15 Fakultätsübergreifend / Sonstige Einrichtung
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Item Open Access Boussinesq’s problem of viscoelasticity(1991) Wolf, DetlefWe consider an isochemical, isentropic, incompressible fluid half-space and study quasistatic viscoelastic perturbations, induced by two-dimensional (2D) surface loads, of a hydrostatic initial state. In view of the regional or local scale required for deformations of planets to be amenable to the half-space approximation, the model is assumed to be externally gravitating. We derive analytic solutions for the displacement and incremental stress components and study several approximations to the expressions. Particular emphasis is placed on discriminating between the material and local incremental stresses. Based on this distinction, deeper insight is gained into the physical significance of the solution.Item Open Access Glacial isostasy and long-term crustal movements in Fennoscandia with respect to lithospheric and asthenospheric processes and properties : comment(1991) Wolf, DetlefRecently, Mörner discussed his model of glacio-isostatic compensation in the light of new seismological models of the upper mantle below Fennoscandia. He concluded that the P-wave velocity distribution is in "full agreement" with his estimate of the viscosity distribution as inferred from glacio-isostatic relaxation. Whereas the consistency of seismological and geodynamical earth models is a necessary condition for their soundness, the particular type of agreement sought by Mörner is not required or expected, nor can his method of attaining such agreement be approved. For easier understanding of my criticism, I briefly recall the type of information provided by the seismological and by the glacio-isostatic evidence.Item Open Access Master-event correlation of weak local earthquakes by dynamic waveform matching(1993) Joswig, Manfred; Schulte-Theis, HartwigDynamic waveform matching (DWM) performs a non-linear correlation between two seismograms that are similar in shape but may be squeezed or stretched relative to each other. It extends the application of master-event comparisons to seismograms of greater spatial distance and retains the high-timing resolution of correlation techniques that act on the original time series. The DWM approach is applied to data recorded by a small array being part of the BOCHUM UNIVERSITY GERMANY (BUG) network which monitors the mining-induced seismicity in the Ruhr basin of NW Germany. The observed epicentres occur in clusters and therefore display only a limited number of seismogram waveform types. In one application an automatized cluster association with DWM obtains a resolution of about 100 metres at an epicentral distance of 200 to 40 km, using 10-20 defined master events for each region. These results are confirmed both by seismograms from a near-site station for mining-induced events from the Hamm region and by blast reports for a quarry region near Wuppertal. In another application of DWM, array traces from the BUG array are correlated to yield azimuth and slowness for epicentre location. as for the master event application, this approach is tuned for high performance on weak local events using a priori information about the approximate epicentral region. The implemented processes are shown to be capable of locating events with a rate of success equal to the performance of an experienced seismologist when processing all seismogrmas of four years BUG registration.Item Open Access Knowledge-based seismogram processing by mental images(1994) Joswig, ManfredThe impact of pictorial knowledge representation is demonstrated for two examples of time series analysis in seismology. The approaches perform a) automated recognition of known event signatures and b) high-resolution onset timing of later phases. Both methods work well under extreme conditions of noise and achieved human-like performance in recognizing known situations. Crucial for this success of pictorial knowledge representation was the design of suitably scaled images. They must be simple and robust enough to transform the complexity of “real life” data into a limited set of patterns. These patterns differ significantly from the initial data; they correspond more closely to the non-linear weighting of recognized impressions by an experienced scientist. Thus the author addresses the pictorial presentations as mental images. For both reported applications, part of their power comes by model-based image modifications. However, this enhancement is far from demanding a complete theory. Any fractional model already enhances the image adaptation, so mental images are best suited to deal with incomplete knowledge like any other artificial intelligence approach. Cognitive plausibility was found for both the non-linear image scalings and the model-based image modifications. In general, the author's method of pictorial knowledge representation conforms to the concept of mental images by Kosslyn. Any new task will demand the composition of new, dedicated image transformations where some generalized design criteria are derived from the author's applications.Item Open Access Über den Nachweis von Aminosäuren in Kalksteinen