Soil baseline geochemistry and plant response in areas of complex geology. Application to NW Euboea,Greece

A soil and vegetation survey was undertaken in NW Euboea Island, Greece. The objectives of the study were to establish the geochemical baseline of soil and identify the impact of local geology on threshold values of potentially harmful elements. The studied area is characterized by complex geology comprising metamorphic and ultramafic rocks as well as active hot springs. A total of 117 soil samples were collected from 89 sites at depths of 0–25 cm and 25–50 cm. Eighteen vegetation samples were also collected representing prevalent indigenous perennial species in the region. Soil samples from the present study were enriched in As, Ca, Cu, Mg, Ni with concentrations reaching 233 mg/kg, 38%, 336 mg/kg, 10.8%, 1560 mg/kg respectively. Factor analysis revealed three main factors controlling the chemical composition of soil reflecting the influence of ultramafic rocks (Cr, Ca, Mg, Ni), hot spring deposits (Ca, S, Sr, As) and paedogenesis processes (Fe, Co, V, Mn, Al). The first two of these factors showed significant spatial correlation with the geological features within the study area. Subsequently, baseline concentrations based on statistical and spatial data were estimated within sub-areas reflecting the influence of local geology in soil composition. Concentrations of potentially harmful elements in the plant tissues of indigenous perennial vegetation species showed a wide range of variation from below the detection limit up to 1700 mg/kg for Ni in the hyperaccumulator Alyssum chalcidicum demonstrating that plant species have adapted to the stressful conditions caused by high elemental concentrations in soil. The results of this study can be utilized in future studies at areas of similar geology by providing an objective basis for setting realistic threshold values for pollution assessment and remediation.     

Restoring capability of bilinear hysteretic seismic isolation systems

The restoring capability (or re‐centering capability) is identified by the current design codes as a fundamental feature of seismic isolation systems. In this paper, the restoring capability of bilinear hysteretic or frictional seismic isolation systems is investigated in some detail. Certain energy considerations are examined first in order to provide insight into and reveal governing parameters on individual aspects of the problem. The restoring capability is then investigated through an extensive parametric study of smooth bilinear single‐degree‐of‐freedom hysteretic systems, with parameters covering a range of typical seismic isolation systems, subjected to a large group of recorded earthquakes. The results of the parametric analyses are processed statistically and regression analysis relations are derived that show the dependence of the residual displacement after the earthquake and the cumulative build up of displacements after a series of successive earthquakes on the governing parameters. Based on the analysis results, the features of the bilinear system that ensure sufficient restoring capability are identified. Copyright © 2007 John Wiley & Sons, Ltd.     

Origin and distribution of surface sediments and human impacts on recent sedimentary processes. The case of the Amvrakikos Gulf (NE Ionian Sea)

The sedimentology of the floor of the Amvrakikos Gulf, a river influenced, semi-enclosed relatively shallow-silled embayment, lying along the northeastern Hellenic coast of the Ionian Sea (eastern Mediterranean Sea), is investigated with respect to its origin (terrigenous and/or biogenic), the prevailing oceanographic conditions and human interference. Nearshore (water depths approximately <10 m) sediments, especially along the northern margin of the Gulf, consist mostly of biogenic sands, as the result of water exchange between the freshwater lagoonal waters and the surface waters of the Gulf. An exception to this is the mouth area of the Arachthos River, which is dominated by the terrigenous riverine sediment influx. The offshore (water depths >10 m) bottom surficial sediments are fine-grained (silty and clayey) of terrigenous origin (>70%); this is attributed to the inter-seasonal, strong two-layer stratification of the water column in the Gulf which restricts benthic productivity by inhibiting the downward flux of surface eutrophic waters and the development of nearbed disoxic conditions in water depths >40 m. River damming has reduced also the riverine terrigenous sediment supply; this is more profound in the case of the Arachthos River where not only the deltaic evolution has been affected, but also the textural character of the seabed sediments of the mouth area has been altered; this is expected to influence the benthic communities of prodeltaic surficial sediment.     

