The present study reveals several unexpected results that can be summarized as follow.First, the high-resolutionbathymetry highlights the trace of a major fault strand through Izmit Bay that is more linear than previously thought. Second, vertical motion is highly asymmetric about the fault, with rapid deformation affecting the southern fault block, and a relatively stable northern fault block. Lastly, surface slip from the 1999 earthquake arrested or tailed off abruptly halfway through Izmit Gulf rather than propagating another 30 km westward, as was suggested from the analysis of other geophysical data. These results are detailed in the article and a model is proposed that can account for them.