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Arşivlenen Tez
Yoğun kentsel ağlarda kaydedilen kuvvetli yer hareketi verilerine göre azalım ilişkilerinin yerelleştirilmesi
The regional dependency of ground motions underlines the necessity of adopting a more localized approach in the estimation of ground motion parameters (GMPs). This thesis kicks off with a consistency assessment of the five most suitable regional or global ground motion prediction equations (GMPEs) for the interested area and our local database including 6,534 individual horizontal-component ground motions recorded by the İstanbul Earthquake Rapid Response and Early Warning System (IERREWS) network during 78 small-to-moderate earthquakes. The examination uncovers a systematic overestimation tendency in GMPEs. Using the same database, an analysis is conducted to ascertain whether there are any regional azimuth-dependent effects on ground motions. Due to the vagueness of azimuthal effects, the ground motion recording axes are converted to their principal axes, indirectly introducing the azimuthal influence into the analyses. This thesis suggests a station-specific methodology to refine GMP estimations by isolating regional variations. Evaluation of regression outcomes, distance scalings, and residuals guide the selection of the most appropriate functional forms for the empirical equation. Comparisons of the spatial distribution of peak ground acceleration (PGA) for hypothetical and actual earthquakes serve as the basis for the evaluation of the result consistency. Local variations between GMPEs' estimates and station-specific approximations provide insight into the impact of regional effects on ground motions. The assertion is substantiated by the finding that PGAs calculated from actual earthquake records demonstrate a closer match with station-specific methodology's predictions, especially in regions with observed local differences.
Makine öğrenmesi siniflandirma algoritmalari ile yapay veri seti kullanilarak deprem hasari tahmin modeli geliştirilmesi
Assessing the potential damage to buildings due to a possible earthquake in a region and taking measures, such as strengthening or reconstruction of vulnerable structures, is critically important to minimize social and economic losses that are likely to occur. Evaluating the seismic performance of structures is a comprehensive and time-consuming process. However, using well-trained machine learning prediction models instead of traditional structural performance analyses can significantly reduce computation time. This thesis focuses on developing a damage prediction model using classification-based machine learning algorithms, utilizing a two-dimensional reinforced concrete frame system dataset that represents low to mid-rise, non-ductile buildings. The structural features forming the dataset are obtained from a comprehensive literature review on building stock characteristics in the Marmara region. Nonlinear time-history analyses are conducted using actual earthquake records with the OpenSeesPy framework. The maximum inter-story drift ratio is used as an engineering demand parameter to classify the damage state of buildings. Reliable machine learning models are developed with a balanced dataset. Twenty-four models are created using six variant ground motion intensity measures and four classification algorithms: k-Nearest Neighbors, Support Vector Machine, Decision Tree, and Random Forest. The best-performing model is determined by comparing performance metrics and the confusion matrix. In conclusion, the model developed with a dataset incorporating peak ground velocity and utilizing the Random Forest classification algorithm demonstrates the most effective performance with 92% prediction accuracy.
İstatiksel yöntemlerle gerçek zamanlı yapı sağlığı izleme
The detection of structural damage relies on understanding the long-term variation of modal parameters and their relationship to changes in atmospheric conditions. This thesis aims to address this challenge by developing a real-time algorithm for structural health monitoring systems, which are becoming increasingly important. The algorithm uses statistical models developed by analyzing four years of modal frequencies, damping ratios, and mode shapes of Hagia Sophia, a UNESCO World Heritage structure, and their correlation with atmospheric parameters such as temperature, humidity, and wind speed. The algorithm uses four different regression models to predict the modal frequency as a function of the atmospheric conditions and selects the most suitable one.It then compares the predicted and measured frequencies to identify structural anomalies. The algorithm also employs the Modal Assurance Criterion (MAC), Coordinate Modal Assurance Criterion (COMAC), and Enhanced Coordinate Modal Assurance Criterion (ECOMAC) methods to examine the long-term variation of mode shapes. The algorithm is implemented in a user interface software called "AISHM," which displays the modal parameters and the 3-D animation of the structure in real-time. The software also has the capability to track earthquakes and analyze the structural response in real-time. In summary, this thesis presents a comprehensive approach to real-time structural health monitoring using statistical models and advanced analysis techniques, which can have significant implications for maintaining and preserving historical structures.
