The Rethymnon Prefecture in the Crete Island, Greece, suffers from severe landslide phenomena due to its complicated
geological structure with intensive tectonic fragmentation. This research applies the analytical hierarchy process (AHP)
method for landslide susceptibility analysis in the Potamon watershed located inside the Rethymnon Prefecture. The
following landslide conditioning factors were selected: geological formations, slope angle, aspect, curvature, distance to
faults, distance to roads, distance to rivers, land use types and normalized difference vegetation index (NDVI) extracted
from a Landsat-ETM satellite image. A landslide susceptibility map is prepared on the basis of available digital data. The
landslide susceptibility map is validated through the comparison of the results with the already documented landslides
occurring in the study area. The results indicate that the predicted susceptibility map is in good agreement with the past
landslide occurrences, and, therefore, the map is trustworthy for future land-use planning of the study watershed.
A. Savvaidis, B. Margaris, N. Theodoulidis, V. Lekidis, Ch. Karakostas, M.-D. Mangriotis, I. Kalogeras, S. Koutrakis, A. Vafidis, M. Steiakakis, Z. Agioutantis, D. Rozos, C. Loupasakis, Th. Rondoyanni, P. Tsangaratos, U. Dikmen, N. Papadopoulos, A. Sarris, P. Soupios, E. Kokkinou, I. Papadopoulos, M. Kouli, F. Vallianatos
For the seismic action estimation according to Eurocode (EC8) one has to characterize site conditions and suitably estimate soil amplification and corresponding peak ground motion for the site. For this reason, as specified, one has to define a design spectrum through the ground-type/soil-category (S), and the peak ground acceleration (PGA) of the reference return period (TNCR) for the corresponding seismic zone and for structural technical requirements chosen by the designer. Ground type is defined through geophysical/geotechnical parameters, i.e. (a) the average shear wave velocity up to 30 meters depth, (b) the Standard Penetration Test blow-count, and (c) the undrained shear strength of soil. Through the “GEO-CHARACTERIZATION” THALIS-PROJECT we combine different geophysical and geotechnical methods in order to more accurately define the ground conditions in selected sites of the Hellenic Accelerometric Network (HAN) in the area of Crete Island. More specifically in the present efforts, geological information shear wave velocity and attenuation model calculated from seismic surface geophysical measurements is used. Additionally we utilize the ground acceleration recorded through HAN from intermediate depth earthquakes in the broader area of South Aegean Sea. Using the recorded ground motion data and the procedure defined in EC8, the corresponding elastic response spectrum is calculated for selected sites. The resulting information are compared with the values defined for the corresponding EC8 spectrum for the seismic zone comprising the island of Crete. As a final outcome of this work we intend to propose regional normalized elastic spectra for seismic design of structures and urban development planning and compare them with Eurocode.
The lifelines seismic risk assessment is based on a fuzzy classification on parameters related to geometry (effective length distribution L) and constructive details (material type C) along with urban (U) and economic (E) parameters. Then a functional value G = f(L, C, U, E) is constructed as an indicator of risk of the element/system under investigation. In the present study a new functional Fg is introduced in a GIS environment. The application of spatial analysis methods provides a better understanding of the possible failure patterns and trends in water distribution networks. The Fg parameter takes into account the influence of geological and seismotectonic environment in a local scale, constructed in a way to reflect the amplification factor A (X), where X local coordinate of the cell, which experimentally could be estimated. The Fg= f(A(X), U(X), L(X)) is strongly affected by the local geotectonic conditions as well the spatial distribution of population and the geometrical lattice of pipe line system. The proposed index was applied in the city of Chania, Crete island, as the functioning of the infrastructure during and especially after a destructive earthquake, in the front of the Hellenic Arc, is of vital importance for the society and contributes to the rescue and emergency operations. We propose Fg mainly for systems where site effects are important and present a significant spatial inhomogeneity while at the same time the examined urban system has no constructive variability it time and space.
The Digital Elevation Model (DEM) for the Crete Island with a resolution of approximately 20 meters was used in order to delineate watersheds by computing the flow direction and using it in the Watershed function. The Watershed function uses a raster of flow direction to determine contributing area. The Geographic Information Systems routine procedure was applied and the watersheds as well as the streams network (using a threshold of 2000 cells, i.e. the minimum number of cells that constitute a stream) were extracted from the hydrologically corrected (free of sinks) DEM. A number of a few thousand watersheds were delineated, and their areal extent was calculated. From these watersheds a number of 300 was finally selected for further analysis as the watersheds of extremely small area were excluded in order to avoid possible artifacts. Our analysis approach is based on the basic principles of Complexity theory and Tsallis Entropy introduces in the frame of non-extensive statistical physics. This concept has been successfully used for the analysis of a variety of complex dynamic systems including natural hazards, where fractality and long-range interactions are important. The analysis indicates that the statistical distribution of watersheds can be successfully described with the theoretical estimations of non-extensive statistical physics implying the complexity that characterizes the occurrences of them.
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