Since 1985, Earth tidal signals in borehole tilt- and well level data are investigated with respect to changes in the state of deformation along a 60km long segment of the North-Anatolian Fault, about 200 km east of Istanbul, Turkey. Modifications of up to 100% in amplitude and 80° in phase (with respect to the response on a laterally homogeneous earth) of the static tidal tilt response functions are essentially explained by the presence of the fault zone. The strong influence of the shear zone varies over time by not more than 4% in amplitude and 3%deg; in phase. Despite the short distance of the 6 stations to the epicenters of the 1999 catastrophic earthquakes of Izmit and Duzce (60 km -110 km and 17 km - 44 km, respectively) no significant pre-, co- or postseismic variations of the local tidal tilt response functions were detected.