İstanbul metropol alanında sismik dalgaların uzun periyotlu amplifikasyonu
Istanbul is a megacity located very close to the North Anatolian Fault and thus is highly vulnerable to seismic hazards. During the 2019 Mw5.7 Silivri earthquake the recorded displacements show site amplification at long-periods and prolonged duration corresponding to the frequency range of 0.1-1.0 Hz. The excitations in these frequency range cannot be explained with variations in very shallow structure only and requires an analysis that considers deeper sedimentary basins. Amplifications in this frequency range cause resonance effects and serious damage tall and high-rise buildings and infrastructure. The Mw 5.9 Silivri earthquake of September 26, 2019, provided a good dataset for investigating site-specific amplification effects. This thesis analyzes acceleration records from nine AFAD strong-motion stations distributed over different geological units to evaluate the characteristics of long-period amplification. As an initial test, we compare synthetic waveforms using two velocity: (i) a crustal model from Karabulut et al. (2020), and (ii) an AFAD-based station specific shallow velocity model which includes near-surface velocity layers from AFAD station reports. We show that neither of the models work well for amplified waveforms especially on the motion recorded in stations on the European part of Istanbul. Instead we generate synthetic seismograms for each station. We try two approaches. First, we generate synthetic waveforms at the surface of the crustal model which is assumed to represent a hard-rock reference waveform. Then we randomly generate 2 layer structures on top of this structure and optimize the fit to the data in the frequency domain. As a second approach we calculate the synthetic waveforms at a depth of 2 km. We then again optimize for each station the layered structure that represent first two km beneath the station. For each trial we calculate the amplified waveforms using the transfer function of these two layers for SH waves. For each station we generate 5000 velocity models and optimize the fit between the acceleration spectrum of data and synthetics. The best-fitting velocity structure was obtained by spectral fitting of synthetic and recorded waveforms. Results show that the site amplification largely varies with local geological conditions: stations located on stiff geological units (e.g., 3405, 3413, 3417) have minimal amplification, while soft sediment sites (e.g., 3411, 3412, 3416) undergo strong amplification and long shaking. Station 3412 displays anomalous amplification and longer oscillations probably due to very thick unconsolidated sediments or local site complexities. While the AFAD-based velocity model underestimated the observed amplification, the crustal model fits better for hard rock sites but failed to capture the amplification at soft sediment stations. Based on our modeling results, we estimate that stations 3407, 3411, 3413, and 3416, which are situated on soft sediment, have sediment thicknesses ranging between 120 and 200 meters with underlying layers exhibiting shear wave velocities of 248 m/s, 87 m/s, 420 m/s, 188 m/s for first layer, respectively. For the second layer values for each station 254 m/s, 294 m/s, 789 m/s, 220 m/s for station 3407, 3411, 3413, 3416 respectively and the layer thickness for second layer ranging between 200 m to 1000 m. The better fit at a depth of 2 km for these stations suggests that deeper sedimentary layers significantly influence wave amplification. In comparison, AFAD's velocity models provide shear wave velocities of 597 m/s for 3407, 323 m/s for 3411, 452 m/s for 3413, and 420 m/s for 3416 for first layer and 2000m/s for 3407, 523 m/s for 3411, 772 m/s for 3413 and 849 m/s for 3416 for the second layer, indicating some discrepancies between our estimated values and the reference models. These differences highlight the need for further refinement, considering potential lateral variations and deeper structural influences. When compared to AFAD's reference models, our synthetic seismograms show good agreement for stations 3407, 3411, 3413, 3416 where both amplitude and spectral content are well captured. However, discrepancies at other stations suggest that additional factors, such as lateral heterogeneities or path effects, may be influencing the results. In general, for significantly amplified stations on the Anatolian side, it is to refine these models further, it is necessary to incorporate additional earthquake records from different directions to assess whether the observed variations persist across different source locations and azimuths.
Yenilikçi teknikler kullanarak sismik güçlendirme tasarımı: Bir okul binası örneği
Seismic retrofitting plays a critical role in ensuring the safety and resilience of structures in earthquake-prone regions. This study investigates the performance of fluid viscous dampers (FVDs) as an alternative retrofitting technique for improving the seismic performance of buildings. The Büyük Halkalı Primary School Building in Istanbul, originally constructed in 1997 and retrofitted twice using conventional methods (in 2006 and 2019), was selected as a case study. The study aims to propose an innovative retrofitting solution that minimizes construction time, operational disruptions, and associated costs while enhancing seismic resilience. A comparative analysis was conducted between the conventional retrofit approach (reinforced concrete shear walls) and the proposed alternative retrofit solution incorporating FVDs. The evaluation considered seismic performance, cost-effectiveness, serviceability, and architectural impact. Nonlinear time-history analyses were performed using TBDY-2018 and ASCE 41-23 standards, with a particular focus on near-fault effects, including forward directivity effects that were not considered in previous retrofits. The results demonstrated that the incorporation of FVDs significantly improved seismic performance by reducing inter-story drift and structural damage. Furthermore, the alternative retrofit method resulted in shorter construction periods and minimized the necessity for building evacuation, ensuring continuous serviceability. The findings highlight that using FVDs in seismic retrofitting can be a viable solution, particularly for structures requiring uninterrupted functionality during construction, such as school buildings.
