Summary From 1996 to 1999, we have studied ground tilts at depths of between 2 m and 5 m at three sites in the Lower Rhine Embayment (LRE), western Germany. The LRE is a tectonically active extensional sedimentary basin roughly 50 km × 100 km. The purpose of the tilt measurements was (a) to provide insight into the magnitude, nature and variability of background tilts and (b) to assess possible limitations of high‐resolution GPS campaigns and microgravity surveys due to natural ground deformation. The tilt readings, sensed by biaxial borehole tiltmeters of baselength 0.85 m, cover a frequency range from 10−8 Hz to 10−2 Hz (periods from minutes to years). Assuming that the tilt signals represent ground displacements on a scale typically not larger than several times the tiltmeters' baselength, and that tilt signals at shallow depth could in a simple geometric way be related to changes in surface elevation and gravity, we try to estimate the magnitude level of point movements and corresponding Bouguer gravity effects that is generally not surpassed. The largest tilt signals observed were some ± 50 µrad yr−1. If they were observable over a ground section of extension, e.g. 10 m, the converted rates may correspond to about ± 0.5 mm per 10 m yr−1 in vertical ground displacement, and ± 0.1 µgal yr−1 in Bouguer gravity effect, respectively. Large signals are mostly related to seasonal effects, probably linked to thermomechanical strain. Other causes of ground deformation identified include seepage effects after rainfalls (order of ± 10 µrad) and diurnal strains due to thermal heating and/or fluctuations in the water consumption of nearby trees (order of ± 1 µrad). Episodic step‐like tilt anomalies with amplitudes up to 22 µrad at one of the observation sites might reflect creep events associated to a nearby active fault. Except for short‐term ground deformation caused by the passage of seismic waves from distant earthquakes, amplitudes of non‐identified tilt signals in the studied frequency range seem not to exceed ± 2 µrad. As the larger tilt signals are close to the precision achieved with modern GPS systems and superconducting gravimeters when converted into height and gravity changes, further enhancement in resolution of these techniques may require simultaneous recording of local ground deformation at the observation sites.

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Five years of geodetic monitoring data are processed to evaluate recurrent sliding at Dunaszekcső, which are characteristic geomorphological processes affecting the high banks of the Middle Danube valley in Hungary. The integrated geodetic observations provide accurate three dimensional coordinate time series, and these data are used to calculate the kinematic features of point movements and rigid body behavior of point blocks. Additional datasets are borehole tiltmeter and hydrological recordings of the Danube and soil water wells. These data, together with two dimensional final element analyses, are utilized to gain a better understanding of the physical, soil mechanical background and stability features of the high bank. Here we show that the main trigger of movements appears to be the changing groundwater levels, which have an effect an order of magnitude higher than that of river water level changes. Varying displacement rates of the sliding blocks are interpreted as having been caused by basal pore water pressure changes originating from shear zone volume changes, floods of the River Danube through later seepage and rain infiltration. Both data and modeling point to the complex nature of bank sliding at Dunaszekcső. Some features imply that the movements are rotational, some reveal slumping. By contrast, all available observational and modeling data point to the retrogressive development of the high bank at Dunaszekcső. Regarding mitigation, the detailed analysis of three basic parameters (the direction of displacement vectors, tilting, and the acceleration component of the kinematic function) is suggested because these parameters indicate the zone where the largest lateral displacements can be expected and indicate the advent of the rapid movement phase of sliding that affect high banks along the River Danube.2 Keywords: River Danube; Groundwater; Bank failure; Tilting; Kinematic and dynamic evolution IntroductionMass movements are considered the major geomorphic processes that govern the morphological evolution of high banks along the River Danube on both shorter and longer timescales. In Hungary abrupt and disastrous landslides along the river were documented and their possible mechanisms were explained from geomorphic-hydrogeological point of view in the last century (e.g. Domján, 1952;Kézdi, 1970;Horváth and Scheuer, 1976;Scheuer, 1979). Active sliding phases commenced owing to the likely interplay of high water stands of the Danube, increased precipitation input and anthropogenic activity (Juhász, 1999;Kleb and Schweitzer, 2001; Szabó, 2003;Kraft, 2005). Such sliding events also occurred during the Medieval and Roman times and a rate of bluff retreat of 5-15 m per 100 years over the last 2,000 years was estimated (Lóczy et al., 1989(Lóczy et al., , 2012. Previously, the bank failures were described after the main sliding phase and as yet only one real observational record is available from Hungary which includes deformation monitoring data from close to the initiation to the main phase of a l...