Orta Marmara fayının kinematiğinin GPS ölçmeleriyle belirlenmesi
Determination of Central Marmara fault kinematics with GPS
Yazar: VOLKAN ÖZBEY
Danışman: DOÇ. DR. TURAN ERDEN
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Geomatik Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2017
Konu: Jeodezi ve Fotogrametri = Geodesy and Photogrammetry
Dizin: GPS = Global Positioning System ; Kuzey Anadolu fay zonu = North Anatolian fault zone

Özet:
Yerküreyi oluşturan tektonik levhalar, Yer Bilimleri için her zaman önemli bir çalışma konusu olmuştur. 1912 yılında Alman fizikçi Alfred Wegener tarafından ortaya atılan "Kıtaların Kayma Teorisi" ile yerküreyi oluşturan levhaların birbirine göre yavaş fakat sürekli bir hareket halinde oldukları düşüncesi ortaya atılmıştır. 1970'li yıllarda ortaya çıkan "Levha Tektoniği Kuramı" ile levhaların birbirine göre hareketlerinin yeryüzünde çeşitli sonuçlar doğurduğu, bu hareketler sonucunda meydana gelen olaylardan birinin de "deprem" olduğu kanıtlanmıştır. 
Levha sınırlarını oluşturan fayların üzerinde biriken gerilmenin jeodezik ölçme yöntemleriyle belirlenebilmesi fikri ilk kez 1906 San Francisco Depremi ile ortaya çıkmıştır. Depremin meydana geldiği San Andreas Fayı üzerinde deprem öncesi ve sonrasında fayın her iki tarafında yersel ölçmeler yapan  Harry F. Reid'in çalışmaları, fay üzerinde biriken gerilmenin varlığının sadece deprem anında değil, deprem öncesinde de var olduğunu kanıtlamıştır. Gelişen teknolojiyle birlikte yersel ölçme teknikleri yerini zaman, bütçe ve doğruluk açısından son derece daha iyi sonuçlar veren uydu jeodezisi tekniklerine bırakmıştır.
1960'lı yılların sonunda temelleri atılan GPS tekniği başlarda sadece askeri amaçlar için kullanılmaktayken zaman içerisinde sivil kullanıcılarında erişebildiği, teknolojik gelişmelerle birlikte doğruluğu son derece yüksek, gece-gündüz ve her türlü hava şartlarında ölçme yapılabilen, kişisel hataların büyük çoğunluğunun elemine edildiği ve en önemlisi yeryüzü üzerindeki bir noktanın konumunun anlık olarak belirlenebildiği bir sistem olarak günümüze gelmiştir. Bütün bu avantajlarıyla birlikte GPS tekniği günümüzde, levha hareketleri gibi yavaş ve sürekli hareketlerin gözlenebilmesi için en kullanışlı teknik olmuştur.
Ülkemiz tektonik olarak son derece aktif olan "Akdeniz Himalaya Kuşağı'nda" yer almaktadır. Ülkenin genel tektonik yapısını bölge üzerinde bulunan Kuzey Anadolu Fayı (KAF) ve Doğu Anadolu Fayı (DAF) oluşturmaktadır. Doğuda Bingöl'den başlayıp batıda Saros körfezine kadar uzanmakta olan KAF, dünyanın en aktif sağ yanal atımlı faylarından biridir. Geçtiğimiz yüzyılda sismik olarak son derece aktif olan KAF üzerinde gerçekleşen 1939 Erzincan (M_w= 8.0), 1999 İzmit (M_w=7.4) ve 1999 Düzce (M_w=7.2) depremleri ülkemiz için hem maddi hem de manevi açıdan son derece derin yaralar açan ve etkisi uzun süre boyunca hissedilen olaylardır. Özellikle 1999 İzmit Depremi sonrasında KAF'ın Marmara Denizi içerisinde bulunan segmentlerinin gerilme birikiminin belirlenmesi önem kazanmıştır. Adalar segmentinin elastik deformasyon ürettiğini son dönemde yapılan çalışmalar ortaya koymaktadır. Orta Marmara segmenti üzerindeki sismik boşluğun nedenlerinin belirlenmesi ise son derece önemli hale gelmiştir.  
Bu amaçla, çalışma kapsamında faya yakın ve uzak alanlarda tesis edilen istasyonlardan oluşan bir jeodezik ağda 2015 ve 2016 yıllarında kampanya tipi GPS ölçmeleri gerçekleştirilmiştir. Toplanan GPS verileri MIT tarafından geliştirilen GAMIT/GLOBK yazılmı ile değerlendirilmiş ve değerlendirme sonucunda istasyonlara ilişkin, Avrasya levhası sabit kabul edilerek ITRF sisteminde üç boyutlu konum ve hız bilgileri elde edilmiştir. Elde edilen bu bilgiler ile Orta Marmara Segmentinin kinematiğinin belirlenmesi amaçlanmıştır.

Abstract:
The tectonic plates that creates the Earth have always been an important topic to work on for Geosciences. In 1912, the thought of the plates forming the globe were in a slow but continuous motion relative to each other was put forward with the idea of "Slippery of the Titans" by the German physicist Alfred Wegener. The "Plate Tectonic Theory" that emerged in the 1970s proved that the movements of the plates in relation to each other had various consequences on earth and that one of the events that took place as a result of these movements proved to be an "earthquake".
