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81.
Björn Heincke Thomas Günther Einar Dalsegg Jan Steinar Rønning Guri Venvik Ganerød Harald Elvebakk 《Journal of Applied Geophysics》2010,70(4):292-306
We present a combined 3-D geoelectric and seismic tomography study conducted on the large Åknes rockslide in western Norway. Movements on the slope are strongly influenced by water infiltration, such that the hydrogeological regime is considered as a critical factor affecting the slope stability. The aim of our combined geophysical study was to identify and visualize the main shallow tension fractures and to determine their effect on hydraulic processes by comparing the geophysical results with information from borehole logging and tracer tests. To resolve the complex subsurface conditions of the highly fractured rock mass, a three-dimensional set-up was chosen for our seismic survey. To map the water distribution within the rock mass, a pattern of nine intersecting 2-D geoelectric profiles covered the complete unstable slope. Six of them that crossed the seismic survey area were considered as a single data set in a 3-D inversion. For both methods, smoothing-constraint inversion algorithms were used, and the forward calculations and parameterizations were based on unstructured triangular meshes. A pair of parallel shallow low-velocity anomalies (< 1400 m/s) observed in the final seismic tomogram was immediately underlain by two anomalies with resistivities <13 kΩm in the resistivity tomogram. In combination with borehole logging results, the low-velocity and resistivity anomalies could be associated with the drained and water-filled part of the tension fractures, respectively. There were indications from impeller flowmeter measurements and tracer tests that such tension fractures intersected several other water-filled fractures and were responsible for distinct changes of the main groundwater flow paths. 相似文献
82.
Analysis of two continuous, high‐resolution palaeo‐flood records from southern Norway reveals that the frequency of extreme flood events has changed significantly during the Holocene. During the early and middle Holocene, flood frequency was low; by contrast, it was high over the last 2300 years when the mean flood frequency was about 2.5–3.0 per century. The present regional discharge regime is dominated by spring/summer snowmelt, and our results indicate that the changing flood frequency cannot be explained by local conditions associated with the respective catchments of the two lakes, but rather long‐term variations of solid winter precipitation and related snowmelt. Applying available instrumental winter precipitation data and associated sea‐level pressure re‐analysis data as a modern analogue, we document that atmospheric circulation anomalies, significantly different from the North Atlantic Oscillation (NAO), have some potential in explaining the variability of the two different palaeo‐flood records. Centennial‐scale patterns in shifting flood frequency might be indicative of shifts in atmospheric circulation and shed light on palaeo‐pressure variations in the North Atlantic region, in areas not influenced by the NAO. Major shifts are found at about 2300, 1200 and 200 years ago (cal. a BP). Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
83.
Nathalie van Vliet Ole Mertz Andreas Heinimann Tobias Langanke Unai Pascual Birgit Schmook Cristina Adams Dietrich Schmidt-Vogt Peter Messerli Stephen Leisz Jean-Christophe Castella Lars Jørgensen Torben Birch-Thomsen Cornelia Hett Thilde Bech-Bruun Amy Ickowitz Kim Chi Vu Kono Yasuyuki Jefferson Fox Christine Padoch Alan D. Ziegler 《Global Environmental Change》2012,22(2):418-429
This meta-analysis of land-cover transformations of the past 10–15 years in tropical forest-agriculture frontiers world-wide shows that swidden agriculture decreases in landscapes with access to local, national and international markets that encourage cattle production and cash cropping, including biofuels. Conservation policies and practices also accelerate changes in swidden by restricting forest clearing and encouraging commercial agriculture. However, swidden remains important in many frontier areas where farmers have unequal or insecure access to investment and market opportunities, or where multi-functionality of land uses has been preserved as a strategy to adapt to current ecological, economic and political circumstances. In some areas swidden remains important simply because intensification is not a viable choice, for example when population densities and/or food market demands are low. The transformation of swidden landscapes into more intensive land uses has generally increased household incomes, but has also led to negative effects on the social and human capital of local communities to varying degrees. From an environmental perspective, the transition from swidden to other land uses often contributes to permanent deforestation, loss of biodiversity, increased weed pressure, declines in soil fertility, and accelerated soil erosion. Our prognosis is that, despite the global trend towards land use intensification, in many areas swidden will remain part of rural landscapes as the safety component of diversified systems, particularly in response to risks and uncertainties associated with more intensive land use systems. 相似文献
84.
