Tekin Yürür

The East Anatolian Fault : an oblique collisional belt

Abstract The tectonic setting for the area around the Arabia-Africa-Anatolia triple junction is described from combined Landsat-SPOT satellite image analysis and field observations. Since the Late Miocene the motion along the East Anatolian Fault generated major structures corresponding to shortening with a sinistral-slip component. The 150 km wide area of the triple junction is highly deformed by folding and thrusting, distributed mainly on the border of the Anatolian block. In addition, kinematic reconstructions confirm that the Arabia-Anatolia relative motion is both sinistral and convergent. The sinistral strike-slip faults of the East Anatolian Fault zone are of second-order and local consequences of the N-S Arabia-Anatolia collision.

Emplacement of volcanic vents and geodynamics of Central Anatolia, Turkey

Abstract Observations on Synthetic Aperture Radar (SAR) scenes of the European Remote Sensing (ERS) satellite and Digital Elevation Models (DEMs), complemented by field structural analysis permit a new understanding of relationships between tectonics and volcanism since the late Miocene (10 Ma) in Central Anatolia. Volcanic edifices form elongate stratovolcanoes, linear clusters and volcanic ridges. They indicate emplacement on tension fractures and tail-crack or horsetail features. For instance, the Kara Dag volcano is rooted on a tail-crack which accommodates a horizontal left-lateral throw component at a fault termination. Caldera complexes of Cappadocia are associated with horsetail fault patterns. The emplacement of volcanoes also benefits from larger-scale tectonic structures: the Erciyes Dag volcano is localized by the Sultan Saz releasing bend which opens along the sinistral strike-slip Ecemis fault. Deformation has been analysed from tension fractures—which are perpendicular to the direction of extension—and from field structural analysis. On a regional scale, the tectonic regime responsible for the distribution of volcanic vents in this area of convergence and lateral extrusion, is not compression but extension. The Central Taurus range is the thermally uplifted shoulder of the Adana–Cilicia basin, which is related to lithosphere thinning. Westward movements in the northwestern part of the studied area are influenced by the active back-arc Aegean extension situated to the west. Farther to the south, the direction of motion turns southwest and south, under the influence of the opening of the Adana–Cilicia basin. We interpreted that extension in the Central Anatolian plateau is related to crustal blocks moving above sub-horizontal detachment surfaces located in the lower crust. This is based on several facts: the Tuz Golu fault zone is a within-crust detachment; the Tuz Golu basin does not affect the whole lithosphere because otherwise it would have been bordered by thermally uplifted shoulders; movements change trend within a small (50 km) region.

The Maras Triple Junction (southern Turkey) based on digital elevation model and satellite imagery interpretation

This paper describes major structures in the area of the triple junction of the African, Anatolian and Arabian plates near Maras (southern Turkey). A review of the literature on the paleogeographic evolution since mid-Cretaceous time leads to the idea of the southern Tethys (Mesogea) persisting between Anatolia and Africa-Arabia until middle-late Miocene. Consequently, collision may have started later and northward subducting lithosphere may still exist under Anatolia. The Dead Sea fault may have initiated near the first collision between the Anatolian continent and the western corner of the African/Arabian continent at which point it may have propagated southward. A digital elevation model, SPOT and Landsat-MSS images, and field work suggest relief js mainly related to finite deformation resulting from on going collision that began at around 13 Ma. The images show that the East Anatolian fault does not crosscut the central Taurus belt. Field data argue that this belt is a left-lateral oblique-slip fault zone. The southern contact of Anatolia passes north of the Amanos range (continental par t of the African plate) and connects with the Misis range. To the southwest, the Adana low plain may be regarded as a basin formed at a releasing bend. The Karasu fault zone, which belongs to the Dead Sea fault zone, seems to be transpressive, and in this case the Karasu basin is not a graben. North of the Amanos range, the Giirun arc is thrust to the north and may be considered the result of local collision of the uplifting Amanos range into Anatolia. The Maras triple junction is accompanied by deformations affecting all plates at the regional scale.