The idea of determineting the tension that accumulates on the faults forming the plate boundaries by geodetic survey methods first appeared in the 1906 San Francisco Earthquake. The work of Harry F. Reid, who made terrestrial measurements on both sides of the fault before and after the earthquake on the San Andreas Fault, where the earthquake occurred, proved that the presence of the strain on the fault exists not only during the earthquake but also before the earthquake. Together with the developing technology, terrestrial surveying techniques have been replaced by satellite geodesy techniques, which provide much better results in terms of time, budget and accuracy. For this purpose, VLBI and SLR techniques were used initially in studies that require extremely high accuracy, such as solid earth tides, ocean loading displacements, and monitoring of plate movements. The complexity of VLBI (Very Long Baseline Interferometry) and SLR (Satellite Laser Ranging) techniques has brought the need to use of GPS technology, a relatively simpler system.
Global Positioning System, which was based on the end of 1960s, was only used for military purposes in the beginning, became accessable by civil users over time,  with the improving technology, as a system which has together with extremely high accuracy, and also which can measure day and night and all kinds of weather conditions, can eleminate the personal errors and most importantly a system in which the position of a point on the Earth can be determined instantaneously. With all these advantages, GPS technique is now the most useful technique for observing slow and continuous movements such as the plate movements. There are some sources of error that affect GPS technic, although it provides extremely accurate and instantaneous position information, comparing to the past techniques. Among those errors, the errors that was caused by the satellite and receiver time are because of the times difference between the actual GPS time and the GPS time displayed on the receiver can be corrected/adjusted by various methods. The only personal error that can be observed in GPS is that the incorrect reading of the antenna height can be corrected by accurately measuring the correct position of the receiving antenna. Other than these, the satellite ephemeris errors can be corrected by using the precise orbital information, and the signal reflection errors can be corrected by making it sure that when the station point is determined, around of the point is clear and there is no structure to cancel the signal sent from the satellite. In addition, ionospheric effect and troposphere effect, which are atmospheric faults, are being eliminated by using various models.
Our country is located in the tectonically active "Mediterranean Himalayan Belt". The general tectonic structure of the country is composed of the North Anatolian Fault (NAF) and the Eastern Anatolian Fault (EAF) that are located on the region. The North Anatolian Fault, which is one of the most important active strike-slip faults in the world, extends, starting from Bingöl in the east and throughout North Anatolia from the west to the Saros Gulf. As it is known, the line that can be traced on the land, in the east it passes through or close Bingöl, Varto, Karlıova, Erzincan, Suşehri, Reşadiye, Niksar, Erbaa, Ladik, Havza, Kamil, Kargı, İsmetpaşa Station, Gerede, Bolu respectively, and cuts Ilgaz Mountains between Havza and Boyalı. Then it passes through Elmalı Vadileri, Kelkit, Destek Strait in the east and Soğanlı Vadileri, Abant and Mudurnusuyu in the west. After making a break in this area, it passes through the middle of Manyas and Geyve (Sakarya River) and extends from Biga peninsula to Saros Gulf. 
1939 Erzincan (M_w = 8), 1999 Izmit (M_w = 7.4) and 1999 Düzce (M_w = 7.2) earthquakes that occurred on the seismically highly active KAF in the past century have been extremely deeply affected both in material and moral terms, their effects have been felt for a long time. Especially after 1999 Izmit earthquake, determination of the strain accumulation of the segments of the KAF in the Marmara Sea has gained importance. Recent studies have shown that the Prince Island segment produces elastic deformation. However, studies that are focused on the Central Marmara segment, that is located offshore Istanbul, a giant metropolis that has more than 14 million population, do not conclude about the presence of a seismic gap, capable of generating a big earthquake. Therefore determination of the causes of the seismic gap on the Central Marmara segment has became extremely important.
For this purpose, campaign-type GPS measurements were carried out in 2015 and 2016 in a geodetic network consisting of stations based on near and remote areas of the fault. At least 16 hours of data were collected for each station using the static measurement method of GPS positioning methods. At least two days of measurements were carried out at each station and these measurements were performed simultaneously. The stations in the study area that are constantly observing are included in the collected GPS data. 16 stations from the CORS-TR network and 10 stations from the ISKI-UKBS network were also included in the evaluation. In addition, 16 continuously monitored station points connected to IGS, a global scale network, were included in the study to increase the accuracy of the data evaluation process. The evaluation of the data was done by the GAMIT / GLOBK software, which was developed by MIT.  In order to be able to evaluate the data with GAMIT / GLOBK software, the collected data has been converted to RINEX (Receiver Independent Exchange Format) format which is a format independent from the receiver. Station coordinates, atmospheric parameters, zenite delays, satellite and receiver clock errors were determined for each session using the GAMIT module. Using this set of data, first daily and yearly repeatability were produced for all stations. By evaluating the repetitions produced, the day(s) that are not suitable to make tectonic interpretation are excluded from evaluation. Then, using the GLOBK module, three-dimensional position and speed information in the ITRF (International Terrestrial Reference Frame) system was obtained by assuming that the Eurasian plate was fixed. The obtained velocities were compared with the results of previous studies in the region and various deductions were made. With this information obtained, it is aimed to determine the kinematics of the Central Marmara Segment.