The response of an elastic half‐space under a momentary shear line impulse

The response of an ideal elastic half‐space to a line‐concentrated impulsive vector shear force applied momentarily is obtained by an analytical–numerical computational method based on the theory of characteristics in conjunction with kinematical relations derived across surfaces of strong discontinuities. The shear force is concentrated along an infinite line, drawn on the surface of the half‐space, while being normal to that line as well as to the axis of symmetry of the half‐space. An exact loading model is introduced and built into the computational method for this shear force. With this model, a compatibility exists among the prescribed applied force, the geometric decay of the shear stress component at the precursor shear wave, and the boundary conditions of the half‐space; in this sense, the source configuration is exact. For the transient boundary‐value problem described above, a wave characteristics formulation is presented, where its differential equations are extended to allow for strong discontinuities which occur in the material motion of the half‐space. A numerical integration of these extended differential equations is then carried out in a three‐dimensional spatiotemporal wavegrid formed by the Cartesian bicharacteristic curves of the wave characteristics formulation. This work is devoted to the construction of the computational method and to the concepts involved therein, whereas the interpretation of the resultant transient deformation of the half‐space is presented in a subsequent paper. Copyright © 2003 John Wiley & Sons, Ltd.     

Metamorphism in Archaean greenstone belts: calculated fluid compositions and implications for gold mineralization

An inescapable consequence of the metamorphism of greenstone belt sequences is the release of a large volume of metamorphic fluid of low salinity with chemical characteristics controlled by the mineral assemblages involved in the devolatilization reactions. For mafic and ultramafic sequences, the composition of fluids released at upper greenschist to lower amphibolite facies conditions for the necessary relatively hot geotherm corresponds to those inferred for greenstone gold deposits (X_CO2= 0.2–0.3). This result follows from the calculation of mineral equilibria in the model system CaO–MgO–FeO–Al₂O₃–SiO₂–H₂O–CO₂, using a new, expanded, internally consistent dataset. Greenstone metamorphism cannot have involved much crustal over-thickening, because very shallow levels of greenstone belts are preserved. Such orogeny can be accounted for if compressive deformation of the crust is accompanied by thinning of the mantle lithosphere. In this case, the observed metamorphism, which was contemporaneous with deformation, is of the low-P high-T type. For this type of metamorphism, the metamorphic peak should have occurred earlier at deeper levels in the crust; i.e. the piezothermal array should be of the ‘deeper-earlier’type. However, at shallow crustal levels, the piezothermal array is likely to have been of ‘deeper-later’type, as a consequence of erosion. Thus, while the lower crust reached maximum temperatures, and partially melted to produce the observed granites, mid-crustal levels were releasing fluids prograde into shallow crustal levels that were already retrograde. We propose that these fluids are responsible for the gold mineralization. Thus, the contemporaneity of igneous activity and gold mineralization is a natural consequence of the thermal evolution, and does not mean that the mineralization has to be a consequence of igneous processes. Upward migration of metamorphic fluid, via appropriate structurally controlled pathways, will bring the fluid into contact with mineral assemblages that have equilibrated with a fluid with significantly lower X_CO2. These assemblages are therefore grossly out of equilibrium with the fluid. In the case of infiltrated metabasic rocks, intense carbonation and sulphidation is predicted. If, as seems reasonable, gold is mobilized by the fluid generated by devolatilization, then the combination of processes proposed, most of which are an inevitable consequence of the metamorphism, leads to the formation of greenstone gold deposits predominantly from metamorphic fluids.     

Elastic solutions for stresses in a transversely isotropic half‐space subjected to three‐dimensional buried parabolic rectangular loads

In many areas of engineering practice, applied loads are not uniformly distributed but often concentrated towards the centre of a foundation. Thus, loads are more realistically depicted as distributed as linearly varying or as parabola of revolution. Solutions for stresses in a transversely isotropic half‐space caused by concave and convex parabolic loads that act on a rectangle have not been derived. This work proposes analytical solutions for stresses in a transversely isotropic half‐space, induced by three‐dimensional, buried, linearly varying/uniform/parabolic rectangular loads. Load types include an upwardly and a downwardly linearly varying load, a uniform load, a concave and a convex parabolic load, all distributed over a rectangular area. These solutions are obtained by integrating the point load solutions in a Cartesian co‐ordinate system for a transversely isotropic half‐space. The buried depth, the dimensions of the loaded area, the type and degree of material anisotropy and the loading type for transversely isotropic half‐spaces influence the proposed solutions. An illustrative example is presented to elucidate the effect of the dimensions of the loaded area, the type and degree of rock anisotropy, and the type of loading on the vertical stress in the isotropic/transversely isotropic rocks subjected to a linearly varying/uniform/parabolic rectangular load. Copyright © 2002 John Wiley & Sons, Ltd.     

