A simplified approach for including the incidence angle effect in seismic risk assessment

A simplified procedure is developed to consider the azimuthal orientation of buildings when estimating seismic risk. Two square-plan reinforced concrete building models are considered as a testbed, one with similar and one with dissimilar properties along the two principal horizontal axes. The fragility of both structures is analysed using a set of ground motion records rotated to multiple incidence angles to develop orientation-dependent fragility functions. It has been observed that, re-orienting all records so that these structures have the same azimuth vis-à-vis the corresponding epicentre leads to significant differences compared to assuming random orientations. Additional results stemming from single-degree-of-freedom oscillators further confirm such findings, showing a dependence to the proximity to the faults and the level of dissimilarity in the principal horizontal axes of the structure. The end results point to a non-negligible bias in assessment studies when a structure's orientation with respect to governing rupture scenarios is not taken into account. It is shown that the median of fragility curves calculated for un-rotated incidence angles can be bias-corrected through shifted by an amount that depends on the azimuthal orientation and level of axes-dissimilarity of structures.     

Residual Terrain Modelling: The Harmonic Correction for Geoid Heights

Surveys in Geophysics - The harmonic correction (HC) is one of the key quantities when using residual terrain modelling (RTM) for high-frequency gravity field modelling. In the RTM technique,...     

Examining urban sprawl in Europe using spatial metrics

Urbanisation is a global phenomenon with an important impact on the quality of human life. Europe has been widely affected by urbanisation. One of the main characteristics of urban growth is sprawl, a negative form of urban expansion, which affects large cities and most types of urban landscapes. Spatial indicators are applied to CORINE Urban Morphological Zones (UMZ) changes in order to measure urban sprawl between 1990–2000 and 2000–2006 in 24 European countries. The indicators calculate urban morphological properties such as shape, aggregation, compactness and dispersion. The results revealed that the urban areas (UMZ) increased by 146% during 1990–2006 and the urbanisation becomes more circle-shaped and less complex where mostly sprawl occurs. Moreover, urban form becomes less clumped or aggregated. Therefore, due to accelerating rates of urban sprawl, European urban planning should intensify appropriate initiatives to avoid negative impacts on human life.     

Band-Limited Analysis of Current Satellite-to-Satellite Tracking, Gradiometry and Combined Earth Gravity Models

Several satellite-only gravity models based on the analysis of satellite-to-satellite tracking (SST) data have become available in the course of the last decade. The realization of the satellite missions CHAllenging Minisatellite Payload (CHAMP) and Gravity Recovery And Climate Experiment (GRACE) enabled the practical implementation of two modes of the SST principle, namely the high–low and the low–low SST. Though similar in their fundamental idea, which is the indirect observation of the gravity field based on the position of two satellites orbiting the Earth, the different architecture and geometrical layout of these techniques capture different fingerprints of the observed field. In the last few years, satellite-only gravity models based on the analysis of satellite gravity gradiometry (SGG) data became available and led to a new insight into the gravity field. The implementation of the SGG principle became possible after the launch of Gravity field and steady-state Ocean Circulation Explorer (GOCE), the first gravitational gradiometry mission. Based on the principle of differential accelerometry, GOCE provides the gravitational gradients which can be used in gravity field retrieval as primary observations of the field at satellite altitude. In the present study, we consider some of the current satellite-only and combined gravity models based on the analysis of CHAMP, GRACE, GOCE, gravimetry and altimetry data. In order to perform a thorough analysis of the models, we present an overview of tools for their quality assessment both in an absolute and relative sense in terms of computing spectral quantities, such as correlation or smoothing coefficients per degree and per order, attempting to demonstrate possible non-isotropic features in the models. Furthermore, typical geodetic measures in computing second-order derivatives, such as degree and order variances and difference variances, have been also evaluated for the same models, using the combined model EGM2008 as reference. Apart from these standard spectral assessment quantities, a systematic spatial representation of the second derivatives at satellite altitude has been performed. The combination of the two analysis steps (spectral and spatial) permits a first detailed assessment of the models, focusing especially on the identification of characteristic interpretable bandwidths.     

Herbage Production and Species Richness in Sub-alpine Grasslands of Different Soil Parent Material in Northern Greece

Several abiotic and biotic factors were investigated as possible predictors of local species richness in two sub-alpine grasslands of Jenna and Belles Mountains in Northern Greece.For species richness modelling a hierarchical modelling framework based on generalized additive models was adopted.The two sub-alpine grasslands differed in aspect,altitude and soil parent material（volcanic origin,mostly trachyte,and andesite（TA） for Jenna and metamorphic rocks,mostly gneiss（G） for Belles）.12 fenced squared plots,16 m2 each,were used per grassland,where soil properties,herbage production,species presence and cover of grasses,legumes and forbs were estimated.Mean herbage production was significantly affected by slope and altitude,soil K content and floristic composition as expressed by an ordination axis.Soil p H,floristic composition and average herbage production were significant predictors of forbs and total species richness.For the former,soil N content and for the latter the occurrence of Agrostis capillaris,were also included as significant terms in the predictive model.Thepredictors for grasses species richness were N content,having a positive effect,and average herbage production.In all cases higher species richness was predicted for intermediate values of average herbage production.Differential responses were found between forbs and grasses.The predictors of their species richness were different while for the case of the common predictor（N） the responses of the two groups were also different（grasses species numbers increase and forbs species numbers decreased with increasing N）.Maximum species richness of grasses was observed at relatively low production levels while forbs species richness maximized at relatively high production levels.     

