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81.
William Blumen 《地球物理与天体物理流体动力学》2013,107(1-3):89-104
Abstract Adiabatic, two-dimensional, steady-state finite-amplitude, hydrostatic gravity waves produced by flow over a ridge are considered. Nonlinear self advection steepens the wave until the streamlines attain a vertical slope at a critical height zc. The height zc , where this occurs, depends on the ridge crest height and adiabatic expansion of the atmosphere. Dissipation is introduced in order to balance nonlinear self advection, and to maintain a marginal state above zc. The approach is to assume that the wave is inviscid except in a thin layer, small compared to a vertical wavelength, where dissipation cannot be neglected. The solutions in each region are matched to obtain a continuous solution for the streamline displacement δ. Solutions are presented for different values of the nondimensional dissipation parameter β. Eddy viscosity coefficients and the thickness of the dissipative layer are expressed as functions of β, and their magnitudes are compared to other theoretical evaluations and to values inferred from radar measurements of the stratosphere. The Fourier spectrum of the solution for z ≫ zc is shown to decay exponentially at large vertical wave numbers n. In comparison, a spectral decay law n ?-8/3 characterizes the marginal state of the wave at z = zc . 相似文献
82.
Ivan G. Wong James R. Humphrey Janet A. Adams Walter J. Silva 《Pure and Applied Geophysics》1989,129(3-4):369-405
In the summer of 1984, a three-dimensional, high-resolution microearthquake network was operated in the vicinity of two coal mines beneath Gentry Mountain in the eastern Wasatch Plateau, Utah. During a six-week period, approximately 3,000 seismic events were observed of which the majority were impulsive, higher frequency (>10 Hz), short duration (<2–3 sec) events probably associated with the caving of the roof from a longwall operation. In contrast, 234 of the largest located events appeared to occur predominantlybeneath the mines to a depth of 2 to 3 km consistent with previous studies. The magnitudes of these events ranged from less thanM
c
0 to 1.6. In addition to the unusual depths of these latter events, an anomalous aspect displayed by the events was an apparent dilatational focal mechanism suggesting a non-double-couple, possibly implosional source. Implosional events have been observed in other studies of mine seismicity; however, the generally inadequate instrumental coverage of the focal sphere has cast some doubt on the validity of such mechanisms. Previously suggested source mechanisms for such implosional events have included tensional failure through strata collapse, and a shear-implosional displacement mechanism. Shear failure must be involved in the failure process of the Gentry Mountain implosional events as evidenced by well-defined shear waves in the observed seismograms. Simultaneous monitoring in the East Mountain coal mining area to the south by the University of Utah revealed typical shear failure events mixed with implosional events. The observed double-couple, reverse focal mechanisms at East Mountain were similar to mechanisms determined in previous studies and a composite focal mechanism determined in this study for a sequence outside the mining areas. This suggested that the shear events within the mining areas are being influenced by the regional tectonic stress field. Thus in addition to the seismic events associated with caving of the roof from the longwall operation, there appear to be at least two other types of mining-induced seismic events occurring in the eastern Wasatch Plateau, both submine in origin: (1) events characterized by apparent non-double-couple possibly implosional focal mechanisms and well-defined shear waves; and (2) shear events, which are indistinguishable from tectonic earthquakes and may be considered mining triggered earthquakes. The small mining-induced stress changes that occur beyond a few hundred meters from the mine workings suggest both types of seismic events are occurring on critically stressed, pre-existing zones of weakness. Topography, overburden, method of mining, and mine configuration also appear to be significant factors influencing the occurrence of the implosional submine events. 相似文献
83.
Mark Francek 《地球表面变化过程与地形》1988,13(2):183-186
The roadcuts of Belize's Mountain Pine Ridge feature numerous coarsely textured earth pillars less than 10 cm in height. Preferential impregnation of iron occurs over a buried pebble resulting in a dripline. The higher concentration of iron along the buried pebble's dripline is later oxidized and exposed to the surface by rainsplash erosion. For slopes greater than five degrees, the intensity of sheetwash erosion is great enough to remove pillars. Earth pillar genesis thus seems a function of laterization, slope angle, and sheetwash intensity. 相似文献
84.
本文分析了广东山区工业发展的有利条件与存在问题,提出山区工业发展要采取超常规,跳跃式发展战略,立足本地优势资源,发展资源型工业,重点发展以生物资源为原料的工业,把资源优势转变为经济优势,同时根据市场需求发展市场型工业,尤其高新技术工业;既要立足理现有工业,加速改造挖潜,促其上水平、上规模、出效益、又要选准项目,大胆投入,发展有造血功能的骨干企业并调整和优化工业结构。 相似文献
85.
86.
天山高山冰缘环境的融冻泥流作用 总被引:2,自引:0,他引:2
根据实地观测结果分析,本文得出:天山冰缘环境发育的融冻泥流分布在海拔2500─3600m间的阴坡。融冻泥流发育要求地下含水丰富,粒度以细粉砂为主,地表坡度10─31°。融冻泥流的形态多数为长宽比小于1的叶状,少量为舌状。融冻泥流表面平均运动速度为11.14cm/a,舌前缘前进的平均速度的1.86cm/a,中轴部位的运动速度比两侧大。 相似文献
88.
南太行——中条山植物区系地理研究 总被引:8,自引:0,他引:8
南太行—中条山地区是中国种子植物区系研究薄弱地区之一。本区约有种子植物1627种,隶属618属142科。通过该区种子植物各类地理成分分析及与相关地区的比较,得出:本地区植物区系具有温带区系特点,又具有温带向亚热带区系过渡性质,是华北植物区系分区南部亚区的一条重要界线。该地区存在许多古老及残遗植物,表明该区系起源古老,同时也是产生新分化的中心之一。 相似文献
89.
本文利用矿山爆破,进行了地形对地面运动影响的观测研究.9次爆破的结果表明,山顶处位移和速度的谱曲线的峰区较山前和其它测点的集中,振幅的量值也大,其放大倍率约为3,其中与山体走向平行的水平分量放大得最大,与之垂直的次之,而垂直于地面的最小;山顶测点不同分量上最大位移所对应的周期接近,其对山前的放大量值近于2,也是水平分量大于垂直分量;山顶处地面运动的延续时间取决于爆破的药量和方式,山前等测点延时的放大为3-4倍,也是水平分量大于垂直分量.山顶上地面运动的这种特殊性,是由于入射波所激发的山体共振所引起的. 相似文献
90.
新疆阿拉套山花岗岩类的岩石化学 总被引:6,自引:0,他引:6
新疆阿拉套山南坡东西向展布的花岗岩石的岩石化学研究表明,本区同时存在I型和S型两种类型的花岗岩,其分布受构造环境控制,靠近古板块缝合线为I型花岗岩分布区、远离古板块缝合线为S型花岗岩分布区。源岩性质和作用强弱等因素可能是造成岩石化学成分差异的原因。 相似文献