N. Sabatakakis

Landslide susceptibility zonation in Greece

The objective of this study is to perform a preliminary national-scale assessment of the landslide susceptibility in Greece using a landslide inventory derived from historical archives. The effects of controlling factors on landslide susceptibility combined with multivariate statistics have been evaluated using GIS aided mapping techniques. Thousand six hundred thirty-five landslide occurrences, mainly earth slides obtained from Public Authorities archives, covering a long time period were recorded and digitally stored using a spatial relational database management system. Ten landslide predisposing factors (predictors) were identified, while digital thematic maps on the spatial distribution of those factors were generated. The correlation between the landslide locations and predictor classes was analyzed by using the Landslide Relative Frequency. R-mode factor analysis was applied to study the interrelations between predictors (independent variables) while weighting coefficients were determined. Landslide susceptibility was derived from an algorithm which modeled the influence of predictors, and a susceptibility map was compiled. The landslide susceptibility map was verified using a data set of 375 new landslide locations. It is the first comprehensive attempt to illustrate the landslide susceptibility in the total country based on the interpretation of historical data only.

Landslide Hazard Zonation in Greece

Landslide occurrences in Greece, covering a long time period (1950–2004) 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.

Ground zoning against seismic hazard in Athens, Greece

Abstract The 1999, Ms=5.9, Athens earthquake caused serious structural damage to buildings in the western part of Athens, Greece. This paper presents the ground zoning against seismic hazard proposed shortly after the earthquake in order to aid reconstruction of the area. Existing engineering geological and geotechnical data were combined with local observations to provide a unified set of classification criteria, consistent with provisions of the Greek Seismic Code EAK. The accuracy and the possible limitations of this zoning procedure are addressed through comparison with observed damage distribution as well as results from seismic ground response analyses performed at sites with well established soil profiles. There is clear evidence that the proposed zones correspond to geological formations exhibiting grossly different seismic response with regard to the design of common engineering structures. However, the mostly qualitative nature of the guidelines for ground categorisation provided by EAK and the general lack of systematic, site-specific geotechnical data for the whole area induce uncertainties in the definition of the seismic design actions for the different zones. These objective uncertainties certainly demand increased conservatism but do not limit application of the proposed methodology for first aid, preliminary planning in the event of destructive earthquakes.

Evaluation of Rockfall Restitution Coefficients

Restitution coefficients for various slope surfaces affected by extensive rockfalls are proposed from back–analysis calculations that have been carried out in several sites of the Western Greece. These occurrences have been thoroughly studied in order to investigate the extent of the events, assess the hazard and propose protective measures. The falling boulders were varied in size, while the strong earthquakes, the heavy rainfall and the wildfires were the principal triggering factors.

Preliminary results from active landslide monitoring using multidisciplinary surveys

ABSTRACT This study presents the synergy of multidisciplinary surveys for the monitoring of an active landslide in Western Greece. The aim of this paper is to highlight and validate a methodology based on multiple sensors data integration which can successfully be used to manage natural disasters or to improve the knowledge of a specific phenomenon in order to prevent and mitigate the risk. Photogrammetric and interferometric processing has been applied to a complex set of remote sensing data such as high resolution satellite images, digital airphotos, aerial photos acquired from an Unmanned Aerial Vehicle and radar data. Global Navigation Satellite System measurements and continuous inclinometer measurements are being performed. The multifunctional technology of Geographic Information Systems is used in order to collect, storage, manage, process, analyze and cartographically represent the previously described complex geoscientific information.

