Fluid flow, deformation rates and the submarine record of major earthquakes in the Sea of Marmara, along the North-Anatolian Fault system

Abstract

The submerged portions of the North-Anatolian Fault (NAF) in the Sea of Marmara and the NE-Aegean Sea are sites of large magnitude earthquakes, that leave diagnostic geological "signatures" in the sedimentary record in the form of mass-wasting deposits, turbidites, and fluid and gas escape features. This is due to the interplay of seismic-shaking, mass- and turbidity flows, sediment resuspension and fluids circulation in relatively small sub-basins with a complex paleo-oceanography, steep slopes, high rates of deformation, and diffuse fault-controlled gas and fluid seeps. To unravel the complex interrelations of these phenomena during earthquake cycles, we carried out paleoseismological studies at several key locations. Here, we report results of these studies, carried out onboard the R/V Urania over a decade, starting soon after the Mw 7.4, 1999 ?zmit earthquake. Our work included high resolution mapping of active faults through multibeam bathymetry and high resolution seismic reflection profiles, multi-parameter analysis of sediment cores, as well as seafloor observations using sensors mounted on remotely-operated vehicles (ROV). The main objectives were to map active faults, determine slip-rates and earthquake recurrence times along major fault strands, and assess connections between fault deformation and fluid activity. We mapped fault geometry in the gulfs of ?zmit, Gemlik and Saros, showing the trans-tensive nature of these depressions. The average slip-rates for the last ~ 10 ka was found to be 10 mm/y in the gulfs of ?zmit and Saros, at the eastern and the western ends of the NAF northern strand, and 3-4 mm/yr in the Gulf of Gemlik, along the middle strand of the NAF. These rates, integrated over 10 ka of NAF activity, are smaller than those determined by the GPS geodetic measurements. Submarine paleoseismological studies in the Gulf of ?zmit detected the sedimentary records of earthquakes for the last 2.4 ka, suggesting an average recurrence time of 300 years for major events. Multisensor observations and monitoring of the seafloor have shown widespread emissions of gas and fluids along the submerged part of the NAF, associated with reduced black sediments; we investigated their possible connection with the earthquake cycle.