İsmail Kuşçu

An active, deep marine strike‐slip basin along the North Anatolian fault in Turkey

The Tekirdag depression within the Marmara Sea in the Mediterranean region is an active, rhomb-shaped strike-slip basin along the North Anatolian fault with a basin floor at a water depth of −1150 m. New multichannel seismic reflection data and on-land geological studies indicate that the basin is forming along a releasing bend of the strike-slip fault and is filled with syntransform sediments of Pliocene-Quaternary age. The basin is bounded on one side by the North Anatolian fault and on the other side by a subparallel normal fault, which forms the steep submarine slope. In cross section the basin is strongly asymmetric with the thickness of the syntransform strata increasing from a few tens of meters on the submarine slope to over 2.5 km adjacent to the North Anatolian fault. Seismic sections also show that the slope-forming normal fault connects at depth to the North Anatolian fault, implying that the basin is completely detached from its substratum. The whole structure can be envisaged as a huge, rather flat, negative flower structure. The releasing bend of the North Anatolian fault, responsible for the formation of the basin, is flanked by a constraining bend. Along the constraining bend, the syntransform strata are being underthrust, implying a recent change in the direction of the regional displacement vector. This thrusting is responsible for the uplift of the submarine slope to a height of 924 m, possibly by a mechanism of elastic rebound. Regional geology suggests that most of the syntransform strata are lacustrine with only the topmost few hundred meters consisting of deep marine clays. The anomalous present depth of the Tekirdag depression is due to reduced Quaternary sedimentation coupled with high rates of displacement along the North Anatolian fault, which amounts to 20 mm/yr in the Marmara Sea region.

Active faults in the Gulf of Izmit on the North Anatolian Fault, NW Turkey: a high-resolution shallow seismic study

The northern strandof the North Anatolian Fault enters the Sea of Marmara through the Gulf of Izmit which was affectedby the Mw = 7.4 I zmit earthquake on August 17, 1999. A significant segment of the fault rupturedin between the area west of Go « lcu « k andeast of Lake Sapanca d uring the earthquake. In the southeastern corner of the gulf andfrom Go« lcu « k westwardthe active trace plunges into the sea andis lost to view. We investigatedthe Gulf of I zmit by means of high-resolution shallow seismic data acquired during a post-August 17, 1999 earthquake to locate and map the active faults. In the area, considering the neotectonic features around the gulf, two different sets of faults were differentiated: an earlier and now mostly inactive set of faults that are responsible for the formation of the large pull-apart depression in which the Gulf of Izmit is locatedanda younger, secondset of active faults in the gulf that cut through the former set. The second set was further divided into two groups: the main fault and the secondary faults. The main fault, which extends roughly in an E^W direction as rather throughgoing and longer segments, was tracedbetween the southeast endof the gulf in the east andsouth of Dar|ca in the west where it joins the Sea of Marmara Fault. The secondary faults, on the other hand, lie along the main fault; they are shorter and their strikes are controlled by the bathymetry. Two main seismic sequences were identified in the gulf according to the seismic profiles and existing borehole data: Holocene marine sediments and pre-Holocene fluvio-lacustrine sediments. > 2002 Elsevier Science B.V. All rights reserved.

Investigation of the submarine active tectonism in the Gulf of Gökova, southwest Anatolia–southeast Aegean Sea, by multi-channel seismic reflection data

Submarine active tectonism in the Gulf of Gokova located at the southwest Anatolia–southeast Aegean Sea region was investigated by means of multi-channel seismic reflection data. The Gokova basin is filled by the latest Miocene–Pliocene–Quaternary sediments with maximum thickness of about 2.5 km. The Lycian Nappes, which predominantly cover extreme southwestern Anatolia, constitutes the basement rocks for the Gokova province. The gulf was mainly opened by a buried major listric normal fault, so-called Datca Fault, which has not been previously discussed in the literature. The north-dipping, mainly E–W-trending Datca Fault is located at the southern part of the gulf, whereas its associated antithetic faults are located at the north. The onset time of the opening of the gulf is possibly in the latest Miocene–Pliocene. In terms of local rather than regional effects, the activity of the Datca Fault has decelerated, possibly since the Pleistocene. The Datca Fault might have gained its curved fault plane as it evolved, beginning as planar and/or using antecedent planes of the Lycian Nappes in the area. As the extension progressed, i.e., as the hanging wall block slipped further north, gravity may have impeded rather than helped the faulting. On the other hand, continuing extension in the area may have initiated a second phase of faulting, i.e., WNW–ESE-oriented subgrabens in the gulf and major E–W normal faulting in the northeast margin. A bathymetric low in the mid-gulf area and a horst–graben system in the eastern part of the gulf are observable from the bathymetric data and are well correlated to the seismic data. Although the main orientation of the gulf is E–W, more recent WNW–ESE structures are remarkable in the mid-gulf and in the eastern part of the gulf. The latest WNW–ESE structures are also in agreement with the results of GPS and SLR studies as well as plate motion modelling by total moment tensor of earthquakes in the western Anatolia–Aegean Sea region, particularly in southwestern Anatolia. The amount of total N–S extension within the gulf is estimated as at least 5.5 km since the latest Miocene–Pliocene with overall constant extension rate of at least 1.1 mm/y where the estimated extension factor is about β=1.3.