Soil–structure interaction in the time domain using halfspace Green's functions

A time-domain formulation is proposed for the transient response analysis of general, three-dimensional structures resting on a homogeneous, elastic halfspace subjected to either external loads or seismic motions. The formulation consists of two parts: (a) the time domain formulation of the soil behaviour and (b) the coupling of the corresponding soil algorithms to the Finite Element Code ANSYS. As far as the structure is concerned, this coupling opens the way for the analysis of non-linear soil–structure interaction. The approach is based on halfspace Green's functions for displacements elicited by Heaviside time-dependent surface point loads. Hence, the spatial discretisation can be confined to the contact area between the foundation and the soil, i.e. no auxiliary grid beyond the foundation as for conventional boundary element formulations is required. The method is applied to analyse the dynamic response of a railway track due to a moving wheel set by demonstrating the influence of ‘through-the-soil coupling’.     

Dimethylsulfoniopropionate (DMSP) in icealgae and its possible biological role

During the EPOS I expedition (leg 1, 1988) into the WeddellSea (Antarctica) the dimethylsulfoniopropionate (DMSP) contents of various ice-algal assemblages and phytoplankton populations in the open water and in the ice edge zones were investigated. The chlorophyll a content in the ice samples was 25–70 times higher than that of the open water column, and about 100–390 more than in the under-ice water column. The DMSP content in ice-algae was about 20–56 times higher than in the open water, and 107–245 than in the under-ice water. There was no strict (linear ) correlation between pigment content and DMSP concentration, although high chlorophyll values were always accompanied by high DMSP contents. The variability of DMSP data can be explained by variation in species composition. Especially high concentrations were observed in samples where Phaeocystis pouch-etii was present. In ice DMSP may have a twofold biological role: as an osmolyte and/or as a cryoprotectant (antifreeze).     

Veränderungen im Stoff- und Mineralbestand während mehrphasiger Mylonitisierung der Kellerjoch-Gneise (Tirol)

Zusammenfassung Die mittelostalpinen Kellerjochgneise (ehemals Normalgranite) wurden einer mehrphasigen Mylonitisierung unterzogen. Die variszische, in weiten Bereichen homogene Mylonitisierung erfaßte den gesamten Granitkomplex unter retrograden Bedingungen der oberen bis unteren Grünschieferfazies und wird von einer statischen Temperung abgeschlossen. Hierbei kam es zur Ausbildung eines variszischen Deckenbaus.Während der alpidischen Deckenschübe werden die älteren Deckengrenzen unter retrograden, inhomogenen Mylonitisierungen der unteren Grünschieferfazies reaktiviert. Dabei reagierten die Kellerjochgneise als eigenständige alpine Decke. Reste variszischer Deckengrenzen haben nur lokale Bedeutung.Die Kellerjochgneise zeigen drei verschiedene Deckengrenzen-Typen, an denen sich der Mineralbestand, das Gefüge sowie der Pauschalchemismus in charakteristischer Weise verändert und unterschiedliche Deformationsbedingungen widerspiegelt.Auffällig sind in Deckengrenzen-Nähe jüngere Quarzblasten mit schlauchartigen Korrosionen. Für deren ausschließlich metamorphe Bildung wird der Begriff der Keimbildungskorrosion vorgeschlagen.

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Summary The middle austroalpine Kellerjochgneiss — formerly a granitic complex — was subjected to a polyphase retrograde shearing. The Variscan, predominantly homogeneous mylonitisation affected the whole granitic complex under retrograde conditions of upper and lower greenschist facies metamorphism and ceased with a static annealing. In this connection a Variscan nappe structure developed.During the alpidic nappe transports older nappe boundaries were reactivated with heterogeneous mylonitisation and under lower greenschist facies conditions. Thereby the Kellerjochgneiss-complex was treated as a separated Alpidic nappe. Relics of the Variscan nappe boundary were locally preserved.The Kellerjochgneiss nappe reveals three different types of nappe boundaries with characteristical alterations of mineral composition and structure. Changes in major element abundances are corresponding with these alterations, reflecting different conditions of deformation.Close to nearly all nappe boundaries, young blastic quartz grains with corrosion tubes attract attention. For their exclusively metamorphic genesis the term nucleation corrosion is proposed.

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Résumé Les gneiss du Kellerjoch des Alpes autroalpines moyennes (autrefois un complexe granitique) ont été soumis à une mylonitisation polyphasée. La mylonitisation varisque homogène sur une grande échelle, a affecté le complexe granitique dans les conditions de métamorphisme régressif du facies schiste vert supérieur à inférieur, et s'est clôturée par une empreinte statique. En même temps se développait une tectonique en nappes. Au cours du déclanchement des nappes, les anciennes limites de nappes ont été réactivées avec mylonitisation hétérogène et régressive du facies schiste vert inférieur. A cette occasion, les gneiss du Kellerjoch se sont comportés comme une nappe indépendante. Les restes des limites entre nappes varisques n'ont plus qu'une importance locale. — Les gneiss du Kellerjoch montrent trois types différents de limite de nappes où la constitution minérale, la texture et la constitution chimique se modifient de façon caractéristique et reflètent des conditions de déformation différentes. — A proximité des limites des nappes, on trouve du quartz blastique plus jeune avec corrosions tubulaires. Pour leur développement métamorphique on propose le terme de « Keimbildungskorrosion ».

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Kellerjoch'a, - , . ; , . . . Kellerjoch'a , . . Kellerjoch'a , , , . , , . Keimbildungskorrosion.

