Structural framework of onshore and offshore Avcilar, Istanbul under the influence of the North Anatolian fault

To investigate the onshore/offshore structural framework of the northern shelf of the Sea of Marmara, a multidisciplinary study was carried out including multichannel and single-channel seismic reflection profiling, multibeam bathymetry sounding, side-scan sonar imaging on offshore as well as land studies for S-wave velocity estimation by passive and active array measurements and monitoring of block deformations by Global Positioning System (GPS). Based on the multidisciplinary data, possible interactions between landslides and active faulting have been reviewed and their possible relation to the North Anatolian Fault Zone (NAFZ) has been discussed. It is observed that structurally the most deformed subsurface zone offshore coincides with the most undulated landform due to landslides in the area. This observation leads to idea that the structural complexities of the area may also contribute to land sliding as much as other contributing mechanisms such as slope instability, shallow groundwater level, lithology and liquefaction. The Catalca Fault Zone, a branch of the inactive Western Black Sea (WBS) Fault, may constitute weakness surfaces that contribute to land sliding in the deformed Miocene layers in the study area. Based on the multidisciplinary and new data sets, we show that ongoing land sliding in the study area should be related not only to common causes of landslides but also the structural framework of the area.