SORRY, I have not collected substantial information on the faulting yet. Here I present just an outline of the fault with background information. Please kindly inform me of valuable link for more information [20 Augsut 1999].
Magnitude in parentheses is in Ms after Ambraseys (1988)
The North Anatolian fault ruptured between 40E and 31E during a series of earthquakes in 1939 through 1967. The portion of the fault between 29E and 31E has not ruptured following the series and hence regarded as a seismic gap. The 17 August 1999 earthquake ruptured the northern strand of the fault [namely Izmit-Sapanca fault] in the gap around Izmit. Over 80km surface rupture with 2 to 3 m right-lateral offset is being confirmed by various sources.
Lots of geophysical and geological investigation have been conducted to evaluate the seismic risk of the gap, but there seemed to be no solid forecast as far as I know. From paleoseismological point of view, we did not have much information on the Izmit-Sapanca fault, compared with the southern strand [namely Iznik-Mekece fault]. The area along the strand has been under so intensive cultivation and other huma activities that geologists were not able to carry out trenching survey.
Concerning the Iznik-Mekece fault, Yoshioka and Kuscu  recognized the penultimate event in 3rd or 4th century B.C. and estimated the recurrence interval to be 1700 to 2200 years with the estimated age of the last event between 200 to 500 year before present [Honkura and Iskara 1991]. This recurrence time might be too long.
As to the present-day geodynamics based on GPS survey, Straub et al. [1997, JGR 102 B12] present an excellent image of the ongoing tectonic deformation.
Ambrasay's ariticle in 1988 is one of the most comprehensive catalogues of large earthquake in Turkey during this century with abundant figures.
Paleoseismology of the North Anatolian fault homepage by Koji.
Geotechnical Earthquake Engineering Server at University of Southern California
Kandilli Observatory and Earthauake Reserach Institute, Bogazici University
U.S. Geological Survey Geologic Hazard Team
Ambraseys, N.  Engineering Seismology, Earthquake Engineering and Structural dynamics, 17, 1-105.
Honkura, Y. and Iskara, A.M.  Multidisciplinary research on fault activity in the western part of the North Anatolian Fault zone. Tectonophysics, 193, 347-357.
Straub, C., Kahle, H-G., and Schindler, C.  GPS and geologic estimates of the tectonic activity in the Marmara Sea region, NW Anatolia, Jour. Geophys. Res., 102, B12, 27587-27601.
Yoshioka, T. and Kuscu, I  Late Holocene faulting events on the Iznik-Mekece fault in the western part of the North Anatolian fault zone, Turkey, Bull. Geol. Surv. Japan, 45, 677-685.