Influence of wind turbines on seismic stations in the upper rhine graben,SW Germany

By analysing long- and short-term seismological measurements at wind farms close to the town of Landau, SW Germany, we present new insights into ground motion signals from wind turbines (WTs) at local seismic stations. Because of their need to be located in similar regions with sparsely anthropogenic activities, wind turbines impact seismic stations and their recordings in a way that is not yet fully understood by researchers. To ensure the undisturbed recording tasks of a regional seismic array or a single station by a protected area around those endangered stations, it is very important to investigate the behavior of WTs as a seismic source. For that reason, we calculate averaged one-hour long spectra of the power spectral density (PSD) before and after the installation of a new wind farm within the investigated area. These PSD are ordered according to the rotation speed. We observe a clear increase of the PSD level after the WT installation in a frequency range of 0.5 to 10 Hz up to a distance of 5.5 km away from the WT. By analysing seismic borehole data, we also observe a decrease of the PSD of wind dependent signals with depth. The impact of wind-dependent signals is found to be much more pronounced for the shallower station (150 m depth) than for the deeper one (305 m depth). Using short-term profile measurements, we fit a power-law decay proportional to 1/r ^b to the main WT-induced PSD peaks and differentiate between near-field and far-field effects of ground motions. For low frequencies in the range from 1 to 4 Hz, we determine a b value of 0.78 to 0.85 for the far field, which is consistent with surface waves. The b value increases (up to 1.59) with increasing frequencies (up to 5.5 Hz), which is obviously due to attenuating effects like scattering or anelasticity. These results give a better understanding of the seismic wavefield interactions between wind turbines (or wind farms) with nearby seismic stations, including borehole installations, in a sedimentary setting.     

Regional geoid of the Weddell Sea,Antarctica, from heterogeneous ground-based gravity data

We present a geoid solution for the Weddell Sea and adjacent continental Antarctic regions. There, a refined geoid is of interest, especially for oceanographic and glaciological applications. For example, to investigate the Weddell Gyre as a part of the Antarctic Circumpolar Current and, thus, of the global ocean circulation, the mean dynamic topography (MDT) is needed. These days, the marine gravity field can be inferred with high and homogeneous resolution from altimetric height profiles of the mean sea surface. However, in areas permanently covered by sea ice as well as in coastal regions, satellite altimetry features deficiencies. Focussing on the Weddell Sea, these aspects are investigated in detail. In these areas, ground-based data that have not been used for geoid computation so far provide additional information in comparison with the existing high-resolution global gravity field models such as EGM2008. The geoid computation is based on the remove–compute–restore approach making use of least-squares collocation. The residual geoid with respect to a release 4 GOCE model adds up to two meters and more in the near-coastal and continental areas of the Weddell Sea region, also in comparison with EGM2008. Consequently, the thus refined geoid serves to compute new estimates of the regional MDT and geostrophic currents.     

Towards an understanding of the Of?p star HD 191612: optical spectroscopy

We present extensive optical spectroscopy of the early-type magnetic star HD 191612 (O6.5f?pe–O8fp). The Balmer and He  i lines show strongly variable emission which is highly reproducible on a well-determined 538-d period. He  ii absorptions and metal lines (including many selective emission lines but excluding He  ii λ4686 Å emission) are essentially constant in line strength, but are variable in velocity, establishing a double-lined binary orbit with   P _orb= 1542 d, e = 0.45  . We conduct a model-atmosphere analysis of the spectrum, and find that the system is consistent with a ∼O8 giant with a ∼B1 main-sequence secondary. Since the periodic 538-d changes are unrelated to orbital motion, rotational modulation of a magnetically constrained plasma is strongly favoured as the most likely underlying 'clock'. An upper limit on the equatorial rotation is consistent with this hypothesis, but is too weak to provide a strong constraint.     

