Reconstructing spatio-temporal patterns of debris-flow activity using dendrogeomorphological methods   总被引：2，自引：0，他引：2  

Michelle Bollschweiler  Markus Stoffel  Melanie Ehmisch  Michel Monbaron 《Geomorphology》2007,87(4):337-351

Debris flows are a major threat in many parts of the Alps, where they repeatedly cause severe damage to infrastructure and transportation corridors or even loss of life. Nonetheless, the spatial behavior of past debris-flow activity and the analysis of areas affected during particular events have been widely neglected in reconstructions so far. It was therefore the purpose of this study to reconstruct spatio-temporal patterns of past debris flows on a forested cone in the Swiss Alps (Bruchji torrent, Blatten, Valais). The analysis of past events was based on a detailed geomorphic map (1:1000) of all forms related to debris flows as well as on tree-ring series from 401 heavily affected trees (Larix decidua Mill. and Picea abies (L.) Karst.) growing in or next to deposits. The samples were analyzed and growth disturbances related to debris-flow activity assessed, such as tangential rows of traumatic resin ducts, the onset of reaction wood or abrupt growth suppression or release.In total, 960 growth disturbances were identified in the samples, belonging to 40 different event years between A.D. 1867 and 2005. In addition, the coupling of tree-ring data with the geomorphic map allowed reconstruction of eleven formerly active channels and spatial representation of individual events. Based on our results we believe that before 1935, debris flows preferentially used those channels located in the western part of the cone, whereas the eastern part of the cone remained widely unaffected. The spatial representation of the 40 events also allowed identification of five different spatial patterns for debris flows at the study site.  相似文献   

Dual models of pore spaces     

Roland Glantz  Markus Hilpert 《Advances in water resources》2007

We present a model for pore spaces that consists of two parts related by duality: (1) a decomposition of an open polyhedral pore space into open contractible pore bodies separated by relatively open interfaces and (2) a pore network that is homotopy equivalent to the pore space. The dual model is unique and free of parameters, but it relies on regularity conditions for the pore space. We show how to approximate any pore space by the interior of a polyhedral complex such that the regularity conditions are fulfilled. Thus, we are able to calculate the dual model from synthetic porous media and images of real porous media. The pore bodies are unions of relatively open Delaunay cells with respect to the corners of the pore boundary, and the pore network consists of certain at most two-dimensional (2D) Voronoi cells with respect to the corners of the pore boundary. The pore network describes the neighborhood relations between the pore bodies. In particular, any relatively open 2D Delaunay face f separating two pore bodies has a unique (relatively open) dual network edge. In our model, f is a pore throat only if it is hit by its dual network edge. Thus, as opposed to widespread intuition, any pore throat is convex, and adjacent pore bodies are not necessarily separated by pore throats. Due to the duality between the pore network and the decomposition of the pore space into pore bodies it is straightforward to store the geometrical properties of the pore bodies [pore throats] as attributes of the dual network vertices [edges]. Such an attributed network is used to perform 2D drainage simulations. The results agree very well with those from a pore-morphology based modeling approach performed directly on the digital image of a porous medium. Contractibility of the pore bodies and homotopy equivalence of the pore space and the pore network is proven using discrete Morse theory and the nerve theorem from combinatorial topology.  相似文献   

PLL Tracking Performance in the Presence of Oscillator Phase Noise   总被引：3，自引：3，他引：3  

Markus Irsigler  Bernd Eissfeller 《GPS Solutions》2002,5(4):45-57

The tracking performance of a Phase Lock Loop (PLL) is affected by the influence of several error sources. In addition to thermal noise and dynamic stress error, oscillator phase noise can cause significant phase jitter which degrades the tracking performance. Oscillator phase noise is usually caused by two different effects: Allan deviation phase noise is caused by frequency instabilities of the receiver's reference oscillator and the satellite's frequency standard. It can be termed as system-inherent phase noise and is relevant for both static and dynamic applications. “External” phase noise, however, is caused by vibration and is a major problem for dynamic applications. In the context of this paper, both types of phase noise will be modeled and the resulting integrals will be evaluated for PLLs up to the third order. Besides, phase jitter induced by thermal noise and signal dynamics will also be discussed, thus providing all necessary formulas for analyzing the performance of a phase lock loop in case of different forms of stress. Since the main focus is centered on the effects of oscillator phase noise, the overall PLL performance is graphically illustrated with and without consideration of oscillator phase noise. © 2002 Wiley Periodicals, Inc.  相似文献   

