Creep in rock as a stochastic process

The heterogeneous character of rock suggests the use of statistical mechanics for the formulation of models of plasticity and creep. A stochastic creep model which allows for large variations in strength and size of the involved rock mass is outlined. The model, which is analogous to a previously developed concept for clastic materials, is shown to account rather well for typical creep behaviour of rock at moderate stresses and temperatures. Thus, it yields the often observed linear relation between the creep strain and the logarithm of time.     

Late Holocene sea-level changes and isostasy in western Denmark

Cores and exposed cliff sections in salt marshes around Ho Bugt, a tidal embayment in the northernmost part of the Danish Wadden Sea, were subjected to ¹⁴C dating and litho- and biostratigraphical analyses to reconstruct paleoenvironmental changes and to establish a late Holocene relative sea-level history. Four stages in the late Holocene development of Ho Bugt can be identified: (1) groundwater-table rise and growth of basal peat (from at least 2300 BC to AD 0); (2) salt-marsh formation (0 to AD 250); (3) a freshening phase (AD 250 to AD 1600?), culminating in the drying out of the marshes and producing a distinct black horizon followed by an aeolian phase with sand deposition; and (4) renewed salt-marsh deposition (AD 1600? to present). From 16 calibrated AMS radiocarbon ages on fossil plant fragments and 4 calibrated conventional radiocarbon ages on peat, we reconstructed a local relative sea-level history that shows a steady sea-level rise of 4 m since 4000 cal yr BP. Contrary to suggestions made in the literature, the relative sea-level record of Ho Bugt does not contain a late Holocene highstand. Relative sea-level changes at Ho Bugt are controlled by glacio-isostatic subsidence and can be duplicated by a glacial isostatic adjustment model in which no water is added to the world's oceans after ca. 5000 cal yr BP.     

A lacustrine GDGT-temperature calibration from the Scandinavian Arctic to Antarctic: Renewed potential for the application of GDGT-paleothermometry in lakes

Quantitative climate reconstructions are fundamental to understand long-term trends in natural climate variability and to test climate models used to predict future climate change. Recent advances in molecular geochemistry have led to calibrations using glycerol dialkyl glycerol tetraethers (GDGTs), a group of temperature-sensitive membrane lipids found in Archaea and bacteria. GDGTs have been used to construct temperature indices for oceans (TEX₈₆ index) and soils (MBT/CBT index). The aim of this study is to examine GDGT-temperature relationships and assess the potential of constructing a GDGT-based palaeo-thermometer for lakes. We examine GDGT-temperature relationships using core top sediments from 90 lakes across a north-south transect from the Scandinavian Arctic to Antarctica including sites from Finland, Sweden, Siberia, the UK, Austria, Turkey, Ethiopia, Uganda, Chile, South Georgia and the Antarctic Peninsula. We examine a suite of 15 GDGTs, including compounds used in the TEX₈₆ and MBT/CBT indices and reflecting the broad range of GDGT inputs to small lake systems.GDGTs are present in varying proportions in all lakes examined. The TEX₈₆ index is not applicable to our sites because of the large relative proportions of soil derived and methanogenic components. Similarly, the MBT/CBT index is also not applicable and predicts temperatures considerably lower than those measured. We examine relationships between individual GDGT compounds and temperature, pH, conductivity and water depth. Temperature accounts for a large and statistically independent fraction of variation in branched GDGT composition. We propose a GDGT-temperature regression model with high accuracy and precision (R² = 0.88; RMSE = 2.0 °C; RMSEP = 2.1 °C) for use in lakes based on a subset of branched GDGT compounds and highlight the potential of this new method for reconstructing past temperatures using lake sediments.     

New INTEGRAL sources and TeV emission

INTEGRAL is operational since more than three years and producing high quality data that allows to detect fainter new hard X-ray sources. The new sources, identified until now, are mostly active galactic nuclei and absorbed or transient high mass X-ray binaries. TeV emission could be expected from the new high mass X-ray binaries accreting dense clumps of stellar wind. INTEGRAL sources with TeV counterparts are discussed. Based on observations with INTEGRAL, an ESA project with instruments and science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, Spain), Czech Republic and Poland, and with the participation of Russia and the USA.     

Field testing cellulose-water oxygen isotope relations in periphyton for paleohydrological reconstructions

Journal of Paleolimnology - The oxygen isotope composition (δ18O) of aquatic cellulose extracted from lake sediment cores has long been used to reconstruct past hydrological responses to...     

Spatial exposure aspects contributing to vulnerability and resilience assessments of urban critical infrastructure in a flood and blackout context

Blackouts aggravate the situation during an extreme river-flood event by affecting residents and visitors of an urban area. But also rescue services, fire brigades and basic urban infrastructure such as hospitals have to operate under suboptimal conditions. This paper aims to demonstrate how affected people, critical infrastructure, such as electricity, roads and civil protection infrastructure are intertwined during a flood event, and how this can be analysed in a spatially explicit way. The city of Cologne (Germany) is used as a case study since it is river-flood prone and thousands of people had been affected in the floods in 1993 and 1995. Components of vulnerability and resilience assessments are selected with a focus of analysing exposure to floods, and five steps of analysis are demonstrated using a geographic information system. Data derived by airborne and spaceborne earth observation to capture flood extent and demographic data are combined with place-based information about location and distance of objects. The results illustrate that even fire brigade stations, hospitals and refugee shelters are within the flood scenario area. Methodologically, the paper shows how criticality of infrastructure can be analysed and how static vulnerability assessments can be improved by adding routing calculations. Fire brigades can use this information to improve planning on how to access hospitals and shelters under flooded road conditions.

     

Electron microscopic examination of hydrothermally treated bentonite clay

Water-saturated Na bentonite clay with a bulk density of 2 g/cm³ was autoclaved at 150 and 200°C for up to 0.5 years and then left to rest under confined conditions at room temperature for several weeks. Transmission electron microscopy with elemental micro-analysis was applied to study hydrothermally induced changes, which were found to have the form of particle reorganization and, at 200°C, release and precipitation of silica. The precipitations are suspected to be hydrated amorphous silica gels. The microstructural alteration, which was more obvious at 200°C than at 150°C, involved regrouping of previously dispersed and expanded stacks of montmorillonite flakes to yield dense branches of interwoven, contracted stacks separated by large voids.     

Post-seismic relaxation following the great 2004 Sumatra-Andaman earthquake on a compressible self-gravitating Earth

The   M _w γ 9.0  2004 December 26 Sumatra-Andaman and   M _w = 8.7  2005 March 28 Nias earthquakes, which collectively ruptured approximately 1800 km of the Andaman and Sunda subduction zones, are expected to be followed by vigorous viscoelastic relaxation involving both the upper and lower mantle. Because of these large spatial dimensions it is desirable to fully account for gravitational coupling effects in the relaxation process. We present a stable method of computing relaxation of a spherically-stratified, compressible and self-gravitating viscoelastic Earth following an impulsive moment release event. The solution is cast in terms of a spherical harmonic expansion of viscoelastic normal modes. For simple layered viscoelastic models, which include a low-viscosity oceanic asthenosphere, we predict substantial post-seismic effects over a region several 100s of km wide surrounding the eastern Indian Ocean. We compare observed GPS time-series from ten regional sites (mostly in Thailand and Indonesia), beginning in 2004 December, with synthetic time-series that include the coseismic and post-seismic effects of the 2004 December 26 and 2005 March 28 earthquakes. A viscosity structure involving a biviscous (Burgers body) rheology in the asthenosphere explains the pattern and amplitude of post-seismic offsets remarkably well.