9711号北上台风演变及暴雨过程的位涡诊断分析

通过对 971 1号台风登陆北上穿过山东造成山东特大暴雨过程的湿位涡的分析 ,并从湿位涡的角度研究了台风演变及山东特大暴雨的形成机制 ,揭示了冷空气在台风演变及暴雨过程中的重要作用。结果表明 :倾斜涡度发展是暴雨产生和台风加强的重要机制之一 ,暴雨产生在 θe线陡立密集区内 ;湿位涡在这次暴雨过程中对流层低层具有 MPV1 <0 ,MPV2 >0的特征 ,此次暴雨产生在负的MPV1等值线密集区中 ;对流层上部及平流层下部高位涡的下传使得低层斜压性增大 ,引起低层的对流稳定度减小 ,促使气旋性涡度发展 ,有利于位势不稳定能量的释放 ,使得暴雨增幅 ,导致台风的加强并演变为温带气旋。     

北京地区两次沙尘(暴)天气过程对比分析

通过对 2 0 0 0年 4月 6日和 4月 9日北京地区两次沙尘 (暴 )天气过程的对比分析认为 :蒙古气旋型和不伴有气旋的西北槽型所造成的北京沙尘天气的严重程度不同 ;沙源地区中低层较强上升运动的主要作用是将当地沙尘垂直输送到空中 ,然后在70 0hPa较强西北气流的引导下将卷起的沙尘水平输送到下游地区 ;不稳定层结又加强了沙尘天气 ;沙尘暴区上空z 螺旋度分布的特征是高层为负值 ,低层为正值 ,对流层中低层螺旋度正的大值区与卫星云图显示的沙尘暴区具有较好的一致性 ,对沙尘暴的预报有一定的指示意义     

四川新康风化淋滤型海泡石的热相变研究

以四川新康风化淋滤型海泡石为研究对象，利用X射线衍射分析和红外光谱分析技术，对海泡石的热相变过程及特征进行了研究。结果发现，四川新康风化淋滤型海泡石的相变过程与沉积型、热液型海泡石相变过程明显不同，其相变过程可以划分为两个阶段：800℃以下保持海泡石相；800℃以上海泡石相转化为斜顽辉石相。     

清代陕南秦巴山地的人类行为及其与环境的关系

对人类行为空间特征认识的不足,是地理学人地关系理论与实践研究的主要障碍。本文以文化、风俗、政策等影响人类行为的人文因素为切入点,运用时空剖面分析法,考察了清代陕南流民空间行为选择的基本取向。结果表明,人类空间选择行为遵循风俗相近原则,而不是地理环境最优原则。追求单位时间上效果最大化是流民行为选择的普遍趋势。人类空间行为的选择性强化了自然差异的等级和水平,不同区域人类行为结果的外部关联性,指出传统的仅从区域内部或某一种人类行为来寻求简单的"人—地"因果关系的缺陷。从系统或流域的观点来考察人类环境行为的相互影响关系,是认识和把握人地关系实质与机理的重要途径。     

双相各向异性介质中弹性波方程的有限元解法及波场模拟

基于双相各向异性介质模型,首先推导了双相各向异性介质中弹性波传播的动力学方程及其Galerkin变分方程和有限元运动方程,然后给出了孔隙弹性波方程的有限元数值解法以及二维双相PTL介质中波场模拟的人为吸收边界条件. 最后,利用本文给出的有限元方法对双相PTL介质和双相各向同性介质中的弹性波传播进行了数值模拟. 结果表明:有限元方法和吸收边界条件有效、可行,在理想相界条件下,不论是从固体位移,还是从流体位移的波场快照都能看到明显的慢速拟P波;在黏滞相界情况下,能否观察到慢速拟P波,与含流体地层介质的耗散性质有关.对实际含流体介质,从流体位移分量的波场快照比从固体位移波场快照更容易观察到慢速拟P波.     

韩国济州岛柑橘园景观与空间分布演变（1526—2019年）

韩国济州岛的柑橘园景观具有重要的文化遗产价值,是当地人利用济州岛特殊的气候、水文、植被环境所塑造的独特农业景观。16世纪朝鲜王朝建立柑橘进贡制度,济州官府设置柑橘园,此后至今,济州岛柑橘园区域分布与地理景观都呈现较大变迁。文章结合气候、水资源等自然因素与韩国柑橘产业政策、市场、社会变化与技术进步等人文因素,分析16世纪以来济州岛柑橘园景观与空间分布变化,探讨济州岛柑橘生产空间变迁原因与驱动力。结果显示：16世纪至2019年,济州岛柑橘生产经历了发展、没落、强力复兴的大起大落发展历史,呈现从北到南的生产空间大迁移,柑橘生产空间逐渐扩大。济州岛的柑橘园生产经历从朝鲜时期的官府果园到现代观光体验农场的转变。柑橘生产空间变迁与地理景观变化的原因与驱动力较复杂,水资源是影响朝鲜时期柑橘园分布的主要自然因素。社会制度、交通与市场是16世纪以来影响柑橘园生产空间扩展的主要人文因素,在近500年的柑橘生产空间发展变迁的过程中,人文因素不断加强,影响柑橘空间与地理景观的优化调整。20世纪70年代以来,水资源开发技术的进步改变了现代柑橘园生产空间分布格局。对济州岛柑橘园长时段的生产空间与地理景观变化及其作用机制的研究,可以为中国传统柑橘栽培地区打造具有地方特色柑橘园文化景观与民俗、文化产品,以及中国柑橘产业的升级发展提供参考。     

基于地理视角的智慧城市规划与建设的理论思考

智慧城市建设是推动城镇化发展的重要动力,其建设除了技术支撑之外,还应充分考虑信息技术对城市政府、企业和居民活动及其空间的影响。本文在对国内智慧城市建设现状与问题分析思考的基础上,认为智慧城市的出现是适应当前城市化战略转型、公共服务提升、社区发展和城市问题解决的必然趋势,从多源异构数据整合、信息系统和空间分析平台两个方面梳理智慧城市建设的关键技术,从流动空间以及新的人地关系、时空协调发展等方面提出智慧城市的理论支撑,并进一步明确地理学应对和研究重点。同时,提出基于城市地理研究的智慧城市规划与建设实践的主要方向,包括顶层设计、功能和空间布局、基础设施整合、城乡治理等内容。