Flood Events in the Rhine Basin: Genesis,Influences and Mitigation   总被引：4，自引：1，他引：4  

Disse  Markus  Engel  Heinz 《Natural Hazards》2001,23(2-3):271-290

The paper analyses the hydrological regime of the Rhine catchment,the genesis of recent floods,and recommends some research and practical activities to mitigate flood damage. The catchment of the Rhine River can be divided into four main subcatchments: the alpine region with the Aare River as its main tributary and downstream the lower mountain regions of the tributaries Neckar, Main and Moselle. These four basins generate very different hydrographs. Due to the geographical conditions, the average discharge maximums shift from summer to winter downstream the Rhine. Moreover, the spatial and temporalprecipitation patterns of each river have a strong influence on the individual flood events. Some recent extraordinary floods are used to illustrate the parameters that have influenced these events.A strong relationship between recent climate change observationsand the occurrence of flood levels cannot be proven. However, the consequences of human interventions and the resulting changes to the river system (the Rhine and its tributaries) for the hydrograph can be quantified precisely.The influences of different land-use and climatic scenarios on flood conditions in the Rhine basin have not yet been separately identified. Thus, the Dutch-German project LAHoR was established. The primary aim of this project is to giveadvice for the ``Action Plan on Flood Defence' of the International Commission for the Protection of the Rhine (IKSR). In this plan a multidisciplinary approach to mitigating floods is suggested.It is anticipated that the plan willgenerate synergistic effects between flood prevention, water management, regional planning, agriculture, forestry and ecological demands.  相似文献   

Evolution of late pleistocene and holocene climates in the circum-south pacific land areas     

Vera Markgraf  John R. Dodson  A. Peter Kershaw  Matt S. McGlone  Neville Nicholls 《Climate Dynamics》1992,6(3-4):193-211

Paleovegetation maps were reconstructed based on a network of pollen records from Australia, New Zealand, and southern South America for 18 000, 12000, 9000, 6000, and 3000 BP and interpreted in terms of paleoclimatic patterns. These patterns permitted us to speculate on past atmospheric circulation in the South Pacific and the underlying forcing missing line mechanisms. During full glacial times, with vastly extended Australasian land area and circum-Antarctic ice-shelves, arid and cold conditions characterized all circum-South Pacific land areas, except for a narrow band in southern South America (43° to 45°S) that might have been even wetter and moister than today. This implies that ridging at subtropical and mid-latitudes must have been greatly increased and that the storm tracks were located farther south than today. At 12000 BP when precipitation had increased in southern Australia, New Zealand, and the mid-latitudes of South America, ridging was probably still as strong as before but had shifted into the eastern Pacific, leading to weaker westerlies in the western Pacific and more southerly located westerlies in the eastern Pacific. At 9000 BP when, except for northernmost Australia, precipitation reached near modern levels, the south Pacific ridges and the westerlies must have weakened. Because of the continuing land connection between New Guinea and Australia, and reduced seasonality, the monsoon pattern had still not developed. By 6000 BP, moisture levels in Australia and New Zealand reached their maximum, indicating that the monsoon pattern had become established. Ridging in the South Pacific was probably weaker than today, and the seasonal shift of the westerlies was stronger than before. By 3000 BP essentially modern conditions had been achieved, characterized by patterns of high seasonal variability.Contribution to Clima Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate Program  相似文献   

Deep seismic reflection experiments at Kiruna     

Dr. Markus Båth  Cand. Eysteinn Tryggvason 《Pure and Applied Geophysics》1962,51(1):79-90

Summary In August 1955 a series of specially arranged quarry blasts in the Kiruna iron ore mines was recorded with a refraction apparatus at approx. 10 km distance. The experiments are the first seismic investigations of the deeper crustal structure in Fennoscandia and were mainly undertaken in order to study near-vertical reflections from crustal discontinuities. The records show clear directP waves with sharp onsets and a velocity of 5.65±0.13 km/sec (in porphyry), furthermoreS waves of less definite onsets and sound waves through the atmosphere.P waves reflected from crustal discontinuities are weak and of erratic occurrence, in agreement with theoretical expectation for near-vertical reflections. Approx. depths to the Conrad and the Mohorovii'c discontinuities are calculated as 19 km and 33–34 km. There is general agreement with the explosion records written by the Grenet seismograph at Kiruna, and the differences which exist can be explained by the different frequency response of the two instruments.

