Accumulation of elastic strains in the upper crust on the locked transform faults and the tectonomagnetic effect

Plate tectonics only allows small deformations in the lithospheric plates. The laboratory experiments with the rock specimens show that the creep is transient when the creep strain is at most 1%. Hence, if we assume that the creep strain in the lithospheric plates is below this threshold, the creep is transient. The present paper addresses the role of the elastic, brittle (pseudo-plastic), and creep rheology of the lithosphere during the accumulation of elastic shear strains on the locked faults in the Earth’s crust, i.e., during the process of preparation of the earthquakes. The effective viscosity characterizing the transient creep is lower than that under the steady-state creep and it depends on the characteristic time of a given process. The characteristic duration of the stress and strain accumulation process in the vicinity of the locked faults is a few dozen years. On these time intervals, the thin upper crustal layer behaves as brittle; the underlying layer behaves as elastic (it is just this layer which accommodates stress accumulation leading to the earthquake), whereas the transient creep is predominant in the lower crust and mantle lithosphere. Transient creep entails nonlinear time dependence of the strains arising in the vicinity of the locked fault in the elastic crust. The perturbations in the magnetic field induced by these strains can be treated as the magnetic precursor of the earthquake.     

Influence of the boundary layer height on the global air–sea surface fluxes

Results from large-eddy simulations and field measurements have previously shown that the velocity field is influenced by the boundary layer height, z _i , during close to neutral, slightly unstable, atmospheric stratification. During such conditions the non-dimensional wind profile, φ _m , has been found to be a function of both z/L and z _i /L. At constant z/L, φ _m decreases with decreasing boundary layer height. Since φ _m is directly related to the parameterizations of the air–sea surface fluxes, these results will have an influence when calculating the surface fluxes in weather and climate models. The global impact of this was estimated using re-analysis data from 1979 to 2001 and bulk parameterizations. The results show that the sum of the global latent and sensible mean heat fluxes increase by 0.77 W m⁻² or about 1% and the mean surface stress increase by 1.4 mN m⁻² or 1.8% when including the effects of the boundary layer height in the parameterizations. However, some regions show a larger response. The greatest impact is found over the tropical oceans between 30°S and 30°N. In this region the boundary layer height influences the non-dimensional wind profile during extended periods of time. In the mid Indian Ocean this results in an increase of the mean annual heat fluxes by 2.0 W m⁻² and an increase of the mean annual surface stress by 2.6 mN m⁻².     

Spectra of CO<Subscript>2</Subscript> and Water Vapour in the Marine Atmospheric Surface Layer

Spectra of CO₂ and water vapour fluctuations from measurements made in the marine atmospheric surface layer have been analyzed. A normalization of spectra based on Monin–Obukhov similarity theory, originally developed for wind speed and temperature, has been successfully extended also to CO₂ and humidity spectra. The normalized CO₂ spectra were observed to have somewhat larger contributions from low frequencies compared to humidity spectra during unstable stratification. However, overall, the CO₂ and humidity spectra showed good agreement as did the cospectra of vertical velocity with water vapour and CO₂ respectively. During stable stratification the spectra and cospectra displayed a well-defined spectral gap separating the mesoscale and small-scale turbulent fluctuations. Two-dimensional turbulence was suggested as a possible source for the mesoscale fluctuations, which in combination with wave activity in the vertical wind is likely to explain the increase in the cospectral energy for the corresponding frequency range. Prior to the analysis the turbulence time series of the density measurements were converted to time series of mixing ratios relative to dry air. Some differences were observed when the spectra based on the original density measurements were compared to the spectra based on the mixing ratio time series. It is thus recommended to always convert the density time series to mixing ratio before performing spectral analysis.     

Storm surges in the Western Baltic Sea: the present and a possible future

Globally-coupled climate models are generally capable of reproducing the observed trends in the globally averaged atmospheric temperature or mean sea level. However, the global models do not perform as well on regional/local scales. Here, we present results from four 100-year ocean model experiments for the Western Baltic Sea. In order to simulate storm surges in this region, we have used the General Estuarine Transport Model (GETM) as a high-resolution local model (spatial resolution ≈ 1?km), nested into a regional atmospheric and regional oceanic model in a fully baroclinic downscaling approach. The downscaling is based on the global model ECHAM5/MPI-OM. The projections are imbedded into two greenhouse-gas emission scenarios, A1B and B1, for the period 2000–2100, each with two realisations. Two control runs from 1960 to 2000 are used for validation. We use this modelling system to statistically reproduce the present distribution of surge extremes. The usage of the high-resolution local model leads to an improvement in surge heights of at least 10% compared to the driving model. To quantify uncertainties associated with climate projections, we investigate the impact of enhanced wind velocities and changes in mean sea levels. The analysis revealed a linear dependence of surge height and mean sea level, although the slope parameter is spatially varying. Furthermore, the modelling system is used to project possible changes within the next century. The results show that the sea level rise has greater potential to increase surge levels than does increased wind speed. The simulations further indicate that the changes in storm surge height in the scenarios can be consistently explained by the increase in mean sea level and variation in wind speed.     

