Non-stationary response of structures excited by random seismic processes with time variable frequency content

Seismic random processes are characterized by high non-stationarity and, in most cases, by a marked variability of frequency content. The hypothesis modeling seismic signal as a simple product of a stationary signal and a deterministic modulation function, consequently, is hardly ever applicable. Several mathematical models aimed at expressing the recorded process by means of a system of stationary random processes and deterministic amplitude and frequency modulations are proposed. Models oriented into the frequency domain with subsequent response analysis based on integral spectral resolution and models oriented into the time domain based on the multicomponent resolution are investigated. The resolution into individual components (non-stationary signals) is carried out by three methods. The resolution into intrinsic mode functions seems to possess the best characteristics and yields results almost not differing from the results obtained by stochastic simulation. An example of the seismic response of an existing bridge obtained by two older models and three variants of multicomponent resolution is given.     

The causes of land-use and land-cover change: moving beyond the myths

Common understanding of the causes of land-use and land-cover change is dominated by simplifications which, in turn, underlie many environment-development policies. This article tracks some of the major myths on driving forces of land-cover change and proposes alternative pathways of change that are better supported by case study evidence. Cases reviewed support the conclusion that neither population nor poverty alone constitute the sole and major underlying causes of land-cover change worldwide. Rather, peoples’ responses to economic opportunities, as mediated by institutional factors, drive land-cover changes. Opportunities and constraints for new land uses are created by local as well as national markets and policies. Global forces become the main determinants of land-use change, as they amplify or attenuate local factors.     

A distribution-free ordinal classification of floods based on moments

ABSTRACT

Classification of floods is often based on return periods of their peaks estimated from probability distributions and hence depends on assumptions. The choice of an appropriate distribution function and parameter estimation are often connected with high uncertainties. In addition, limited length of data series and the stochastic characteristic of the occurrence of extreme events add further uncertainty. Here, a distribution-free classification approach is proposed based on statistical moments. By using robust estimators the sampling effects are reduced and time series of different lengths can be analysed together. With a developed optimization procedure, locally and regionally consistent flood categories can be defined. In application, it is shown that the resulting flood categories can be used to assess the spatial extent of extreme floods and their coincidences. Moreover, groups of gauges, where simultaneous events belong to the same classes, are indicators for homogeneous groups of gauges in regionalization.     

Geo-ecological spatial pattern analysis of the island of Fogo (Cape Verde)

With its small-scale climatic, floristic and geo-ecological differentiation, the island of Fogo is an optimal research area for understanding semi-arid island ecosystems in the marginal tropics. Because of the high variability in precipitation, the archipelago of Cape Verde has a potentially high ecological vulnerability, which is caused mainly by population growth, intensification of agricultural land use and increasing tourism.In this context, a geo-ecological spatial pattern analysis has been conducted for Fogo, including several types of geo-ecological layers like vegetation, elevation, aspect, soil and geology. The different kinds of spatial patterns that are detected can be used as a first tool to display distinctive levels of ecological vulnerability. These levels could constitute a base for sustainable land use planning and the redevelopment of agricultural strategies.     

Geological interpretation of gravity profiles through the Karlovy Vary granite massif (Czech Republic)