Rift-Parallele Schildwellungen in Arabien und auf den Zirkum N-Atlantischen Tafeln

Zusammenfassung Sowohl in Arabien, ne-Afrika und auf den den Atlantik umgebenden kontinentalen Tafeln können große, epirogene Wellenwürfe ausgemacht werden. All diese Undulation-Systeme sind im Streichen parallel zu benachbarten Riftsystemen ausgerichtet, und ihre Wellenlänge nimmt mit Abstand vom Rifttrog zu. Die Untersuchungen am arabischen Beispiel zu den Zusammenhängen zwischen Bildung ozeanischer Kruste einerseits und deren tektonischen Auswirkungen auf kontinentale Tafeln, wie Magmatismus, Orogenese und besonders in intra-platten dynamischer Hinsicht andererseits, scheinen neue Gesichtspunkte zur Paläogeographie zu eröffnen, und zum Verstehen der Ursachen und Evolution der Schildwellungen beizutragen. Sie zeigen, daß die Schildwellungen nicht im vollen morphologischen Ausmaß mit Beginn des Rifting einsetzen, sondern die Schildbereiche allmählich von der Riftseite her durchdringen (± 40 m. a.) und etwa 80 m. a. zur Vollentwicklung brauchen. Rift-parallele Becken und Schwellen sind in Rift-Nähe am ältesten und werden mit Abstand von letzeren jünger. Über die paläogeographischen Entwicklungen kann ferner gezeigt werden, daß der Wellungs-Prozeß nicht kontinuierlich, sondern in Schüben verläuft.Blattverschiebungen im Rahmen diagonal angelegter Scherung sind eine konjugate Reaktion zur kompressionellen Wellung oder Faltung. Große und kleinere Störungen oder Störungssysteme dieser Kategorie sind im Bereich der Schildwellungen fast immer vorhanden. Schildwellung, die in dieser Arbeit absichtlich etwas überbetont wird, scheint auf alten, auf tiefe Stockwerke erodierten und stark konsilidierten Kratonen gegenüber Scherung zu überwiegen (z. B. Arabischer Schild), während Scherung und Bruchschollen-Tektonik im Sedimentmantel jüngerer, wenig tief erodierter und wohl möglich weniger konsolidierter, kratonisierter Areale ausgeprägter ist (z. B. Europäisches Schollenmosaik).Es wird abgeleitet, daß die Schildwellungen wie die Scherungstektonik von horizontalen, kompressioneilen Verspannungen ausgelöst werden und letztere mit der Bildung und Ausbreitung ozeanischer Kruste (Mantel-Diapirismus, Ocean-Floor Spreading) in ursächlichem Zusammenhang stehen. Die aus tektonischen Gründen vermutete kompressionelle Verspanung kontinentaler Tafeln und deren Symmetriebindung an das world rift system scheint sich nunmehr durch direkte Messungen zu bestätigen, jedenfalls passen sowohl seismo-tektonische Herdmechanismen-Analysen, wie in situ-Druckmessungen in Europa ausgezeichnet zum tektonischen Modell.Arabien wird als Modell-Beispiel für Schildwellungen im Rahmen geodynamischer Beanspruchungen angesehen.

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Large and gentle warping sets are recognizable in Arabia, ne-Africa and on the continents, which surround the n-Atlantic rifts (former Laurasia). All these undulation systems are aligned parallel to neighbouring rift-systems and their wavelength increases with the distance from the rifts. In Arabia studies of the geodynamic interrelations of generation of new oceanic crust, on the one side, and its structural effects on the shield area, like magmatism, orogeny and especially intra-plate dynamics, on the other side, seem to provide new aspects and a better understanding for the causes and evolution of these warping structures. These studies imply that warping sets are not developed to their full morphological extend with the beginning of continental rifting, they seem to penetrate the shield areas slowly (± 40 m. a.) and grow gradually (± 80 m. a.), i. e. they are oldest next to the oceanic rift troughs and become younger with distance from them. It also can be stated that rift-parallel basins and uplifts are developed sporadically during episodes of increased tectonic activity.Lateral movements along diagonally arranged shear zones are a conjugate reaction to compressional shield folding; major faults or fault systems of this category are usually recognizable in warped areas. Shield warping, which is purposely overemphasised in this article, seems to be predominant on old, deeply eroded and strongly consolidated cratons, while shearing and block-tilting seem to prevail on younger, less deeply eroded and consolidated, cratonised areas.Continental warping as well as shearing is thought to be due to horizontal, compressional stresses caused by the injection and spreading of mantle derived, new oceanic crust (mantle diapirism, ocean-floor spreading). The postulated, horizontally compressional stress environment on continental plates and its symmetry relation to spreading-ridges seem now confirmed by two independant means, i. e. fault-plane solutions and in situstress measurements, especially in Europe.Arabia is considered as the model-example for crustal-warping and its causal relations to geodynamic processes.

