Abstract
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. 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. 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. 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. 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. 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. 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. 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.
Highlights
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 2011; Gasperini et al 2011a), several marine geological studies were carried out by different international teams
The Cinarcik segment (Fig. 5) is formed by a N296° striking fault running along the northern continental slope and by a typical transtensional pattern delimited towards the south by en échelon antithetic fault segments
A newly compiled morphobathymetric map of the NorthAnatolian Fault below the Sea of Marmara was presented in this work
Summary
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 2011; Gasperini et al 2011a), several marine geological studies were carried out by different international teams. The main objectives of such studies were mapping the active fault strands (Le Pichon et al 2001; Armijo et al 2005; Şengör et al 2014), estimating their slip-rate at the scale of several seismic cycles (Polonia et al 2004; Gasperini et al 2011b), and evaluating the effect of major earthquakes in the sedimentary sequence (MCHugh et al 2006; Beck et al 2007; Çağatay et al 2012; Drab et al 2012, 2015; Yakupoğlu et al 2019). Parke et al (2002), Okay et al (2000), Amijo et al (2002), Meghraoui et al (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. 1)
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