We examined the shape of the Late Variscan Karlovy Vary granite massif located south of the Ohre/Eger graben in Northern Bohemia by reinterpretation of existing gravity data on two perpendicular profiles. The granite body of about 360 km² total outcrop size has the elongation ratio 0.35 with the major axis trending NE-SW. The SW part of the body was crossed in the nineties by the seismic profile 9HR which localized the bottom of granites in a depth of about 10 km. We used this value as a reference datum in our gravity profiles. We positioned one of our profiles along the seismic profile 9HR and the other one perpendicularly, i.e. parallel with the elongation of the outcrop surface. We interpret the shape of the main granite body in the vicinity of Karlovy Vary as a continuous desk whose floor is horizontal (or subhorizontal) and varies along its whole extension about a depth of 10 km. This thickness is approximately identical with that of the Saxothuringian nappes imaged by seismic reflection. The near surface upper contact of the granite body is mildly inclined, and outward dipping. It changes to steep sides or inward inclined contacts in deeper levels. The Lesny-Lysina (Kynžvart) massif is a separate granite body about 324 km thick, not continuously connected with the main Karlovy Vary massif. The gravity curve suggests that granites often enclose in their endocontact large blocks of country metasediments or metabasites the existence of which is partly evidenced by their outcrops outside the line of the profile. The granite body is found density-homogenous. Minor density differences between granite varieties are caused mainly by more intense hydrothermal alterations in younger suite granites. We interpret vertical conduits for the ascent of granitic magmas to be parallel to the Jáchymov-Gera and Ohře (Eger) lineaments or the Mariánské Lázně fault zone as indicated by the elongation of some outcrops. However, they are not clearly imaged from the gravity data. The effect of the depression of the Sokolov basin along the faults parallel with the Ohře (Eger) lineament is shallow and it is not indicated by any change in the floor depth of the granite body. Comparison of the seismicity distribution suggests that the hypocenters occur mostly outside of the granite bodies or near their contact with the country rock.     

Morphological signatures of normal faulting in low‐gradient alluvial rivers in south‐eastern Louisiana,USA

We explore the fluvial response to faulting in three low‐gradient, sand‐bed rivers in south‐eastern Louisiana, USA, that flow across active normal faults from footwall (upstream) to hangingwall (downstream). We calculate sinuosity, migration rate and migration direction in order to identify anomalies spatially associated with fault scarps. In two of the rivers we model one‐dimensional steady water flow to identify anomalies in surface water slope, width‐to‐depth ratio, and shear stress. In each of these rivers there is one location where flow modeling suggests potential channel incision through the footwall, as indicated by relatively high surface water slopes and shear stress values. In one of these footwall locations, the river straightens and width‐to‐depth ratios decrease, likely contributing to higher surface water slopes and shear stress. This is in contrast to previous studies that have proposed increased sinuosity across fault footwalls and decreased sinuosity across hangingwalls. However, in two hangingwall locations we also observe relatively less sinuous channels. Other planform changes on the hangingwall include topographic steering of channels along and towards the fault and one example of an avulsion. The most notable anomaly in migration rate occurs on the hangingwall of a fault where a river has cut off a meander loop. Although fluvial response to faulting varies here, comparatively large and small channels exhibit similar responses. Further, Pleistocene fault slip rates are orders of magnitude lower than the channel migration rates, suggesting that faulting should not be a major influence on the fluvial evolution. Nonetheless, notable channel anomalies exist near faults, suggesting that recent fault slip rates are higher than Pleistocene rates, and/or that low‐gradient alluvial channels are more sensitive to faulting than previous studies have suggested. Rivers appear to be influenced by faulting in this setting, however background rates of meander loop cutoff may be just as influential as faulting. Copyright © 2015 John Wiley & Sons, Ltd.     

Mineralogical and geochemical alteration of low-grade metamorphic black slates due to oxidative weathering

Low-grade metamorphic black slates of Silurian and Lower Devonian ages (from the Thüringisches Schiefergebirge in Germany) were investigated to identify mineralogical and geochemical alterations that occur during the oxidative weathering black slates.The slates exhibit an intense total organic carbon decrease (>90 wt%) due to oxidative weathering. The organic matter in black slate consists mainly of non-pyrolysable material with only minor portions of pyrolysable material. In contrast to the non-pyrolysable organic matter, the concentration of pyrolysable organic matter is not decreased during weathering. Heating experiments have yielded information about a potential protection of pyrolysable organic matter against weathering, which is probably caused by a structural configuration or the intergrowth of organic matter and illite.The slates consist mainly of illite. Iron oxide (goethite) and phosphate encrustations were formed on slate surfaces as a result of oxidative and acid weathering of both iron sulfide and monazite. Kaolinite often occurs as an older encrustation beneath the iron oxide encrustations. Encrustations of iron oxide and phosphate are major sinks for trace elements, released during oxidative weathering.     

