Kandilli Rasathanesi ve Deprem Araştırma Enstitüsü

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1-D local crustal structures from seismological data in the Cyprus Subduction Zone and Antalya bay
(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2013., 2013.) Perk, Şükran.; Karabulut, Hayrullah.
The eastern Mediterranean is a tectonically complex region, where long-term subduction and accretion processes have shaped the overall evolution. Recently, many seismic tomography studies have shown subducted slabs of the Neo-Tethyan lithosphere, continuing its subduction in the Hellenic trench, stalled in the Cyprus trench and being torn near the intersection between them. Antalya bay is a key region located on the western flank of the Cyprus Subduction Zone (CSZ), close to the junction between the Hellenic and Cyprus Arcs. Here deep earthquakes are nucleated, which otherwise cannot be seen anywhere else along the CSZ. For this reason, we focus our attention specifically to the Antalya Bay area but also the remaining parts of the CSZ. Several regional studies have been carried out to define the velocity structure beneath the region but none have been able to locate the CSZ. One of the main reasons for this was the lack of incorporation of a wide seismic network in those regional studies. We compile a large catalog of seismicity and relocate earthquakes to infer 1D local crustal structure using the clusters of seismicity. We used seismic data between 2005 – 2011 which are recorded at more than 250 seismic stations operated by several agencies and portable deployments. The data-set is composed of over 10,000 events and earthquakes can be grouped in several distinct clusters. We defined five of these clusters, where the total number of events is more than 4500, among which we selected over 2000 events with the highest data quality. 1-D local P-wave velocity models are developed using this high quality data-set and the earthquakes are relocated using the local velocity models. The compiled and reanalyzed data will contribute to perform local earthquake tomography. Moreover, obtained local velocity models represent a fundamental step towards an improved seismic tomography studies in a very crucial region in the eastern Mediterranean.
3-D crustal structure of the Isparta angle region from local earthquake tomography
(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2011., 2011.) Çakır, Ersin.; Türkelli, Niyazi.
Isparta Angle is a seismically active and complex zone in terms of tectonic and geologic features. A temporary seismic network consisting of nineteen three-component broadband stations were installed around Isparta Angle (IA) and surroundings to address some of the important questions. Detailed crustal structure of the Isparta Angle were obtained using the seismic data collected over two years from July 2006 to June 2008. Results of this study will contribute to beter characterize the crustal structure and the seismicity of the region. In this study, local earthquake data that were collected from temporary broad-band seismic array operated in the region, data from permanent stations of Kandilli Observatory and Earthquake Research Institute (KOERI), permanent stations of Disaster and Emergency Management Presidency (DEMP) and Süleyman Demirel University (SDU) in order to determine the upper crust seismic P wave velocity structure of IA and the surrounding regions by three-dimensional (3-D) Local Earthquake Tomography (LET) method. S-wave arrival times were not included due to strong attenuation and higher picking errors of S-phases. The result of tomographic processes, 3-D velocity model, was compared with the seismological and tectonic features of the region and also compared with the results of the previous studies in the region. The results suggest that low-velocity zones beneath Isparta Angle in the depth range between 0-10 km can be related to alluvial deposits, and the velocity variation below 20 km depth can be related with the transition from upper crust to lower crust.
3-D crustal structure of the Simav - Küyahya and surrounding regions
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2017., 2017.) Duran, Nuray.; Konca, Ali Özgün.
Kütahya and surroundings are quite complex structures from a tectonic and geological perspective. On May 19, 2011, an earthquake of magnitude M = 5.9 occurred in Simav. The purpose of this thesis is determination of the 3-D seismic velocity structure applying the local earthquake tomography method, using earthquakes that occurred between the years 2010 and 2015 in Kütahya Simav and surroundings. The signifigance of this study is that the first 1-D and 3-D tomographic inversion for Simav, Kütahya and surroundings is done by this study. The region's 1-D velocity model, 3-D velocity model and crustal structure are obtained. In this study, the 3-D velocity distribution up to 30 km depth of upper crust of the study area is determined with tomographic inversion methods. For this purpose, by creating data sets, travel time of phases were prepared by tomographic inversion format, appropriate model structure has been created, Vp, Vs and Vp/Vs models that obtained with appropriate resolution parameters and tomographic inversion, has been interpreted with geological and tectonic features of the area. At 30 km depth, P and S waves velocity structure of Kütahya, Simav and surroundings were obtained. The Graben system of the region is supported by the velocity cross-section obtained. The depth of the graben is determined as 20 km. The relationship between the hypocentre of the recorded earthquakes in the region and Vp, Vs, and Vp/Vs anomalies has been revealed with horizontal and vertical cross-sections. Comments are made about the structural differences of the region’s P wave and S wave velocity information and the physical properties of the rock’s Vp/Vs ratio information. Fault systems, potential fault zones and earthquake activity of the region are discussed with the combined results of the study.
