Landslide hazard zonation in high risk areas of Rethymno Prefecture,Crete Island,Greece

The central part of Rethymnon Prefecture, Crete Island, suffers from severe landslide phenomena because of its geological and geomorphological settings alternated by the human activities. The main landslide preparatory and triggering causal factors are considered to be the ground conditions (lithology), geomorphological processes (fluvial erosion, etc.), and the man-made actions (excavations, loading etc.). The purpose of this study is to develop a decision support and continuous monitoring system of the area by composing landslide hazard and risk maps. For that reason, several approaches of the weighted linear combination (WLC), a semi-quantitative hazard analysis method, were adopted in a Geographic Information Systems (GIS) environment. The results were validated using a pre-existing landslide database enriched with new landslide locations mapped through image interpretation of a processed IKONOS satellite image. The validation results showed that the WLC method coupled with remote sensing (RS) and GIS techniques can support engineering geological studies concerning landslide vulnerability of hazardous areas.     

Recursive anisotropy: a spatial taphonomic study of the Early Pleistocene vertebrate assemblage of Tsiotra Vryssi,Mygdonia Basin,Greece

By applying advanced spatial statistical methods, spatial taphonomy complements the traditional taphonomic approach and enhances our understanding of biostratinomic and diagenetic processes. In this study, we elaborate on a specific aspect – spatial anisotropy – of taphonomic processes. We aim to unravel the taphonomic history of the Early Pleistocene vertebrate assemblage of Tsiotra Vryssi (Mygdonia Basin, Greece). Circular statistics are used for the fabric analysis of elongated elements; geostatistics (directional variograms), wavelet and point pattern analyses are applied for detecting anisotropy at the assemblage level. The anisotropy of magnetic susceptibility (AMS) of sedimentary magnetic minerals is also investigated. The results, integrated with preliminary remarks about the differential preservation of skeletal elements, sedimentological and micromorphological observations, suggest multiple dispersion events and recurrent spatial re‐arrangement of a lag, (peri)autochthonous assemblage, consistent with the cyclical lateral switching of a braided fluvial system. Furthermore, this study offers a contribution to the building of a spatial taphonomic referential framework for the interpretation of other fossil vertebrate assemblages, including archaeo‐palaeontological ones.     

Extended MSRS rule for seismic analysis of bridges subjected to differential support motions

This paper introduces a generalized formulation of the multiple support response spectrum (MSRS) method (Earthquake Engng Struct. Dyn. 1992; 21 :713–740) and extends it by accounting for the quasi‐static contributions of truncated modes. The generalized formulation allows consideration of response quantities that involve support degrees of freedom (DOF). This situation arises for many response quantities of interest when rotational DOF are condensed out. New cross‐correlation coefficients are introduced in the extended rule and a parametric study is performed to gain insight and identify cases of ground motion spatial variability in which these terms are significant. An efficient computer implementation of the extended MSRS method is described and used for comprehensive analysis of two real bridge models with vastly different structural characteristics. The specified input is in accordance with standards used in engineering practice. The effects of differential support motions, including the influence of spatially varying soil conditions, on the pseudo‐static and dynamic components and the total response are examined and the improvement achieved with the extended MSRS method is assessed. Copyright © 2011 John Wiley & Sons, Ltd.     

Petrography,mineralogy, and geochemistry of deep gravelly sands in the Eyreville B core,Chesapeake Bay impact structure

