A controlled source tomography in Sarımeşe, İzmit, at the western section of North Anatolian Fault Zone

: A high-resolution two-dimensional tomographic velocity image in the eastern Marmara region along a 1.2 km long N-S trending seismic profile, which crosses the surface rupture of the İzmit earthquake on the North Anatolian Fault (NAF) is presented. A vibroseis source at more than 180 points with 50 receivers was used along the long profile. A regularized inversion technique was applied to the first arrival travel times. More than 6500 first arrivals from 129 shot gathers were analyzed to construct velocity images and were qualitatively evaluated for the fault zone-related effects. The velocity model was constrained to a maximum depth of 175 m. The results indicate a fault zone of ~100 m thick with clear velocity contrasts with surrounding blocks. The P wave velocity on the southern block varies between a range of 1.4–1.7 km/s and 1.7–2.0 km/s on the northern block the velocity decreases to 1.4 km/s within the fault zone down to 100–150 m depth. Three component recordings and fan shots also indicate the presence of the fault zone consistent with the tomographic image.