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Résumé En Arabie comme aussi dans le NE de l'Afrique et tout autour de l'Atlantique, les plaques continentales sont affectées d'ondulations épirogéniques. Celles-ci ont une direction parallèle à celle du rift voisin et leur longueur d'ondes croît avec la distance au rift. Les recherches en Arabie sur les rapports entre la formation de la croûte océanique et le dynamisme interne des plaques continentales ont favorisé de nouvelles idées sur la paléogéographie et contribué à la compréhension du principe de l'ondulation des boucliers: elles montrent que l'ondulation des plaques ne commence qu'avec une faible dimension morphologique et qu'elle pénètre le bouclier successivement du côté du rift (+ou –40 m.a.). Le développement final est atteint après 80 m.a. environ. Les bassins proches du rift sont donc les plus vieux, tandis qu à plus grande distance sont les plus jeunes. Le développement paléogéographique montre en outre que l'ondulation se produit de façon discontinue et plutôt sporadique. Le décrochement latéral dans le système du cisaillement diagonal est une réaction équivalente à l'ondulation compressive ou du plissement.Des failles plus ou moins grandes ou des familles de failles de ce type existent presque toujours en association avec les ondulations des boucliers. Cette ondulation des boucliers semble l'emporter sur le cisaillement dans des cratons bien consolidés et profondément érodés, tandis que le cisaillement et la tectonique de microplaques caractérisent les couches sédimentaires des socles (peut-être cratonisés) moins profondément érodés.Il faut donc admettre que l'ondulation des bouckliers aussi bien que la tectonique de cisaillement se développe à cause de la compression latérale. La compression est en rapport avec la genèse et le développement de la croûte océanique (ocean-floor spreading, diapirs du manteau). On peut constater que la compression des plaques (supposée par la tectonique) et leur rapport avec le world rifting system est confirmé par des mesures directes. En tout cas, les analyses sismotectoniques et les mesures de pression in situ sont bien conformes au modèle tectonique. L'Arabie est prise comme modèle pour l'ondulation des boucliers et ses rapports avec la contrainte géodynamique.

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Prof. R.Brinkmann zum 83. Geburtstag gewidmet

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Kurzfassung zu Vorträgen gehalten am 19. und 20. 2. 1968 auf der 58. Jahresversammlung der Geologischen Vereinigung in Göttingen und am 27.2. 1975 auf der 65. Jahresversammlung in Karlsruhe.     

Meteorological triggering of earthquake swarms at Mt. Hochstaufen, SE-Germany

A growing body of evidence suggests that fluids are intimately linked to a variety of faulting processes. Yet, the particular mechanisms through which fluids and associated parameters influence the stress regime and thus the seismicity of a particular area are not well understood.We carry out a study of the spatio-temporal behavior of earthquakes, fluid-related parameters (groundwater levels) and meteorological observables (precipitation) in the swarm earthquake area of Bad Reichenhall, southeastern Germany. The small volume in which the earthquakes take place, almost yearly occurring earthquake swarms and a permanent, seismo-meteorological monitoring network, provide nearly controlled experimental conditions to study the physics of earthquake swarms and to infer characteristic properties of the seismogenic crust.In this paper we (1) describe this fairly unique study area in terms of geology, seismicity and atmospheric conditions; (2) present two cases of earthquake swarms that seem to follow above-average rainfall events; and (3) examine the observed migration of hypocenters with a simple pore pressure diffusion model.We find significant correlation of seismicity with rainfall and groundwater level increase, and estimate an average hydraulic diffusivity of D = 0.75 ± 0.35 m²/s for Mt. Hochstaufen in 2002.     

