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Earthquake shaking can trigger a large number of landslides in hilly or mountainous areas, considerably aggravating the impact of the seismic event in terms of overall damage and loss of life. Thus, the delineation of slope areas that have a significant probability of failing under future seismic action appears imperative for disaster mitigation. In the present study, we follow a time probabilistic approach for the evaluation of earthquake-induced landslide hazard in Greece through the estimation of the minimum resistance required for slopes to remain within a prefixed value of exceedance probability of failure. Taking into account the characteristics of seismicity affecting Greece, we constructed maps representing the spatial distribution of critical acceleration values that imply a 10% probability that Newmark's displacement will exceed significant thresholds in a time interval of 50 years. These maps provide the spatial distribution of the strength demand required for slopes to resist failures under the action of the regional seismicity. Such maps allow an assessment of whether particular slopes have a significant failure probability by comparing the strength demand estimated at the location of the slope with its actual critical acceleration calculated from slope material properties and slope angle. To exemplify the possible use of these strength demand maps in local hazard estimates, we compare, within a GIS framework, the critical acceleration values obtained by the application of the time probabilistic approach with actual in situ critical acceleration values for a coastal area of the Western Gulf of Corinth.

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Abstract. Landslide occurrences in Greece, covering a long time period were recorded and digitally stored using a relational database management system. The first evaluation of engineering geological data and the geographical distribution of the recorded cases led to the determination of most critical landslide prone geological formations, regarding lithology and structure and to a landslide hazard map compilation at a national scale. Keywords. Hazard zonation, database management, Greece IntroductionA systematic inventory of data concerning landslides and their quantitative expression in Greece, through a relational database management system, was firstly attempted at the end of 1980s by Koukis and Ziourkas (1991), following the general trends of similar studies in other countries. Furthermore, statistical analyses of the main factors affecting landslide phenomena and their interrelations were established by Koukis et al. (1994Koukis et al. ( , 1996Koukis et al. ( , 1997, based upon data recordings through the database of landslide movements covering the as above period of more than 45 years.In the last decade, the landslide activity is increasingly high as a result of increased urbanization and development (transportation routes, dams and reservoirs, industrial and urban activities) in landslide-prone areas, continued deforestation and extreme meteorological events. An increment of about 20% of the landslide occurrences has been recorded during the last five years all having serious socio-economic consequences resulted in a significant increase of total economic losses, fortunately without casualties.After those events, the authorities have focused their attention on mitigating the problem by avoiding the hazards or reducing the damage potential. To aid this planning the Department of Geology of Patras University and the Institute of Geology and Mineral Exploration (IGME) were commissioned to undertake an extensive study regarding landslide hazard zonation. The techniques used were in accordance with the required national and regional scale of zonation of extensive areas according to their susceptibility to slope instability phenomena and they mainly included: (a) detailed inventory of slope instability processes and their study in relation to engineering geological setting, (b) analyses of causing and triggering factors and (c) spatial distribution of these factors.The aim of this paper is to evaluate some first considerations regarding the influence of the geological conditions on landslide frequency distribution in the Greek territory using simple statistics and direct mapping methodology for landslide hazard zonation. Geological Setting and Landslide PhenomenaIn Greece, which has been experienced a complicated history of geophysical development during the Alpine orogenic cycle, several geotectonic zones or regions can be distinguished by fundamental differences both in lithology and structure (Figs. 37.1 and 37.2). The elongation of those zones more or less coincides with the trend of the main mountain ran...

Representative landslide phenomena in western Greece induced by heavy rainfalls, in terms of the geological composition and structure of the affected materials, are thoroughly studied and analyzed. The studied cases involved composite landslides on weathered mantle of flysch and Neogene marls that constitute the most critical landslide prone geological formations in Greece. Their shear strength characteristics were determined from back analyses while low-cost remedial measures, focused on surface and groundwater control, were designed. The effective contribution of the finally constructed works on ground stabilization was systematically monitored by surface and subsurface measurements of ground displacements during a time period after their construction.

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