3-D P wave velocity structure of Marmara Region using local earthquake tomography
(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2013., 2013.) Işık, Sezim Ezgi.; Gürbüz, Cemil.
The 3D P wave velocity model of upper and lower crust of the Marmara Region between 40.20 - 41.20 N and 26.50 - 30.50 E is obtained by tomographic inversion (Simulps) of 47034 P wave arrivals of local earthquakes recorded at 90 land stations, 30 OBO stations and 14162 shot arrivals recorded at 35 OBO stations (Seismarmara Survey, 2001) between October 2009 and December 2012. We first obtained a 1D minimum model with Velest code in order to use it as an initial model for 3D inversion with 648 well located earthquakes located within the study area. We first developed a 1D model by VELEST code then used it as an initial model for 3D tomography. After trial 3D inversions we decided to create a more adequate initial model for 3D inversion. Choosing the initial model we estimated the 3D P wave velocity model representing the whole region both for land and sea. The results are tested by making Checkerboard Test, Restoring Resolution Test and Characteristic Test, and the reliable areas of the resulting model is defined in terms of RDE, DWS, SF and Hit count distributions. By taking cross sections from the resulting model we observed the vertical velocity change along profiles crossing both land and sea. All the profiles crossing the basins showed that the high velocities of lower crust make extensions towards the basin area which looks like the force that gives a shape to the basins. Under the north of the Central Basin and Çınarcık Basin high velocity zones appeared which look like resisting walls holding the north of the basins between 5 km and 15 km. The same is also observed under the southern Tekirdağ Basin between 5 km and 15 km. These extensions of lower crust towards the basins appeared with an average velocity of 6.3 km/s. These extensions might be the result of the deformation due the shear in the region and it is also interpreted that the development of these high velocities coincides with the development of the basins. Thus, both the basins and the high velocity zones around them might be resulted from the entrance of the NAF into the Marmara Sea when also a shear regime is dominated due to the resistance of the northern Marmara Region (Yılmaz, 2010). The seismicity is observed between 5 km and 15 km after the 3D location of the earthquakes. The locations of the earthquakes improved and the seismogenic zone is determined well, between 5 km and 15 km. The depths of the pre-kinematic basement and crystalline basement showed great differences under the sea. It is observed that the velocity under sea becomes compatible with land after 8 km.
3-D P-wave velocity structure beneath eastern Turkey applying local earthquake tomography (LET) method
(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2005., 2005.) Teoman, Uğur Mustafa.; Türkelli, Niyazi.
Eastern Turkey is a seismically active region exhibiting a complex structure in terms of both tectonic and geologic· features. A temporary seismic network consisting of 29 broadband three-component broadband stations were installed in the scope of Eastern Turkey Seismic Experiment (ETSE) to address the important questions. Detailed and accurate evidences relevant to the crustal and upper mantle structure of the region were obtained using the seismic data collected in between October 1999 and August 2001. Results of the ETSE project had a considerable contribution to understanding and interpreting the tectonic evolution along with the seismicity of the region. In this study, local earthquake data from the ETSE project were used in order to determine the upper crust seismic P wave velocity structure of Eastern Turkey and the surrounding regions by three-dimens}onal (3-D) Local Earthquake Tomography (LET) method. As far as resolution is concerned, S waves were not included in this study due to strong attenuation, insufficient number of S phase readings and higher picking errors with respect to P phases. LET is the 3-D imaging process ofthe velocity structure of a target volume by using the travel time data of the earthquakes recorded within the seismic network in an active region. To provide accurate tomographic results, a high quality data set, initial hypocentral parameters and a minimum one-dimensional (1-D) velocity model that adequately represents the region are required. Initially, data compilation and earthquake locations were determined. Initial locations of 9*4 events were performed by HYPOCENTER algorithm using an initial 1-D velocity model, which was obtained from the previous studies in the region. Following the earthquake location procedure, higher quality events were selected in order to construct the 1-D minimum velocity model for the region. As a basic data selection criteria, events with azimuthal gap (GAP) ::; 200° and number of observations (P) ~ 8 were selected from the initial data set (6978 P-phase readings). 