Microseismicity and faulting geometry in the Gulf of Corinth (Greece)

During the summer of 1993, a network of seismological stations was installed over a period of 7 weeks around the eastern Gulf of Corinth where a sequence of strong earthquakes occurred during 1981. Seismicity lies between the Alepohori fault dipping north and the Kaparelli fault dipping south and is related to both of these antithetic faults. Focal mechanisms show normal faulting with the active fault plane dipping at about 45° for both faults. The aftershocks of the 1981 earthquake sequence recorded by King et al . (1985 ) were processed again and show similar results. In contrast, the observations collected near the western end of the Gulf of Corinth during an experiment conducted in 1991 ( Rigo et al . 1996 ), and during the aftershock studies of the 1992 Galaxidi and the 1995 Aigion earthquakes ( Hatzfeld et al . 1996 ; Bernard et al . 1997 ) show seismicity dipping at a very low angle (about 15°) northwards and normal faulting mechanisms with the active fault plane dipping northwards at about 30°. We suggest that the 8–12 km deep seismicity in the west is probably related to the seismic–aseismic transition and not to a possible almost horizontal active fault dipping north as previously proposed. The difference in the seismicity and focal mechanisms between east and west of the Gulf could be related to the difference in the recent extension rate between the western Gulf of Corinth and the eastern Gulf of Corinth, which rotated the faults dipping originally at 45° (as in the east of the Gulf) to 30° (as in the west of the Gulf).     

Voronoi tessellation on the ellipsoidal earth for vector data

Voronoi tessellation, and its dual the Delaunay triangulation, provide a cohesive framework for the study and interpretation of phenomena of geographical space in two and three dimensions. The planar and spherical solutions introduce errors in the positional accuracy of both Voronoi vertices and Voronoi edges due to errors in distance computations and the path connecting two locations with planar lines or great circle arcs instead of geodesics. For most geospatial applications the introduction of the above errors is insignificant or tolerable. However, for applications where the accuracy is of utmost importance, the ellipsoidal model of the Earth must be used. Characteristically, the introduction of any positional error in the delimitation of maritime zones and boundaries results in increased maritime space for one state at the expense of another. This is a situation that may, among others, have a serious impact on the financial activities and the relations of the states concerned. In the context of previous work on maritime delimitation we show that the Voronoi diagram constitutes the ideal solution for the development of an automated methodology addressing the problem in its entirety. Due to lack of a vector methodology for the generation of Voronoi diagram on the ellipsoid, the aforementioned solution was constrained by the accuracy of existing approaches. In order to fill this gap, in this paper we deal with the inherent attributes of the ellipsoidal model of the Earth, e.g. the fact that geodesics are open lines, and we elaborate on a methodology for the generation of the Voronoi diagram on the ellipsoid for a set of points in vector format. The resulting Voronoi diagram consists of vertices with positional accuracy that is only bounded by the user needs and edges that are comprised of geodesics densified with vertices equidistant to their generators. Finally, we present the implementation of the proposed algorithm in the Python programming language and the results of two case studies, one on the formation of closest service areas and one on maritime boundaries delimitation, with the positional accuracy set to 1 cm.     

Modelling monthly soil losses and sediment yields in Cyprus

The aim of this study was to map soil erosion on the Mediterranean island of Cyprus. The G2 model, an empirical model for month-time step erosion assessments, was used. Soil losses in Cyprus were mapped at a 100?m cell size, while sediment yields at a sub-basin scale of 0.62?km² mean size. The results indicated a mean annual erosion rate of 11.75?t?ha^?1?y^?1, with October and November being the most erosive months. The 34% of the island's surface was found to exceed non-sustainable erosion rates (>10?t?ha^?1?y^?1), with sclerophyllous vegetation, coniferous forests, and non-irrigated arable land being the most extensive non-sustainable erosive land covers. The mean sediment delivery ratio (SDR) was found to be 0.26, while the mean annual specific sediment yield (SSY) value for Cyprus was found to be 3.32?t?ha^?1?y^?1. The annual sediment yield of the entire island was found to be 2.746?Mt?y^?1. This study was the first to provide complete and detailed erosion figures for Cyprus at a country scale. The geodatabase and all information records of the study are available at the European Soil Data Centre (ESDAC) of the Joint Research Centre (JRC).