Submarine fault scarps in the Sea of Marmara pull‐apart (North Anatolian Fault): Implications for seismic hazard in Istanbul

Abstract

International audienceEarthquake 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

Recent and active deformation pattern off the easternmost Algerian margin, Western Mediterranean Sea: New evidence for contractional tectonic reactivation

“…The Chirp data have proved to be especially well suited for identifying sub-surface scarps of a few meters high related so single events (see e.g. recent results in the sea of Marmara, in Armijo et al, 2005).…”

An earthquake gap south of Istanbul

“…There is also a debate on whether the entire Marmara Zone might rupture as a single through-going strike-slip event, or in several en-echelon normal and oblique faulting events. In the latter case, there might be smaller impacts from the ground motion, but a higher potential for tsunami generation owing to ocean floor elevation changes [9][10][11] .…”

Estimation of successive coseismic vertical offsets using coeval sedimentary events – application to the southwestern limit of the Sea of Marmara's Central Basin (North Anatolian Fault)

“…Armijo et al, 2005). In the following, we will focus on the Central Basin's recent sedimentary fills and additional data on the Çinarcik Basin, aiming (1) to reconstruct a succession of earthquake-induced sedimentary "events" during the pre-Holocene infilling, and (2) to use part of this succession to analyze the activity of the fault zone corresponding to the southern limit of the "inner" Central Basin (as named by Uçarkuş, 2010).…”

“…1), several offshore surveys have been dedicated to analyze its submerged section. Morphological and sedimentary impacts of major recent earthquakes have been searched using seismic reflection with different resolutions and penetrations, multibeam and side scan sonar, different types of coring, and remote operating vehicles (ROV) (Armijo et al, 2005). The different results concern (1) deep fluids expulsion related to seismotectonic activity (Géli et al, 2008;Tary et al, 2012;Burnard et al, 2012, etc.…”

“…); (2) mass wasting and creep (Zitter et al, 2012;Shillington et al, 2012); (3) deep sedimentation specificities Sari and Çagatay, 2006;Çagatay et al, 2012;Drab et al, 2012); and (4) detection and dating of historical coseismic scarps (Armijo et al, 2005;Uçarkuş, 2010). Historical tsunami reports and modeling (Altinok et al, 2011;Hébert et al, 2005) complete these different data, taking into account the fact that these phenomena are not systematically associated with Armijo et al (2002Armijo et al ( , 2005, and GPS kinematics from McClusky et al (2000) and Reilinger et al (2006). earthquakes .…”