1-D velocity model was calculated by VELEST algorithm performing a simultaneous and iterative 1- D velocity inversion. New hypocentral parameters and station corrections were also calculated in addition to the minimum velocity model. Three different trial velocity models were used in order to construct an initial velocity model based on the results of a set of inversions with ten iterations and four calculation steps. Each velocity model were constructed in 0-42 depth range in accordance with the crustal structure of the region, however, accurate results were obtained down to~ 15-20 km due to the depth distribution ofthe events. The relocation of the earthquakes was performed by VELEST via the 1-D minimum velocity model and the relevant station corrections. In the final step, various stability tests were applied to check the resolution capability minimum 1-D velocity model. As a result of these tests, it was suggested that 1-D minimum velocity model adequately represented the region. After the derivation of the most appropriate velocity model, 3-D tomographic inversions were applied to the final data set. Events with GAP :::;; 180° and P > 8 were reselected from the data set. Number of events for the tomographic inversion reduced to 504 after applying this criteria (Total number of 6742 P-phase readings). 3-D tomographic inversion was iteratively and simultaneously performed by SIMULPS 14 algorithm using node-grid geometry for model parameterization. Considering the event-station distribution, a horizontal grid with 30x30 km grid spacing was chosen. In vertical direction, depth values taken from the 1-D velocity model were used. Modeling was made down to 42 km. Tomographic inversions with four iterations and two processing steps were initiated after determining the appropriate control parameters and the damping factor. At the end of these processes, 3-D P wave velocity model and the resulting hypocenters were determined. A significant reduction in data variance (- %50) and in residuals (-%50) was observed during these processes. In order to assess the solution quality and the resolving power of the 3-D model, tests with the synthetic data were performed. Critical parameters affecting the resolution estimates were calculated and mapped along with absolute velocities (Vp) and% perturbations relative to the 1-D initial velocity model in both horizontal and vertical cross-sections. Consequently, after the tomographic applications, the compatibility of the results with the tectonic and seismological features of the region were evaluated and also compar~d with the results of the previous studies in the region. The differences between the initial and the final hypocentral parameters were emphasized in various cross-sections. XV
3-D velocity structure of eastern Marmara region from local earthquake tomography
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2008., 2008.) Denli, Alper.; Gürbüz, Cemil.
Local earthquakes located in 40-41.5 N and 28-30.5 E geographic coordinates between the dates January,2003-October,2007 were selected to use for local earthquake tomography. Data were obtained from short period and broadband seismic stations dispersely located in the region. This study was conducted to reveal 3-D P wave velocity structure in the target area. To prepare data set, relocation procedure was done. To determine the 1-D velocity model for the study region, earthquakes which have azimuthal gap less than 1800 and recorded at least by 7 stations were selected. Obtained 1-D velocity model has 32 km depth. Reliable solutions were observed to 17 km due to the depth distributions of the earthquakes. To consolidate the robustness of the velocity model, shifting test was applied and quarry blast data were used. Results show that the 1-D velocity model represents the study region. Using reference earth model for local earthquake tomography was decided. Later on, observing more confidential parts of the velocity changes in the study region, synthetic models were produced for the checkerboard test. At the same time, control parameters were set to obtain reasonable solution after running tomography algorithm. 3-D tomographic inversion based on damped least square inversion was applied to 14329 P wave arrival times and the results of 3-D tomographic inversion were tried to correlate with geologic verifications in the region. Generally low velocities change between 5.3-5.7 km/s through vertical extension of the faults. Vertical extensions of the NAF branches are observed between 2 -15 km depths when the resolution parameter of the data set taken into account. These properties are relatively similar for extracted profiles. Location of the vertical extensions of the fault zones mainly show the same depth range similar to done previous studies in the region.
A comparison and evaluation of different soil-structure-interaction approaches for bridges
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2019., 2019.) İnci, Oytun.; Şafak, Erdal.; Önem, Göktürk.
