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241.
T. Masuda S. Nakayama N. Kimura K. Onodera A. Okamoto 《Journal of Structural Geology》2004,26(12):2203-2209
A rare metachert pebble containing amphibole grains with microboudin structures in a wide range of orientations provides an opportunity to perform stress analysis in two orthogonal orientations on the foliation surface. The sample was analysed by the microboudin method to infer the triaxial stress state during microboudinage. Stress parameters proportional to the far-field differential stress were determined for sodic amphibole grains in the two orientations. The ratio of the stresses in the two orthogonal orientations (σ1−σ2)/(σ1−σ3) was calculated to be 0.64, indicating that σ2 lies closer to the midpoint between σ1 and σ3 than to σ3. 相似文献
242.
We perform a global statistical investigation into the problem of Coulomb stress triggering of earthquakes by using the Harvard CMT catalogue of shallow earthquakes from 1976 to 2001. We consider ‘earthquake pairs’, i.e., pairs of successive earthquakes occurring near each other with similar focal mechanisms, and address the problem of whether or not the change of the Coulomb failure stress (CFS) produced by the first earthquake of the pair ‘encourages’ the occurrence of the second one. An interesting feature is that such a Coulomb stress-triggering phenomenon has an apparent focal mechanism dependence: for thrust earthquakes, a more evident triggering effect can be observed. 相似文献
243.
宁夏香山荒漠草原区植物群落多样性时空特征 总被引:10,自引:0,他引:10
采用多个多样性指数对宁夏香山荒漠草原区植物群落多样性时间、空间动态进行分析。结果表明,该地区群落时、空动态特征不明显。长期过度放牧导致环境恶化,生境碎化,这些作用的长期性、循环性是造成物种、群落格局与原有时、空动态规律相悖的主要因素,这些因素消除了物种或群落在时间梯度上应有的变化规律。干旱山地物种在长期进化过程中成功的发展了对环境的适应机制,环境的波动性强烈导致了群落多样性在原来消长动态基础上的复杂化,也使多样性动态机制复杂化。应用多种指数数学模型对研究对象进行综合评价,能够真实地反映群落多样性动态。 相似文献
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Regions and sustainable development: regional planning matters 总被引:1,自引:0,他引:1
This paper looks at how the term 'sustainable development' has been used in the process of regional plan making over the past decade. It emphasizes the differing geographies of these debates within England, in terms of how sustainable development has been used to justify different types of approach in different parts of the country. Both drawing on and challenging recent work on state theory, the paper argues the need to see regional planning as a part of a multi-scalar governance system, whose importance should not be underestimated. 相似文献
248.
F. García-Rodríguez D. Metzeltin P. Sprechmann R. Trettin G. Stams L.F. Beltrán-Morales 《Journal of Paleolimnology》2004,32(2):117-135
Paleolimnological data are presented on trophic development in relation to sea level variation in Rocha Lagoon, a 72 km2 coastal lagoon in southern Uruguay. Using sediment cores that extended to ∼20,000 yr BP, analyses of grain size, organic matter, carbonate, total carbon, nutrients, and diatoms allowed us to infer changes in trophic state and paleosalinities, which were closely related to Holocene relative sea level variation. Higher trophic states were observed during regressive events, most probably due to increases in runoff and erosion as regressions progressed. Diatom Association Zones (DAZ) were identified in both cores. Those DAZ corresponding to transgressive events were dominated by marine/brackish taxa and relatively low organic matter and nutrient values, while those DAZ corresponding to regressive events showed increases in brackish/freshwater diatoms and both organic matter and nutrients. Although the lagoon formed after the first Holocene marine transgression, our data indicate the existence of a marine/brackish aquatic system during upper Pleistocene (i.e., before 15,000 yr BP), but by ∼20,000 yr BP, the system was still likely to be a semi-arid terrestrial system. 相似文献
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