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   

Analysis of Physical and Chemical Parameters for Discrimination of Water Origin in a Hydroelectric Reservoir     

Wagner José Barreto  Ieda Scarminio  Maria Cristina Solci  Dílson Norio Ishikawa  Melissa Tiemi Ogasawara  Sônia Naomi Nomi  Sônia Regina Giancoli Barreto 《洁净——土壤、空气、水》2007,35(3):239-245

Seventeen physical and chemical parameters were obtained from a hydroelectric reservoir located in a tropical region in the south of Brazil. Multivariate Principal Component Analysis (PCA) and Hierarchical Group Analysis (HGA) were used to identify the parameters discriminating the origin of water from the Tibagi and the Primeiro de Maio River, after it has passed the mixing region. The study was conducted during the dry and rainy seasons in July 2002 and February 2003 at three depths and three sampling sites located 0, 5, and 10 km away from the mixing region. The statistical methods showed to be appropriate for identifying the contribution of each tributary in the water mixing site of a complex water system. The most important discriminating parameter was the absorbance relation A(253 nm)/A(203 nm), followed by the concentrations of Fe(III), Mn(III), and Ni(II). An anthropogenic interference was found in the reservoir due to high Ni(II) and orthophosphate concentrations caused by a nearby town sewage discharge. The interference was more important during the dry periods due to the lower dispersion of the pollutants. Urgent initiatives should be taken from the state government to build treatment stations for the wastewater of the small cities around the Capivara hydroelectric reservoir to prevent the drinking water quality from deteriorating.  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   

Seismicity, seismotectonics and crustal structure of the southern Kenya Rift—new data from the Lake Magadi area     

M. Ibs-von Seht  S. Blumenstein  R. Wagner  D. Hollnack  J. Wohlenberg 《Geophysical Journal International》2001,146(2):439-453

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The postglacial environmental development of Raffles Sø, East Greenland: inferences from a 10,000 year diatom record   总被引：1，自引：0，他引：1  

Holger Cremer  Bernd Wagner  Martin Melles  Hans-Wolfgang Hubberten 《Journal of Paleolimnology》2001,26(1):67-87

A 341 cm long sediment sequence was recovered from the unofficially named Raffles Sø on Raffles Ø, outer Scoresby Sund region, East Greenland. The sediment sequence consists in the upper part (0–230 cm) of a stratified gyttja enriched in organic carbon and biogenic silica whereas the lower core part (235–341 cm) is composed of terrigenous, consolidated glacio-limnic sediments. ¹⁴C-AMS measurements indicate that the sediment sequence represents the entire Holocene lake history from 10,030 calibrated radiocarbon years.The geochemical parameters (opal, total organic carbon (TOC), total nitrogen (TN)) and the total diatom concentration show similar developments during the Holocene, and reflect changes in biological production and nutrient input into the lake. These records clearly reveal a broad Holocene TOC-opal-maximum interval between 5200 and 1800 cal. yrs BP.The diatom flora consisted of 66 taxa representing 20 genera but only seven taxa were abundant and, sometimes, these were monospecifically dominant during the Holocene. In the sediment core from Raffles Sø four successive stratigraphical zones can be distinguished. Accumulation of diatom valves began at 9900 cal. yrs BP with a Stephanodiscus minutulus (Kütz.) Cleve and Möller dominated assemblage (stratigraphic zone 1) followed by a diatom flora dominated by Cyclotella pseudostelligera Hustedt and, less frequently, by Diatoma tenuis Agardh (9400 until 5900 cal. yrs BP, zone 2). Cyclotella sp. A, a taxon which belongs to the Cyclotella rossii-comensis-tripartita-complex, was the dominant floral element between 5200 and 1800 cal. yrs BP (zone 3). From 1800 cal. yrs BP, the periphytic taxa Fragilaria capucina var. gracilis (Østr.) Hustedt and F. capucina var. rumpens (Kütz.) Lange-Bertalot attained highest relative abundances, also almost monospecifically (zone 4).The distribution and composition of the diatom assemblages in the sediment record from Raffles Sø probably reflect past variations in the extent of the lake-ice cover during the growing season. More or less ice-free conditions during summer may have prevailed during the early Holocene until ca. 1800 cal. yrs BP, which allowed growth of planktonic diatoms (Cyclotella taxa) in the pelagic lake region. From 1800 cal. yrs BP, colder conditions lead to a perennial lake-ice cover with a small ice-free moat in summer which favored the growth of periphytic, littoral species (Fragilaria capucina varieties).  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   

On Geodynamic Evolution of Simao Region (Southwestern Yunnan, China) during Late Paleozoic and Triassic     

Helmcke DGZG  University of Goettingen  D Goettingen  GermanyIngavat Helmcke Rc/o GZG  University of Goettingen  D Goettingen  GermanyFeng QinglaiFaculty of Earth Sciences  China University of Geosciences  Wuhan Wagner B Heppe KGZG 《中国地质大学学报(英文版)》2001,12(3)

ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅＳｉｍａｏｒｅｇｉｏｎ (ＳＷＹｕｎｎａｎ ,Ｃｈｉｎａ) ,ｓｉｔｕａｔｅｄｂｅ ｔｗｅｅｎｔｈｅＡｉｌａｏｓｈａｎｂｅｌｔｉｎｔｈｅｅａｓｔａｎｄｔｈｅＬａｎｃａｎｇｊｉａｎｇｚｏｎｅｉｎｔｈｅｗｅｓｔ (Ｆｉｇ .1) ,ｉｓａｋｅｙａｒｅａｔｏｃｈｒｏｎｏｌｏｇｉｃａｌｌｙｃｏｎｓｔｒａｉｎｌａｔｅＰａｌｅｏｚｏｉｃｃｏｍｐｒｅｓｓｉｏｎａｌｄｅｆｏｒｍａｔｉｏｎｓａｎｄｔｈｕｓｏｆｐｒｉｍｅｉｎ ｔｅｒｅｓｔｗｈｅｎｄｉｓｃｕｓｓｉｎｇｔｈｅｐｌａｔｅ ｔｅｃｔｏｎｉｃｈｉ…  相似文献   

Temporal variability of global Topex/Poseidon altimetry: tide and annual signals?     

C. A. Wagner  C. K. Tai  J. M. Kuhn 《Journal of Geodesy》1995,69(4):244-251

Summary The global power of the differences of altimetric sea heights at collocated points in the first 44 cycles of the Topex/Poseidon (T/P) mission, apparently shows the influence of errors in the major tides and long period ocean signals. Results show the principal semidiurnal tides (M2/S2 lumped together) in the Cartwright and Ray (1991) model are probably in error globally by 3–4 cm (rms). The dominant fluctuation in the differences over the 44 cycles (14 months total) arises from an annual signal of 4–6 cm (rms), significantly greater than long term climate data suggests (but with considerable uncertainty due to unresolved semiannual effects).  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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