During the last fifty years, bridge construction has increased extensively throughout the world, including on areas with bad soil conditions, to meet the transportation needs of expanding urban areas. Although Soil-Structure-Interaction (SSI) procedures for performance-based design of buildings have been introduced in design guidelines, seismic provisions are not clearly stated for bridges. There are two main approaches to include SSI in performance-based design of the bridges; direct method and substructure method. In the direct method, bridge and soil systems are analyzed as a single system under seismic shaking, defined at bedrock. As an alternative, the substructure method is introduced to solve the system as substructures in two stages, called kinematic interaction and inertial interaction. The nonlinear response of piled foundation systems of bridges are subjected to kinematic interaction; whereas, the nonlinear response of superstructure is subjected to inertial interaction. In this study, first, he linear design of two different bridges are introduced by considering their geometry and the number of spans. Bridge-I has three spans with uneven pier heights, and Bridge-II has four spans with identical piers and the geometry. Both bridges are designed based on a response spectrum created according to site response analysis and used in the performance-based design of the bridges. 19 different records are selected and scaled according to the criteria given in AASHTO LRFD Bridge Design Specifications Article 4.7.4.3.4 (AASHTO, 2012) Seismic Design Guidelines. Seismic records are categorized with respect to soil parameters, chosen for both strength-based and performancebased design of bridges. Secondly, using the direct method, the Nonlinear Time History (NTH) analyses are performed for both bridges to investigate the behavior of structural elements. The nonlinear responses of the bridges are re-calculated by using the substructure method, including the kinematic and inertial interactions. Responses of the structural elements are combined according to commonly-used combination rules. Finally, results of these methods are compared with each other, as well as the linear response of the structures, to underline how the behavior of the structures vary according to different analysis methods.
A method to calibrate analytical models of multi-story buildings from earthquake records
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2014., 2014.) Kocakaplan, Sedef.; Şafak, Erdal.
For multi-story buildings, the standard approach to develop analytical models from earthquake records is to match the modal characteristics (i.e., modal frequencies, damping ratios and mode shapes) of the model with those identified from the data. Typically, the response of the building is recorded in the basement, roof and a few intermediate floors. When the number of the instrumented floors is less than the total number of floors, an analytical model cannot be constructed uniquely. In other words, more than one model can match the recorded response. This study presents a new method based on the transfer matrix formulation of the response. The method requires that vibration time histories are known at every floor. Since they are typically not recorded at every floor, we first present a methodology to estimate vibration time histories at non-instrumented floors from those of the instrumented floors. We assume that, at each modal frequency, the mode shape of a multi-story building can be approximated as a linear combination of the corresponding mode shapes of a shear beam and a bending beam. We determine the combination factors by using the least-squares approximation to the mode shapes identified from the records. The accuracy of the methodology is tested by using recorded motions from two buildings that have instruments at every floor. Assuming that only a few floors had instruments, the vibration time histories at other floors are calculated and compared with the recorded time histories. The results of the methodology are also compared with those from other approximation techniques, such as linear or cubic interpolations, and found to be much superior. Once the vibration time histories are known at every floor, we present a new approach to calibrate analytical models of multi-story buildings based on the transfer matrix formulation of the response. The methodology utilizes top-to-bottom spectral-ratios at each story and shows that these spectral ratios are not influenced by any structural changes in the stories below. Thus, starting from the top story, the stiffnesses of each story can be determined uniquely by matching the dominant frequencies of the spectral ratios, assuming that the mass of each floor is known or estimated. A numerical example is presented to confirm the validity of the approach. The study proves that the story stiffnesses of a multi-story building can be determined uniquely by using vibration records taken from only a few floors.
A new insight into the crustal structure of the central Anatolia to eastern mediterranean from a wide angle seismic data
(Thesis (Ph.D.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2016., 2016.) Denli, Alper.; Özel, Nurcan Meral.
As a part of the CyprusArc project a seismic wide angle reflection/refraction profiles, the 300 km and 45 km long north-south trending profiles extended from Cihanbeyli in Central Anatolia to Anamur in eastern Mediterranean and in southern Cyprus, respectively, in March 2010. The seismic experiment was comprised of two land explosions of 1125 kg explosives onshore and 98 cubic liters airguns offshore. 76 three-component and 119 vertical-component sensors were deployed along ~300 km distances between Cihanbeyli and Anamur with an average spacing of 1.25 km. 25 three-component sensors and 25 vertical component sensors were installed along 45 km distances on land at southern Cyprus with an average spacing of 1.25 km. Appropriate band pass filter was applied for each controlled sources to pick the arrival times. Modelling of the CyprusArc profiles data show that a Moho depth of 38 km at the northern end of the profile which increases 45 km through the southern end of the profile from central Anatolia to eastern Mediterranean. An average P-wave velocity is 6.5 km/s beneath Tuz Golu basin till approximately 23 km depth. P-wave velocity of some rock materials which brought into the open by Taurus Mountains is 5.5 – 5.6 km/s till 5 km thickness. A high velocity block (average P-wave velocity is 6 km/s) between 120 -150 km offset, till 8 km thickness probably correspond to ophiolite complex belong to Troodos. 2-D crustal P-wave velocity model shows crustal thinning between south Turkey and Cyprus from 45 km to 30 km. Final 2-D P-wave velocity models were further refined by generating synthetic seismograms to observe the theoretical travel times and amplitudes of the various arrivals. Additionally, 2-D gravity modelling was done to check robustness of the unresolved part of models by seismic phases and the all results were correlated with geology, tectonics and previous investigations in the study area.