Active landslide monitoring using remote sensing data, GPS measurements and cameras on board UAV

An active landslide can be monitored using many different methods: Classical geotechnical measurements like inclinometer, topographical survey measurements with total stations or GPS and photogrammetric techniques using airphotos or high resolution satellite images. As the cost of the aerial photo campaign and the acquisition of very high resolution satellite data is quite expensive the use of cameras on board UAV could be an identical solution. Small UAVs (Unmanned Aerial Vehicles) have started their development as expensive toys but they currently became a very valuable tool in remote sensing monitoring of small areas. The purpose of this work is to demonstrate a cheap but effective solution for an active landslide monitoring. We present the first experimental results of the synergistic use of UAV, GPS measurements and remote sensing data. A six-rotor aircraft with a total weight of 6 kg carrying two small cameras has been used. Very accurate digital airphotos, high accuracy DSM, DGPS measurements and the data captured from the UAV are combined and the results are presented in the current study.

A multisource approach for coastal mapping purposes: Limeni bay, Mani and surrounding area, southern Greece

A multipurpose engineering geological map of a natural heritage site including inland and offshore areas has been compiled to provide information on many aspects for land use optimization, sustainable development and environmental protection. The mapping approach was based on data provided by conventional onland field works, marine remote sensing survey and aerial photo interpretation. These data sources were integrated into a GIS platform allowing reliable mapping solutions. The geological formations encountered were grouped into individual geotechnical units according to uniformity in lithological character, while the seabed sub-bottom structure was also obtained through several seafloor thematic map compilation. Shoreline variability and evolution for a long time period (1945–2008) were also investigated and mapped. The synergistic use of the results deducted from those disciplinary surveys is finally presented in a single engineering geological map covering the onshore and offshore area.

Landslide monitoring using airphotos time series and GIS

Western Greece is suffering by landslides. The term landslide includes a wide range of ground movement, such as slides, falls, flows etc. mainly based on gravity with the aid of many conditioning and triggering factors. Landslides provoke enormous changes to the natural and artificial relief. The annual cost of repairing the damage amounts to millions of euros. In this paper a combined use of airphotos time series, high resolution remote sensing data and GIS for the landslide monitoring is presented. Analog and digital air-photos used covered a period of almost 70 years from 1945 until 2012. Classical analog airphotos covered the period from 1945 to 2000, while digital airphotos and satellite images covered the 2008-2012 period. The air photos have been orthorectified using the Leica Photogrammetry Suite. Ground control points and a high accuracy DSM were used for the orthorectification of the air photos. The 2008 digital air photo mosaic from the Greek Cadastral with a spatial resolution of 25 cm and the respective DSM was used as the base map for all the others data sets. The RMS error was less than 0.5 pixel. Changes to the artificial constructions provoked by the landslideswere digitized and then implemented in an ARCGIS database. The results are presented in this paper.

The effect of microstructure on mi strength parameter variation of common rock types

A series of laboratory tests was conducted on selected intact sedimentary (sandstones and limestones) and igneous (granites and andesites-dacites) rocks obtained from several sites of Greece. Physical and mechanical properties were determined, while the investigation was focused on strength parameters determination and especially on Hoek-Brown strength parameter mi through the triaxial compression. Mineral composition of grains, as well as microstructure (grain size, shape and interlocking) was estimated through microscopic examination using some well known petrographic indices. The alteration and weathering state for the studied igneous rocks were also microscopically quantified. Regression analysis of laboratory data have clearly shown a direct strong intrinsic influence of microstructure as quantitatively described by the petrographic indices and by textural interlocking of the grains, as well as of grain deterioration on measured mi value. The mi value generally increases with the increasing grain size of studied clastic and igneous rocks, but it decreases to a power expression with sparitic material of limestones. The increase of weathering and alteration state also decreases the mi parameter of tested igneous rocks.

3D subsurface geological modeling using GIS, remote sensing, and boreholes data

The current paper presents the combined use of geological-geotechnical insitu data, remote sensing data and GIS techniques for the evaluation of a subsurface geological model. High accuracy Digital Surface Model (DSM), airphotos mosaic and satellite data, with a spatial resolution of 0.5m were used for an othophoto base map compilation of the study area. Geological – geotechnical data obtained from exploratory boreholes and the 1:5000 engineering geological maps were digitized and implemented in a GIS platform for a three – dimensional subsurface model evaluation. The study is located at the North part of Peloponnese along the new national road.