Die statistische Auszählung von Punktediagrammen auf ebenen Projektionen     

Felix Ronner 《Mineralogy and Petrology》1962,8(2):218-247

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  相似文献   

The Aegir Rift: Crustal Structure of an Extinct Spreading Axis     

Grevemeyer  Ingo  Weigel  Wilfried  Dehghani  G. Ali  Whitmarsh  Robert B.  Avedik  Felix 《Marine Geophysical Researches》1997,19(1):1-23

Two seismic refraction and gravity lines were obtained along and normal to the axis of the Aegir Rift, an extinct spreading centre in the Norway Basin. Velocity-depth solutions and crustal structure models are derived from ocean-bottom records using two-dimensional ray tracing and synthetic seismogram modelling techniques. Gravity data are used to generate models consistent with the lateral variations in thickness of the layers in the crustal models. The resulting models require considerable degree of lateral inhomogeneity along and perpendicular to the rift axis. Crust within the extinct spreading centre is found to be thinner and of low P-wave velocity when compared with the crust sampled off-axis. To explain reduced velocities of the lower crust we suggest that, due to the relationship between fracturing and seismic velocity, the decreasing spreading rate leading up to extinction let the mechanically strong layer thicken, so that faulting and fracturing extended to greater depths . Low velocities are also observed in the uppermost mantle underlying the extinct spreading ridge. This zone is attributed to hydrothermal alteration of upper mantle peridotites. Furthermore, after spreading ceased 32-26 my ago, ongoing passive hydrothermal circulation was accompanied by the precipitation of alteration products in open void spaces, thereby decreasing the porosity and increasing the velocity. Consequently the typical low velocities of layer 2 found at active mid-ocean ridges have been replaced by values typical of mature oceanic crust.  相似文献   

Life in the Goldilocks Zone: Perceptions of Place Disruption on the Periphery of the Bakken Shale     

Anne N. Junod  Jeffrey B. Jacquet  Felix Fernando  Lynette Flage 《社会与自然资源》2018,31(2):200-217

Community impacts from oil development in the Bakken Shale, located in the north central region of the United States, have been well reported in the press, including highly publicized accounts of social disruption. Less examined are communities on the periphery of such development, which experience related impacts unique to their location. Twenty-eight long-time residents from three Bakken periphery communities were interviewed to evaluate social and environmental impact perceptions, including perceived risks of place disruption. Findings suggest that whereas place meanings and identities were disrupted by the oil boom in Bakken core communities, they remain intact in these periphery communities. Findings further suggest periphery residents view their proximal location to the Bakken region as a social and economic “Goldilocks Zone:” close enough to benefit from spillover economic impacts, yet far enough away to avoid serious negative social impacts. This research extends understanding of place disruption and development impacts in energy periphery communities.  相似文献   

Determining cooling rates from mica 40Ar/39Ar thermochronology data: Effect of cooling path shape     

Christopher S. McDonald  Clare J. Warren  Felix Hanke  Julian Chard 《地学学报》2019,31(3):234-246

Tectonic models are commonly underpinned by metamorphic cooling rates derived from diffusive‐loss thermochronology data. Such cooling ages are usually linked to temperature via Dodson's closure temperature (T_C) formulation, which specifies a 1/time‐shaped cooling path (Contributions to Mineralogy and Petrology, 1973, 40, 259). Geologists, however, commonly discuss cooling rates as a linear temperature/time shape. We present the results of a series of simple finite‐difference diffusion models for Ar diffusion in muscovite and biotite that show that the difference in recorded age between 1/t and linear cooling paths increases significantly with hotter starting temperatures, slower cooling rates and smaller grain sizes. Our results show that it is essential to constrain the cooling path shape in order to make meaningful interpretations of the measured data.  相似文献   

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

Stefan Burla  Felix Oberli  Ulrich Heimhofer  Uwe Wiechert  Helmut Weissert 《地学学报》2009,21(5):401-409

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.  相似文献   

The Arctic Coastal Dynamics Database: A New Classification Scheme and Statistics on Arctic Permafrost Coastlines     