A parametric study for the characterization of site amplification
(Thesis (Ph.D.)-Bogazici University.Kandilli Observatory and Earthquake Research Institute, 2020., 2020.) Fercan, Nazife Özge.; Şafak, Erdal.; Ansal, Atilla.
In earthquake engineering, the approximation of site amplification by using practical ways has been an important issue. Various site parameters were proposed and applied in the engineering practice. Among these, time averaged shear wave velocity for the top 30 m, Vs30, and fundamental frequency, f0, have been used widely. In this study, we investigated the reliability of Vs30 parameter, and the performance of alternative time averaged shear wave velocities (e.g., Vs40, Vs50, etc.) and shear wave travel times (Ttz) at various depths for the estimation of site amplification. For the same bedrock depth, we considered 17 shear wave velocity profiles, changing from convex (i.e., the velocities changing faster near the surface and slower near the bedrock) to concave (i.e., the velocities changing slower near the surface and faster near the bedrock). We divided the soil media, first into layers with equal thickness, and then into layers with equal wave travel times. For each layering type and soil profile, we calculated the site amplification factors and fundamental frequencies, and studied their correlations with time averaged shear wave velocities (Vsz) and wave travel times (Ttz) for different depths, z. We have also investigated the correlation of site amplification factors, surface PGAs (Peak Ground Accelerations), and fundamental soil frequencies (f0) for each case. We have identified the optimal averaging depths for the averaged shear wave velocity and the wave travel time to characterize site amplification. The study showed that there is a sharp change in the correlations when switching from convex to concave profiles. By gradually increasing the bedrock acceleration levels, we have also studied the nonlinear soil response and its correlations with linear soil response. We presented guidelines to estimate nonlinear soil amplification factors and fundamental frequency from the linear ones. Considering that the linear fundamental frequency and amplification can easily be calculated from field tests (e.g., ambient noise measurements for f0 detection), these guidelines provide a useful tool to estimate nonlinear ones.
A proposed ground motion selection and scaling procedure for nonlinear response history analysis
(Thesis (Ph.D.)-Bogazici University.Kandilli Observatory and Earthquake Research Institute, 2016., 2016.) Zengin, Esra.; Akkar, Sinan.
With the advancement in performance-based earthquake engineering, nonlinear response history analysis of structures has become more common in recent years. The selection and scaling of ground motions for use in nonlinear response history analysis is one of the most critical steps in performance-based seismic assessment procedures. This study presents ground motion selection and scaling procedure that addresses the uncertainty in the spectral demand with the preserved dispersion within the ground motion set. The candidate ground motion sets are constructed based on dispersion statistics about the target spectral demand. The optimum ground-motion set is linearly scaled by using an optimization algorithm that minimizes the error between scaled median and target spectra. The scaling stage ensures that the median record spectrum provides a reasonable match to target median in a previously defined period interval. This procedure allows performing further modification on each scaled ground motion in order to match the target variance of the scenario-based spectrum. In this study, a novel probabilistic framework is presented to propagate the uncertainties in both ground motion intensity and the structural response on fragility curve estimations. To investigate the effects of uncertainties on seismic damage estimations, the results of this study are compared with those obtained by the conventional fragility curve approach.
A rapid estimation of moment magnitude Mw for the October 23, 2011 Van earthquake using strong-motion records
(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2014., 2014.) Kılıç, İrfan.; Özel, Nurcan Meral.