E. S. Mo T. Throndsen P. Andresen S. A. Bäckström A. Forsberg S. Haug B. Tørudbakken 《International Journal of Earth Sciences》1989,78(1):305-317
The Midgard Field offshore mid-Norway is a gas-condensate accumulation with a thin oil leg reservoired in Early and Middle Jurassic sandstones. There are two potential source rocks in the area; the Late Jurassic Spekk Formation is a marine shale with type II kerogen and a rich potential for oil, and the Åre Formation of Early Jurassic age which is a thick coal-bearing sequence with type III kerogen and potential mainly for gas. Geochemical analyses indicate that both the condensate and the oil leg are sourced mainly from the coal-bearing Åre Formation. Any contribution from the Spekk Formation appears to be of minor importance. Computer simulation of hydrocarbon generation in the drainage area for the Midgard Field indicates that huge volumes are formed, and confirms that hydrocarbon generation from the Åre Formation is volumetrically far more important than from the Spekk Formation. The simulation results also exclude any contribution to the reservoired gas from the Spekk Formation.
Zusammenfassung Das Midgard Feld vor der Küste Mittelnorwegens ist eine Gas-Kondensat-Akkumulation mit einem nur geringen Ölanteil innerhalb unter- und mitteljurassischer Sandsteine. In diesem Gebiet gibt es zwei mögliche Muttergesteine: Einmal die oberjurassische Spekk-Formation, bei der es sich um einen marinen Schiefer mit Typ II Kerogen handelt und die ein hohes Ölpotential darstellt. Zum anderen gibt es die unterjurassische Åre-Formation, eine mächtige Kohle-führende Folge mit Typ III Kerogen und ein möglicher Gaslieferant. Geochemische Analysen deuten darauf hin, daß sowohl das Gas-Kondensat als auch das Öl des Midgard Feldes auf diese Kohle-führende Åre-Formation zurückzuführen sind. Jede Zufuhr aus der Spekk-Formation scheint von geringer Bedeutung zu sein. Eine durch Computersimulation rekonstruierte Kohlenwasserstofferzeugung im Einzugsgebiet des Midgard Feldes spricht für eine hohe Bildungsrate und bestätigt die Annahme, daß die Kohlenwasserstoff-produktion der Spekk-Formation gegenüber der Åre-Formation zu vernachlässigen ist. Die Simulation ergab ferner, daß keinerlei Gas von der Spekk-Formation dem Reservoir zugeführt wurde.
Résumé Le champ off-shore de Midgard (Norvège moyenne) est une accumulation de gaz condensé accompagnée d'un mince corps d'huile, accumulation renfermée dans des grès d'âge jurassique inférieur et moyen. Il existe dans le secteur deux sources possibles: la formation de Spekk (shale marins du Jurassique tardif, à kérogène de type II, possédant un riche potentiel en huile) et la formation d'Åre (série épaisse jurassique inférieure, à couches de charbon, à kérogène de type III et potentiel essentiellement en gaz). Les analyses géochimiques montrent que le gaz condensé et l'huile ont tous deux comme origine la formation charbonneuse de Åre. La formation de Spekk ne semble être intervenue que de manière subordonnée. Une simulation par ordinateur de la genèse de l'hydrocarbure dans l'aire d'alimentation du champ de Midgard fait apparaître que des volumes importants ont été formés et confirme la large prépondérance de la formation de Åre parmi les roches-mères. De plus, cette simulation exclut toute expèce de contribution de la formation de Spekk dans la genèse du gaz.
