Die statistische Auszählung von Punktediagrammen auf ebenen Projektionen

Zusammenfassung An einen Dichteplan werden verschiedene Forderungen bezüglich Übersichtlichkeit und Vergleichbarkeit von Gefügeregelungen gestellt; diese Forderungen sind durch eine einzige Beziehung erfüllbar:Auf 1% der Netzfläche entfallen x% Pole. Danach wird die statistische Auszählung der Punktediagramme vorgenommen. Die Alternative: flächentreue Projektion—winkeltreue Projektion wird untersucht und die flächentreue Projektion (Schmidtsches Netz) als günstiger befunden, da bei der stereographischen Projektion eine Vergleichbarkeit der Maximaflächen wegen veränderlicher, netzbedingter Größenverzerrungen (14 vom Zentrum zur Peripherie) nicht gegeben erscheint. Beim flächentreuen Netz wird dagegen die Bedingung an die Auszählfigur, daß sie von beständiger Form sei, nicht erfüllt. Der Kreis als richtigste Auszählform wird bei dieser Projektionsart peripheriewärts zu ellipsenähnlichen Ovaloiden abgeplättet. Es wird festgestellt, daß diese Verzerrungen innerhalb der Genauigkeitsgrenzen der Meßmethoden liegen und daher nicht störend sind. Die Entwicklung der Auszählmethoden mit Kreisen auf demSchmidtschen Netz wird verfolgt. Entscheidend für die Güte (Richtigkeit) eines Dichteplans sind die Größe des Zählkreises (Radius r) und des Zählpunktabstandes (a). Vom Zählkreis 1/4% bis zu 4% werden alle Größen, meist sogar in einem Diagramm verwendet. Dies ist abzulehnen, weil nur der 1%-Kreis der eingangs aufgestellten Beziehung entspricht; alle anderen bewirken eine Überhöhung (bei kleinerem) bzw. Verflachung (bei größerem Zählkreis). Verschiedene r in einem Diagramm stören die Vergleichbarkeit. (Vergleichbarkeit verschiedener Dichtepläne ist bei guter Gefügeregelung bereits ab zirka 60 Daten gegeben, die Genauigkeit — Feinheit — steigt jedoch mit wachsender Anzahl.) Der Zählpunktabstand a ist möglichst klein zu halten; damit steigt die Richtigkeit des Diagrammes. Beim absoluten Wert a=0 ist eineFläche gleicher Besetzungsdichte als der geometrische Ort aller Mittelpunkte, deren dazugehörige Zählkreise eine bestimmte Anzahl von Polen umschließen, definiert. Nach diesem Satz wird eine einfache Konstruktionsmethode beschrieben, die das Optimum an Richtigkeit darstellt und die für Spezialfragen empfehlenswert ist. Für bloße Übersichtsdiagramme genügt die schnellere Zählpunktmethode mit konstant gehaltenem 1%-Zählkreis (r=R/10) und Zählpunktabstand (eines Quadratnetzes) a=r/2.

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Concerning the clearness and comparability of a density plan (there) exist several requirements. Those requirements are only be fulfitted by the following relation:1% of the net surface carries x% poles. The counting procedure of the point-diagrams than follows accordingly. The alternative: surface-true projection vs. angle-true projection is examined. The surface-true projection (Schmidt-net) is considered to be the more applicable one, because in case of the stereographic projection a comparability of the maxima-surfaces does not exist. The size-distortions (14 from the center to the circumference) are too great. In case of the surface-true net on the other hand the counting area is not consistent and hence another basic condition not fulfitted. The circle, which is the most correct counting-frame, is in that case toward the circumference flattened to an ellipsoidal ovaloid. It then is stated that those distortions are within the limit of acurracy and therefore can be ignored. A consideration of the different counting procedures on theSchmidt-net follows. Decisive for the correctness of a density plan is the size of the counting-circle (radius r) and the point distance (a). All sizes of counting circles 1/4%–4% aer used, mostly even within one diagram. Such methods should not be applied, for only the 1% circle fulfitts the relation which is stated at the beginning. All others procedures cause exaggerations (in case of smaller counting-circles) or a flattening (in case of a larger counting-circle). Different radii (r) disturb the comparability of the diagrams. (A comparability of different density-plans in case of a well developed orientation of the fabric exists already starting with 60 poles, however the accuracy increases with an increasing number of poles.) A small point-distance (a) is suggested, this furthers the correctuess of the diagram. In case of the absolute value a=0,a surface of equal point-density is definedas the geometric location of all centers the counting-circles of which contain an equal number of poles.After this statement a simple method of construction is described. It gives the optimum of accuracy and should be used in case of special problems. For simple reconnaissance diagrams a faster counting method with a consistant 1% counting-circle (r=R/10) and consistant point-distance (of a square-net) a=r/2 is sufficiant.

