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

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 [Ambraseys, N.N., and Jackson, J.A., (2000), Seismicity of the Sea of Marmara (Turkey) since 1500, Geophys. J. Int., 141, (3), F1-F6. (doi:10.1046/j.1365-246x.2000.00137.x: Ambraseys, N., (2002), The seismic activity of the Marmara Region over the last 2000 years, Bull. Seism. Soc. Am., 92, 1-18; Parson, T., (2004), Recalculated probability of M >= 7 earthquakes beneath the Sea of Marmara, Turkey,J. Geophys. Res., 109, B05304, doi: 10.1029/2003JB002667: Pondard, N., Armijo, R., King, G.C.P., Meyer, B., Flerit, F, (2007), Fault interactions in the Sea of Marmara pull-apart (North Anatolian Fault): earthquake clustering and propagating earthquake sequences, Geophys. J. hit., 171, 1185-1197, doi: 10;1111/j.1365-246X.2007.03580.x] -, 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 [Carton, H., Singh, S.C., Hirn, A., Bazin, S., de Voogd, B., Vigner, A., Ricolleau, A., Cetin, S., Ocakoglu, N., Karakoc, F. and Sevilgen, V., (2007), Seismic imaging of the three-dimensional architecture of the Cmarcik Basin along the North Anatolian Fault,J. Geophys. Res., 180, B06101, doi:10.1029/2006JB004548; Okay, A.I., Kashlar-Ozcan, A., Imren, C., Boztepe-Guney, A., Demirbag, E., and Kuscu, I., (2000). Active faults and evolving strike-slip basins in the Sea of Marmara, northwest Turkey: a multichannel seismic reflection study, Tectonophysics, 321,189-218], which displayed micro-seismic activity after the 1999 events [Ozalabey, S., Ergin, M., Aktar, M., Tapirdamaz, C., Bicmen, F., Yoruk, A., (2002), The 1999 Izmit Earthquake Sequence in Turkey: seismological and tectonic aspects, Bull. Seism. Soc. Am., 92,376-386; Karabulut, H., Bouin, M.P., Bouchon, M., Dietrich, M., Cornou, C., Aktar, M., (2002), The seismicity in the Eastern Marmara Sea after the 17 August 1999 Izmit earthquake, Bull. Seismol. Soc. Am., 92, 387-393]. 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.