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[ 1] Earthquake scarps associated with recent historical events have been found on the floor of the Sea of Marmara, along the North Anatolian Fault ( NAF). The MARMARASCARPS cruise using an unmanned submersible ( ROV) provides direct observations to study the fine-scale morphology and geology of those scarps, their distribution, and geometry. The observations are consistent with the diversity of fault mechanisms and the fault segmentation within the north Marmara extensional step-over, between the strike-slip Ganos and Izmit faults. Smaller strike-slip segments and pull-apart basins alternate within the main step-over, commonly combining strike-slip and extension. Rapid sedimentation rates of 1-3 mm/yr appear to compete with normal faulting components of up to 6 mm/yr at the pull-apart margins. In spite of the fast sedimentation rates the submarine scarps are preserved and accumulate relief. Sets of youthful earthquake scarps extend offshore from the Ganos and Izmit faults on land into the Sea of Marmara. Our observations suggest that they correspond to the submarine ruptures of the 1999 Izmit ( Mw 7.4) and the 1912 Ganos ( Ms 7.4) earthquakes. While the 1999 rupture ends at the immediate eastern entrance of the extensional Cinarcik Basin, the 1912 rupture appears to have crossed the Ganos restraining bend into the Sea of Marmara floor for 60 km with a right-lateral slip of 5 m, ending in the Central Basin step-over. From the Gulf of Saros to Marmara the total 1912 rupture length is probably about 140 km, not 50 km as previously thought. The direct observations of submarine scarps in Marmara are critical to defining barriers that have arrested past earthquakes as well as defining a possible segmentation of the contemporary state of loading. Incorporating the submarine scarp evidence modifies substantially our understanding of the current state of loading along the NAF next to Istanbul. Coulomb stress modeling shows a zone of maximum loading with at least 4-5 m of slip deficit encompassing the strike-slip segment 70 km long between the Cinarcik and Central Basins. That segment alone would be capable of generating a large-magnitude earthquake ( Mw 7.2). Other segments in Marmara appear less loaded.

This paper presents selections from and a synthesis of a high resolution bathymetric, sparker and deep-towed seismic reflection data set recently acquired by the French Ifremer R. V Le Suroit in an E-W deep trough that forms the northern half of the Sea of Marmara in NW Turkey. It includes the first high resolution complete bathymetric map of this area. A single, throughgoing dextral strike-slip fault system, which is the western continuation of the northern branch of the North Anatolian Fault, cuts this trough lengthwise and joins the 1999.8.17 Kocaeli earthquake fault with the 1912.8.09 Sarkoy-Murefte earthquake fault, both of which display strike-slip offset. In its eastern one fourth, the structure follows closely the northern margin of the deep trough, whereas in the west it hugs its southern margin. The eastern one fourth of the structure has a minor component of its displacement distributed across the deep trough owing to a possible original bend in the course of the dextral structure. The present course of the North Anatolian Fault in the Sea of Marmara originated some 2 x 10(5) a ago, by cutting across the older basin fabric generated by a dominant NNE-SSW extension before it began taking up major motion in the Pliocene. (C) 2001 Published by Elsevier Science B.V.