Midgard / / . : Spekk — , 2, , Are , 3 . . . , Are. Spekk, , . Midgard , Are . , , Spekk .相似文献
85.
The purpose of the geoscientific Observatory at Schiltach in the Black Forest in SW-Germany is to measure and monitor motions and deformations of the earth in a frequency band as broad as possible. The spectrum of geodynamic signal contains
- • - the short period waves (up to 40 Hz) of near earthquakes,
- • - the longer period body and surface waves from teleseismic events,
- • - the free oscillations of the earth excited by giant earthquakes,
- • - the earth tide deformations caused by the gravitational forces of the moon and the sun having periods of 12 h and longer,
- • - deformations of the earth in a wide period range from other sources (e.g. atmosphere).
86.
The paper briefly discusses the view and actions of the Norwegian Government in relation to environmental protection and development and the minimization of the effects of industry. Governments and supra-national bodies, industry, municipal bodies, science and training bodies and voluntary and non-governmental organizations all have a major and integrated role in protecting the environment. It is emphasized that as many of the problems are transboundary and trans-sectoral their solution requires an intersectoral approach. 相似文献
87.
Tore Prestvik Calvin G. Barnes Bjrn Sundvoll Robert A. Duncan 《Journal of Volcanology and Geothermal Research》1990,44(3-4)
Peter I Øy is located in the Bellinghausen Sea, 400 km NE of Thurston Island, West Antarctica. It is a Pleistocene volcanic island situated adjacent to a former tranform fault on the continental rise of the presently passive margin between the Pacific and Antarctica. New K-Ar age determinations ranging from 0.1 to 0.35 Ma show that the volcanism responsible for this island took place at the same time as post-subduction, rift-related volcanism occurred in the nearby Marie Byrd Land and the Antarctic Peninsula. The rocks of the island are alkalic basalt and hawaiite, benmoreite and trachyte. The basic tocks typically contain phenocrysts of olivine (Fo61–84), diopsidic augite, and plagioclase (ca. An60). Small xenoliths are present and consist of mantle-type spinel lherzolite, cumulate clinopyroxenite and gabbro and felsic inclusions that consist of medium-grained strained quartz, plagioclase, and abundant colorless glass. Chemically, the basic rocks are characterized by rather high MgO (7.8–10.2 wt.%) and TiO2 (3.1–3.7 wt.%) and relatively low CaO (8.4–9.5 wt.%) contents. They have steep REE patterns, [(La/Yb)N = 20] with HREE only 5 x chrondrite. Y and Sc are almost constant at relatively low levels. Compatible trace elements such as Ni and Cr show considerable variation (190–300 and 150–470 ppm, respectively.), whereas V shows only little variation. Sr and Nd isotope ratios vary slightly with 87Sr/86Sr averaging 0.70388 and 143Nd/144Nd 0.512782, both typical for ocean island volcanism. Lead isotope ratios are consistently high in basalts; 206Pb/204Pb = 19.194, 207Pb/204Pb = 15.728 and 208Pb/204Pb = 39.290, whereas benmoreïte is somewhat less radiogenic. Oxygen isotope analyses average δ18O = +6.0‰. Incompatible trace elements vary by a factor of 1.5–2.0 within the range of the basic rocks. It is proposed that the incompatible trace-element variations represent different degrees (<10%) of partial melting, and that these melts were later modified by minor (<15‰) olivine and spinel fractionation. The very small variation in Y (and Sc) and the very fractionated REE pattern indicate that the source had an Y- and HREE-rich residual phase, most probably garnet. Furthermore, it is suggested that the source was slightly hydrous and that melting took place at 18–20 kbar. Trachyte was derived by multiphase fractionation of ne-normative basalts, and benmoreite from hy-normative parental liquids. The rocks of Peter I Øy are generally of the same type and age as those outcropping in extensional regimes on the nearby continent, and therefore, these occurrences may be related to each other in some way. However, the Peter I Øy rocks are considerably more radiogenic in strontium and less radiogenic in neodymium than the rocks of the Antarctic Peninsula and Marie Byrd Land. Possible explanations are that Peter I Øy represent asthenospheric hot spot activity, or transtensional rifting as subduction ceased. 相似文献
88.
