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991.
992.
Breaching in fine sands and the generation of sustained turbidity currents in submarine canyons 总被引:6,自引:0,他引:6
Abstract Natural, moderately loosely packed sands can only erode from the surface of the bed after an increase in pore volume. Because of this shear dilatancy, negative pore pressures are generated in the bed. In cases of low permeability, these negative pressures are released relatively slowly, which retards the maximum rate of erosion. This effect is incorporated in a new, analytically derived, pick‐up function that can explain the observation of gradual retrogressive failure of very steep subaqueous slopes, sometimes more than 5 m high, in fine non‐cohesive sands. This process, termed ‘breaching’ in the field of sediment dredging, may produce large failures in sand bars or river banks. The analytical function that describes the breaching process in fine sand is incorporated in a one‐dimensional, steady‐state numerical model of turbidity currents describing the spatial development of flow. This model is applied to simulate a large ‘flushing’ event in Scripps Submarine Canyon, Pacific coast of California. Breach retrogradation and the successive evolution in time of the resulting turbidity current in the canyon are predicted in a sequence of discrete steps. Predicted velocities are compared with values measured during a flushing event. Implications for the interpretation of deep‐water massive sands are discussed. 相似文献
993.
994.
矿业权管理制度与矿业权市场对促进矿业经济健康发展具有十分重要的意义,本对矿业权及其价值进行了界定,分析了中国矿业权市场发展现状,矿业权及矿业权市场的特性,在此基础上,对中国矿业权市场未来发展提出了建议。 相似文献
995.
An academic geophysical research as a regional gravity survey was made during 1994 in the Western White Nile to infer the shallow crustal structures in the area. The result of the survey was compiled as a Bouguer anomaly map with a contour interval of 2 ×10-5m/s2. It is found that the negative residual anomalies are related to the Upper Cretaceous sediments (Nubian Sandstone Formation) filling all depressions in the Basement complex surface while the positive residual anomalies are attributed to the relatively shallow or outcropping Basement rocks and the steep gravity gradients are resulting from the sharp contacts between the sedimentary infill and the Basement rocks. To define the geological structures in the area, 9 profiles were studied. For each of the profiles, measured and computed Bouguer gravity anomalies, crustal density model, subsurface geology evaluation were performed. A G-model computer program was applied in the gravity modeling, which is based on the line-integral method of gravity computation. A geological/structural map was proposed showing inferred sedimentary basins, faulting troughs and uplifted Basement block and tectonic trends. The basins are believed to be fault-controlled which developed by extensional tectonics (pull-apart mechanism). As for the mechanism and cause of faulting, the area is considered as a part of the Central Sudan rift system which had been subjected to several tectonic events since Early Cambrian to Tertiary times which resulted in the formation of several fracture systems associated with block subsidence, rifting and basin formation. 相似文献
996.
997.
为了检验高密度电法和瞬变电磁法在城市活断层探测中的有效性 ,在福州市区及周围进行了试验探测① ,文中主要介绍对八一水库尚干断裂的探测结果。八一水库尚干断裂是一条穿过福州市区的主要断裂带 ,其主断裂在八一水库测区位于一条由新店通往古城的水泥马路东侧 ,在横向上表现为东西宽几十米的电阻率低异常带 ,在纵向上从盖层底部向下延伸到基底深处。试验表明 ,高密度电法和瞬变电磁法可以互相补充和验证 ,从而提高整体探测效果 相似文献
998.
Torben Mikkelsen Hans E. Jørgensen Morten Nielsen Søren Ott 《Boundary-Layer Meteorology》2002,105(3):483-505
Concentration fluctuation data from surface-layer released smokeplumes have been investigated with the purpose of finding suitable scaling parametersfor the corresponding two-particle, relative diffusion process.Dispersion properties have been measured at downwind ranges between 0.1 and 1 km from a continuous, neutrally buoyant ground level source. A combinationof SF6 and chemical smoke (aerosols) was used as tracer. Instantaneous crosswind concentration profiles of high temporal (up to 55 Hz) and spatialresolution (down to 0.375 m) were obtained from aerosol-backscatter Lidar detectionin combination with simultaneous gas chromatograph (SF6) reference measurements. The database includes detailed crosswind concentration fluctuation measurements. Each experiment, typically of 1/2-hour duration, containsplume mean and variance concentration profiles, intermittency profiles andexceedence and duration statistics. The diffusion experiments were accompanied by detailed in-situ micrometeorological mean and turbulence measurements. In this paper, a new distance-neighbour function for surface-released smoke plumes is proposed, accompanied by experimental evidence in its support. The new distance-neighbour function is found to scale with the surface-layer friction velocity,and not with the inertial subrange dissipation rate, over the range of distance-neighbour separations considered. 相似文献
999.
Introduction In the years when the reliable data could not be obtained and in the analysis of strain property and magnitude in history, the intensity, property and activity pattern of strain field were mainly inferred on the bases of geometric characters of surface traces and behaviors (especially the faults) as well as the characteristics of petrology (XIE, et al, 1993; Molnar, Tapponnier, 1975, 1977; Tapponnier, Molnar, 1977; FU, et al, 2000). However, they are the averaged results accumu… 相似文献
1000.
我国钻孔应力-应变地震前兆监测台网的现状 总被引:10,自引:3,他引:10
当今的地震成因理论表明:地震是地应力(应变)积累到一定程度,使断层滑动而发生的。由此可见地应力-应变观测的重要性。我国的钻孔应力-应变地震前兆监测网,是全国地震前兆监测台网的一个组成部分。观测对象包括:体应变,分量应变,分量应力和钻孔应力-应变差应变。文章通过分析调查结果,比较详细地介绍了我国的钻孔应力-应变地震前兆监测台网的现状。 相似文献