Güney Karadeniz şelfinde Cide açıklarının çok kanallı sismik yansıma verileri ile araştırılması
The investigation offshore Cide in the Southern Black Aea shelf by using multi-channel seismic reflection data
Yazar: SEVGİ KAYA
Danışman: DOÇ. DR. NESLİHAN OCAKOĞLU GÖKAŞAN
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Jeofizik Mühendisliği Ana Bilim Dalı / Jeofizik Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2019
Konu: Jeofizik Mühendisliği = Geophysics Engineering

Özet:
Tez çalışması kapsamında Güney Karadeniz şelfinde deniz tabanı morfolojisi, sismik stratigrafik ve yapısal özellikler toplam 160 km uzunluğundaki çok kanallı sismik yansıma verisi ile ilk kez araştırılmıştır. Çok kanallı sismik yansıma verileri rutin veri işlem adımları ile işlenmiştir. Veriler İstanbul Teknik Üniversitesi (İTÜ) Jeofizik Mühendisliği Bölümü, 'Nezihi Canıtez Veri İşlem Laboratuvarı'nda bulunan ve Linux işletim sistemi altında çalışan Paradigm 'Echos' sismik veri-işlem yazılımı kullanılarak işlenmiştir. 1991 yılında Türkiye Petrolleri kurumu tarafından toplanan çok kanallı sismik yansıma verileri TÜBİTAK-114Y057 numaralı araştırma projesi kapsamında çalışmaya dahil edilmiştir.
Verilere rutin veri-işlem adımları uygulanmıştır. Bu adımlar SEG-Y formatındaki ham atış verilerinin okutulması, gürültülü veya bozuk izlerin ayıklanması, hatların geometrilerinin programa tanımlaması, atış-alıcı derinlik düzeltmesi, kesme işlemi, çentik (notch) filtreleme, bant geçişli trapozoidal filtreleme, genlik analizi, CDP veri gruplarının elde edilmesi, hız analizi, normal kayma zamanı (NKZ) düzeltmesi ve kesme işlemleri, yığma, zaman ortamı sismik göç uygulaması ve otomatik genlik kazanımı şeklindedir.
Sismik kesitler öncelikle stratigrafik olarak yorumlanmıştır. Başlıca dört sismik ünite ayırtlanmıştır. Bu ünitelerden en altta yer alan kaotik yansıma şekillenmesi ile akustik temeli oluşturan SU4 birimidir. Bu ünitenin üst yüzeyi kuvvetli bir yansıma karakteri ile sismik kesitlerde işaretlenmiş ve yansıtıcı yüzeyin derinde bir çukur ve sırt geometrisi göstermektedir.
SU4' ün üzerinde paralel açılı yansıma karakteri ile daha genç çökeller olan SU3 birimleri yer alır. Bu birimin içerisinde yer yer heyelan seviyeleri görülmektedir. SU3'ün üzerinde şelf yamacı ve derinliklerinde genellikle heyelan malzemesi olarak görülen kaotik dalgalı yansıma şekillenmesine sahip göreceli olarak daha genç birim olan SU2 yer alır. Bu birimin üzerinde şelfin derinleşerek abisal düzlüğe ulaştığı yerde en genç çökeller olarak yatay tabakalı iç yansıma şekillenmesine sahip SU1 birimleri yer alır. Batimetri şelf düzlüğünde yaklaşık -100 metrelerden abisal düzlüğe doğru -2200 metrelere kadar derinleşir.
Yapısal yorumlama sonucu şelf alanında pek çok aktif ve pasif fay haritalanmıştır. Aktif faylar doğrultu atım karakterli olup yer yer sıkışma bileşenine sahiptir. Bu faylar deniz tabanına kadar ulaşır. Şelf alanında D-B uzanımlı haritalanan bu faylar bölgede güncel bir K-G yönelimli sıkışma tektoniğinin delillerini ortaya koymaktadır.

Abstract:
In this study, the seafloor morphology seismic stratigraphic and structural features offshore Cide in the southern Black Sea shelf were investigated by multi-channel seismic reflection data for the first time. The data with the total of 160 km long were acquired by the Turkish Petroleum Company (TP) in 1991. This study was supported by The Scientific and Technological Research Council of Turkey with Project no. TUBITAK- 114Y057.

Multi-channel seismic reflection data were processed by using conventional data processing steps. Echos software developed by Paradigm Company was used during data processing in the Istanbul Technical University (ITU) Geophysical Engineering Department, Nezihi Canitez Data Processing Laboratory. 

Westward escape of the Anatolian plate due to the compression between the Eurasian and the Arabian plate forms the neotectonics of Turkey. The tectonic regime was controlled by two important faults, the North Anatolian Fault (NAF) and the East Anatolian Fault (EAF). The Anatolian plate moves westward along these faults and in the east, the plate turns counterclockwise and overthrusts the Hellenic arc. The compression onto the Anatolian plate creates a contraction regime at the east Anatolia while the west Anatolia expands. 
 