It is well known that the Richter scale (local magnitude scale, ML) based on the measurement of the amplitude in a narrow- band time domain saturates for large crustal earthquakes, and the possibility of observing clipping on seismograms is high. Therefore it is insufficient to use the local magnitude for reliable magnitude estimation. A typical example of this situation is confronted in case of the October 23, 2011 Van Earthquake ( ML 6.6 vs MW 7.2) . Here MW is the moment magnitude obtained from the far-field displacement spectrum of body waves. On the other hand, a better match is expected in the range of 3 < ML < 7 because in this range the empirical relation between seismic moment M0 and ML is almost the same with the relation between M0 and MW (Thatcher and Hanks, 1973; Hanks and Kanamori, 1979). Hence, there is a1234E need to find a way for the determination of MW from near-field records too.The aim of this study is to determine moment magnitude of earthquakes very soon after occurrence, before any source or focal mechanism inversions have been performed. In this respect (Delouis et al., 2009) proposed the MWSYNTH method. In this method, observed displacement spectra are compared with synthetic spectra computed for a variety of finite dimension source models scaled with MW. In this study we have tried to obtain a rapid estimation of Mw for the October 23, 2011 Van Earthquake from the strong-motion records in the epicentral distances about 120 km using MWSYNTH method. Using strong motion records of only two stations we obtained an agreeable estimation of moment magnitude MW=6.9. The result may be improved (approach more seriously to the reference moment magnitude MW ref=7.15) by doing computation for more stations and it is foreseen that a correct recovery of MW for the Van Earthquake within about 100 sec after origin time (recording+computing time) will be possible if the procedure is automated.
A review of the tectonics of the aegean region
(Thesis (M.S.)- Bogazici University. Kandilli Observatory and Eartquake Research Institute, 1998., 1998.) Komut, Tolga.; Küleli, H. Sadi.
The Aegean region is a remarkably deforming part of the Alpine-Himalayan orogenic belt, which has the highest seismic activity in Europe. An extensional deformation regime has led to subsidence of the continental crust over all the Aegean region behind the south Aegean consumption boundary. The region that is mainly under pure shear stress is an internally deforming part of the counterclockwise rotating (relative to Eurasia) Anatolian plate. To understand the tectonics and dynamic evolution of the region many geoscientists have collected numerous data and interpreted them. In the present study, all available data have been compiled into a unique database. For this purpose, as a first step, raw and processed information have been compiled and classified with their sources, date information and criticism of their accuracy and limitations. This step allows the comparison of similar types of study and data in order to· understand basic problems more clearly. As the second step, all interpretations of the studies are discussed and critically reviewed by considering associated data and methodology on a regional scale. The goal of the work is to determine the problems with highest priority, find the gaps in the database.
A seismic vulnerability analysis procedure for urban loss assessment
(Thesis (Ph.D.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2008., 2008.) Tüzün, Cüneyt.; Aydinoğlu, M. Nuray.
The assessment of seismic vulnerability of buildings in seismically active urban areas is of great importance in terms of engineering, economical and social aspects. In this study an analytical procedure has been developed in order to obtain the vulnerability functions of existing buildings. The building information included over all geometry of the structure, as-built dimensions and configuration of the structural members, complete with reinforcement details of beams and columns, which are extracted from the design dossiers available in the Bolu municipality archives. Totally 120 buildings, 20 from each class, are classified depending on their number of stories ranging from 2 to 7 story and nonlinear response history analysis has been performed in order to obtain damage distributions by using 20 spectrum compatible ground motions. In the first chapter a brief explanation of the role of loss estimation studies in urban planning, urban disaster management and mitigation has been given. In the second chapter, existing building vulnerability relationships have been evaluated and particular examples of studies that have made important contribution to the development are briefly cited. In the third chapter, basic steps of a standard derivation of analytical vulnerability functions are identified and the importance of each step in the process has been explained. In the fourth chapter, the procedure based on real building data has been explained in detail including the ground motion characterization, properties of building data, analytical methods used in the analysis, damage definition and quantification, statistical process and the determination of the vulnerability parameters. Results are presented in the form of lognormal vulnerability curves with respect to spectral acceleration or spectral displacement. In the fifth chapter, the conclusions are presented and the contribution of the study to the existing knowledge in the field has been evaluated
A simplified non-linear soil-structure interaction (SSI) model for the earthquake response of surge vessels resting on shallow foundations
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2017., 2017.) Turandan, Kenan.; Uçkan, Eren.
In this study, earthquake response of a surge vessel which consists of 8 interconnected tanks is studied. This HPV unit is located in western Saudi Arabia with 600.000 m³/day desalination capacity. The focus of this study is to see and evaluate the response of the structure under soil structure interaction effects. Therefore the properties of the superstructure are kept the same for all the analysis. SSI parameters and earthquake input motions are changed in order to represent the various properties of soil and earthquake motions. The comparisons of analyses results to earthquake codes are made. Some suggestions are made to overcome the existing weakness and increase the performance of the structures. SSI model is developed and various non-linear analyses are conducted and the results are evaluated and compared. Also the difference in response of the structure is compared with and without SSI considered. In the first chapter of this study, the scope of the work and general information about the surge vessel is given. In the second chapter, the methodology is explained. In the third chapter modelling and analyses are explained. Modelling and analyses are not kept as separate chapters in the name of being compatible with the development flow of the study. And the analyses results are evaluated and comparisons are made along with the development. In the fourth and final chapter conclusions are presented and suggestions for improving this study are proposed.
