Kinematics of two deep-seated landslides in Greece

The long-term - probably the longest existing-geodetic monitoring record (>20 years) of a major, slow-moving (about 150 mm/year) deep-seated landslide in northern Greece was analysed. Kinematics of all control points established on the sliding mass, as well as of another neighbouring major landslide, were found to follow the same exponential trend. Least-square-derived spectral analysis of the unevenly spaced residuals of the fitting revealed that superimposed on this trend are events of accelerated movement with a mean return period of 4·0-7·5 years, most likely triggered by meteorological factors. Such a kinematic pattern, derived for the first time owing to the scarcity of detailed long-term landslide monitoring records, shows that, except for some major deep landslides for which there is evidence of seasonal variation of their movement, there are landslides with a much larger periodicity (some years).