During a 7 days cruise in the Sea of Marmara we obtained:
We have established a data base of very accurate sea-bottom topography and shallow subbottom profiles over key portions of the eastern Marmara Sea, including the Izmit Gulf west of Hersek delta, the continental shelf just south of Istanbul between Buyuk Cekmece and Bakirkoy, and the shelf between the Princess Islands and Tuzla. We have successfully located faults with an accuracy of 1-2 m. Coring of sediments over faults with such an accuracy will allow us to correlate disturbances in the sediment column with submarine fault activity. These capabilities will allow us in the future survey Spring 2000 to characterise Holocene slip rates and, we hope, individual earthquakes on fault segments of the North Anatolian plate boundary.
Some faults were tentatively identified in AREA A. A major right-lateral east-west branch of the NAF bisects the surveyed AREA D. This latter is probably the main branch of the system west of the fault that ruptured in 1999. There are some other faults in this area and on the shelf south of the Princess Islands and Tuzla (AREA C), which probably play secondary roles in the plate motion but may affect the behavior of the major faults. Active structures that were revealed include thrust faults and folds, suggesting horizontal shortening as well as right-lateral motion in these areas.
These new findings will contribute to our understanding the interaction between faults in the system over times measured in hundreds or thousands of years. This understanding will provide the basis for interpreting instrumental data on current seismicity in terms of the interaction between faults at shorter time scales
We found a very peculiar seismic stratigraphy out of the Bosphorous into the Marmara Sea. possibly related to the end of the last glacial period. We also tentatively identified sand dunes covered by a marine transgressional mud-drape. They were formed on the continental shelf when sea level in the Marmara was much lower than at present. This evidence is expected to contribute new key elements to the complex late Quaternary evolution of the Marmara Basin from a lacustrine to a marine environment and of the water exchange between the Mediterranean and the Black Seas.
The bathymetric, chirp and core data will be analyzed and intrepreted within the next two months in time for the planning of the major expedition of the project by R/V CNR-Urania in Spring 2001. During this expedition side-scan sonar mapping and subbottom profiling will be done and carefully positioned sediment cores will be recovered to understand the shallow geometry and kinematics of portions of the fault system in the northeastern Marmara Sea. We hope to distinguish individual slip events, such as the 1509 and 1766 earthquakes, on fault segments of the North Anatolian plate boundary in eastern part of the Marmara Sea. Such data can then be used to infer the future behaviour of the faults.
No problem have to be reported about people, environment and equipment, and we were very happy with the beautiful weather, too (Fig.33).