     

The238U spontaneous fission decay constant re-determined by fission tracks

The decay constant(λ_f²³⁸) for the spontaneous fission of²³⁸U was re-determined by means of a man-made uranium glass of known age (126 yr). The spontaneous U fission tracks that had accumulated since the date of manufacture were counted on internal faces of the glass with an error of less than 1.7%. No thermal annealing of the spontaneous tracks was observed. The U content was determined by induced fission tracks. The value obtained forλ_f²³⁸ is(8.57 ± 0.42) × 10^?17yr^?1. Main sources of error are the date of glass melting and the determination of the thermal neutron dose.     

Über ein Datolithvorkommen am Basaltkontakt im Kaliwerk Buggingen (Südbaden)

Zusammenfassung Kleine Datolith-Knöllehen wurden unmittelbar auf dem Kontakt von Ankaratrit-Gängen mit dem Unteren Kalilager auf dem Kaliwerk Buggingen aus hydrothermalen Lösungen im Gefolge der Gangbildung und vielleicht im Zusammenhang mit der Serpentinisierung gebildet. Ihre Bildungstemperatur ließ sich aus der volumenkonstanten Umwandlung der Sylvinite in Hallt-Gesteine im Kontaktbereich zu etwa 300° C abschätzen.

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Small spherolites of datolite occur immediately on the contact of the lower potash seam with cross-cutting ankaratrite-dikes in the mine of Buggingen, southern Baden. They are hydrothermal in origin and perhaps connected with the serpentinization of the ankaratrites. Their temperature of formation of about 300° C was estimated from the fact, that the volum of the potash seam remained constant during the metasomatic replacement of sylvite by halite in the neighbourhood of the dikes.

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Herrn Prof. Dr.C. W. Correns zum 70. Geburtstag gewidmet.     

Comparison of acoustic and elastic full-waveform inversion of 2D towed-streamer data in the presence of salt

Over the last years, full-waveform inversion has become an important tool in the list of processing and imaging technologies available to the industry. For marine towed-streamer data, full-waveform inversion is typically applied using an acoustic approximation because S-waves do not propagate in water and elastic effects in recorded data are generally assumed to be small. We compare acoustic and elastic modelling and full-waveform inversion for a field data set acquired offshore Angola over sediments containing a salt body with significant topology. Forward modelling tests reveal that such geological structures lead to significant mode conversions at interfaces and, consequently, to significant relative amplitude differences when elastically and acoustically modelled traces are compared. Using an acoustic approach for modelling in full-waveform inversion therefore leads to problems matching the synthetic data with the field data, even for recorded pressure data and with trace normalization applied. Full-waveform inversion is unable to find consistent model updates. Applying elastic full-waveform inversion leads to more consistent and reliable model updates with less artefacts, at the expense of additional computation cost. Although two-dimensional marine towed-streamer data are least favourable for the application of full-waveform inversion compared to three-dimensional data or ocean-bottom data, it is recommended to check on the existence of elastic effects before deciding on the final processing and imaging approach.     

Spatial and temporal distribution of floating kelp in the channels and fjords of southern Chile

Numerous studies suggest that floating macroalgae contribute to population connectivity of the algae themselves as well as of associated organisms. In order to evaluate the importance of floating macroalgae for population connectivity in southern Chile we analysed their spatial and temporal distributions. We estimated the abundance of floating kelp in the Interior Sea of Chiloé and the Los Chonos Archipelago via ship surveys conducted during austral spring (November) and winter (July) of the years 2002–2005. Highest densities of floating kelp (Macrocystis pyrifera and Durvillaea antarctica) were found during spring. Generally, the density of floating kelp was relatively low in areas with high supply of freshwater, and highest abundances were found in large channels opening to the open ocean. We suggest that this pattern is caused by the scarcity of natural kelp beds combined with rapid degradation of floating kelp in the interior fjords and by seaward surface outflow. The maximum densities of floating kelps were found in an area known to be an extensive convergence zone (i.e. estuarine front), which appears to act as a retention zone. In accordance with this distribution pattern, we propose that connectivity between local populations via floating kelp is higher in the outer channels with oceanic influence than in the inner fjords with high freshwater influx.     

Two-dimensional time dependent hurricane overwash and erosion modeling at Santa Rosa Island

A 2DH numerical, model which is capable of computing nearshore circulation and morphodynamics, including dune erosion, breaching and overwash, is used to simulate overwash caused by Hurricane Ivan (2004) on a barrier island. The model is forced using parametric wave and surge time series based on field data and large-scale numerical model results. The model predicted beach face and dune erosion reasonably well as well as the development of washover fans. Furthermore, the model demonstrated considerable quantitative skill (upwards of 66% of variance explained, maximum bias − 0.21 m) in hindcasting the post-storm shape and elevation of the subaerial barrier island when a sheet flow sediment transport limiter was applied. The prediction skill ranged between 0.66 and 0.77 in a series of sensitivity tests in which several hydraulic forcing parameters were varied. The sensitivity studies showed that the variations in the incident wave height and wave period affected the entire simulated island morphology while variations in the surge level gradient between the ocean and back barrier bay affected the amount of deposition on the back barrier and in the back barrier bay. The model sensitivity to the sheet flow sediment transport limiter, which served as a proxy for unknown factors controlling the resistance to erosion, was significantly greater than the sensitivity to the hydraulic forcing parameters. If no limiter was applied the simulated morphological response of the barrier island was an order of magnitude greater than the measured morphological response.