Gas emissions and active tectonics within the submerged section of the North Anatolian Fault zone in the Sea of Marmara

Abstract

The submerged section of the North Anatolian fault within the Marmara Sea was investigated using acoustic techniques and submersible dives. Most gas emissions in the water column were found near the surface expression of known active faults. Gas emissions are unevenly distributed. The linear fault segment crossing the Central High and forming a seismic gap-as it has not ruptured since 1766, based on historical seismicity, exhibits relatively less gas emissions than the adjacent segments. In the eastern Sea of Marmara, active gas emissions are also found above a buried transtensional fault zone, which displayed micro-seismic activity after the 1999 events. Remarkably, this zone of gas emission extends westward all along the southern edge of Cinarcik basin, well beyond the zone where 1999 aftershocks were observed. The long term monitoring of gas seeps could hence be highly valuable for the understanding of the evolution of the fluid-fault coupling processes during the earthquake cycle within the Marmara Sea.

Comparative metagenomics of bathypelagic plankton and bottom sediment from the Sea of Marmara

“…Finally, around 7% of Ma29 archaea belonged to the Methanosarcinales, with some sequences very closely related to members of the ANME2 group (Figure 1 and Supplementary S12). The presence of ANME sequences is not surprising, as the Marmara Sea harbors several scattered cold seep areas (Géli et al, 2008;Zitter et al, 2008) where the anaerobic oxidation of methane likely occurs. However, the relatively low proportion of archaea is consistent with the 'normal' bottom-sediment nature of the Ma29 sediment.…”

“…Sediment communities are extremely diverse, with particularly high relative abundances of Deltaproteobacteria, many of them are sulfate reducers, and planctomycetes, which are important in carbon cycling. Methanogenic and/or methanotrophic archaea were not abundant in the surface sediment sample, indicating that the transition to the methanogenesis zone is deeper and that the sediment is not actually influenced by intense seeping activity, which, in Marmara, is restricted to localized black patches along the main North Anatolian Fault (Géli et al, 2008;Zitter et al, 2008). Future comparison with metagenome sequences from those seep areas in the same location would be interesting to reveal specific adaptations to those environments.…”

“…In addition to this agitated history, the Marmara basin is highly dynamic from a geological point of view, as its Northern slope is traversed by the seismically more active branch of the North Anatolian Fault, the Main Marmara Fault. Gas seeps and water seeps have been unevenly observed in the three major basins found along this fault (from West to East: Tekirdag, the Central basin and Cinarcik) (Géli et al, 2008;Zitter et al, 2008). Gas or cold seeps are enriched in methane and can be seen directly as bubbles coming out from the sediment, or can be detected indirectly by the presence of dark patches revealing areas of strong redox activity in which sulfate reduction occurs just beneath the surface.…”

“…These patches are often colonized by siboglinid polychaetes and bivalves likely associated with symbiotic bacteria and may be covered by white, little-structured mats of sulfide-oxidizing bacteria. The distribution of gas seeps may provide indications of fault activity (Géli et al, 2008). Water seeps are observed more sporadically.…”

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)

“…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).…”