Gömülü eklemeli boru hatlarının deprem yer hareketi altında davranışının sayısal modellemesi
Earthquakes severely impact infrastructure, disrupting essential services like water pipelines. Understanding and improving the mechanical behavior of pipelines and their joints under permanent ground deformations is crucial to minimize potential damage and ensure the continuity of their service. In this study, three-dimensional numerical models of buried segmented ductile iron pipes were developed to investigate their nonlinear behavior under lateral strike-slip surface faulting. Fault crossing angle, position, and vector were selected as variable parameters, and pipeline performance was evaluated based on different faulting scenarios and two soil models covering a total of 20 cases. The numerical models were validated using experimental and finite element data from the literature. The results indicate that when the fault crossing angle was perpendicular to the pipeline axis, the system was able to accommodate the most amount of fault displacement. Narrower fault crossing angles induced axial separations or compression to the pipeline. Under compression, the pipeline undergoes joint crushing failure by exceeding the material limits, while tensile forces primarily lead to joint pullout. A joint interlocking phenomenon was observed in tension cases when the fault crossed directly through the joint and effectively delayed or prevented failure by uniting adjacent pipe segments. The results also highlighted the sensitivity of pipeline performance to design criteria, where a 2 cm increase in pullout threshold resulted in up to 20 cm of additional fault displacement capacity. Lastly, the study emphasized that while soil models influenced pipeline response under tension, their effect was limited in compression scenarios due to more premature failure.
Istanbul'da bulunan Ayasofya'nın doğrusal olmayan yapısal modellemesi
Hagia Sophia in Istanbul is one of the most iconic architectural and engineering achievements in history. Constructed in the sixth century, the structure has remained standing for over 1500 years, despite being exposed to numerous destructive earthquakes that caused significant damage, including partial collapses. Its location in a high seismic hazard zone makes the evaluation of its structural performance essential. Since the 1990s, studies on Hagia Sophia have mostly relied on linear analyses and idealized geometries, largely neglecting long-term deformations. This thesis focuses on the evaluation of the level and extent of the present-day deformations on the structure; the creation of a finite element model based on the actual geometry rather than the idealized one; the assessment of the contribution of permanent deformations to the static and dynamic structural response; nonlinear static and dynamic modeling to understand the structure's present and future earthquake behavior; and the assessment of potential collapse mechanisms of the structure. The deformed geometry of the building was obtained using three-dimensional laser scanning and converted into a mesh. A model with ideal geometry was first developed in SAP2000 and then updated to reflect the observed deformations. Both deformed and undeformed models were transferred to ANSYS and subjected to static and dynamic analyses. Real earthquake records were used in the linear dynamic analyses. The nonlinear modeling was carried out using calibrated material definitions based on recordings from the Mw 6.1 Silivri earthquake on April 23, 2025. Additional analyses were performed using both real and synthetic ground motion records. The results were evaluated in terms of structural response and collapse mechanisms, with a particular emphasis on the influence of geometric deformation.
Doğu anadolu fayı güneybatı bölümünün mekansal ve zamansal sismik tehlike analizi
Türkiye is one of the most seismically active regions in the world due to its location at the intersection of the Eurasian, Arabian, and African tectonic plates. The country's tectonic regime is primarily governed by two major strike-slip fault systems, namely the North Anatolian Fault (NAF) and the East Anatolian Fault (EAF). On February 6, 2023, southeastern Türkiye experienced a devastating earthquake doublet, with moment magnitudes of 7.8 and 7.6, occurring nine hours apart along different segments of the EAF system. These events caused widespread destruction across 11 provinces, affecting millions of people and significantly altering the stress regime of the region. This study investigates the seismic behavior of the southwestern part of the EAF system before and after the 2023 earthquakes to understand the seismic hazard potentials. To achieve this, a combined approach was adopted involving Coulomb stress modeling, b-value analysis, and geodetic deformation assessment. Coulomb stress change calculations were performed to evaluate stress transfer and potential triggering in adjacent fault segments. In addition, the b-values, derived from the Gutenberg-Richter frequency-magnitude relationship, were used to detect spatiotemporal stress accumulation and release zones, with additional sub-period analysis revealing the impact of the 2023 events and background seismicity of the region. To complement these two approaches, coseismic deformation was analyzed using the InSAR technique, observing displacement patterns across the affected region. Additionally, strain rate fields were reviewed from regional GPS data to identify areas of increased tectonic stress. By integrating these geodetic and seismological datasets, the study highlights overlapping regions characterized by high strain accumulation, low b-values, and positive coulomb stress changes. The convergence of these datasets contributes a comprehensive framework for understanding tectonic stress evolution and improving future seismic hazard assessments along the southern and southwestern parts of the EAF system.