Modeling of unsaturated granular flows by a two-layer approach

Flows of partially saturated grain-fluid mixtures over complex curved topography are commonly observed in nature. However, comprehensive understanding of the physics behind them is to date out of reach. To investigate their dynamic process, a two-layer approach is proposed, in which the fluid-saturated granular layer is overlaid by the pure granular material. More specifically, the lower layer is described by a two-phase mixture theory of density preserving solid and fluid constituents. For the upper layer, the single-phase granular mass is treated as a frictional Coulomb-like continuum, and the dilation effect and the influence of the interstitial air are ignored. The capillarity effects and grains-size segregation are not considered in both the layers. The lower and upper layers interact at an interface which is a material surface for the fluid phase, but across which the mass exchange for the granular phase may take place. The granular mass exchange across the layer interface is parameterized by an entrainment type postulate. In addition, the classical jump conditions are employed to connect both layers at the interface dynamically. Furthermore, we perform the depth-averaged technique for the saturated grain-fluid mixture lower layer and the pure granular upper layer, respectively, to simplify the governing equations established. It is demonstrated that the resulting model equations can be reduced to most of the existing single-layer pure granular flow models and saturated two-phase single-layer debris flow models. Numerical solutions demonstrate that the present two-layer model can describe flows of partially saturated grain-fluid mixtures and the transition process of a saturated grain-fluid mixture into an under-saturated state.     

A mesocosm experiment investigating the effects of substratum quality and wave exposure on the survival of fish eggs

In a mesocosm experiment, the attachment of bream (Abramis brama) eggs to spawning substrata with and without periphytic biofilm coverage and their subsequent survival with and without low-intensity wave exposure were investigated. Egg attachment was reduced by 73% on spawning substrata with a natural periphytic biofilm, compared to clean substrata. Overall, this initial difference in egg numbers persisted until hatching. The difference in egg numbers was even increased in the wave treatment, while it was reduced in the no-wave control treatment. Exposure to a low-intensity wave regime affected egg development between the two biofilm treatments differently. Waves enhanced egg survival on substrata without a biofilm but reduced the survival of eggs on substrata with biofilm coverage. In the treatment combining biofilm-covered substrata and waves, no attached eggs survived until hatching. In all treatments, more than 75% of the eggs became detached from the spawning substrata during the egg incubation period, and <1% of these detached eggs survived within the substratum interstices. Hence, detached eggs contributed little to the reproductive success we observed. The implications of these results on the spawning success of fish species that use freshly inundated spawning substrata in shallow waters are discussed.     

Validation of temperature measurements from MIPAS-ENVISAT with balloon observations obtained by MIPAS-B

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), a limb sounding Fourier transform interferometer in the mid-infrared band, on board the polar-orbiting ENVIronmental SATellite (ENVISAT) was launched in March 2002 by the European Space Agency (ESA). For the MIPAS data validation, three balloon flights with MIPAS-B, a balloon version of MIPAS, were carried out on the 24th and 25th of September 2002 from Aire sur l’Adour (France 44°N, 0°E), on the 20th and 21th of March, and on the 2nd and 3rd of July 2003 from Esrange, Kiruna (Sweden 68°N, 21°E). The MIPAS operational data version 4.61 for the temperature vertical profiles were compared with the correlative MIPAS-B measurements via the coincident comparison and the trajectory comparison approaches, respectively. The precision of the MIPAS temperature was estimated to be 1.04–2.48 K in the region 123–8 hPa (15–33 km) and beyond the expectation. The systematic difference shows that the absolute accuracy of the MIPAS temperature is within the total combined errors between 356 and 3 hPa (8–39 km). The agreements in the middle stratosphere are better than in the lower stratosphere and upper troposphere. The maximum difference of 1.9 K (0.9%) was found at 228 hPa (11 km). The biases of MIPAS measurements are ?0.39 K (?0.19%) and +0.25 K (+0.12%) (“+” positive bias, “?” negative bias) corresponding to the altitude regions 143–31 hPa (14–24 km) and 31–5 hPa (24–37 km), respectively.