Mineral precipitation associated with vertical fault zones: the interaction of solute advection,diffusion and chemical kinetics

This article is concerned with chemical reactions that occur between two interacting parallel fluid flows using mixing in vertical faults as an example. Mineral precipitation associated with fluid flow in permeable fault zones results in mineralization and chemical reaction (alteration) patterns, which in turn are strongly dependent on interactions between solute advection (controlled by fluid flow rates), solute diffusion/dispersion and chemical kinetics. These interactions can be understood by simultaneously considering two dimensionless numbers, the Damköhler number and the Z‐number. The Damköhler number expresses the interaction between solute advection (flow rate) and chemical kinetics, while the Z‐number expresses the interaction between solute diffusion/dispersion and chemical kinetics. Based on the Damköhler and Z‐numbers, two chemical equilibrium length‐scales are defined, dominated by either solute advection or by solute diffusion/dispersion. For a permeable vertical fault zone and for a given solute diffusion/dispersion coefficient, there exist three possible types of chemical reaction patterns, depending on both the flow rate and the chemical reaction rate. These three types are: (i) those dominated by solute diffusion and dispersion resulting in precipitation at the lower tip of a vertical fault and as a thin sliver within the fault, (ii) those dominated by solute advection resulting in precipitation at or above the upper tip of the fault, and (iii) those in which advection and diffusion/dispersion play similar roles resulting in wide mineralization within the fault. Theoretical analysis indicates that there exists both an optimal flow rate and an optimal chemical reaction rate, such that chemical equilibrium following focusing and mixing of two fluids may be attained within the fault zone (i.e. type 3). However, for rapid and parallel flows, such as those resulting from a lithostatic pressure gradient, it is difficult for a chemical reaction to reach equilibrium within the fault zone, if the two fluids are not well mixed before entering the fault zone. Numerical examples are given to illustrate the three possible types of chemical reaction patterns.     

Following the Money: Corruption,Conflict, and the Winners and Losers of Suburban Land Acquisition in China

Land acquisition in suburban China is not merely the administrative means through which land is transferred from collectively owned rural land to state‐owned urban land; it is also a process of unlawful profit grabbing by rent‐seeking stakeholders. This licentiousness has been the source of intense controversy in recent years, becoming a major source of social unrest in contemporary China. Although standards of compensation are legally governed by strict policies, these standards are rarely followed as prescribed. As a result, we know very little about how revenue from land acquisition is shared in practice. This is because, as a contentious political issue rife with corrupt practices, accurate data are extremely difficult to obtain. This paper aims to address this vast empirical gap by tracing the flow of profit proliferation and distribution in a land acquisition case, using a suburban village in Shandong province, China, as an example. To expedite the drawn‐out acquisition process, the local government permits the corrupt behaviour of the village party secretary, who exploits his position to amass a great personal fortune. In contrast to previous research, which emphasises low compensation standards or excessive profit grabbing by local government, we find that villagers' protests are triggered by the corrupt practices of the village party secretary.     

Modelling the Lost City hydrothermal field: influence of topography and permeability structure

The Lost City hydrothermal field (LCHF) is hosted in serpentinite at the crest of the Atlantis Massif, an oceanic core complex close to the mid‐Atlantic Ridge. It is remarkable for its longevity and for venting low‐temperature (40–91°C) alkaline fluids rich in hydrogen and methane. IODP Hole U1309D, 5 km north of the LCHF, penetrated 1415 m of gabbroic rocks and contains a near‐conductive thermal gradient close to 100°C km^?1. This is remarkable so close to an active hydrothermal field. We present hydrothermal modelling using a topographic profile through the vent field and IODP site U1309. Long‐lived circulation with vent temperatures similar to the LCHF can be sustained at moderate permeabilities of 10^?14 to 10^?15 m² with a basal heatflow of 0.22 W m^?2. Seafloor topography is an important control, with vents tending to form and remain in higher topography. Models with a uniform permeability throughout the Massif cannot simultaneously maintain circulation at the LCHF and the near‐conductive gradient in the borehole, where permeabilities <10^?16 m² are required. A steeply dipping permeability discontinuity between the LCHF and the drill hole is required to stabilize venting at the summit of the massif by creating a lateral conductive boundary layer. The discontinuity needs to be close to the vent site, supporting previous inferences that high permeability is most likely produced by faulting related to the transform fault. Rapid increases in modelled fluid temperatures with depth beneath the vent agree with previous estimates of reaction temperature based on geochemical modelling.     