Polyphased block tectonics along the North Anatolian Fault in the Tosya basin area (Turkey)

Abstract The Tosya basin is located in the bending segment of the North Anatolian Fault (NAF) in Turkey. We have obtained original observations on the neotectonics from SAR ERS images, Digital Elevation Model (DEM) and field structural analysis. Regional Neogene deformation is characterised by the occurrence of several basins that are superimposed in time and space. They result from differently oriented movements since 12 Ma, including southwestward motion along a fault subparallel to the NAF. We propose a model of polyphased tectonics related to the displacement of several individualised blocks. In the first stage (Tortonian), the North Tosya block has moved toward the N250° azimuth, parallel to the dextral N70°-striking segment of the NAF. As a consequence, a triple-junction-related compatibility basin was opened at the intersection with a N60° to N30°-striking fault. This pattern is similar to the Karliova corner where the NAF and the East Anatolian Fault meet. In the second stage (Early Pliocene–Middle Pleistocene), a segment of the former N70°-NAF was abandoned and the NAF propagated eastward to form a N90°-striking segment (N90°-NAF), cutting the former Tosya block and basin into two parts. The North Tosya block has moved again and this new geometry has permitted a South Tosya block to move parallel to the NAF but with a higher rate which has induced compression in the Tosya basin. In the third stage (Holocene), the South Tosya block moved toward N240°, obliquely to any of the NAF segments. This has resulted in the formation of two Holocene pull-apart type basins along the previous N60° to N30°-striking fault while extensional faults were formed in the South Tosya block. Estimated dextral displacement along the NAF is 5.9 to 8.5 km at this stage. This model of blocks moving in different directions, including Holocene local movements toward N240°, means that the NAF can be considered not to be a simple transform fault. Our model implies that the N90°-NAF was non-existent before the Early Pliocene.

Slip-motion estimation along the Ovacik fault near Erzincan (Turkey) using ERS-1 radar image: Evidence of important deformation inside the Turkish plate

Abstract A synthetic aperture radar ERS-1 scene, used to complement a Landsat TM scene, allows better understanding of the structure of the active Ovacik fault, southwest of Erzincan (Turkey). The radar image shows that the Ovacik fault is interrupted at its crossing point with the Kemaliye fault. Recent compressive displacements have reactivated the Kemaliye fault, while a pull-apart basin has been generated along the Ovacik fault. Estimates of offsets of major rivers and analysis of the complex fault geometry given an estimated left-lateral strike slip displacement of 12.5–20 km along the Ovacik fault for the last 13 Ma, which is similar to the rate of movement along the East Anatolian fault located in the east and forming the boundary of the Turkish plate.

Attenuation characteristics of peak ground acceleration from fault trace of the 1999 Kocaeli (Turkey) earthquake and comparison of spectral acceleration with seismic design code

The 17 August 1999 Kocaeli earthquake in Turkey produced a majorsurface rupture. We traced this surface rupture from Gölcük toDüzce and located it accurately by using GPS. The closest distancefrom the surface rupture to the strong motion observation sites weredetermined. Then the attenuation characteristics of the observed peakground acceleration were compared with the attenuation relation given byFukushima and Tanaka (1992), which is suitable for the near-fault zone inJapan and gives results that closely match data recorded during the 1995Hyogo-ken Nanbu earthquake in Japan. Although this attenuation relationwas developed for Japan, we found that it agreed well with the KOCAELIearthquake. Furthermore, the observed spectral acceleration of 5%damping was compared with the building design code of Turkey and theobserved level was lower than the code.

Could the coseismic fractures of a lake ice reflect the earthquake mechanism?: (Afyon earthquakes of 2 March 2002, Central Anatolia, Turkey)

Abstract Eyewitness reports that the two moderate earthquakes (3 February 2002) in Afyon, Central Anatolia, Turkey, produced fractures at the icy surface of a partially frozen lake near the reactivated fault scarp. In places along the shoreline, the ice thrusted towards the land. Far from the shoreline, several fractures developed on the approximately 15 cm-thick ice of the lake. Among them, geometric features of two fracture junctions suggest that fractures accommodated lateral movements. Almost no coupling should exist between the ice and the shaking ground because of the water beneath the ice, these fractures cannot be directly associated to ground ruptures. Alternatively, we propose that the great inertia of the ice mass caused the collision of the ice layer with the shore land when the ground beneath this layer moved towards the lake. As a result, the ice-ground interface deformed and the icy “hinterland” fractured. The orientations of the stress axes deduced from fracturation fit with those suggested by focal mechanism solutions and ground rupturing. Consequently, the ice of the lake surface seems to indirectly record the mechanism of the Afyon earthquakes.