Seismotectonic scheme of Central and Eastern Europe

Summary The distribution of earthquake foci in the crust and the upper mantle indicates the position of mobile zones. Comparing epicentral maps of Central and Eastern Europe, known tectonic lines, results of deep seismic sounding and gravimetric survey enables a scheme of potential seismogenic zones, which correspond to active fault zones separating plates and blocks in the area, to be compiled. The level of earthquake activity varies along the investigated boundaries and can be considered as a measure of the intensity of the present geodynamic processes.Paper presented at the joint symposium AlO of the XVIIth General Assembly of the European Seismological Commission and of the 7th Annual Meeting of the European Geophysical Society, Budapest (Hungary), Aug. 21. – 29., 1980.     

Time pattern of large earthquake sequences in Europe in 1976–1979

Summary The time development of three large sequences, Friuli 1976, Thessaloniki 1978 and Monte Negro-Albania 1979, was investigated by analysing the characteristics of the time distribution of magnitudes of the events, M(t), of average magnitudes, (t), and of the number of events, n(t), as well as the strain release curves and the magnitude-frequency relations, N(M). The existence of time gaps and of an anomalous decay of the numbers of shocks before major events, as well as the oscillation of ( const b^–1) may be considered as precursory phenomena. The clustering of events has been tested by the Poisson and negative binomial laws.Communication presented at the XVIIth General Assembly of the European Seismological Commission in Budapest, 21–29 August, 1980 under the title Properties of Seismic Regime and Recent Earthquake Sequences in Europe.     

Olivine phenocrysts of Hawaiian olivine tholeiite and oceanite

Olivine phenocrysts of Hawaiian tholeiites display a variety of textures and a variation in composition which is due to supercooled crystallization. The highest forsterite content measured is 91%, and the highest magnesia content estimated for a tholeiitic liquid is 17%, using the olivine geothermometer. The liquid of this composition may be either a primary magma or a primitive magma. It is not yet possible to specify any particular composition range for the primary Hawaiian tholeiites.     

Hypersthene-ilmenite(/magnetite) symplectites in coronitic olivine-gabbronorites

Symplectitic intergrowths of hypersthene (host) with ilmenite and minor magnetite (vermicules) in a gabbroic sill from the Precambrian of southwest Sweden occur as replacement products of olivine, and are thought to have formed simulataneously with the replacement of nearby crystals of ilmenite and Timagnetite by biotite and hornblende (and spinel). These interrelated replacement processes may have taken place during, or immediately after, the final stages of the magmatic crystallization, at temperatures of about 660–680°C, as part of the inherent metamorphism of the gabbroic rock. Another expression of this metamorphic imprint is the occurrence of two-tiered corona shells of hypersthene/hornblende (+spinel) at the interface of olivine and plagioclase crystals.     

The solubility mechanisms of volatiles in silicate melts and their relations to crystal-andesite liquid equilibria

The anionic structure of magmatic liquids has been estimated at 1 atm and at pressures corresponding to those of the upper mantle. These estimates are based predominantly on spectroscopic data on binary metal oxide-silica and ternary metal oxide-silica-alumina melts. Structural information on melt compositions in aluminate-silica joins has been used to provide detailed information on the role of Al³⁺ in natural magma at atmospheric and high pressure.Regardless of pressure, andesitic melts may be described as combinations of chain, sheet, and three-dimensional network units. Nearly all Al³⁺ in the magmatic liquid resides in the three-dimensional network units. This Al³⁺ is locally charge-balanced with Na⁺, K⁺, Ca²⁺, and Mg²⁺. In the latter two cases, Al³⁺ and Si⁴⁺ are ordered, whereas for Na⁺ and K⁺, Si⁴⁺ and Al³⁺ are randomly mixed. Solution of water in natural magma results in the formation of new nonbridging oxygens in addition to OH groups attached to Si⁴⁺ and metal cations.On the basis of determined solution mechanisms of CO₂ and H₂O in silicate melts, thermodynamic properties of HO+CO₂, fluids and hydrous silicate melts and melting phase relations in peridotite-H₂O-CO₂, systems, it is found that natural andesitic magma in equilibrium with spinel Iherzolite in the upper mantle (10–20 kbar) must contain at least 5–7 wt.% H₂O. Andesitic magma with 5–7 wt.% H₂O in solution may be described as a mixture of Al-free three-dimensional units, sheets, and chains with a small proportion (less than 10%) of monomers.     

