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    Fault-controlled gas escapes in the shelf sediments of the Saros Gulf, NE Aegean Sea
    (TUBİTAK, 2021) Önder, Şebnem; Görür, Naci; Polonia, Alina; Gasperini, Luca
    High-resolution marine seismic reflection studies on the eastern shelf of the Saros Gulf have revealed the presence of gas-charged sediments across a narrow submarine valley incised by the Ganos Fault along the North Anatolian Fault system. Quaternary sediments, accumulated during glacial and interglacial periods through transgressional and progradational units, were controlled by glacio-eustatic sea-level fluctuations and tectonic deformation. The transgressional units made of upward-fining deposits created seals at their tops to form gas accumulation pockets. Conversely, the progradational units appear heavily eroded at their top, which is unfavorable for gas accumulation. The sediment’s gas accumulation features include enhanced reflections, acoustic blanking (or blanket), acoustic turbidity, acoustic curtain, and acoustic columns. In contrast, the gas escape features consist of acoustic plumes, cloudy turbidity, domes, and pockmarks. Their concentration along the Ganos Fault indicates that active deformation, punctuated by large magnitude earthquakes, has played an essential role in their formation, storage, and seep. Understanding these interactions may provide valuable contributions to hydrocarbon explorations and early-warning strategies against earthquake risk.
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    Öğe
    Subaqueous fault scarps of the North Anatolian Fault in the Gulf of Saros (NE Aegean); where is the western limit of the 1912 Murefte-Sarkoy earthquake rupture?
    (Oxford Univ Press, 2022) Aksoy, M. Ersen; Meghraoui, Mustapha; Polonia, Alina; Cagatay, M. Namik; Yavuzoglu, Asli Zeynep; Onder, Sebnem; Ulgen, Umut B.
    The westernmost segment of the North Anatolian fault in NW Turkey lies mostly offshore, in the Sea of Marmara and the Gulf of Saros (NE Aegean), respectively to the E and W of a 45 km inland central portion. The 9 August 1912 Murefte-Sarkoy (M-s 7.4) and 13 September 1912 (M-s 6.8) earthquakes occurred along this segment. To date, the segment was studied mostly onshore although estimated magnitude and location suggest an offshore extension. Recent studies show the eastern rupture extension in the Sea of Marmara, while its western counterpart in the Gulf of Saros remains less documented. Here we use new observations from high-resolution marine geophysical data (multibeam bathymetry, side-scan-sonar, and seismic reflection profiles), to constrain the offshore 1912 ruptures in the Gulf of Saros. Detailed mapping of the subaqueous fine-scale morphology and structure of the fault provides a new insight for the western limit of the two 1912 surface ruptures. Distribution of fresh scarps, 3-D structural reconstructions, the complexity of fault segments, and the recent seismicity, altogether suggest that the western termination of the 1912 rupture(s) ends 37 km offshore in the Gulf of Saros. Following the 1999 Kocaeli earthquake, in the eastern Sea of Marmara, the unruptured segment length between the 1999 and 1912 ruptures became a critical issue, because of its implication for future earthquakes in the so-called Marmara seismic gap. If a 150-160 km total rupture length for the two 1912 earthquakes is assumed, a western rupture termination point at the inner Saros basin margin means that the eastern extension of the 9 August earthquake rupture reached the Central Marmara Basin. This outcome necessarily has implications for the seismic hazard in the Marmara coastal area that includes the Istanbul metropolitan area.