des Weißen Jura der Schwäbischen Alb(1967) Hiller, Karl; Kull, UlrichEs wird über einen erstmaligen, papierchromatographischen Nachweis von Aminosäuren in Kalksteinen des Weißen Jura der Schwäbischen Alb berichtet. In den Kalksteinen der Algen-Schwamm-Riffe treten unterschiedliche Gehalte an Aminosäuren in der vorwiegend anorganisch entstandenen Grundmasse einerseits und in den eng benachbarten, organischen Komponenten (Schwammumien, Kalkkrusten, Stromatolithen) andererseits auf.Item Open Access Inductive coupling between idealized conductors and its significance for the geomagnetic coast effect(1982) Wolf, DetlefA problem of current interest is the inductive coupling between an ocean, a solid earth conductor and a conductosphere. The anomaly of this configuration is modelled by (i) the inductive response of a two-dimensional system consisting of two thin half sheets and an underlying thin whole sheet or (ii) the superposition of the responses of two related systems, each consisiting of only one of the two half sheets and the whole sheet. The conductivity of these conducting planes is assumed to be perfect, and rigorous solutions for the erived by conformal mapping. induced magnetic fields are a comparison between the anomalies (i) and (ii) permits us to ascertain the degree of inductive coupling between the idealized conductors. This establishes a reference for estimating the inductive coupling between more realistic conductors and may therefore assist in the interpretation of complicated magnetic variation anomalies in coastal regions. Our substitute configurations can also be used directly for the rapid modelling of the inductive response of the earth in the vicinity of coastlines. This is demonstrated by analyzing some field data from the recent literature.Item Open Access Thick plate flexure re-examined : research note(1985) Wolf, DetlefThe flexure of an incompressible, thick elastic plate floating on an inviscid substratum and subject to an external gravity field is re-analysed. The solution is derived from momentum equations which account for the advection of hydrostatic pre-stress. This is contrasted with a recently published thick-plate solution derived from momentum equations without a pre-stress term. It is demonstrated that neglecting pre-stress advection renders the solution singular when the model degenerates into an inviscid half-space. If pre-stress advection is included, the solution remains correct in this limit. A numerical comparison of both types of thick-plate solution with results based on conventional thin-plate theory further shows that, for geophysically relevant models, the difference in the momentum balance entails discrepancies between the thick-plate solutions which are comparable to the errors introduced by the thin-plate approximation.Item Open Access On the relation between two-dimensional and axisymmetric loads in plate flexure problems(1984) Wolf, DetlefThis note has attempted to clarify the relation between straight-edged axisymmetric loads and straight-edged two-dimensional loads by emphasizing the critical role of the elastic plate in this relation. It has been shown that loads of widely varying scale can be approximated by two-dImensional edges, provided that the lithosphere is sufficiently thin. As the distance from the edge of the load increases, the displacement w decreases. This results in enhanced relative discrepancies between the two models in the region of the peripheral bulge. Whether this is significant when modelling data will ultimately depend on the magnitude of the errors associated with the measurements.Item Open Access The changing role of the lithosphere in models of glacial isostasy : a historical review(1993) Wolf, DetlefDuring the last 125 years, the role of the lithosphere in models of glacial-isostatic adjustment experienced several changes. Following the postulation of glacial isostasy by Jamieson in 1865, the lithosphere was generally regarded as comparable in importance for the adjustment process to the fluid substratum. This changed with the initiation of quantitative modelling by Van Bemmelen and Berlage and by Haskell in 1935, whereupon effects due to the lithosphere were commonly neglected in interpretations of postglacial uplift for 30 years. After the development of a layered viscous earth model with an elastic surface layer by McConnell in 1965, the lithosphere was eventually reintroduced into models of glacial isostasy. Subsequent studies largely confirmed the original ideas regarding the importance of the lithosphere for the adjustment process, although the effects are pronounced only for short-wavelength deformations. Using this response characteristic of the lithosphere, estimates of its thickness have recently become available for several tectonic provinces.Item Open Access Reply to comments by Robert P. Comer [Letter to the editor](1986) Wolf, DetlefIn his letter, Comer (1986) addresses three different points which bear on three related publications on load-induced flexure of elastic plates (Comer 1983; Ward 1984; Wolf 1985a). As his first point is primarily an annotation to his own publication on the subject (Comer 1983), I will restrict my reply to the remaining two points.