Deprem kayıtlarının istatistiksel analizi ile fay uzaklığına ve kayıtlara dayalı şiddet haritalarının oluşturulması
Generation of intensity maps based on fault distance and earthquake records through statistical analysis of seismic data
Yazar: HAKAN TURAN
Danışman: DOÇ. DR. BEYZA TAŞKIN ; DR. KEREM PEKER
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Deprem Mühendisliği Ana Bilim Dalı / Deprem Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2024
Konu: Deprem Mühendisliği = Earthquake Engineering

Özet:
Bu tez çalışması, depremler ve özellikle deprem riskinin değerlendirilmesi üzerine odaklanmıştır. Depremler, dünya genelinde sıkça görülen doğal afetlerden biridir ve bu çalışmada, depremlerin şiddet haritaları aracılığıyla değerlendirilmesi üzerine önemli bir perspektif sunulmaktadır. Avrupa Makrosismik Ölçeği (EMS-98), şiddet seviyelerine ve yapısal özelliklere dayanarak potansiyel yapısal hasarı öngörmek için bir çerçeve sunar. Sismik aktiviteye detaylı bir yaklaşım, doğru ve hızlı oluşturulan şiddet haritaları ile birleştirildiğinde, depremlerin neden olduğu potansiyel hasarı gösteren dağılım haritalarının oluşturulmasına imkân sağlar. Bu yöntem, deprem senaryolarına uygulandığında sadece yüksek riskli alanları tanımlamakla kalmaz, aynı zamanda etkili afet yönetimi planlarının geliştirilmesine de katkıda bulunur.
Çalışmada, Türkiye genelinde 1995-2023 yılları arasında meydana gelen 161 depremden elde edilen 464 istasyon kaydı kullanılmıştır. İlk aşamada, doğrusal en küçük-kareler regresyon yöntemi kullanılarak çeşitli deprem parametreleri ve mühendislik şiddetleri ile en büyük yer ivmesi (PGA) arasında korelasyonlar geliştirilmiştir. Bu parametreler en büyük yer hızı, kümülatif mutlak hız, arias şiddeti, gerçek zamanlı şiddet ve yıkıcı şiddettir. Çalışmanın kritik bir yönü de Türkiye genelinde deprem şiddeti (IEMS) ile maksimum yer ivmeleri (PGA) arasında yerel bir korelasyon oluşturmaktır. Bu korelasyon, şiddeti bilinen sekiz depremin 74 istasyon kaydı ile doğrulandı ve depremden etkilenen bölgelerde hızlıca şiddet haritası oluşturulması için temel oluşturdu.
Daha sonra, 30 Ekim 2020 tarihinde meydana gelen Sisam Adası açıklarındaki depremden (Mw=6.6) etkilenen bölgenin Vs30, ivme ve şiddet haritaları oluşturulmuştur. Haritaların oluşturulabilmesi için depremin merkezüssü konumlandırılmış ve bu süreçte Yunanistan'ın deprem izleme ağı (ITSAK) ve Türkiye deprem izleme ağına (AFAD) ait toplamda 18 istasyon kullanılmıştır. Hem tek istasyon verisi hem de çok istasyon verisi kullanılarak merkezüssü konumlandırma yöntemleri uygulanmış ve sonuçlar karşılaştırılmıştır.
Zemin etkilerinden bağımsız azalım ilişkisi kullanılarak hesaplanan ivme değerlerine zemin büyütme etkisi de eklenerek, depremden etkilenen bölgenin en büyük yer ivmesi haritası oluşturulmuştur. Bu çalışma, elde edilen IEMS-PGA korelasyonu ile şiddet seviyelerinin ivme sınır değerlerini belirleyerek, depremden etkilenen bölgenin şiddet haritasını oluşturma amacını taşımaktadır.

Abstract:
Earthquakes, as one of the most widely observed natural disasters globally, pose significant challenges to communities worldwide. Understanding their magnitude and assessing associated risks are critical aspects of earthquake preparedness and mitigation efforts. Shakemaps, instrumental in determining the severity of seismic tremors, play a pivotal role in evaluating earthquake risk in specific geographical regions, aiding in the development of robust disaster management plans.
The EMS-98 provides a framework for predicting potential structural damage based on severity levels and structural characteristics. A nuanced approach to seismic activity, when combined with accurate and swift intensity maps, enables the creation of distribution maps illustrating potential damage caused by earthquakes. This method, when applied to earthquake scenarios, not only identifies high-risk areas but also informs the development of effective disaster management plans.
This thesis study meticulously analyzed 464 station records from 161 earthquakes in Turkey spanning nearly three decades. The focus was on earthquakes with peak ground acceleration (PGA) values exceeding 50 cm/sec2. Employing the linear least-squares regression method, correlations were established between various earthquake parameters and engineering intensities. These parameters included peak ground velocity, cumulative absolute velocity, arias intensity, real-time intensity, and destructive intensity. The rigorous analysis of seismic data entailed meticulous examination and classification of earthquake events based on their magnitudes, depths, and epicenter coordinates, ensuring comprehensive coverage of seismic activity within the study region. The utilization of the linear least-squares regression method allowed for the quantification of relationships between seismic parameters and engineering intensities, facilitating a deeper understanding of the factors influencing ground motion and structural response during seismic events. Furthermore, the inclusion of diverse earthquake parameters such as peak ground velocity, cumulative absolute velocity, Arias intensity, real-time intensity, and destructive intensity provided a multifaceted perspective on the dynamics of seismic activity and its potential impact on built infrastructure and human settlements. Despite exhibiting a wide dispersion, the correlations established between these parameters and peak ground acceleration are intended to illuminate future studies.
