An example of secondary fault activity along the north Anatolian Fault on the NE Marmara Sea Shelf, NW Turkey

Seismic data on the NE Marmara Sea Shelf indicate that a NNE-SSW-oriented buried basin and ridge system exist on the sub-marine extension of the Paleozoic Rocks delimited by the northern segment of the North Anatolian Fault (NS-NAF), while seismic and multi-beam bathymetric data imply that four NW-SE-oriented strike-slip faults also exist on the shelf area. Seismic data indicate that NW-SE-oriented strike-slip faults are the youngest structures that dissect the basin-ridge system. One of the NW-SE-oriented faults (F1) is aligned with a rupture of the North Anatolian Fault (NAF) cutting the northern slope of the Cinarcik Basin. This observation indicates that these faults have similar characteristics with the NS-NAF along the Marmara Sea. Therefore, they may have a secondary relation to the NAF since the principle deformation zone of the NAF follows the Marmara Trough in that region. The seismic energy recorded on these secondary faults is much less than that on the NAF in the Marmara Sea. These faults may, however, produce a large earthquake in the long term

Shallow seismic characteristics and distribution of gas in lacustrine sediments at Lake Ercek, Eastern Anatolia, Turkey, from high-resolution seismic data

The high-resolution analysis of single-channel, seismic reflection data from Lake Ercek (Eastern Anatolia) revealed a wide range of shallow gas anomalies consisting of enhanced reflections, seismic chimneys, acoustic blanking/acoustic turbidity, strong reflectors, and pockmarks, including both surface and buried pockmarks. The enhanced reflections are represented by the higher amplitude reflection patterns resulting from high acoustic impedance variations. They are mostly clustered in the NW-corner of the lake. Seismic chimneys are represented by vertical and thinned columnar disturbances of amplitude blanking and mostly occurred in deep basinal and faulted sections in the West and East of the lake. Some seismic chimneys, occurring together with pockmarks, represent vertical vent activations. Acoustic gas masking was represented by chaotic and diffuse seismic reflection patterns, including acoustic blanking and acoustic turbidity. As diffuse acoustic turbidity indicates gas-charged sediments, columnar disturbances showing acoustic blanking indicate degassing of the sediments. These features extend from SE to NW, coinciding with the deep basin morphology of the lake. A very local strong reflector was identified in the W-section of the lake, simulating the lake floor. This reflector is due to extended enhanced reflections, suggesting shallow free gas. Pockmarks observed in the lake are structurally classified into the two distinct types; surface (active) pockmarks found in the SE-part of the lake and buried (passive) pockmarks found in the NW. The former enlarge through deeper gas reservoir feedback, as the layering is impermeable, while the latter have resulted from a cessation of the reservoir feedback mechanism and/or permeable layering. In the lake, shallow gas distribution is controlled by faults, that provide the faulting-driven depositional control and earthquakes, that provide the seismicity-driven overpressure control. The shallow gas is then vertically-horizontally distributed and shaped by asymmetric depositional-stratigraphic factors. This study of Lake Ercek presents complementary information about a possible tectono-thermal origin of observed shallow gas