The morphotectonics of the Gulf of Izmit and surroundings

Abstract

In this study, the morphology of area surrounding the Gulf of Izmit located on North Anatolian Fault, one of the most important active tectonic elements of the world, is examined by using quantitative methods, and the role of young tectonics on the morphological evolution of the region is investigated.In recent years a number of new approaches have emerged in the study morphotectonics. These fall into three categories: use of new techniques, search for new types of data (such as digital elevation data), application to geomorphological studies. At the simplest level, landforms can be characterized in terms of their size, elevation (maximum, minimum, or average), and slope. Quantative measurements allow to us objectively to compare different landforms and to calculate less straightforward parameters (geomorphic indices) that may be useful for identifying a particular characteristic of an area. Some geomorphic indices have been developed as basic reconnaissance tools to identify areas experiencing rapid tectonic deformation. This information is used for planning research to obtain detailed information about active tectonics. Geomorphic indices are particularly useful in tectonic studies because they can be used for rapid evaluation of large areas and necessary data often can be obtained easily from topographic maps (especially digital elevation data).The drainage basins are determined from the digital terrain models of the region. Then the morphometrical analysis, hypsometric curve and hypsometric integral, drainage basin asymmetry, mountain-front sinuosity, ratio of valley-floor width to valley height are applied to these basins. Hypsometry has been generally used to infer the stage of geomorphic development. From an analysis of numerous drainage basins, has shown that a convex shaped hypsometric curve characterizes basins in the youth stage, an S-shaped hypsometric curve (concave upwards at high elevations and concave downwards at low elevations) characterizes basins in the stage of maturity, and a concave hypsometric curve characterizes basins in the peneplain stage. Drainage basin asymmetry is the tectonic influences on drainage networks. Tectonic tilting at the scale of drainage basins can be detected from the Asymmetry Factor (AF). For a stable setting, AF = 50. The more that AF departs from 50, the more the influence of tectonic tilting. Mountain-front sinuosity (Smf index) is defined as mountain fronts associated with active tectonics and uplift are relatively straight, with low values of Smf. If the rate of uplift is reduced or ceases, the erosional processes will carve a more irregular mountain front, and Smf will increase. Ratio of valley floor width to valley height (Vf index) differentiates between broad floored canyons, with relatively high values of Vf, and shaped valleys with relatively low values. The study area is formed of different morphological regions. The Gulf of Izmit is east-west trending depression on the northern branch of the young depression placed on the North Anatolian Fault. This depression is delimited by to mountainous belt in the north and south. Drainage basin asymmetry values on the selected drainage basins indicate that the northern belt (Kocaeli Peninsula) is northward tilted as peneplain. Southern part of this peneplain was cut by the North Anatolian Fault. The watershed is very close to the south. On the south-facing slope headward erosion is main morphologic activity. Geomorphic indices indicate that this southern slope is very young and related with the North Anatolian Fault. Southern part of the depression, Samanlı Mountains are higher than the northern part. It is elevated as positive flower structure between the northern and middle branch of the North Anatolian Fault. In the north-facing slope of this area deeply incised valleys and large alluvial fans are the main geomorphic entities. Lithology of the rock forming this area is also affected the morphology. This can be seen hypsometric integrals and other geomorphic indices. In the light of mountain front sinuosity (Smf index) and ratio of valley floor width to valley height (Vf index) values we applied it is clear that the morphology of the region was heavily affected by active faults which have been affecting the southern region rather than northern region.The analysis results indicate that a) rock types, b) the structural features of the rocks, c) the NE and NW trending faults older than the North Anatolian Fault, and d) the active E-W trending North Anatolian Fault controlled the morphological evolution of the region.

Özet

Dünyanın önemli aktif tektonik unsurlarından biri olan Kuzey Anadolu Fayı (KAF) üzerinde yer alan İzmit Körfezi çevresinin morfolojisi ölçüye dayalı (kantitatif) yöntemlerle araştırılmış ve genç tektoniğin bölgenin morfolojik evrimindeki rolü anlaşılmaya çalışılmıştır. Bu bağlamda çeşitli veri setleri kullanılarak, karşılaştırma ve tümdengelim yöntemiyle morfometrik analizler yapılabilmektedir. Bunun için, önce bölgenin sayısal yükseklik modelleri üretilerek drenaj havzaları belirlenmiş, daha sonra bu havzalar üzerinde hipsometrik eğri ve integral, drenaj havzası asimetrisi, dağ cephesi eğrilik oranı, vadi tabanı genişliğinin vadi yüksekliğine oranı olarak bilinen morfometrik analizler uygulanmıştır. Bölgede kuzey kuşağı oluşturan peneplen morfolojisinin drenaj havzası asimetri-si değerleri, seçilen drenaj havzalarında kuzeye eğimlenmeyi göstermektedir. Dolayısıyla günümüz su bölümü çizgisi güneye daha yakın ve Körfez’e akan dereler kısa, dar ve derin deşilmiş vadilere sahip bir morfoloji sergilemektedir. Morfolojik indisler, KAF ile ilişkili olarak güneydeki yamaçların daha genç olduğunu göstermektedir. Güney kuşağı oluşturan Samanlı Dağları, kuzey bölümden daha yüksektir. Bu alanda kuzeye bakan yamaçlarda derin deşilmiş vadiler ve kalın alüvyal yelpazeler başlıca morfolojik özelliklerdir. Kayayı şekillendiren litoloji ise morfolojiden etkilenmiştir. Bunlar hipsometrik integral ve diğer morfolojik indislerde açıkça görülmektedir. Dağ cephesi eğriliği değerlerine bakıldığında güneyin dağ cephesi kuzeyin dağ cephesinden daha fazla aktif faylarla kontrol edildiğini göstermektedir. Vadi tabanı genişliğinin, vadi yüksekliğine oranı ile ilgili elde edilen düşük değerlerin KAF’ın güneyindeki vadilerde elde edilmesi, bu dar vadilerde aktif bir yükselmeyi işaret etmektedir. Bu analiz sonuçları bölgenin morfolojik evriminde a) kaya türlerinin b) kayaların yapısal özelliklerinin, c) KAF’dan önce bölgede etkin olan KD ve KB uzanımlı fayların, d) halen aktif olan D-B uzanımlı KAF’ın etkili olduğunu işaret etmektedir.