A critical aspect of the study was to establish a local correlation between earthquake intensity (IEMS) and peak ground acceleration (PGA) across Turkey. To demonstrate the consistency of this correlation, it was compared with the intensity-peak ground acceleration relationships generated in 6 different studies found in the literature. For comparison, 74 station records from eight earthquakes with known intensity were utilized as test data. It was observed that the correlation established in this study provided results closest to the observed intensity values compared to previous studies. This validated correlation formed the basis for swiftly generating shake maps in earthquake-affected areas. The case study of the Samos earthquake in 2020 exemplified the application of this correlation, emphasizing the importance of accurate epicenter positioning, appropriate attenuation relationships, and a nuanced understanding of local ground properties.
Swift and accurate epicenter determination is essential in earthquake scenarios, influencing the effectiveness of disaster response and mitigation efforts. The study incorporated 18 stations, leveraging both single-station and multi-station data for epicenter determination. The effectiveness of these methods was rigorously assessed, comparing results with the actual epicenter position from the AFAD database. As a result of this comparison, it was observed that the use of multiple stations provided more accurate results in epicenter determination. This finding underscores the importance of employing a multi-station approach in seismic data analysis for enhanced precision and reliability in determining earthquake epicenters. The integration of data from multiple stations enables a more comprehensive assessment of seismic activity, taking into account variations in ground motion across different locations. Moreover, the utilization of diverse datasets from multiple stations enhances the robustness of the epicenter determination process, mitigating potential errors associated with individual station data. By leveraging the combined information from multiple stations, the study achieved a higher level of confidence in epicenter localization, thereby contributing to more effective earthquake response and mitigation strategies.
Soil properties play a crucial role in the transmission of seismic waves, as they can significantly influence the intensity and duration of ground shaking during an earthquake. Expanding upon the recognition of this intricate interaction between soil properties and seismic waves, the study delved into various aspects to enhance the understanding of ground behavior during seismic events. Recognizing the complex interaction between soil properties and seismic waves, the study employed an attenuation relationship specifically designed for Turkey, independent of soil properties. The ground motion acceleration induced by the energy released from the earthquake source was extracted from the bedrock (Vs30>1050 m/s) and transferred to relevant points.This approach aimed to provide a more accurate assessment of ground movements and their potential impact on structures and communities.
An insightful observation emerged when considering earthquakes within Turkey's borders: the incurred damage is not solely a result of the energy released but is also significantly influenced by ground conditions. The case study of the Samos earthquake highlighted the impact of local ground conditions on losses incurred in the Bayraklı district of Izmir, emphasizing the need for detailed information on soil conditions (Vs30) in risk analyses and disaster management planning.
The study employed the topographic slope-based method developed by the United States Geological Survey (USGS) to determine average shear wave velocities (Vs30) up to a depth of 30 meters in earthquake-affected regions. This information was crucial in understanding the ground conditions and, consequently, assessing potential damage during earthquakes.
Detailed amplification factors dependent on point-specific soil properties (Vs30) were calculated, and acceleration values were amplified. Thus, the potential maximum ground acceleration (PGA) was obtained and mapped. Point-based PGA values were compared with 5 different attenuation relationships found in the literature. As a result of the comparison, it was observed that the method used in the study yielded better results.
Acceleration values, calculated with an attenuation relationship independent of soil effects, formed the basis for determining maximum point accelerations experienced by structures, objects, and humans on the surface. Organizing these values into a matrix facilitated the creation of a peak ground acceleration (PGA) map of the earthquake-affected region.
Utilizing the correlation between IEMS and PGA established in the thesis, intensity level thresholds were defined, contributing to the generation of a shakemap for the earthquake-affected area. This approach, based on instrumental data, holds promise for the rapid generation of intensity maps in future earthquake disasters. After obtaining point-based intensity levels, the potential damages predicted by EMS-98 according to the damageability classes of the structures can be considered as probable damages. 
The exemplary study examined within the scope of the thesis is suitable for considering the earthquake epicenter as a point source. However, earthquakes that cause long fault ruptures and have significant moment magnitudes need to be considered as linear sources.
The integration of comprehensive information about existing building stock opens avenues for creating potential damage distribution maps alongside intensity maps. This dual approach not only enhances our understanding of the potential impact of seismic events but also streamlines decision-making in situations requiring prompt intervention.
In conclusion, this thesis study significantly contributes to earthquake risk assessment and disaster management. The comprehensive analysis of seismic data, establishment of local correlations, and meticulous consideration of ground conditions provide valuable insights for effective strategies in mitigating the impact of seismic events. The methodologies developed in this study offer a pathway for future research and application, fostering a more resilient and prepared global community in the face of earthquakes.