The western termination of the 1999 Izmit earthquake still remains as an intriguing problem for researchers and the people residing around the Sea of Marmara. There have been numerous off shore mapping and modelling studies performed in the Gulf of Izmit. However, the main debate about the western termination of the 1999 Izmit surface rupture is linked to the Hersek Peninsula and corresponding fault geometry. We focused our efforts at resolving the fault geometry on the Hersek Peninsula by applying geological mapping, geomorphic analyses, palaeoseismic trenching and geophysical surveys. Our studies reveal that the North Anatolian Fault forms a restraining stepover and did not experience surface rupture during 1999 Izmit earthquake in the vicinity of Hersek Peninsula. We tested this fault geometry with a finite element model in half elastic space and correlated the results successfully with the existing topography. In addition, we ran a simple Coulomb model to explain the possible cause of surface rupture termination at this specific location. Our studies, combined with detailed off shore bathymetry data, suggest that the restraining step of the North Anatolian Fault on the Hersek Peninsula is capable of creating an efficient earthquake rupture barrier.