Experimental study of the effect of variation in in‐situ stress on capillary residual trapping during CO2 geo‐sequestration in sandstone reservoirs

During a geo‐sequestration process, CO₂ injection causes an increase in reservoir pore pressure, which in turn decreases the reservoir net effective stress. Changes in effective stress can change all the reservoir and cap‐rock properties including residual saturations. This article presents the results of an experimental work carried out to understand the potential change in the volumes of residually trapped CO₂, while the porous medium tested underwent change in the net effective stress under in‐situ reservoir conditions of pore pressure and temperature. The experimental results obtained show that an initial 1725 psi (11.9 MPa) decrease in the net effective pressure caused 1.4% reduction in the volumes of residually trapped CO₂, while another 1500 psi (10.3 MPa) reduction caused a further 3.2% drop in the residual saturation of CO₂.     

Large-scale Debris Flow Disasters: Hazard-Risk-Vulnerability Analysis Approach in Taiwan

Catastrophic disasters may cause irreversible damage to cultural heritage. This study identified the risk to cultural heritage sites in Taiwan posed by large-scale debris flow disasters. The cultural heritage sites that may be affected by debris flows were identified through risk identification and by using GIS. Subsequently, an on-site field survey was conducted to confirm the cultural heritage sites that are potentially vulnerable to debris flow disasters. The research findings are as follows: (a) the top three cultural heritage sites that are most affected by debris flows are municipal, county, and city monuments, historical buildings, and historical sites; (b) the number of cultural heritage sites affected is related to environmental exploitation; (c) the cultural heritage sites at high risk of being affected by disasters were primarily located in Taitung and Chiayi Counties.     

1995-2010年中国省际人口迁移态势与空间格局演变——基于社会网络分析的视角

采用第五次人口普查、2005年人口抽样调查和第六次人口普查数据,基于社会网络分析的视角,研究了省级尺度下中国人口迁移态势与空间格局演变特征。结果显示:(1)1995-2010年间,中国人口迁移规模迅速增大,省际间人口迁移规模差异明显;上海、浙江人口迁入率显著上升,河南、安徽人口迁出率显著上升。(2)北京、上海、安徽、四川等13省是我国人口迁移网络的核心节点,人口迁移网络表现出中心性、收敛性和地区非均衡性特点。(3)京津地区、长三角地区、广东是我国主要人口辐合流场,安徽、四川、河南、湖南等中部省份是我国主要人口辐散流场。研究表明,不同地区的人口迁移有显著的空间异质性,各地应根据自身人口迁移趋势及在全国人口迁移网络中角色,科学制定区域人口政策与经济社会发展规划。     

我国旅游流研究进展与展望

旅游流研究是旅游地理学研究的核心问题之一,为了总结我国旅游流研究成果,找出我国旅前流研究的不足并指出未来的研究方向,本文对1987-2010年我国旅游流文献进行了梳理。我国旅游流研究历程可以划分为起步、成长和发展三个阶段,可划分为时间分布特征、空间结构特征、时空演化特征、影响因素、驱动机制和规模预测等六类研究主题,但我国旅游流研究也存在六方面的不足,特别是要深入挖掘研究内容,创新研究方法,以推动我国旅游流研究更进一步发展。     

中国城市间交通流强度的空间格局

以全国321个地级以上行政区为研究对象,基于城市间汽车、火车和航空班次联系测算各城市对外联系强度,通过核密度估计、位序-规模及探索性空间数据分析,对多元交通流视角下城市间交通流强度的空间格局进行提取和解析。研究表明:在整个城市体系中,高位次城市规模凸显,中小规模城市有待于进一步发育。基于公路和铁路联系的城际交通流分别表现为由沿海向内陆逐级减弱、以国家铁路大动脉沿线为中心的核心-边缘结构;基于航空联系的城际交通流表现出高度极化和点状镶嵌特征。     

地铁站点可达性、客流与站点商圈零售商业结构关系研究——以广州市为例

地铁与城市商业地域的结构存在极大关系。实地调查获取广州15个地铁站点商圈零售商业营业面积、地铁网络等数据,利用栅格分析方法计算不同地铁站点的可达性程度的差异性。运用回归模型分析不同地铁站点可达性、客流与站点商圈零售商业空间结构的相关关系。以广州天河市级商业中心为例,微观上分析地铁站点客流对商业中心空间结构的影响。结果表明:地铁站点交通可达性、客流量与站点零售商业营业面积存在较强关联性,但换乘站点的可达优势与客流优势在商业上未能完全体现;地铁客流与较高等级的商业存在较大的相关性,而与低等级的商业相关性小,甚至负相关;客流的增加促进了地铁附近的商业形态从传统零售业向更高级业种演化。