Brackish karstic springs model: application to Almiros spring in Crete

A mathematical model is proposed to simulate brackish karstic springs. Rainfall data constitutes model input information while output information is the discharge and the chloride concentration of the water versus time. The model was constructed by considering the mass and mechanical energy balance on the hydrodynamic analog, which includes three reservoirs outflowing in a tube that lies adjacent to the spring. Two reservoirs emulate the karstic system, and the third one emulates the sea. The discharge of the spring is given by the sum of the discharge of the reservoirs, and the chloride concentration by the solution of the mixing problem between the fresh and the salty water, which exists in the tube leading to the spring. The model is applied to the spring of Almiros at Heraklion, Crete, Greece. The agreement between model values and field measurements is very good for depletion periods and satisfactory for recharge periods.     

Stress analysis of buried steel pipelines at strike-slip fault crossings

Existing analytical methods for the stress analysis of buried steel pipelines at crossings with active strike-slip faults depend on a number of simplifications, which limit their applicability and may even lead to non-conservative results. The analytical methodology presented herein maintains the well-established assumptions of existing methodologies, but also introduces a number of refinements in order to achieve a more wide range of application without any major simplicity sacrifice. More specifically, it employs equations of equilibrium and compatibility of displacements to derive the axial force applied on the pipeline and adopts a combination of beam-on-elastic-foundation and elastic-beam theory to calculate the developing bending moment. Although indirectly, material and large-displacement non-linearities are also taken into account, while the actual distribution of stresses on the pipeline cross-section is considered for the calculation of the maximum design strain. The proposed methodology is evaluated against the results of a series of benchmark 3D non-linear analyses with the finite element method. It is shown that fairly accurate predictions of pipeline strains may be obtained for a wide range of crossing angles and fault movement magnitudes encountered in practice.     

North Atlantic Oscillation – Concepts And Studies

This paper aims to provide a comprehensive review of previous studies and concepts concerning the North Atlantic Oscillation. The North Atlantic Oscillation (NAO) and its recent homologue, the Arctic Oscillation/Northern Hemisphere annular mode (AO/NAM), are the most prominent modes of variability in the Northern Hemisphere winter climate. The NAO teleconnection is characterised by a meridional displacement of atmospheric mass over the North Atlantic area. Its state is usually expressed by the standardised air pressure difference between the Azores High and the Iceland Low. ThisNAO index is a measure of the strength of the westerly flow (positive with strong westerlies, and vice versa). Together with the El Niño/Southern Oscillation (ENSO) phenomenon, the NAO is a major source of seasonal to interdecadal variability in the global atmosphere. On interannual and shorter time scales, the NAO dynamics can be explained as a purely internal mode of variability of the atmospheric circulation. Interdecadal variability maybe influenced, however, by ocean and sea-ice processes.     

A new method of quantitative interpretation of SP anomalies produced by a polarized inclined sheet1

A new method is proposed for the quantitative interpretation of SP field data produced by a polarized ore body and simulated by an inclined sheet. The theoretical concept is based on the study of the amplitude Spectrum. It is shown that the SP amplitude Spectrum is not continuous at zero frequency; this leads to the dip angle determination of the inclined sheet. It is also shown that the SP amplitude spectrum is practically nullified at a characteristic amortization frequency that depends on the depth of the polarized body. The maximum amplitude Spectrum value of the SP gradient is used to estimate the depth to the bottom of the polarized body. Thus, the geometrical parameters h and H, the depths to the top and bottom, respectively, as well as the dip angle of the inclined sheet, can be satisfactorily determined. Some problems may arise in the determination of these parameters, affecting their accuracy, whenever unwanted frequency noise is present.     

The record of magma chamber processes in plagioclase phenocrysts at Thera Volcano,Aegean Volcanic Arc,Greece

Lavas and pyroclastic rocks throughout the volcanic stratigraphy of the Tertiary-Quaternary volcanic complex of Thera in the Aegean island arc display inhomogenous plagioclase populations and phenocryst resorption textures, interpreted as indicative of magma mixing. Plagioclase zoning characteristics studied by Nomarski and laser interferometry techniques establish three main categories of plagioclase: (i) inherited plagioclase (nucleated in endmember prior to initial mixing event) (ii) in situ plagioclase (nucleated in mixed or hybrid magma) and (iii) xenocrystic plagioclase. Nomarski contrast images and linearized compositional zoning profiles reveal striking differences between calcic and sodic plagioclases, depending on the composition of the lava in which they are hosted. These differences reflect the contrasting effects of changes in physical-chemical parameters in basic vis-a-vis more acidic melts during magma mixing and/or influx of new magma into the subvolcanic magma chamber, as well as the influence of magma chamber dynamics on plagioclase equilibration. Variations in bulk major and trace element abundances of Thera volcanic products reflect the dominant overprint of crystal fractionation, but decoupling between major and trace element fractionation models and variations in incompatible trace element distributions are all indicative of magma mixing processes, consistent with compositional and textural zoning in plagioclases.