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Zusammenfassung Im August 1955 wurde eine Reihe speziell angeordneten Steinbruchsprengungen in den Eisenerzgruben bei Kiruna mittels einer Refraktionsapparatur in rund 10 km Entfernung registriert. Diese Versuche sind die ersten seismischen Untersuchungen der tieferen Krustenstruktur in Fennoskandien und wurden hauptsächlich wegen eines Studiums von Reflexionen an krustalen Diskontinuitäten bei nahe vertikalem Einfall der Wellen vorgenommen. Deutliche, direkteP-Wellen mit scharfen Einsätzen und einer Geschwindigkeit von 5.65±0.13 km/sec (Porphyr) wurden registriert, ausserdemS-Wellen mit weniger scharfen Einsätzen und Schallwellen durch die Atmosphäre. An krustalen Diskontinuitäten reflektierteP-Wellen sind schwach und unregelmässig, im Einklang mit theoretischen Erwartungen für Reflexionen bei nahe vertikalem Einfall. Die Tiefen der Conrad- und der Mohorovii-Diskontinuitäten wurden annähernd zu 19 km bzw. 33–34 km berechnet. Es besteht allgemeine Übereinstimmung mit den Explosionsregistrierungen des Grenet-Seismographen in Kiruna, und die Unterschiede können lediglich durch die unterschiedliche Frequenzempfindlichkeit der Instrumente erklärt werden.

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A method for determination of epicenters of near earthquakes     

Mr. Ari Ben-Menahem M. Sc.  Dr. Markus Båth 《Pure and Applied Geophysics》1960,46(1):37-46

Summary A method is developed, which permits a rapid and reliable determination of the location of near epicenters (within about 10^o) using the differences of arrival times of a common phase (usually Sg) to a net of three stations. The resulting equation for computation of epicentral distances is solved numerically once for all by an electronic computer for every station triangle and for all possible time differences for every wave used. The calculated epicentral distances and coordinates are arranged in tables with the two travel-time differences for each triangle as entries. Such tables permit an immediate solution of the problem in every special case. The accuracy of the method is investigated, and necessary precautions in its use are emphasized. Application is made to a few cases of Sg recorded at the Swedish stations.

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Zusammenfassung Eine Methode wird entwickelt, die eine schnelle und zuverlässige Bestimmung der Lage von nahegelegenen Epizentren (innerhalb rund 10^o) mittels der Laufzeitdifferenzen einer gegebenen Welle (gewöhnlichSg) in einem Netz von drei Stationen ermöglicht. Die erhaltene Gleichung für die Berechnung der Herdentfernungen wird mittels einer elektronischen Rechenmaschine für jedes Stations-dreieck und für alle möglichen Zeitdifferenzen für jede verwendete Welle ein für allemal numerisch gelöst. Die berechneten Herdentfernungen und-Koordinaten werden in Tabellenform dargestellt mit den beiden Laufzeitdifferenzen für jedes Dreieck als Eingangswerte. Solche Tabellen ermöglichen eine unmittelbare Lösung des Problems in jedem einzelnen Fall. Die Genauigkeit der Methode wird untersucht, und die notwendigen Vorsichtsmassregeln bei ihrer Verwendung werden hervorgehoben. Die Methode wird auf einige Registrierungen vonSg an den schwedischen Stationen angewendet.

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Seismic surface-wave dispersion: A world-wide survey     

Markus Båth 《Pure and Applied Geophysics》1959,43(1):131-147

Summary By means of the long-period records at Uppsala and Kiruna of thirteen specially selected earthquakes, the Love and Rayleigh wave dispersion is determined for all oceans and all continents except for South America. The observations have given information on crustal structure along several paths, not investigated earlier; in other cases, they have confirmed earlier results. The methods are discussed. The results for oceanic areas are summarized in the following table: The observations demonstrate the oceanic structure of the central Arctic area as well as the complete similarity of the Atlantic and Pacific bottom structure. Continental dispersion curves are determined for very long paths over Euro-Asia and for the hitherto longest path over North America as well as for a path crossing Africa. These observations indicate an average crust about 10–15 km thicker along the Euro-Asiatic path than along the North American path, whereas there is perfect agreement between the North American and the African continent. A shear-wave velocity of 4.3–4.4 km/sec is obtained for the upper part of the mantle under the continents. Further conclusions must await the computation of a greater number of theoretical dispersion curves.

