthquake in the study area where the predominant period, amplification, Kg values and bedrock depth are high.
Investigation of Site Properties of the Caldiran (Van, Eastern Turkey) Settlement Area Using Surface Wave and Microtremor Methods
(Pergamon-elsevier Science Ltd, 2023) Alkan, Ayhan; Akkaya, Ismail
Caldiran (Van, eastern side of Turkey) which is a seismically very active region has more than active faults around and the areas under active tectonic effect. The earthquakes and soil characteristics are the significant factors that increase the severity of the damages ratio. For this reason, the characteristics of the engineering structure should be defined accurately and reliably. The shear wave velocity (Vs) obtained from geophysical methods is one of the most important parameters that determine the behavior of the soil during an earthquake. In this study, active and passive source surface wave methods were applied at different measurement points in the study area in order to determine soil properties of the settlement area and its surroundings in Caldiran district the city of Van. As part of this study, 80 boreholes, 95 multichannel analysis of surface wave (MASW) profiles, and 66 microtremor (HVSR) measurements were performed in the study area. The Vs velocity with depth dependent could be determined by using the dispersive behavior of Rayleigh waves in surface wave analysis methods. In order to analyze the engineering characteristic of the region and earthquake-soil-structure relations parameters such as the amplification factor, predominant period (t(0)), Vs velocity, average velocity up to 30 m Vs30, and seismic vulnerability index (Kg) maps have been prepared. In order to reveal the variety of the engineering properties of the area in horizontal and vertical directions, depth cross-sections in different directions were created. When the tectonic structure and regional geology were examined, it was determined that all profile results were compatible with the geological structure.
A New Empirical Correlation Between Pressuremeter Modules (Em) and Shear Wave Velocity (Vs) for Clay Soils
(Elsevier, 2019) Akkaya, Ismail; Ozvan, Ali; Ozvan, Elif E.
The pressuremeter (PMT) and standard penetration (SPT) tests are the most common in situ tests used for determining the engineering properties of soils and rocks. PMT method can be used to determine the deformation and strength properties of soil or very blocky rock masses. PMT procedure is time-consuming and expensive, and it requires advanced testing equipment. Both SPT and PMT methods also require drilling to be performed in the area. The shear wave velocity (V-s) is a parameter obtained using active and passive seismic methods and provides insight into the strength properties of the soil and rock. V-s is easy to obtain with these methods and can be determined in all kinds of field conditions. Due to the difficulties experienced during many types of in-situ tests, numerous empirical equations for the soil or rock units have been proposed in the literature that are based on V-s. In this paper, correlations of Menard Deformation Modules (E-M) with the corrected SPT blow counts (SPT-N-60) and shear wave velocity (V-s) data were conducted. For this purpose, parameters of the pressuremeter were defined as a function of two variables. In order to determine the relationship between the results of these field tests and the results obtained from high-consolidated clayey soils with high and low plasticity properties, 10 boreholes with a depth of 15 m were drilled and in-situ tests were carried out at diverse depths. In addition, seismic measurements were performed at the same locations and depth-based V-s velocity data was obtained. It was concluded that E-M could be predicted as a function of SPT-N60 and V-s values, and the predictions had relatively high R-2 values of 0.77 and 0.75, respectively. This study thereby introduces to the literature empirical equations between E-M and V-s for the first time. As soil properties are heterogeneous and anisotropic, it has been shown that it is more appropriate to use the equations produced from logarithmic and exponential relations in both single and multiple statistical analysis. (C) 2019 Elsevier B.V. All rights reserved.
Seismic Hazard Implications in and Around the Yedisu Seismic Gap (Eastern Türkiye) Based on Coulomb Stress Changes, B-Values, and S-Wave Velocity
(Springer Basel Ag, 2023) Alkan, Hamdi; Ozturk, Serkan; Akkaya, Ismail
The Yedisu Seismic Gap is one of the most important seismic gaps throughout the North Anatolian Fault Zone since it has not produced destructive earthquakes for a long time. To analyze the characteristics of future seismic hazards, the interrelationships between seismotectonic b-values, Coulomb stress changes, and S-wave velocity models of crust are presented in and around the Yedisu Seismic Gap located northwest of the Karliova Triple Junction. For this purpose, the most up-to-date earthquake catalog and the focal mechanism solutions of recent earthquakes are used to image the different depth intervals. Results show that the relatively positive stresses are accumulating along the Varto Fault Zone and Kargapazari and Yedisu Segments between 5 and 15 km depth intervals. At the same time, the lower b-values between 0.6 and 1.0 are found in the same segments. However, in the volcanic regions around the Karliova Triple Junction, the low S-wave velocity zones may be related to high b-values, negative stress changes, and volcanic structures. The region between the Turnadag? volcano and the Varto caldera shows scattered stress and b-value changes in the upper crust. Moreover, the probability of earthquakes for Mw = 6.0, 7.0, and 7.7 in the intermediate term (10 years) is estimated as -65%, -17%, and -5%, respectively. Recurrence of earthquakes with Mw = 6.0, 7.0, and 7.7 are calculated as -10, -55, and -187 years, respectively. Con-sequently, the regions characterized by low strong b-values and positive stress loading reveal high earthquake hazard potential on the whole in the next decade.
