Acoustic data that image below the sea floor (“seismic reflection data”) show a stack of glacial period deltas beneath Marmara Sea, Turkey, south of Istanbul. These deltas formed the basis for a stratigraphic age model for the last half million years. More than 100 seismic reflection profiles were used to create three-dimensional surfaces of 5 stratigraphic horizons. A 3D oblique view down and to the east of the ~540,000 year “Green” horizon is shown above. The northern branch of the North Anatolian fault accommodates stretching west of the Tuzla bend, leading to subsidence of 7-10 mm/yr. in the labeled depocenter. Depocenters for older intervals are located successively west of those for younger intervals, consistent with this fault having right-lateral slip. Motion of the east edges of the depocenters relative to the north side of the fault is about 18 or 19 mm/yr.
This contrasts to several publications from the last decade which suggest that this fault initiated only 200,000 years ago. Older, large displacement faults may be capable of longer ruptures and thus larger magnitude earthquakes.
Graphic Credit: Chris Sorlien