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Zusammenfassung Mittels der langperiodischen Registrierungen in Uppsala und Kiruna von dreizehn speziell ausgewählten Erdbeben ist die Dispersion der Love-und Rayleigh-Wellen für alle Ozeane und alle Kontinente mit Ausnahme von Süd-Amerika bestimmt worden. Die Beobachtungen haben in mehreren Fällen Auskunft über die Krusten-Struktur längs Wellenwege gegeben, die nie früher untersucht worden sind; in anderen Fällen haben sie frühere Resultate bestätigt. Die Methoden werden diskutiert. Die Resultate für ozeanische Gebiete sind in der folgenden Tabelle zusammengefasst: Die Beobachtungen beweisen sowohl die ozeanische Struktur des zentralen Teiles des arktischen Gebietes als auch die vollständige Gleichheit der atlantischen und pazifischen Krusten-Struktur. Kontinentale Dispersionskurven sind für sehr lange Wellenwege über Euro-Asien und für den bisher längsten Wellenweg über Nord-Amerika bestimmt worden. Diese Beobachtungen zeigen, dass die mittlere Krusten-Dicke 10–15 km grösser längs des euro-asiatischen Weges ist als längs des nordamerikanischen Weges; dagegen zeigen die Beobachtungen für Nord-Amerika und Afrika sehr gute Übereinstimmung. Eine Transversalwellen-Geschwindigkeit von 4.3–4.4 km/sek wird für den oberen Teil des Erdmantels unter den Kontinenten gefunden. Weitere Schlussfolgerungen müssen die Berechnung einer grösseren Anzahl theoretischer Dispersionskurven erwarten.

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A continental channel wave,guided by the intermediate layer in the crust     

Dr. Markus Bath 《Pure and Applied Geophysics》1957,38(1):19-31

Summary A study has been made of a new channel wave, denotedLi, using a total of 83 observations from the seismic records of Swedish stations, mainly from earthquakes at normal depth.Li resembles theLg waves in several respects: it propagates only through continental structures, it has a similar particle motion, i.e. mainly transverse horizontal, and only slightly larger period. ButLi has a higher velocity, 3.79±0.07 km/sec, and it is believed to propagate in the intermediate layer in the crust in a way similar to the propagation of theLg waves in the granitic layer.Li is identical withS ^* in records of near-by earthquakes in the same way asLg2 is identical withSg. Li usually exhibits no clear dispersion.

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Zusammenfassung Es wurden Untersuchungen angestellt über eine neue Kanalwelle, welcher die BezeichnungLi gegeben wurde, wobei insgesamt 83 Erdbebenregistrierungen von schwedischen Stationen Verwendung fanden. Hauptsächlich waren es Erdbeben mit normaler Herdtiefe. DieLi-Wellen haben in verschiedener Hinsicht Ähnlichkeit mit denLg-Wellen: Sie pflanzen sich nur im Bereich kontinentaler Struktur fort und sie haben eine ähnliche Partikelbewegung, d.h. hauptsächlich horizontaltransversal.Li hat eine nur unwesentlich höhere Periode als dieLg-Wellen. AberLi hat eine wesentlich höhere Geschwindigkeit, 3.79±0.07 km/sec, und es ist anzunehmen, dass sie sich in der Basaltschicht der Kruste in ähnlicher Weise fortpflanzt wieLg in der Granitschicht.Li ist identisch mitS ^* in Aufzeichnungen von Nahbeben, so wieLg2 identisch mitSg ist.Li weist gewöhnlich keine deutliche Dispersion auf.

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Strike and dip of crustal boundaries — A method and its application     

R. James Brown  Harry Borg  Markus Båth 《Pure and Applied Geophysics》1971,88(1):60-74

Summary If for a point on the earth's surface, the apparent (moveout) seismic velocities have been determined for a number of profiles in different directions, a possibility is offered to calculate true strike and dip of crustal boundaries. In the present paper the theory is developed, partly for a sloping Mohorovii discontinuity only, partly for sloping Conrad and Mohorovii discontinuities with parallel strikes. The theory for the sloping Mohorovii discontinuity is applied to field measurements at a place about 30 km west of Uppsala performed in June 1969. With a crustalP-wave velocity of 6.3 km/sec, a good fit to the observations is obtained for aPn-velocity of 8.55 km/sec and a downdip of Moho of 7.2° in the direction S 3.8° E. These numerical values are not the most important output of this paper. On the other hand, the testing of the method appears far more important, and also that improvements can be suggested in the experimental procedure in future applications of this method.  相似文献