Hugues Lantuit  Pier Paul Overduin  Nicole Couture  Sebastian Wetterich  Felix Aré  David Atkinson  Jerry Brown  Georgy Cherkashov  Dmitry Drozdov  Donald Lawrence Forbes  Allison Graves-Gaylord  Mikhail Grigoriev  Hans-Wolfgang Hubberten  James Jordan  Torre Jorgenson  Rune Strand ?deg?rd  Stanislav Ogorodov  Wayne H. Pollard  Volker Rachold  Sergey Sedenko  Steve Solomon  Frits Steenhuisen  Irina Streletskaya  Alexander Vasiliev 《Estuaries and Coasts》2012,35(2):383-400

Arctic permafrost coasts are sensitive to changing climate. The lengthening open water season and the increasing open water area are likely to induce greater erosion and threaten community and industry infrastructure as well as dramatically change nutrient pathways in the near-shore zone. The shallow, mediterranean Arctic Ocean is likely to be strongly affected by changes in currently poorly observed arctic coastal dynamics. We present a geomorphological classification scheme for the arctic coast, with 101,447?km of coastline in 1,315 segments. The average rate of erosion for the arctic coast is 0.5?m? year^?1 with high local and regional variability. Highest rates are observed in the Laptev, East Siberian, and Beaufort Seas. Strong spatial variability in associated database bluff height, ground carbon and ice content, and coastline movement highlights the need to estimate the relative importance of shifting coastal fluxes to the Arctic Ocean at multiple spatial scales.  相似文献   

Rossberg landslide history and flood chronology as recorded in Lake Lauerz sediments (Central Switzerland)     

Felix Bussmann  Flavio S. Anselmetti 《Swiss Journal of Geoscience》2010,103(1):43-59

The southern slopes of Rossberg mountain, Central Switzerland, on which one of the largest historic landslides of the Alpine region was released in 1806 ad (Goldauer Bergsturz), are prone to large-scale mass wasting processes. This has led to numerous sliding events, which are well-recognizable in the modern topography but lack accurate dating. In order to provide new insights into the timing and the processes associated with past landslides as well as into the frequency of exceptional flood events, long sediment cores were retrieved from the subsurface of Lake Lauerz that lies in the pathway of these landslides and that records strong runoff events with typical flood layers. Analyses of the recovered cores display a sedimentologic succession with variable fingerprints of past landslides and flood events, depending on the coring location within the lake. The landslide signature can be calibrated using the 1806 ad event: An organic-rich peaty unit, which is found in two cores located close to the rockmass impact, points towards a sudden, gravity spreading-induced lateral displacement of the swampy plain where parts of the rock mass were accumulating. This rapid lateral mobilization of soft sediments, and not the rock masses, acted as ultimate trigger for the reported ~15 m-high impulse waves on the lake. In the more distal areas, the 1806 ad event led to the deposition of a thick, organic-rich redeposited layer. The 10 m-long core from the distal basin covers a radiocarbon-dated ~2,000 years sedimentation history and contains a highly similar event layer that was deposited in 810 ± 60 ad. This layer is most likely the product of a major historic landslide, known as Röthener Bergsturz, which, based on scarce historical reports, was commonly dated to 1222 ad. In the 2,000 years record, we identify three periods with enhanced occurrence of flood turbidites dated to 580–850 ad, 990–1420 ad, and 1630–1940 ad. Among the 54 detected flood layers, 6 probably mark exceptionally heavy rainfall events that are dated to ~610, ~1160, ~1290, ~1660, ~1850, and ~1876 ad, the latter being associated to one of the most intense rainfall events ever recorded instrumentally in the region.  相似文献   

Gas cooling in simulations of the formation of the galaxy population     

Naoki Yoshida  Felix Stoehr  Volker Springel  Simon D. M. White 《Monthly notices of the Royal Astronomical Society》2002,335(3):762-772

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Monitoring vegetation condition from NOAA operational polar-orbiting satellites over Indian region     

Ramesh P Singh  Felix Kogan 《Journal of the Indian Society of Remote Sensing》2002,30(3):117-118

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The slow rotation of 253 Mathilde     

Stefano Mottola  William D. Sears  Anders Erikson  Alan W. Harris  Jim W. Young  Gerhard Hahn  Mats Dahlgren  Beatrice E. A. Mueller  Bill Owen  Ricardo Gil-Hutton  Javier Licandro  M. Antonietta Barucci  Claudia Angeli  Gerhard Neukum  Claes-Ingvar Lagerkvist  J. Felix Lahulla 《Planetary and Space Science》1995,43(12)

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.  相似文献