Reflection-seismic Images And Evolution At The Scale Of The Crust And Active Faults Of The Sea Of Marmara Trough (seismarmara 2001)
Abstract
The origin, evolution and present activity of the northern Sea of Marmara that formed on the North Anatolian Fault (NAF) is a matter of debate brought into focus after the 1999 destructive earthquakes that occurred just east of it. Its deep structure, from the recent sediments to the mantle can be resolved by a new set of 2000 km of deep- penetration seismic reflection profiles recorded over the whole North Marmara Trough as the Leg 1 MCS part of the SEISMARMARA survey in August-September 2001. The profiles have an unprecedented depth-penetration due to the 4.5 km length of a 360-channel streamer and the strength of the sources, a 8100 cu. in., or 2900 cu. in., 12-airgun array operated in single-bubble mode. Crustal structure heterogeneity is re- vealed. It can be considered as a record of the evolution in time, for which hints at a preliminary interpretations are provided from on-board brute stacks. A reflective deep crust is imaged under the present Sea of Marmara. Its topography varies east-west and with respect to the Marmara Trough. The preliminary image of this structure suggests that it could have been shaped by the early activity of a propagating rift induced by the incoming tip of the NAF from the east. Over this regional structure, pull-apart basins are imaged that established in the Marmara Trough. Seismic architecture and facies of basins are imaged to their bottom and beneath. They suggest the onset of pull-apart activity some 1-1.5 Ma ago. This could be viewed as a change from the pre- vious propagating rift evolution, as expected if its tip induces itself a new strike-slip segment into the Aegean creating then a releasing sidestep with the original incoming NAF. The amount of finite separation of blocks at pull-aparts since that time allowed recently the strike-slip fault to bypass them and straighten its geometry, cutting now through the smaller western pull-apart basins. The bedding of recent sediments and re- lations with older ones are complex in the large easternmost Cinarcik basin which may continue pull-apart evolution above a large underlapping sidestep in the masterfault at the eastern wide end of the Sea of Marmara. This sets the frame to the present active evolution and geometry of the NAF in the Marmara Trough. Estimation of the present activity of the faults imaged and identified will need close-by earthquake observation of locations and focal mechanisms that have been initiated.
- Publication:
-
EGS General Assembly Conference Abstracts
- Pub Date:
- 2002
- Bibcode:
- 2002EGSGA..27.4792H