Maria Kouli

Structural Analysis for Gold Mineralization Using Remote Sensing and Geochemical Techniques in a GIS Environment: Island of Lesvos, Hellas

Exploration for epithermal Au has been active lately in the Aegean Sea of the eastern Mediterranean Basin, both in the islands of the Quaternary arc and in those of the back-arc region. The purpose of this study was the structural mapping and analysis for a preliminary investigation of possible epithermal gold mineralization, using remotely sensed data and techniques, structural and field data, and geochemical information, for a specific area on the Island of Lesvos. Therefore, Landsat-TM and SPOT-Pan satellite images and the Digital Elevation Model (DEM) of the study area were processed digitally using spatial filtering techniques for the enhancement and recognition of the geologically significant lineaments, as well as algebraic operations with band ratios and Principal Component Analysis (PCA), for the identification of alteration zones. Statistical rose diagrams and a SCHMIDT projection Stereo Net were generated from the lineament maps and the collected field data (dip and strike measurements of faults, joints, and veins), respectively. The derived lineament map and the band ratio images were manipulated in a GIS environment, in order to study the relation of the tectonic pattern to both the alteration zoning and the geomorphology of the volcanic field of the study area. Target areas of high interest for possible mineralization also were specified using geochemical techniques, such as X-Ray Diffraction (XRD) analysis, trace-element, and fluid-inclusion analysis. Finally, preliminary conclusions were derived about possible mineralization, the type (high or low sulfidation), and the extent of mineralization, by combining the structural information with geochemical information.

Landslide susceptibility mapping by comparing the WLC and WofE multi-criteria methods in the West Crete Island, Greece

In the current research, the weighted linear combination (WLC) and the weights of evidence (WofE) methods were applied for landslide susceptibility zonation mapping in the Chania Prefecture of Crete Island, Greece. Several thematic maps representing various landslide conditioning factors, such as geology formations, faults proximity, altitude, slope gradient, aspect, curvature, rivers proximity, precipitation, roads proximity and land use types have been generated in a GIS environment. Three landslide susceptibility maps were created, one for each method and a combined one by applying the logistic regression approach to the WLC and WofE susceptibility maps. The maps were evaluated and validated using the efficiency rate curve, the receiver-operator curve and the spatially agreed areas methods. The resulting landslide susceptibility maps have uncertainties introduced due to the subjective knowledge of experts in the case of WLC method and to the quality of the recorded landslides sample in the case of the WofE method. Nevertheless, the performance of the three approaches was found to be almost equal with all methods to produce quite satisfactory results. Besides the comparison of the applied methods, the current study contributes to the risk management of the area, providing the first landslide susceptibility maps for Chania Prefecture.

Geochemistry and quality of the groundwater from the karstic and coastal aquifer of Geropotamos River Basin at north-central Crete, Greece

In Geropotamos River Basin, located on the north-central part of Crete, Greece, two main factors were believed to be affecting the geochemistry of the groundwater with high salt contents: seawater intrusion and/or Miocene evaporates. To identify the origin of the high salinity in groundwater, a hydrogeochemical and isotopic study was performed. Water samples from 22 wells and 2 springs were analyzed for physico-chemical parameters, major ions analysis, as well as stable isotopes (δ18O, δD). From the present survey, in which detailed hydrogeochemical investigation was conducted, the uncertainty of the contamination sources was decreased in the northern part of Geropotamos Basin. The results complement the scenario in which seawater and the widespread human activities are the principal sources of groundwater contamination. Moreover, the results of the stable isotopes analyses (δ18O and δD) support the same hypothesis and make seawater intrusion the most probable cause for the highest salinity waters. It is indicated that saline intrusion is likely to occur along fractures in a fault zone through otherwise low-permeability phyllite–quartzite bedrock, which demonstrates the critical role of fracture pathways in salination problems of coastal aquifers.

Aquifer characterization using shallow geophysics in the Keritis Basin of Western Crete, Greece

Effective management of groundwater resources is a well-known problem in several areas around the world. It is especially important to areas suffering from an intrinsic lack of fresh water, such as islands. Detailed study of available aquifers is of particular interest in the highly touristic Greek island of Crete. The increasing water demand makes water resources management extremely important for sustainable development. This is the case in the prefecture of Chania in Western Crete, where there has been a lack of success of many different groundwater management plans that have been produced over the years and submitted for application to water management authority. The inefficiency of the management plans is verified by the continuous water shortage reported every year which forces the public authorities to transfer water from far away sources and wells. Until today there are only geological data as well as information from the borehole logs; therefore, the current work is focused to study in detail the tectonic and hydrogeological characteristics of the Keritis watershed to make a correlation of the available geoenvironmental information with the geophysical data of the study aquifer. Transient electromagnetic soundings were conducted to obtain detailed information about: the tectonic, hydrogeological, hydrolithological, and geometrical characteristics of the aquifer under investigation. In addition, optimum areas of water well drilling were identified to minimize the uncertainty and the total cost (economical, managerial, etc.) of future groundwater surveys.

Preliminary GIS based analysis of seismic risk in water pipeline lifeline system in urban infrastructure of Chania (Crete)

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.

Evidence of Hierarchy in the Complex Fractured System of Geropotamos (Crete, Greece), as Extracted from Transient Electromagnetic Responses

The essential goals of this paper are to test the transient electromagnetic (TEM) response in a fractured geological complex medium and to better understand the physics introduced by associating a roughness parameter β to the geological formation. An anomalous fractional diffusion approach is incorporated to describe the electromagnetic induction in rough multi-scaled geological structures. The multi-scaling characteristics of Geropotamos basin in Crete are revealed through the analysis of transient step-off response of an EM loop antenna. The semi-empirical parameters derived from late-time TEM measurements are correlated with the multi-scale heterogeneities of the medium. Certain interesting properties of the late-time slope γ(β) and the power law of near surface resistivity distribution, as extracted from TEM inversion for different depth, are presented. The analysis of the parameter γ(β) which scales the induced voltage in the loop in the late stage of the electromagnetic response leads to a different view of the EM geophysical data interpretation. We show that it is strongly correlated with areas of high fracture density within the geological formations of the Geropotamos area. For that reason, it is proposed as a local multi-scaling empirical index. The results of this paper suggest that anomalous diffusion could be a viable physical mechanism for the fractal transport of charge carriers, explaining observed late-time TEM responses across a variety of natural geological settings.

Integrated GIS and remote sensing analysis for landslide susceptibility mapping in Crete

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.

Geophysical and geochemical study of geropotamos aquifer in the north-central coast of crete

The geological setting of Geropotamos aquifer on the north-central coast of Crete, Greece, is considered complex, while the local tectonic regime of the study area is characterized by two sets of faults orientated NW-SE and NE-SW. Investigation of the aquifer using the Transient ElectroMagnetic method (TEM) has resulted initially in 1D models of geoelectric structures and a final 3D geoelectrical model was constructed, depicting the zones of salination of groundwater in the aquifer. Groundwater samples were analysed and the most important chemical parameters were determined to provide an independent dataset for comparison with the TEM results, while Groundwater Quality Maps were produced. TEM and geochemical data correspond and provide verification of the TEM approach. As a result, saline intrusion is likely to occur along fractures in a fault zone through bedrock, and this work emphasises the critical role of fracture pathways in salination problems of coastal aquifers.

Evidence of nonextensive statistical physics behavior in the watershed distribution in active tectonic areas: examples from Greece

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.

GEO-CHARACTERIZATION ACCORDING TO RECENT ADVANCES OF EUROCODE (EC8)

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.