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Mit 10 Textabbildungen     

Non-radial solar wind flows and IMF Bz during 1973-2003

The characteristics of latitudinal angles of solar wind flow (θ_v) observed near earth have been studied during the period 1973-2003. The average magnitude of θ_v shows distinct enhancements during the declining and maximum phases of the sunspot cycles. A close association of B_z component of IMF in the GSE system and the orientation of meridional flows in the solar wind is found which depends on the IMF sector polarity. This effect has been studied in typical geomagnetic storm periods. The occurrence of non-radial flows is also found to exhibit heliolatitudinal dependence during the years 1975 and 1985 as a characteristic feature of non-radial solar wind expansion from polar coronal holes.     

Prediction of the spatial distribution of the modified mercalli intensity using neural networks

This paper presents the development of an adaptive, non-parametric forecast model for the direct prediction of the spatial distribution of the Modified Mercalli Intensity (MMI) corresponding to an earthquake scenario. The model is based on recent advances in neural networks computation, and is constructed through supervised learning using historical earthquake and regional geological data as training sets. A MMI forecast model for moderate earthquakes with magnitudes between 6 and 7 was developed based on data from the Loma Prieta, Coalinga and Morgan Hill earthquakes. For these data sets, the neural networks forecast model is shown to have excellent data synthesis capability; multiple sets of data can be encapsulated by a relatively simple network architecture. Limited comparison of forecasts made by the neural networks model and conventional models demonstrates that improved accuracy can be achieved. Implementation and operational advantages of the neural networks approach such as general input features, minimum preconceived knowledge of the data sets, the ability to learn and to adapt incrementally and the autonomous and automatic synthesis of the structure underlying the data sets, have been illustrated.     

Improved time control on Cretaceous coastal deposits: new results from Sr isotope measurements using laser ablation

Sr-isotope measurements of unaltered oyster shell calcite using laser-ablation multi-collector ICPMS techniques represent a powerful tool capable of establishing a chronostratigraphic framework for fossil near-shore deposits. This approach is tested on two shoal-water successions from the Portuguese Algarve and Lusitanian basins covering Late Barremian to Albian strata. ⁸⁷Sr/⁸⁶Sr values derived from low-Mg calcite of oyster shells fluctuate between 0.70717 ± 0.00001 and 0.70746 ± 0.00002; absolute values as well as stratigraphic trends match well with the global open-marine seawater signal. The new Sr-isotope results in combination with existing bio- and chemostratigraphic records allow for identification of an Early Aptian biocalcification crisis at both studied localities and show that this event has severely affected coastal environments along the evolving Atlantic. Siliciclastic intervals in the Algarve section are interpreted as near-shore equivalents of enhanced detrital shedding into shelf and deep-sea environments as a consequence of increased chemical weathering rates during humid climate episodes.     

Assessing spatio-temporal characteristics of water storage changes in the mountainous areas of Central Asia based on GRACE

The mountainous areas of Central Asia provide substantial water resources, and studying change in water storage and the impacts of precipitation and snow cover in the mountain ranges of Central Asia is of the greatest importance for understanding regional water shortages and the main factors. Data from the GRACE(Gravity Recovery and Climate Experiment) satellites, precipitation products and snow-covered area data were used to analyze the spatio-temporal characteristics of water storage changes and the effects of precipitation and snow cover from April 2002 to December 2013. The results were computed for each mountain ranges, and the following conclusions were drawn. The water storage in the mountainous areas of Central Asia as a whole increases in summer and winter, whereas it decreases in autumn. The water storage is affected by precipitation to some extent and some areas exhibit hysteresis. The area of positive water storage changes moves from west to east over the course of the year. The water storage declined during the period 2002–2004. It then returned to a higher level in 2005–2006 and featured lower levels in 2007–2009 Subsequently, the water storage increased gradually from 2010 to 2013. The Eastern Tianshan Mountains and Western Tianshan Mountain subzones examined in this study display similar tendencies, and the trends observed in the Karakorum Mountains and the Kunlun Mountains are also similar. However, the Eastern Tianshan Mountains and Western Tianshan Mountains were influenced by precipitation to a greater degree than the latter two ranges. The water storage in Qilian Mountains showed a pronounced increasing trend, and this range is the most strongly affected by precipitation. Based on an analysis of all investigated subzones, precipitation has the greatest influence on total water storage relative to the snow covered area in some areas of Central Asia. The results obtained from this study will be of value for scientists studying the mechanisms that influence changes in water storage in Central Asia.     

The slow rotation of 253 Mathilde

CCD photometry of the NEAR mission fly-by target 253 Mathilde is presented. Measurements taken during 52 nights of observations, from February to June 1995, allow a rotation period of 17.406±0.010 days and a lightcurve amplitude of 0.45±0.02 mag to be determined. A B-V color index of 0.67±0.02 and a V-R of 0.35±0.02 are measured, which are compatible with C-type membership. The determination of the phase relation results in H = 10.28±0.03 and G = 0.12±0.06. Indications that the lightcurve is not strictly singly-periodic are found. A power-spectrum analysis detects a secondary frequency f₂ = 0.0322±0.0010 d⁻¹, which is interpreted as evidence for a complex rotation state.