Slope Instabilities Along the North Anatolian Fault System in the Sea of Marmara
Abstract
The characterization of slope stability in the Sea of Marmara has important implications in term of geohazards assessment in the vicinity of Istanbul. The Sea of Marmara is a tectonically active marine basin, located along the continuation of the North Anatolian Fault system, where coexist numerous factors triggering seafloor instability: steep slopes, reaching more than 18° in some places, high sedimentation rates, high seismicity, deep fluid migration processes, and specific paleoceanographic conditions. Several types of mass wasting processes are imaged with high resolution multibeam bathymetric data. The slopes of the Sea of Marmara are characterized by numerous submarine canyons, displaying erosional processes at their heads and flanks, and by large destabilized areas, covering more than 400 km2 in total, showing complex seafloor morphology with evidence of multiple slope failures, normal faulting and hummocky surface. Catastrophic events occur occasionally since related mass wasting deposits, such as turbidites, debris flows, and avalanche deposits are recognized within the basins. Evidences are debris layers in cores, transparent lenses interbedded with the sedimentation visible on the high resolution echosounder profiles, and seafloor visual observations of scree and boulders at the basis of the slope. At both extremities of the Sea of Marmara, in the entrance of the Izmit Basin and in the Western Tekirdag Basin, creeping masses are covering the fault trace. Moreover, in the Northeast Cinarcik Basin, a 32 km2 large sediment failure occurs where the active fault changes its strike, bending towards north. Large slope instabilities with tens of meters large tumbled blocks and occurence of methane seepages also occur on the southern side of the Cinarcik Basin above a deep-seated transtensional shear zone (Géli et al. 2008 EPSL in press). Fluid and gas seepages are often observed at the toe of submarine landslides, where they may result from loading and compaction or associated to high permeability conduits formed as a consequence of mass wasting processes (e.g. avalanche deposits and coarse turbidites). The dating of the largest slope failures and sediments flows indicate that most of the slope instabilities occurred at the end of the last glacial period (12-17 kyr) and may be accounted by sea-level variation and the transition from lacustrine to marine conditions in the Sea of Marmara. Flux of coarse sedimentation through the canyons is also higher over this period.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.U51A0022Z
- Keywords:
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- 3000 MARINE GEOLOGY AND GEOPHYSICS;
- 3004 Gas and hydrate systems;
- 3022 Marine sediments: processes and transport;
- 3045 Seafloor morphology;
- geology;
- and geophysics;
- 3070 Submarine landslides