Low frequency waves in plasmas with spatially varying electron temperature

Low frequency electrostatic waves are studied in magnetized plasmas with an electron temperature which varies with position in a direction perpendicular to the magnetic field. For wave frequencies below the ion cyclotron frequency, the waves need not follow any definite dispersion relation. Instead a band of phase velocities is allowed, with a range of variation depending on the maximum and minimum values of the electron temperature. Simple model equations are obtained for the general case which can be solved to give the spatial variation of a harmonically time varying potential. A simple analytical model for the phenomenon is presented and the results are supported by numerical simulations carried out in a 2.5-dimensional particle-in-cell numerical simulation. We find that when the electron temperature is striated along B₀ and low frequency waves (_ci) are excited in this environment, then the intensity of these low frequency waves will be striated in a manner following the electron temperature striations. High frequency ion acoustic waves (_ci) will on the other hand have a spatially more uniform intensity distribution.     

Downscaling a twentieth century global climate simulation to the North Sea

The regional ocean model system (ROMS) is used to downscale a 26-year period of the twentieth century 20C3M experiment from the global coupled Bergen climate model (BCM) for the North Sea. Compared to an observational-based climatology, BCM have good results on the mean temperature, except for too low winter temperature. This is connected to a too weak inflow of Atlantic water. The downscaling gives added value to the BCM results by providing regional details, doubling the Atlantic inflow, and improving the mean winter temperature. For mean salinity, BCM has values very close to the climatology, whereas the downscaling becomes too fresh. The downscaling, however, improves the sea surface salinity, the vertical structure, and the Norwegian Coastal Current. It is concluded that the downscaling procedure as presented here is a suitable tool for assessing the future Atlantic inflow and sea temperature in the North Sea based on a global climate projection.     

Diel changes in the feeding behaviour of Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta) in Ellidavatn, a small lake in southwest Iceland

In the lake Ellidavatn, southwest Iceland, the diel activity of Arctic char and brown trout was studied in autumn (September) and spring (April) by removing the fish from gillnets every 3 hours for three days. Additional fish samples, evening and morning, were taken at other times of the year. The catch per unit effort was about 10 times higher during the nighttime than daytime for both char and trout. The median weight of char was lowest near the middle of night (80 g) and highest near the middle of day (140 g). The median weight of trout was also lowest near the middle of night (110 g) and highest near the middle of day (330 g). The main diet of char consisted of the cladoceran Eurycercus lamellatus in September and chironomid larvae in April and the main diet of trout was always sticklebacks. In autumn and spring, the feeding was nocturnal in the char but crepuscular in the trout. The median stomach content of char was highest at dawn (0.52% of body weight) and lowest at dusk (0.14% of body weight). It is proposed that nocturnal char shift through the bottom substrate in search for prey. The median stomach content of trout was highest at 09.00–18.00 and 24.00–03.00 hours (0.13–0.18% of body weight) and lowest at 03.00–06.00 and 18.00–21.00 hours (0.02–0.07% of body weight). Different feeding times may help to secure mutual coexistence of char and trout in a small lake. In autumn and spring, the average daily consumption of char was about 0.8% of body weight, less than half their maximum food intake.     

Hydrogeologic studies for nuclear-waste disposal in Sweden

Safety Report 1997 (SR 97) of the Swedish Nuclear Fuel and Waste Management Company is a comprehensive performance assessment of three hypothetical radioactive waste repositories in Sweden. It includes hydrogeologic studies (data compilation, parameter synthesis, and groundwater flow modeling) to determine groundwater flow and the associated uncertainties for the three sites. This report reviews and compares the hydrogeologic characterization programs, the site characteristics, and the groundwater flow models used in the SR 97 performance assessment. Although differences in site-characterization programs tend to mask differences in site characteristics, the sites do have notable differences that affect the results of the performance assessment. The effects of model uncertainties evaluated by the variant cases appear to be smaller than the variability of results for the base case (best estimate of site conditions) of each site. Electronic Publication     

Climatic change and design criteria in water resources management a regional case study

As a result of the anthropogenic greenhouse effect there is fear of alterations of the world climate, which also may result in hydrological changes and consequently in water resources management. In a case study it was investigated if such changes could be identified for a regional catchment area. Summarized it may be said that the regional analysis of hydro-meteorological data in the catchment area of the Sieg showed the expected effects of the anthropogenic climate change on the regional water cycle. Rises in annual mean temperature and precipitation could be observed over a period from 1892 until 1993. However, a significant relation between evident changes and greenhouse effect could not be stated. Changes in discharge do not show consistent behavior. Especially apparent contradictions show that additional examinations are necessary in order to make the complex natural inter-relationships between climate and regional water cycle with the impacts of existing anthropogenetic interferences visible and applicable for practical engineering tasks.