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

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... aries over time by not more than 4% in amplitude and 3° 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.