The ICDP–USGS Eyreville drill cores in the Chesapeake Bay impact structure reached a total depth of 1766 m and comprise (from the bottom upwards) basement‐derived schists and granites/pegmatites, impact breccias, mostly poorly lithified gravelly sand and crystalline blocks, a granitic slab, sedimentary breccias, and postimpact sediments. The gravelly sand and crystalline block section forms an approximately 26 m thick interval that includes an amphibolite block and boulders of cataclastic gneiss and suevite. Three gravelly sands (basal, middle, and upper) are distinguished within this interval. The gravelly sands are poorly sorted, clast supported, and generally massive, but crude size‐sorting and subtle, discontinuous layers occur locally. Quartz and K‐feldspar are the main sand‐size minerals and smectite and kaolinite are the principal clay minerals. Other mineral grains occur only in accessory amounts and lithic clasts are sparse (only a few vol%). The gravelly sands are silica rich (～80 wt% SiO₂). Trends with depth include a slight decrease in SiO₂ and slight increase in Fe₂O₃. The basal gravelly sand (below the cataclasite boulder) has a lower SiO₂ content, less K‐feldspar, and more mica than the higher sands, and it contains more lithic clasts and melt particles that are probably reworked from the underlying suevite. The middle gravelly sand (below the amphibolite block) is finer‐grained, contains more abundant clay minerals, and displays more variable chemical compositions than upper gravelly sand (above the block). Our mineralogical and geochemical results suggest that the gravelly sands are avalanche deposits derived probably from the nonmarine Potomac Formation in the lower part of the target sediment layer, in contrast to polymict diamictons higher in the core that have been interpreted as ocean‐resurge debris flows, which is in agreement with previous interpretations. The mineralogy and geochemistry of the gravelly sands are typical for a passive continental margin source. There is no discernible mixing with marine sediments (no glauconite or Paleogene marine microfossils noted) during the impact remobilization and redeposition. The unshocked amphibolite block and cataclasite boulder might have originated from the outer parts of the transient crater.     

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.     

Shock metamorphism investigations of quartz grains in clasts from impact breccia of the Eyreville B drill core,Chesapeake Bay impact structure,USA

Abstract– The Chesapeake Bay impact structure, approximately 85 km in diameter, has been drilled in 2005–2006 at Eyreville (Virginia, USA), to a total depth of 1766 m. In the drill cores, the abundance of shock metamorphosed material is very variable with depth. Shocked mineral and lithic clasts, as well as melt particles, are most abundant in suevitic impact breccia section (1397–1451 m depth). Shocked quartz (i.e., quartz grains with planar fractures and/or planar deformation features) and melt particles, although rare, are also dispersed in the Exmore Formation unit (444–867 m depth). Other lithologies in the Eyreville drill cores show no clear evidence of shock metamorphism. Here, we report on the investigations of 40 samples from the impact breccia section. A total of more than 27,000 quartz grains were examined in about 200 clasts. The abundance of highly shocked clasts tends to decrease with increasing depth. Crystalline clasts derived from the crystalline basement are commonly only slightly shocked (contain generally <10 rel% of shocked quartz grains). The clasts of metamorphosed sediments show a low proportion of shocked quartz grains (mostly <10 rel%). Sedimentary clasts show a wide range of proportions of shocked quartz grains, with several of them being highly shocked clasts (most values between 0 and 40 rel%). Conglomerates show the highest proportion of shocked quartz grains of all types of clasts (up to 83 rel%). Polycrystalline quartz clasts are also commonly highly shocked (contain mostly between 10 and 40 rel% of shocked quartz grains). These hard nonporous clasts are possibly more liable to show evidence of shock. The investigations suggest that the intensity of shock metamorphism is the result of several parameters, such as original position in the target (both horizontal and vertical) and the properties of each lithology (e.g., grain size, porosity, and amount of matrix). According to the universal‐stage investigations, the dominant orientations of planar deformation features in quartz are , , and also .     

Subduction initiation and ophiolite crust: new insights from IODP drilling

International Ocean Discovery Program (IODP) Expedition 352 recovered a high-fidelity record of volcanism related to subduction initiation in the Bonin fore-arc. Two sites (U1440 and U1441) located in deep water nearer to the trench recovered basalts and related rocks; two sites (U1439 and U1442) located in shallower water further from the trench recovered boninites and related rocks. Drilling in both areas ended in dolerites inferred to be sheeted intrusive rocks. The basalts apparently erupted immediately after subduction initiation and have compositions similar to those of the most depleted basalts generated by rapid sea-floor spreading at mid-ocean ridges, with little or no slab input. Subsequent melting to generate boninites involved more depleted mantle and hotter and deeper subducted components as subduction progressed and volcanism migrated away from the trench. This volcanic sequence is akin to that recorded by many ophiolites, supporting a direct link between subduction initiation, fore-arc spreading, and ophiolite genesis.     

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.