Empirik koda normalizasyonu ve ınsar yöntemlerini kullanarak kaf'taki depremler için büyüklük tahminleri
This thesis presents an integrated seismological and geodetic study to improve earthquake source characterization along the North Anatolian Fault Zone (NAFZ), a region of high seismic risk and significant tectonic complexity. The primary objective is to resolve inconsistencies in regional earthquake catalogs by developing a homogeneous moment magnitude (Mw) catalog for events with magnitudes ranging from 3.5 to 6.0. To achieve this,the Coda Calibration Technique (CCT) that utilizes the stable, scattered energy of coda waves to derive robust source spectra, mitigating path and site effects common in tectonically complex areas, is applied. The calibration is fixed using independently derived Mw from moment tensor inversion for low frequencies and apparent stress (σA) from coda spectral ratios for high frequencies, resulting in a reliable, homogeneous Mw catalog. Second, for two specific events, the 23 November 2022 M w 6.0 Düzce and the 18 April 2024 Mw 5.6 Tokat earthquakes, we conduct Interferometric Synthetic Aperture Radar analysis using Sentinel-1 data. The resulting coseismic deformation fields are modeled using an elastic dislocation formulation to invert for fault slip distribution, providing independent, geodetically-derived Mw estimates that validate the seismological results. A key finding of this study is the evidence for non-self-similar source scaling in the NAFZ; apparent stress is observed to increase with seismic moment, suggesting that larger earthquakes radiate energy more efficiently than smaller ones. Furthermore, the derived apparent stress values are systematically lower than in other active tectonic regions, indicating a potentially low-stress, low-seismic-efficiency environment for the fault zone. This integrated, multi-physics framework not only produces a critical, homogeneous Mw catalog for improved seismic hazard assessment but also provides fundamental new insights into the earthquake rupture physics of the NAFZ.
Ground motion prediction equations and spatial correlation model for Istanbul - developed by real and simulated ground motions
Bu çalışmada, İstanbul ve yakın bölgesindeki aletsel gözlemlerden (MW 4.0–6.1) ve büyük bir geniş bant benzetimlerinden oluşan veri setlerinden (MW 6.05–7.6) yararlanarak yer hareketi modelleri geliştirilmiştir. İstanbul ve çevresindeki 170'i aşkın istasyondan elde edilen kayıtlar derlenmiş, ve model geliştirmede kullanılmak üzere işlenmiştir. Benzetim oluşturmada kullanılan stokastik benzetim yaklaşımı, zaman ve frekans alanlarında beş küçük-orta büyüklükte Marmara depremine karşı doğrulanmıştır. Doğrulamanın ardından, kırılma modelleri üzerinde beş tarihsel İstanbul senaryosu (1509 MW 7.6; 1766 MW 7.0–7.1; 1894 MW 6.8–6.9) ve buna ek olarak uyarlanmış 13 diğer senaryo (MW 6.05–7.6) için geniş bant yer hareketleri üretilmiştir. Stokastik benzetimler, mevcut 3-B fizik temelli deterministik benzetimlerle birleştirilmiş ve 0.1–20 Hz aralığı kapsaması sağlanmıştır. Üç adet yer hareketi tahmin deklemi (GMPE) oluşturulmuş ve başarımı ölçülmüştür. Bu kapsamda, (i) İstanbul'da kaydedilen Marmara Denizi depremlerine dayanarak oluşturulan ampirik bir GMPE (MW 4.0–6.1); (ii) aynı gözlemsel veri kümesi üzerinde eğitilmiş ve makine öğrenimiyle zenginleştirilmiş bir GMPE; ve (iii) bölgedeki orta-büyük deprem eksikliğini gidermeyi amaçlayan, yalnızca benzetim verisine dayalı bir GMPE (MW 6.05–7.6) geliştirilmiştir. Bu modellerin tahmin başarımı, literatürde yerleşik GMPE'lerle yapılan nicel karşılaştırmalarla değerlendirilmiştir. Mekânsal korelasyon modeli oluşturmak için rezidüel ampirik yarı varyogramları oluşturulmuş ve üstel modellerle karşılaştırılmış; sonuçlar, belirgin bir spektral periyoda bağımlı korelasyon yapısını ortaya koymuştur. Genel olarak, gözlemler ile fiziksel olarak tutarlı geniş bant benzetimlerin bütünleştirilmesi, gerçek verinin sınırlandığı büyüklük–uzaklık aralıklarında tahmin başarımını artırmakta ve İstanbul ve yakın bölgesindeki mühendislik uygulamaları için bölgeye özgü girdiler sağlamaktadır.