Precise electron microprobe age determination in altered uraninite: consequences on the intrusion age and the metallogenic significance of the Kirchberg granite (Erzgebirge,Germany)

An integral method of data evaluation for chemical dating of accessory uraninite by electron microprobe analysis and electron microscopy is proposed. The internal structure of uraninite grains, the contents of Si, Ca, and Fe, and tests for loss or gain of Pb and U are suitable criteria to decide whether or not a given crystal area was affected by secondary alteration. The method was applied to uraninite from the Kirchberg granite, Erzgebirge, Germany, and an age of 330LJ Ma (DŽ†) was constrained. This result supports earlier assumptions that there were at least two events of Hercynian granite magmatism separated by a time gap of about 40 Ma, and that the magmatic evolution of the Kirchberg granite is not related to the formation of the W mineralisation developed in the endocontact of this granite. Secondary alteration of uraninite is probably closely related to the formation of U deposits in the vicinity of the Kirchberg massif which was extensively mined in the past.     

Turbulence characteristics in a near neutrally stratified urban atmosphere

Turbulence measurements from the city of Uppsala, Sweden, are analysed. Measurements were taken at two sites: one in the central area, ca. 6 m above roof level, the average building height being ca. 15 m; the other at ca. 8 and 50 m above the ground on a tower situated 100 m downwind of a sharp discontinuity between the densely built-up urban area and flat grass-covered land. The average stability was close to neutral, the range being -0.2 < z/L < 0.2. The main emphasis of the study is on the non-dimensional standard deviations of the velocity components _i /u _*t and on the corresponding non-dimensional energy spectra, u _*t being a local velocity scale defined as _i /( _l is the local momentum flux). Comparison with results obtained from surface-layer measurements at ideal sites (with u _*, being the ordinary friction velocity) shows good general agreement. The most complete agreement is found for the tower 50 m measurements, a result which is notable as this measurement point is found to be within a distinctly transitional zone between the urban and post-urban boundary layers. The results from the central city measurement point are also fairly close to the ideal results, the deviations found being small in view of the fact that the site is probably inside the layer in which the roughness elements (the buildings) have direct influence. The measurements at the tower 8 m level show certain distinct deviations from ideal results: all three _i /u _*l , are higher by ca. 10%, the excessive energy being found at the low frequency end of the spectrum. Arguments are presented for this feature to be due to a spectral lag effect.     

Spectroscopic studies on natural chloritoids

Room temperature and low temperature Mössbauer and optical absorption spectroscopic data on six natural chloritoids characterized by means of electron microprobe and X-ray powder diffraction techniques are presented. Two narrow quadrupole doublets with widths of 0.25–0.29 mm/s assigned to Fe²⁺ in a relatively large octahedral site and Fe³⁺ in a smaller octahedral site, are observed in the Mössbauer spectra. Polarized optical absorption spectra reveal three main absorption bands. A broad absorption band at 16,300 cm^?1, which is strongly polarized in E‖X and E‖Y and shows a linear increase in integral absorption with increasing [Fe²⁺] [Fe³⁺] concentration product, is assigned to a Fe²⁺+Fe³⁺→Fe³⁺+Fe²⁺ charge transfer transition. This band displays also a temperature dependence different from that of single ion d?d transitions. Two absorption bands at 10,900 cm^?1 and 8,000 cm^?1 are, on the basis of compositional dependence and energy, assigned to Fe²⁺ in the large M(1B) octahedra of the brucite-type layer in chloritoid. Combined spectroscopic evidence and structural and chemical considerations support a distribution scheme for ferrous and ferric iron which orders the Fe²⁺ ions in the M(1B) octahedra and the Fe³⁺ ions in the small M(1A) octahedral sites. Both types of octahedra are found in the brucite type layer of chloritoid.     

The Marsta micro-meteorological field project. Profile measurement system and some preliminary data

A micro-meteorological installation for accurate continuous measurements is described. Air temperature differences are obtained to ±0.02°C. Humidity is measured with the psychrometric method; an accuracy of ±0.03 mb in difference measurements has been obtained after having taken extensive measures to overcome heat conduction and radiation errors. A heating system enables humidity profiles to be obtained during freezing conditions. A number of humidity profiles obtained in connection with turbulent flux measurements have been properly nondimensionalized and plotted against z/L. The result is in clear favour of Monin-Obukhov similarity for the nondimensionalized humidity profiles.     

Upscaling of Geological Models for Reservoir Simulation: Issues and Approaches

Introduction

Upscaling of Geological Models for Reservoir Simulation: Issues and Approaches