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O. G. Gladysheva 《Geomagnetism and Aeronomy》2009,49(3):397-404
Based on the fact that such events as an explosion of the Tunguska cosmic body, which caused the fall of trees in a wide area and the release of radiant energy during the Tunguska disaster, proved to be separated not only in space but also in time, it is concluded that these events are interrelated but different. The assumption is justified that the emission during the Tunguska disaster was caused by the atmospheric discharge at altitudes of 10–90 km above the Earth’s surface. The emission energy, released during this discharge, could reach ~1010 J. 相似文献
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Alan B. Dixon 《Singapore journal of tropical geography》2008,29(3):341-356
Local community based institutions that coordinate the management of natural resources have been linked to socioecological resilience, adaptation and sustainability within rural livelihood systems throughout the developing world. The resilience and sustainability of related local institutions, however, is influenced by their relationship with external actors and institutions, particularly in facilitating, supporting or hindering local institutional arrangements. From this standpoint, this paper examines the case of local community based institutions involved in wetland management in western Ethiopia. Drawing upon the findings of participatory fieldwork undertaken in eight wetland‐using communities of Illubabor and Western Wellega zones in Oromia Region it is argued that although local institutions do play a key role in coordinating wetland management and sustaining the benefits from wetlands, the sustainability and resilience of the institutions themselves is threatened by a range of factors. Despite their grassroots nature, their effectiveness is influenced by their reliance on local government backstopping that appears to have diminished in recent years, as well as a perceived lack of local government support for collective action over individual rights. 相似文献
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—The Tien-Shan orogene is a region in which the earth’s crust undergoes considerable thickening and tangential compression. Under these conditions the lithosphere heterogeneities (composi tion, rheological) create the prerequisites for the development of various phenomena of tectonic layering (lateral shearing, different deformation of layers). To study the distribution of velocity, density and other elastic parameters, the results from a seismic tomography study on P-wave as well as S-wave velocities were used. Using empirical as well as theoretical formulas on the relationship between velocity, density and silica content in rocks, their distribution in the Tien-Shan’s lithosphere has been calculated. In addition, other elastic parameters, such as Young’s modulus, shear modulus, Poisson’s ratio and coefficient of general compressions have been determined. Zoning of different types of crust was carried out for the region investigated. The characteristics of the "crust-mantle" transition have been investi gated. Large blocks with different types of the earth’s crust were distinguished. Layers with inverse values of velocity, density and shear and Young modulus are revealed in the Tien-Shan lithosphere. All of the above described features open new ways to solve geodynamics problems. 相似文献
28.
Size scales over which ordinary chondrites and their parent asteroids are homogeneous in oxidation state and oxygen-isotopic composition 总被引:1,自引:0,他引:1
Literature data demonstrate that on a global, asteroid-wide scale (plausibly on the order of 100 km), ordinary chondrites (OC) have heterogeneous oxidation states and O-isotopic compositions (represented, respectively, by the mean olivine Fa and bulk Δ17O compositions of equilibrated samples). Samples analyzed here include: (a) two H5 chondrite Antarctic finds (ALHA79046 and TIL 82415) that have the same cosmic-ray exposure age (7.6 Ma) and were probably within ∼1 km of each other when they were excavated from the H-chondrite parent body, (b) different individual stones from the Holbrook L/LL6 fall that were probably within ∼1 m of each other when their parent meteoroid penetrated the Earth’s atmosphere, and (c) drill cores from a large slab of the Estacado H6 find located within a few tens of centimeters of each other. Our results indicate that OC are heterogeneous in their bulk oxidation state and O-isotopic composition on 100-km-size scales, but homogeneous on meter-, decimeter- and centimeter-size scales. (On kilometer size scales, oxidation state is heterogeneous, but O isotopes appear to be homogeneous.) The asteroid-wide heterogeneity in oxidation state and O-isotopic composition was inherited from the solar nebula. The homogeneity on small size scales was probably caused in part by fluid-assisted metamorphism and mainly by impact-gardening processes (which are most effective at mixing target materials on scales of ?1 m). 相似文献
29.
U-Pb (SHRIMP-II) isotopic dating has been conducted for zircons of the ash sediments of the Ust’-Suifun Suite, which was the
final stage of Late Cenozoic explosive volcanism in Southwest Primorskii krai. These pyroclastic units are widespread within
sediments that fill in Cenozoic depressions including large coalfields. The concordant dates (23.7–24.6 Ma) are in line with
the results of the K-Ar determinations for volcanic tephra (23.6–27.1 Ma) and correspond to the beginning of the active phase
of spreading and taphrogenesis in the neighboring Trench of the Sea of Japan. These processes started as early as the Eocene
and are reflected in the continental vicinity with the formation of riftogenic depressions and the occurrence of a peculiar
gas volcanism. 相似文献
30.
FluBiDi is a two-dimensional model created to simulate real events that can take days and months, as well as short events (minutes or hours) and inclusive laboratory tests. To verify the robustness of FluBiDi, it was tested using a previous study with both designed and real digital elevation models. The results highlight good agreement between the models (i.e. Mike Flood, SOBEK, ISIS 2D, and others) tested and FluBiDi (around 90% for a specific instant and 95% for the complete time simulation). In the simulated hydrographs, the discharge peak value, time to peak, and water level results were accurate, reproducing them with an error of less than 5%. The velocity differences observed in a couple of tests in FluBiDi were associated with very short periods of time (seconds). However, FluBiDi is highly accurate for simulating floods under real topographical conditions with differences of around 2 cm when water depth is around 150 cm. The average water depth and velocities are precise, and the model describes with high accuracy the pattern and extent of floods. FluBiDi has the capability to be adjusted to different types of events and only requires limited input data. 相似文献