According to GPS velocity studies in Turkey, the horizontal movement rate of the NAF is 23±1 mm/year and 9±1 mm/year westward for the EAF. When the seismicity of the southern Black Sea region was examined, major earthquakes mostly occur on the land along the NAF with a right-lateral strike-slip character. In the region between the Black Sea and the north of the NAF zone, velocity rates are minimum. GPS velocities have been measured around the Sinop peninsula with a rate of 1.4 ± 1.7 mm/year. 
 
Although the neotectonic structures in the region are not active as other regions, some moderate earthquakes have occurred in the near past. In 1968, Bartın earthquake, a thrust fault with a magnitude of 6.8 have occurred near offshore of Bartın which is the evidence that active thrusting is occurring at the southern margin of the Black Sea.
 
There are two basins in the Black Sea separated from each other with an NW-SE oriented ridge. The factors resulting in this structure are the strike-slip faults, contraction/tension boundaries, current direction and sediment condition in the basins. The topography of the southern Black Sea region is characterized by a high mountain range (Pontide Mountain Range) that is dissected by the NAF. The developments of these high morphological features are related to the collision between the Eurasia and Arabia blocks and the subsequent compression that initiated after the closure of branches of the Neo-Tethyan Ocean. 
 
The study area is located in the middle of the south Black Sea shores and the west of the Sinop peninsula at the offshore Cide with ~1695 km shore length and approximately ~5-10 km shelf width. The bathymetry starts around -100 m from shelf plain and deepens -2100 m to the abyssal plain.

To begin with the data processing, the raw shot data have been illustrated. the shot gathers were edited. By edit operator the noisy traces on 241th and 242th channel and 1, 2, 3 and the shots 1372, killed from all lines. Line geometry pattern definition has been done in order to fit the correct shot-receiver accordance by using data acquisition parameters. Secondly, a single seismic section was produced that gave a general idea about the geological view of the line by choosing nearest channel trace from to data each shot. To eliminate noises from the data, a notch filter was applied. After this process, a trapezoidal band pass filtering was applied that's low-cut frequency band 0-10 Hz and high-cut frequency is between 80-100 Hz. Hence the frequencies higher than 100 Hz and lower than 10 Hz were rejected from the all data context. As following, gain analyzing was implemented to compensate descended gain values due to traces. After the editing, geometry definition, notching, filtering and gain analyzing, shot traces converted to the CDP (Common Depth Point) gathers to make velocity analysis and product stack sections.

To obtain CDP gathers, fold number was calculated as 60 by using the acquisition parameters which are group interval, number of channels and shot interval. Then the velocity analysis has been implemented for each 100 CDP group. Analyzing was performed by paying attention to correlation between each of CDP traces. Especially it was important to follow horizontal velocity continuity and not to assign any velocity values inside the sea bottom multiples in order not to define incorrect formations on the stack sections. 

After velocity analysis, NMO (Normal Move Out) correction and mute function are applied both to remove signal stretching on the far offsets and then stack section was produced. To get final seismic section the processing step migration was applied that is in regarded with formations' slope that makes fake affect in view of defining and interpretation of geological structures' correct place.

For the migration step, finite difference wave equation migration and Kirchhoff migration were applied to stack sections. Kirchhoff migration results are well recovered the diffractions and hyperboles than finite difference method.

Finally, AGC (Automatic Gain Control) was applied to time migrated seismic sections with the window of 250 ms to enhance gain of traces from shallow to deep arrival time. In order to clean final sections from noises occurring due to AGC on the top of the sea floor, mute process was applied.

After the data processing, all seismic sections are stratigraphically interpreted. There are four major seismic units detected in the study area. The lowest of these units with its chaotic reflection character is SU4 as the acoustic basement. The upper surface of this unit is interpreted as an unconformity. This surface marked in seismic sections with strong reflection character shows basin and ridge geometry. On top of the SU4, there are younger SU3 sediments with parallel and strong reflection character. In this unit, landslide levels can be detected in some places. On top of the SU3, there is relatively younger SU2 with chaotic and wavy reflection character which is generally considered as landslide deposits at the shelf-slope. On top of this unit where the shelf reaches the abyssal plain, there is SU1. As youngest sediments with parallel layered inner reflection character. The upper surface of SU1 constitutes the seafloor, the seafloor deepens from -100m in shelf plain to -2200 m in the abyssal plain.

As a result of the structural interpretation many active and passive faults were mapped at the shelf area. The active faults including reverse fault, strike-slip faults with compression components reach the seafloor by deforming the seismic units. These faults are extended in E-W direction on the shelf area. This tectonic framework, is the evidence of existence of an active compressional tectonic regime in the N-S orientation offshore Cide in the southern Black sea shelf. The presence of these faults shows that there is an active tectonic in the study area.