![]() ![]() Fault segments follow coseismic faulting, with rupture initiation and termination often displaying a pattern of cumulative deformation. In fact, segmentation reflects structural and geometrical characteristics of continental faults and plate boundaries, where large earthquakes ruptures are limited by major tectonic discontinuities (Wesnousky 2006). To determine whether and to what extent a fault system is segmented is important. ![]() ( 2012) suggested the presence of an oblique segmented shear zone connecting the eastern Izmit segment to the Ganos Fault, at the western side of the Sea of Marmara (Fig. These faults would have been connected by systems of en échelon normal faults bounding individual basins. ( 1995), proposed a pull-apart classic model, with two major strike-slip NE–SW faults delimiting the whole basin. Regarding the overall tectonics of the Sea of Marmara, Barka and Kadinsky-Cade ( 1988), Barka ( 1992) and Wong et al. 2013).ĭespite the large amount of data and a number of papers that shed light on the tectonic setting of this seismically active region, there are still uncertainties and debates, particularly concerning modes of fault segmentation and nature of each individual segment. initiatives, including MarmEsonet (Geli et al. To foster these studies, the Sea of Marmara was included among the strategic sites for monitoring active faults and exploring seismic precursors within some E.C. This effort was preliminary to a reliable seismic risk assessment in the densely populated Istanbul Metropolitan Area, considered a “seismic gap” close to the next rupture (Hubert-Ferrari et al. 2011b), and evaluating the effect of major earthquakes in the sedimentary sequence (MCHugh et al. 2014), estimating their slip-rate at the scale of several seismic cycles (Polonia et al. The main objectives of such studies were mapping the active fault strands (Le Pichon et al. 2011a), several marine geological studies were carried out by different international teams. Starting from the Mw 7.6, 1999 Izmit earthquake, which ruptured over 50 km of the North Anatolian Fault (NAF) below the Gulf of Izmit in the eastern Sea of Marmara (Ucarkus et al. We discuss these findings considering analyses of historical catalogues and available paleoseismological studies for the Sea of Marmara region to formulate reliable seismic hazard scenarios. These data were used as inputs for empirical relationships, to estimate maximum expected Moment Magnitudes, obtaining values in the range of 6.8–7.4 for the Central, and 6.9–7.1 for the Cinarcik and Tekirdag segments, respectively. A quantitative morphometric analysis of the shallow deformation patterns observed by seafloor morphology maps and high-resolution seismic reflection profiles along the entire basin allowed to determine nature and cumulative lengths of individual fault segments. Fault segmentation occurs at different scales, but main segments develop along three major right-lateral oversteps, which delimit main fault branches, from east to west: (i) the transtensive Cinarcik segment (ii) the Central (East and West) segments and (iii) the westernmost Tekirdag segment. In the frame of the right-lateral strike-slip domain characterizing the North Anatolian fault system, three types of deformation are observed: almost pure strike-slip faults, oriented mainly E–W NE/SW-aligned axes of transpressive structures NW/SE-oriented trans-tensional depressions. Given the high deformation rates relative to sediment supply, most active tectonic structures have a morphological expression at the seafloor, even in presence of composite fault geometries and/or overprinting due to mass-wasting or turbidite deposits. We reconstructed kinematics and geometries of individual fault segments, active at the time scale of 10 ka, an interval which includes several earthquake cycles, taking as stratigraphic marker the base of the latest marine transgression. A new analysis of high-resolution multibeam and seismic reflection data, collected during several oceanographic expeditions starting from 1999, allowed us to compile an updated morphotectonic map of the North Anatolian Fault below the Sea of Marmara. ![]()
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