A Simplified Fundamental Period Equation for Rc Buildings
(Croatian Soc Civil Engineers-hsgi, 2021) Yigit, Abdullah; Erdil, Baris; Akkaya, Ismail
Considering the huge differences in the prediction and organization of equations available in the literature, this paper aims at developing a reliable equation including mass and stiffness parameters. Microtremor (ambient vibration) measurements were taken from 23 RC buildings and their fundamental periods were compared to the dynamic analysis results. Building models were then calibrated to account for the infill wall effect. After that, 156 RC buildings were 3D modelled and their dynamic analysis results were used to calibrate the proposed fundamental period equation.
Site Characterization in the Van Settlement (Eastern Turkey) Using Surface Waves and Hvsr Microtremor Methods
(Elsevier Science Bv, 2019) Akkaya, Ismail; Ozvan, Ali
The settlements around Lake Van are generally located on young, unconsolidated, saturated, Quaternary aged, current lake and stream sediments. The region is under active tectonism, and many destructive earthquakes have occurred in the area both recently and in historical times. The site effect plays a very crucial role in the prediction of earthquake damage to existing structures and in the planning and design of new structures. The main purpose of this study is to determine the mechanical and physical properties of soils in and around the settlement area of Van and to determine their behaviour under a possible earthquake. Considering these situations, both borehole-based geological data and data obtained from geophysical methods were collected in the Van settlement area. Within the scope of this study, 247 boreholes (the maximum drilled depth approximately 5 km), 185 shallow seismic profiles, 56 multi-channel analysis of surface wave (MASW) profiles, and more than 200 single-station microtremor measurements were collected in the study region, and the soil structure of the study area was evaluated and mapped by analysing the data obtained. In order to investigate the engineering properties of the study area, the parameters such as shear-wave velocity (Vs) at each layer, average Vs down to 30 m depth (Vs30), soil classification, fundamental frequency (period) and the ground motion amplification factor, have been prepared. All of the geological and geophysical data sets obtained in the study area within the scope of this study were mapped with GIS-based database features, and an updatable database was prepared for future works. (C) 2018 Elsevier B.V. All rights reserved.
A Study of the Relationship Between the Pressuremeter Modulus and the Preconsolidation Pressure Around a Thrust Fault
(Springer, 2019) Ozvan, Ali; Ozvan, Elif E.; Akkaya, Ismail; Akin, Mutluhan; Akin, Muge K.
The study area is in a zone under the influence of the Lake Van water changes and the Van fault, which caused a destructive earthquake in 2011. Due to the level changes of Lake Van, sediments with different thicknesses as well as grain sizes were deposited in this region and the characteristics of these sediments were significantly affected by the morphology and lake water fluctuations in the past. A total of six boreholes were drilled along a 3-km line within the study area to determine the preconsolidation pressure (sigma(pc)) and the pressuremeter test values of the clayey levels of old lake deposits-which are known to have different physical and mechanical properties-with hopes to gain an insight on how they influence the mechanical tests performed in the field and in laboratory conditions. The relationship between these values was also statistically evaluated. When both datasets were evaluated together, it was determined that the stresses in the area close to the Van Thrust Fault plane caused deformations in the soil, which in turn affected the hanging-wall block of the thrust fault in particular. The inspection of E-M and sigma(pc) values for the area within the primary compression zone of the Van Fault revealed that both values of the boreholes on the footwall block were higher compared to other boreholes close to the lake (southwest). This finding indicates that the fault stresses at the footwall block of the fault plane enhance the mechanical characteristics of the soil. The data obtained were also evaluated using regression analysis. Relationships between all available data were investigated and a high coefficient of determination was derived between the Menard deformation modulus (E-M) and the preconsolidation (sigma(pc)) pressure.