A study on the fragility modeling of mid-rise tunnel form RC buildings for Turkey
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2021., 2021.) Özen, Uğur.; Akkar, Sinan.
The mid-rise tunnel form RC buildings in metropolitan cities in Turkey and their dynamic behavior against earthquake action are investigated by deriving a representative model. First of all, the compiled blueprints of the tunnel form RC building inventory are categorized into four different groups and their fundamental features are studied statistically. The first group, which is the focus of this study represents general features of mid-rise tunnel form buildings in Turkey. Secondly, the nonlinear structural model of this building is developed based on the code requirements and guidelines to perform push-pull and pushover analysis for obtaining its simplified SDOF version in the MSc thesis of Curic (2021). The results of these two theses will complete and augment each other in a near-future collaborative work. Then, the ground motions selected and scaled to the target conditional-response spectra developed in Curic (2021) are used together with the provisions in the 2018 Turkish Building Earthquake code, 2004 Eurocode, and 2017 ASCE code to assess the structural performance of the model building (through damage states) for developing fragility curves. The observations from this study show that the performance of mid-rise tunnel form buildings can be called as satisfactory under the requirements dictated by the national and international standards. Another observation is that different engineering demand parameters give different performance assessment results. Hence, novel global and local performance demand parameters should be investigated by studying other categories (mid- and high-rise) tunnel form buildings. The variabilities in (1) engineering demand parameters, (2) structural properties such as story number, types of vertical elements, and mathematical model, and (3) the definition of limit states in both local and global performance levels have a significant effect on the fragility curves. These variabilities are taken into account for performance based assessment.
A tomographic image of the fault zone on the north anatolian fault
(Thesis (M.S.) - Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2006., 2006.) Afacan Ergün, Tuğçe.; Karabulut, Hayrullah.
During the fall of 2003, seismic data were collected in the eastern Marmara Region on the North Anatolian Fault Zone near izmit rupture zone by a controlled source experiment. The fault was clearly exposed on the surface and the thickness of the sediments in the basin is expected to be greater than several hundred meters. The data were acquired along a 1.2 km long nmih-south profile with a total of 50 recorders equipped with 4.5 Hz geophones. 3-component geophones were used near the fault zone to detect trapped waves. The shot spacing was 5 m and receiver spacing was varying from 1Om to 20m. More than 180 shots were fired using a vibroseis. Data were recorded continuously with 1OOHz sampling rate. . This study is a step towards a determination of a shallow P wave velocity structure on the NAFZ near izmit rupture. We applied regularized inversion technique to the first arrival travel times. More than 6500 picks from 129 shot-gathers were used in the analysis. A shallow P wave velocity image (<200m) from travel time tomography was obtained in the izmit basin. The results indicate a fault zone of approximately 100 m thick. A velocity contrast was detected between the fault zone and surrounding blocks. The P wave velocity on the southern block varies between a range 1.4 - 1. 7 km/s and 1. 7 - 2.0 km/s on the northern block the velocity decreases to 1.4 km/s within the fault zone. 3-component recordings and fan shots indicates the presence of the fault zone consistent with the . tomographic image. Previous seismological studies in the region also show that the thickness of the fault zone is on the order of approximately 1OOm.
A Unified approach in GPS accuracy determination studies
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2009., 2009.) Öztürk, Didem.; Şanlı, Uğur.
By the time GPS technology started to be used in Geodesy, it is much easier to reach the desired precision of point positioning. It is significantly a useful technique, thus one can easily predict the accuracy of GPS before a field survey and know about the quality of the observations that have been made on a reference point. Parallel to the improvement of the GPS technology, predicting the accuracy over short and long baselines has really been an important discussion. There have been several studies dealing with precise point positioning and the topic was to determine how the accuracy depends on the baseline length and the duration of the observing session (Eckl et al., 2001, Soler et al., 2005, Do an, 2007, Engin and Sanli, 2009). In the previous studies, the accuracies for the baselines were taken into account separately, and models have been created for the baselines between 30-300 km and 300- 3000 km. For the baselines smaller than 300 km, the accuracy was found to be a function of only the observing session duration (Eckl. et al., 2001) but for the baselines between 300-3000 km the results show that it does not only depend on the observing session it also depends on the inter-station distance (Engin and Sanli, 2009). In this study, the aim was to make the discussion topic certain and to combine a model for baselines ranging from 3 km to 3000 km. To define a unified model, GPS accuracy was tested in IGS network and the results are compared with recent studies by using GIPSY software. 13 baselines and the data of 10 days have been used in this research. Baseline lengths were between 3 km and 2739 km. The data of each day have been divided into sub sessions (6-8-12 and 24 hours) and then evaluated separately. Thus, the relation among GPS point positioning, base length and duration of observation has been examined. The results show that, the point positioning accuracy in IGS network over 3-3000 km depends both on the baseline length and the observing session duration. It is partially possible to define a unified model for baselines between 3 and 3000 km. To define a unified model for this range, could only be possible by testing out the significancy of various sub sets of Least Squares coefficients.
