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161.
本文在总结拉尔玛矿床中自然金及共生矿物一般特点的基础上,对自然金的矿物学和化学组成进行了较系统地研究。提出了决定自然金形成及在矿石、矿物中配分的主要地质因素。 相似文献
162.
The terrestrial noise in the differencial data of geomagnetic total field recorded at 21h in North China was fitted by using
the geomagnetic vector data from Beijing Observatory. The terrestrial noise level and its spatial feature in this region was
discussed. A method, which may be useful for justifying the quality of fitting, was provided in this paper. The analysis indicates
that the terrestrial noise is one of the important noise in tectonomagnetic study. It is shown that the susceptibility effect
is quite small and the orientation effect is the main component in the terrestrial noise in North China. The rough spatial
feature of the magnetic anomaly in crustal substance was infered from the spatial feature of terrestrial noise. The measurement
precision and the source noise level of data at 21h in this region were obtained in the analysis of residual noise.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 441–447, 1993. 相似文献
163.
Evaluating the effect of land development on sediment transport using a probability density function
T. V. Hromadka II R. J. Whitely 《Stochastic Environmental Research and Risk Assessment (SERRA)》1993,7(2):102-108
An important problem in sedimentation analysis is the development of a channel section that preserves, as best as possible, the current sedimentation regime even though the flood frequency tendencies have been altered due to land development within the catchment. In order to accomplish this task, a methodology is needed that estimates sediment transport capacity for various channel configurations. Such a procedure is described which allows the computation of the total sediment transport capacity for each of several T-year return frequency runoff hydrographs. This information is used to obtain an approximate probability distribution for the total sediment transport capacity, and the mean and standard deviation of this distribution are computed.Comparing the results for the catchment in its present state with a future developed state, using a selection of new channel parameters, indicates how to improve the channel to control changes in sedimentation due to development. The analysis procedure provides a basis for estimating a new channel configuration such that the new flow conditions retain, as best as possible, the existing condition sedimentation effects, and hence retain the natural sediment supply and transport trends even though runoff flow rates have changed due to land development within the catchment.The results of Wilson Creek are typical of the several sites examined, see Table 3 below. The T=2, T=5, T=25, and T=100 year values for total sediment transport capacity, in kilotons, are 6.9, 39.4, 61.3, and 96.7 with a mean of 17.1 and standard deviation of 19.3. After development with no change in the channel the respective values increase to: 17.9, 84.6, 128.1, and 258.0 with a mean of 39.1 and standard deviation of 44.3. A new channel can be constructed which will reduce these sediment transport capacity values, after development, to 5.2, 41.0, 62.0, and 124.8 with a mean of 17.4 and standard deviation of 22.0. 相似文献
164.
165.
两次岫岩震群的特征及其预报意义研究 总被引:3,自引:1,他引:2
本文对1988年1月、1999年11月岫岩两次震群的性质及序列特征作了较系统的分析和研究。结果表明:序列各项特征参数及预测指标都显示出了具有明确意义的预报信息。特别是1999年11月前震序的低b值、低h值及多台小震初动符号和波形特征的高度一致性和稳定性都预示着震源区应力的高度集中和稳定,也为短临预报提供了可靠的信息。此外,前震序列的频度分布的时间结构和能量释放的时间过程也明确显示出“密集-平静-发震”和“增强-减弱-发震”的特点。这种临震预报特征与海域地震前震活动的时空结构和时空过程十分相似。本文还讨论了两震群之间特殊部位发生断层贯通的可能性,并给出震级上限的估计。 相似文献
166.
This study uses a numerical model to investigate the groundwater flow and salt transport mechanisms below islands in the Okavango Delta. Continuous evapotranspiration on the islands results in accumulation of solutes and the formation of a saline boundary layer, which may eventually become unstable. A novel Lagrangian method is employed in this study and compared to other numerical methods. The numerical results support the geophysical observations of density fingering on Thata Island. However, the process is slow and it takes some hundreds of years until density fingering is triggered. The results are sensitive to changes of the hydraulic gradient and the evapotranspiration rate. Small changes may lead to different plume developments. Results further demonstrate that density effects may be entirely overridden by lateral flow on islands embedded in a sufficiently high regional hydraulic gradient. 相似文献
167.
Numerical and analytical solutions are presented for the elastic and inelastic response of single‐degree‐of‐freedom yielding oscillators to idealized ground acceleration pulses. These motions are typical of near‐fault earthquake recordings generated by forward rupture directivity and may inflict damage in the absence of substantial structural strength and ductility capacity. Four basic pulse waveforms are examined: (1) triangular; (2) sinusoidal; (3) exponential; and (4) rectangular. In the first part of the article, a numerical study is presented of the effect of oscillator period, strength, damping, post‐yielding stiffness and number of excitation cycles, on inelastic response. Results are presented in the form of dimensionless graphs and regression formulas that elucidate the salient features of the problem. It is shown that conventional R–µ relations may significantly underestimate ductility demand imposed by near‐fault motions. The second part of the article concentrates on elastic‐perfectly plastic oscillators. Closed‐form solutions are derived for post‐yielding response and associated ductility demand. It is shown that all three ground motion histories (i.e. acceleration, velocity, and displacement) control oscillator response—contrary to the widespread view that ground velocity alone is of leading importance. The derived solutions provide insight on the physics of inelastic response, which is often obscured by the complexity of numerical algorithms and actual earthquake motions. The model is evaluated against numerical results from near‐field recordings. A case study is presented. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
168.
玉龙斑岩铜矿含矿与非含矿斑岩元素和同位素地球化学对比研究 总被引:3,自引:3,他引:3
地质地球化学对比研究表明,玉龙含矿与非舍矿斑岩是由岩石圈地慢中交代成因的金云母-石榴石单斜辉石岩脉发生不同程度部分熔融而形成的。分矿斑岩是最早阶段熔融体,主要是由交代成因脉中副矿物(如磷灰石和碳酸盐矿物等)和舍水矿物金云母发生部分熔融而形成的,因而富含 F、Cl 和水等挥岌份,加上该阶段岩浆具有高氧化性特征,从而富含 Cu 等成矿元素;非含矿斑岩是交代成固咏相对较高熔融程度的产物,单斜辉石和石榴石介入了熔融作用,岩浆熔体相对贫乏F、Cl 和水等挥发份,加上该阶段岩浆具有较低的 f_(0_2),从而不利于成矿。斑岩体全岩的 F 和 Cl 含量(舍矿斑岩 F>1200 ppm,Cl>150 ppm;非含矿斑岩 F<1200 ppm,Cl<150 ppm)、K_2O/Na_2O(含矿斑岩>1.2,非含矿斑岩<1.2)和 Sm/Yb(含矿斑岩>6.5,非含矿斑岩<6.5)比值以及黑云母中的 Fe~(3 )/Fe~(2 )比值(含矿斑岩>0.7,非舍矿斑岩<0.7)是区分含矿与非含矿斑岩的重要地球化学参数。含矿斑岩与非分矿斑岩具有非常相似的 Sr-Nd-Pb 同位素组成,,表明含矿与非含矿班岩具有相同的源区。 相似文献
169.
170.
分析了TDRS卫星的轨道特性及传统的地基测距跟踪技术定轨精度不高的现状,研究了基于空基的用户星精密轨道的TDRS卫星定轨,解决了基于空基的一般GEO卫星定轨问题。 相似文献