Potential of radiotelescopes for atmospheric line observations: I. Observation principles and transmission curves for selected sites

Existing and planned radiotelescopes working in the millimetre (mm) and sub-millimetre wavelengths range provide the possibility to be used for atmospheric line observations. To scrutinize this potential, we outline the differences and similarities in technical equipment and observing techniques between ground-based aeronomy mm-wave radiometers and radiotelescopes. Comprehensive tables summarizing the technical characteristics of existing and future (sub)-mm radiotelescopes are given. The advantages and disadvantages using radiotelescopes for atmospheric line observations are discussed. In view of the importance of exploring the sub-mm and far-infrared wavelengths range for astronomical observations and atmospheric sciences, we present model calculations of the atmospheric transmission for selected telescope sites (DOME-C/Antarctica, ALMA/Chajnantor, JCMT and CSO on Mauna Kea/Hawaii, KOSMA/Swiss Alpes) for frequencies between 0 and 2000 GHz () and typical atmospheric conditions using the forward model MOLIERE (version 5). For the DOME-C site, the transmission over a larger range of up to 10 THz () is calculated in order to demonstrate the quality of an Earth-bound site for mid-IR observations. All results are available on a dedicated webpage.     

Efficient finite-difference modelling of seismic waves using locally adjustable time steps

Conventional finite-difference modelling algorithms for seismic forward modelling are based on a time-stepping scheme with a constant (global) time step. Large contrasts in the velocity model or in the spatial sampling rate cause oversampling in time for some regions of the model. The use of locally adjustable time steps can save large amounts of computation time for certain modelling configurations. The computation of spatial derivatives across the transition zone between regions of the model with different temporal sampling requires the definition of the wavefield at corresponding time levels on both sides of the transition zone. This condition can be obtained by extrapolation in time, which is inaccurate, or by multiple time integration in the transition zone. The error in the latter solution is of the same order as the conventional time-stepping scheme because both methods are based on the same iteration formula. The technique of multiple time integration simply requires the use of different sizes of time step. It is applicable only for certain factors of variation of the time step.     

Assessing Possibilities and Limitations for Biomarker Analyses on Outcrop Samples: A Case Study on Carbonates of the Shibantan Member (Ediacaran Period,Dengying Formation,South China)

Abstract: The Shibantan Member (Dengying Formation, South China) represents one of only two carbonate settings with Ediacara-type organisms and offers a rare opportunity to study the biogeochemistry of these ecosystems. To evaluate possibilities and limitations for future biomarker studies on fossil-bearing outcrop samples of the Shibantan Member, we analysed the spatial distribution of hydrocarbons in extractable organic matter (i.e. bitumen) on a millimetre scale. Our study demonstrates that the sample and most likely also other rocks from the same setting are contaminated with petroleum-derived compounds that bear the potential for erroneous interpretations in palaeo-reconstructions. The contamination was revealed by distribution patterns and amounts of extractable n-alkanes and acyclic isoprenoids. The contamination is linked to the external weathering surfaces but also to cracks within the rock, and the extent most likely depends on concentration gradients between these contamination sources. Here we show that contamination can successfully be distinguished from syngenetic signals obtained from non-extractable organic matter (i.e. kerogen) using catalytic hydropyrolysis (HyPy). However, we observed that decalcification is necessary to achieve sufficient yields of kerogen-bound hydrocarbons and to avoid artificial alteration of the biomarker signals due to matrix effects.     

The importance of lithographic limestones for revealing ontogenies in fossil crustaceans

Developmental biology has become a major issue for understanding the evolution of Arthropoda. While usually only the ontogenies of extant species are studied, developmental information of fossil arthropods may exhibit developmental patterns not present in living ones. Crustacea possess, basically, a more gradual development than, for example, pterygote insects and would, therefore, be appropriate candidates for the study of fossil ontogenies. Remarkably, famous fossil deposits like the Devonian Rhynie Chert or the Early Palaeozoic ‘Orsten’-type deposits do not comprise the generally macroscopic malacostracan Crustacea (although most probably adult malacostracan fossils have already been found in the Cambrian). By contrast, the Late Jurassic Solnhofen Lithographic Limestones of southern Germany provide thousands of specimens (although only few morphotypes) that can be identified as malacostracan larvae, together with juvenile specimens differing in certain morphological aspects from their conspecific adults. More recent investigations with up-to-date imaging methodology on additional malacostracan crustacean larvae yielded also reconstructible developmental sequences of species from the Solnhofen deposits. The very similar fossil deposits of the Cretaceous lithographic limestones of Lebanon have also yielded malacostracan larvae and juvenile specimens. We present a summary of the occurrences of crustacean fossils providing developmental information and a demonstration of the potential of the lithographic limestones in this context. The importance of developmental data for understanding crustacean evolution is also highlighted.