Open AccessGas seepage and seismogenic structures along the North Anatolian Fault in the eastern Sea of Marmara
Author(s) -
Gasperini L.,
Polonia A.,
Del Bianco F.,
Etiope G.,
Marinaro G.,
Favali P.,
Italiano F.,
Çağatay M. N.
Publication year - 2012
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2012gc004190
Subject(s) - geology , north anatolian fault , seafloor spreading , methane , fault (geology) , tectonics , seawater , active fault , seismology , induced seismicity , clathrate hydrate , geochemistry , oceanography , mineralogy , hydrate , ecology , chemistry , organic chemistry , biology
We carried out a combined geophysical and gas‐geochemical survey on an active fault strand along the North Anatolian Fault (NAF) system in the Gulf of İzmit (eastern Sea of Marmara), providing for the first time in this area data on the distribution of methane (CH 4 ) and other gases dissolved in the bottom seawater, as well as the CH 4 isotopic composition. Based on high‐resolution morphobathymetric data and chirp‐sonar seismic reflection profiles we selected three areas with different tectonic features associated to the NAF system, where we performed visual and instrumental seafloor inspections, including in situ measurements of dissolved CH 4 , and sampling of the bottom water. Starting from background values of 2–10 nM, methane concentration in the bottom seawater increases abruptly up to 20 nM over the main NAF trace. CH 4 concentration peaks up to ∼120 nM were detected above mounds related probably to gas and fluids expulsion. Methane is microbial ( δ 13 C CH4 : −67.3 and −76‰ versus VPDB), and was found mainly associated with pre‐Holocene deposits topped by a 10–20 m thick draping of marine mud. The correlation between tectonic structures and gas‐seepages at the seafloor suggests that the NAF in the Gulf of İzmit could represent a key site for long‐term combined monitoring of fluid exhalations and seismicity to assess their potential as earthquake precursors.