Emil Makovicky Sven Karup-Møller Milota Makovicky Jhon Rose-Hansen 《Mineralogy and Petrology》1990,42(1-4):307-319
Summary In the present paper current results of experimental investigation of the phase system Pd-Fe-Ni-S at 900°C, 725°C, 550°C and 400°C as well as of the phase system Pt-Fe-As-S at 850°C and 470°C are summarized. A preliminary note on the system Pt-Pd-As-S is added. Individual phase assemblages are presented, data on solubility of PGE in base metal sulphides/arsenides or alloys are given and solid solution ranges of important minerals are described as a function of temperature and phase assemblage. The extent and role of sulphide/arsenide melts in these systems are presented together with hints for, and examples of the application of the current experimental results for the explanation of ore-geological processes.
With 6 Figures 相似文献
Bisherige Ergebnisse experimenteller Untersuchungen in den Systemen Fe-Ni-Pd-S und Fe-Pt-Pd-As-S und ihre Bedeutung für Lagerstätten der Platin-Gruppen-Elemente
Zusammenfassung In der vorliegenden Arbeit werden bisherige Ergebnisse experimenteller Untersuchungen in den Phasensystemen Pd-Fe-Ni-S bei 900°C, 725°C, 550°C sowie 400°C, bzw. Pt-Fe-As-S bei 850°C und 470°C zusammengefasst. Vorläufige Anmerkungen zum System Pt-Pd-As-S werden gegeben. Die Phasenbeziehungen und die Löslichkeitsdaten von PGE's in Buntmetall-Sulfiden/Arseniden sowie deren Verbindungen werden präsentiert. Die Mischungsbereiche der wichtigsten Minerale werden als Funktion von Temperatur und Phasenvergesellschaftung diskutiert. Die Rolle von Sulfid/Arsenid Schmelzen in diesen Systemen und Beispiele für die Anwendung dieser experimentellen Ergebnisse zur Erklärung lagerstättenkundlicher Prozesse werden beschrieben.
With 6 Figures 相似文献
89.
The molecules constituting the first hydrate layers on montmorillonite crystal platelets appear to be characterized by preferred orientation and, depending on the exchangeable cation, by an ice-like configuration. Such organized interlamellar water is concluded to contribute to the high swelling pressure and shear resistance, as well as to the very low hydraulic conductivity at high clay bulk densities. At low densities the parallel arrangement of the lamellae alters to edge-to-face associations and the fraction of free water increases. However, even at very low densities the homogeneity of the clay gel still offers very tortuous passages to flowing water, which is manifested by a very low hydraulic conductivity. 相似文献
90.
Lake Pontchartrain., Louisiana is a 1,630 km2 shallow brackish lagoon with a mean salinity from 1.2‰ in the west to 5.4‰ in the east., The construction of a 120 km long deep-water connection to the Gulf of Mexico in 1963, was expected to cause a 5‰ increase in lagoon salinity. However, the actual increase was everywhere in the lagoon less than 2‰ Analysis of 31 years of daily salinity and discharge records indicates that discharge is the most important factor controlling salinity variations in Lake Pontchartrain., Seventy-four percent of low-frequency salinity variations are explained by freshwater discharge and the completion of the deep-water canal. Lake Pont.-chartrain experiences annual variations of salinity as high as 8‰ This salinity signal has remained constant since the beginning of the salinity records in 1946. It appears that the deep-water canal is not responsible for observed die-back of freshwater swamps and retreat of lagoon shorelines. 相似文献