Acceleration - displacement response spectra (ADRS) for design of seismic isolation systems in Turkey
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2018., 2018.) Yolcu, Aslıhan.; Tanrıcan, Gülüm.; Tüzün, Cüneyt.
Nonlinear Response History Analyses (NLRHA) have been frequently used in seismic isolation system design since the displacement at long period end of the codebased spectra is limited to a certain value and may not accommodate larger displacement demands. The NLRHA is a practical tool to determine the maximum displacement of the system based on prede ned values of e ective period, e ective damping and base shear transmitted to superstructure which are internally connected and requires an iterative process. In order to reduce the process, the methodology which is called as Acceleration-displacement response spectra (ADRS) approach is proposed by Whittaker and Jones (2013, 2014). In this study, ADRS approach is extended considering the new Turkish Building Seismic Design Code (TBSDC, 2018) that will come into force in 2018. Series of nonlinear response history analyses are performed for several isolation system parameters and seismic hazard levels. Displacement spectra are obtained by using bi-linear hysteresis curve model. E ective and robust ADRS graphs which facilitate the preliminary design stage of the seismic isolation systems are obtained in terms of acceleration and displacement demands of earthquakes. The e ects of di erences in fundamental seismic isolation system parameters and ground motion selection criteria on the preliminary design of seismic isolation systems are examined and represented in graphical forms. ADRS graphs provide the base shear and displacement limits of seismic isolation systems in the region under maximum considered earthquake (DD1) and design basis earthquake (DD2) design levels. Shaking levels are obtained from New Probabilistic Seismic Hazard Map of Turkey (TDTH, 2016). The design spectra composition is formed using two site categories (NEHRP C and NEHRP D) and two hazard zones (high and moderate hazard) at each design level. For each design spectra, eleven horizontal ground motion pairs are selected and linearly scaled using the geomean spectral ordinates. Analyses are performed using a combination of eight site-speci c design spectra in total, six e ective isolation system periods and ve yield levels. Evaluation and discussion of the ADRS graphs are provided to develop an overall understanding about the base shear and displacement limits of a seismic isolation systems in the region.
Accuracy of GPS precise point positioning (PPP)
(Thesis (M.S.)-Bogazici University. Kandilli Observatory and Earthquake Research Institute, 2009., 2009.) Tekiç, Simge.; Şanlı, Uğur.
We tried to show how the accuracy of GPS varies with respect to observing session duration by using the method of GIPSY precise point positioning (PPP), and how the site’s coordinates latitude, longitude and ellipsoidal height are affected. We used eleven IGS sites scattered almost evenly across the earth. GPS data were obtained from SOPAC archives at http://sopac.ucsd.edu/cgi-bin/dbDataBySite.cgi in Rinex (Receiver Independent Exchange) format. Processing of the GPS data was achieved through the use of Jet Propulsion Laboratory’s GIPSY OASIS II software and the application of “Precise Point Positioning” method (PPP) by Zumberge et al., (1997). In addition, least squares (LS) analysis was used to model the accuracy of PPP. Our study is based on the mathematical expression of Eckl et al., (2001) in which the dependence of accuracy on observing session is expressed with T. GPS data were segmented into shorter sessions from 1 h to 24 h. For each segment a GPS solution was produced using the PPP routine. We used RMS values from sub-segments to model the accuracy of GPS PPP. Results indicate that accuracy of GIPSY PPP depends only on the observing session T. Observing sessions shorter than 4 hour show dependency on latitude especially for the components longitude and ellipsoidal height. Using session length of 6 or more hours one can model the accuracy of GPS PPP with a simple formulation. Our results also indicate that prediction formulation for PPP is only slightly different from that of relative positioning formulation.

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