Central Anatolian Fault Zone Research Articles

Neotectonic evolution of the northwestward arched segment of the Central Anatolian Fault Zone, Central Anatolia, Turkey

Central Anatolia has undergone complex Neotectonic deformation since Late Miocene–Pliocene times. Many faults and intracontinental basins in this region were either formed, or have been reactivated, during this period. The eastern part of central Anatolia is dominated by a NE–SW-trending, left lateral transcurrent structure named the Central Anatolian fault zone located between Sivas in the northeast and west of Mersin in the southwest. Around the central part, it is characterized by transtensional depressions formed by left stepping and southward bending of the fault zone. Pre-Upper Miocene basement rocks of the region consist of the central Anatolian crystalline complex and a sedimentary cover of Tertiary age. These rock units were strongly deformed by N–S convergence. The entire area emerged to become the site of erosion and formed a vast plateau before the Late Miocene. A NE–SW-trending extensional basin developed on this plateau in Late Miocene–Early Pliocene times. Rock units of this basin are characterized by a thick succession of pyroclastic rocks intercalated with calcalkaline–alkaline volcanics. The volcanic sequence is unconformably overlain by Pliocene lacustrine–fluviatile deposits intercalated with ignimbrites and tuffs. Thick, coarse grained alluvial/colluvial fan deposits of marginal facies and fine grained clastics and carbonates of central facies display characteristic synsedimentary structures with volcanic intercalations. These are the main lines of evidence for development of a new transtensional Hırka–Kızılırmak basin in Pliocene times. Reactivation of the main segment of the Central Anatolian fault zone has triggered development of depressions around the left stepping and southward bending of the central part of this sinistral fault zone in the ignimbritic plateau during Late Pliocene–Quaternary time. These transtensional basins are named the Tuzla Gölü and Sultansazlığı pull-apart basins. The Sultansazlığı basin has a lazy S to rhomboidal shape and displays characteristic morphologic features including a steep and stepped western margin, large alluvial and colluvial fans, and a huge composite volcano (the Erciyes Dağı). The geometry of faulting and formation of pull-apart basins can be explained within the framework of tectonic escape of the wedge-like Anatolian block, bounded by sinistral East Anatolian fault zone and dextral North Anatolian transform fault zone. This escape may have been accomplished as lateral continental extrusion of the Anatolian Plate caused by final collision of the Arabian Plate with the Eurasian Plate.

Comment on “A new intracontinental transcurrent structure: the Central Anatolian Fault Zone, Turkey” by A. Koçyiğit and A. Beyhan

Koçyiğit and Beyhan have described the Central Anatolian Fault Zone (CAFZ), as a >700 km long active strike–slip fault zone in Turkey. If their interpretation is correct, then several major Turkish cities are vulnerable to a significant earthquake hazard which was previously unsuspected, and the existing close agreement between observed slip rates on major strike–slip faults in Turkey and predictions from global plate motion models is spurious. Whether the CAFZ is real, or based on mistaken interpretations of diverse evidence, is thus a matter of some importance. The aim of this comment is to describe difficulties which arise over the published interpretation of the CAFZ, with the aim of encouraging either a retraction or a more thorough presentation of the available evidence in support of the existence of a major active fault zone in the required position. Three main difficulties are discussed in detail. First, strands of the CAFZ have been interpreted in many localities where previous detailed studies have either found no evidence of faulting or have reported ancient faults which have been described as no longer active. Second, many other features which previous studies have explained satisfactorily are reinterpreted as consequences of active strike–slip faulting. Finally, no observational evidence is presented for the slip rate or the timing of the start of the alleged present phase of slip on the CAFZ. The suggestion that it has slipped by 24 km during this present phase of activity is inadequately documented and conflicts with other evidence.

A new intracontinental transcurrent structure: the Central Anatolian Fault Zone, Turkey

Recent neotectonic studies, including remote-sensing, aerial photographs, geological field mapping on various scales and measured stratigraphic section substantiate the existence of a large sinistral intracontinental transcurrent structure, which we call the Central Anatolian Fault Zone (CAFZ). This is an approximately 730-km-long, 2-km- to 80-km-wide, NE-trending, active sinistral strike-slip fault zone that cuts across the Anatolian plateau between Düzyayla in the northeast and Anamur County in the southwest. It continues onward beneath the Eastern Mediterranean Sea and determines the boundary of the Antalya and Adana basins as far as to the west of Cyprus. The CAFZ is a very young neotectonic structure. It resulted from the reactivation and propagation of an older paleotectonic structure, the so-called ‘Ecemis̡ Corridor’, in both NNE and SW directions across the Inner Tauride Suture in the Plio-Quaternary times. Based on geometric discontinuities, the CAFZ is divided into 24 segments. Each of them is characterized by a number of strike-slip morphotectonic features reflecting recent motions. The easternmost part of the Anatolian Platelet is being deformed internally by several dextral to sinistral intraplate strike-slip faults. These are the Lake Salt Fault Zone (LSFZ), the Salanda Fault (SF), the CAFZ, the Göksu-Yazyurdu Fault Zone (GYFZ) and the Malatya-Ovacik Fault Zone (MOFZ). They take up lesser motion and are younger than boundary faults of the Anatolian Platelet. The GYFZ and MOFZ splay from the NATF, cut across the Anatolian Platelet and then meet to the EATF. Whereas, other faults are confined into the Anatolian Platelet and seem to be independent structures. However, present-day structural pattern of all these intraplate faults and boundary faults of the Anatolian Platelet indicates a regional strain pattern of NNW-SSE-directed shortening and ENE-WSW-directed extension, and they seem to have developed to accommodate northward motion of the Arabian Plate since late Early Pliocene times.