Small inflation sources producing seismic and infrasonic pulses during the 2000 eruptions of Miyake-jima, Japan

During the 2000 activity of Miyake-jima volcano, Japan, we detected long period seismic signals with initial pulse widths of 1-2 s, accompanied by infrasonic pulses with almost the same pulse widths. The seismic signals were observed from 13 July 2000, a day before the second summit eruption. The occurrences of the seismic signals were intermittent with a gradual increase in their magnitudes and numbers building toward a significant explosive eruption on 18 August. After the eruption, the seismic and infrasonic events ceased. The results of a waveform inversion show that the initial motions were excited by an isotropic inflation source beneath the south edge of the caldera at a depth of 1.4 km. On the other hand, the sources of the infrasonic pulses were located in the summit caldera area. The times at which the infrasonic pulses were emitted at the surface were delayed by about 3 s from the origin times of the seismic events. It is suggested that small isotropic inflations excited seismic waves in the crust and simultaneously caused acoustic waves that traveled in the conduit and produced infrasonic pulses at the crater bottom. Considering the observed time differences and gas temperatures emitted from the vent, the conduit should have been filled with vapor mixed with SO₂ gas and volcanic ash. The change of the time differences between the seismic and infrasonic signals suggests that the seismic source became shallower within half a day before the August 18 explosive eruption. We interpret the source process as a fragmentation process of magma in which gas bubbles burst and quickly released part of the pressure that had been sustained by the tensional strength of magma.     

Multifield coupling model and its applications for pile foundation in permafrost

In the construction of Qinghai-Tibet railway,to avoid diseases caused by frost heave and thaw col-lapse of frozen ground,besides the normal bridges over the rivers,a lot of dry bridge structures have been built to replace subgrade in the regions of high tem-perature and high ice content frozen soil.So,the problems on forming mechanism of bearing capacity of pile foundation in cold regions already become one of hot spot problems in frozen soil engineering.Freezing force and frost heave force ar…     

The mechanisms of paragenesis and separation of silver, lead and zinc in hydrothermal solutions

On the basis of an experimental study and thermodynamic calculation, the mechanisms of paragenesis and separation of silver, lead and zinc in the hydrothermal system have been studied. At acidic to nearly neutral pH, their chloride complexes are stable, and among them the chloride complexes of zinc are most stable. And the sulfide complexes are the dominant species at nearly neutral to alkaline pH,while the sulfide complexes of silver are most stable. With decreasing temperature, [ Cl^-] ,fO2, and increasing pH, the solubilities of silver, lead and zinc will decrease, leading to their deposition and separation. For sulfide complexes, the concentrations of reduced sulfur and pH are two important factors affecting their stabilities. Complexes of different forms and stabilities respond to the variation of conditions to different extents, which gave rise to the paragenesis and separation of silver, lead and zinc in the whole ore-forming process of dissolution, transport and deposition.     

Geographical knowledge and policy: the positive contribution of discourse studies

The 'discursive turn' has been blamed for a lack of engagement between geographers and policymakers. This paper argues that such a view is fundamentally flawed. It ignores the positive contribution that discourse analysis has made to policy studies and the particular role that geographers have played in developing such analyses. It is based on a misconceived view of the policy process and how knowledge can contribute to policy outcomes. A closer attention to policy discourses reveals exactly how knowledge is constructed within the policy process and can help identify how policy may be improved through discursive means.     

工程破坏区植被发育动态过程的研究 --以古尔班通古特沙漠为例

通过样方法及植被调查法,从纵向和横向两个不同方向对工程破坏后的沙地植被进行比较研究。在纵向上,由于植被恢复时间的不同,其恢复的程度也不同。植被恢复状况可明显的分3个阶段:定居前期(1～6a)主要以多年生羽叶三芒草和小半灌木绢蒿为主;中期(7～11a)主要以多年生小半灌木青杆沙蒿为主;后期(12～16a)主要生长着多年生麻黄及草本沙苔,地表出现大面积的生物结皮。在横向上,将恢复后期的植被与原始植被进行比较。通过对植被发育不同阶段过程中物种重要值、物种多样性、丰富度及生活型的变化等方面的调查,发现在不同阶段,各物种的重要值发生了不同的变化,物种多样性指数,均匀度指数,丰富度指数到后期均增大。     

海底热液硫化物矿体内部流体混合过程的数值模拟:以大西洋TAG热液活动区为例

大型海底热液硫化物矿体的形成机制是涉及多种控制因素的复杂地质过程,其中热液流体同海水的混合扮演着重要角色。大洋钻探计划(ODP)资料表明在大西洋TAG区热液硫化物矿体内部,热液流体同经过改造的海水之间发生着广泛的混合作用,这个过程在很大程度上控制着海底热液硫化物矿体的内部结构和化学组成。以TAG热液硫化物矿体为例,利用数值模拟方法模拟了热液流体与经过不同程度改造的海水的混合过程,试图探讨海水与热液流体混合在热液硫化物矿体形成中的作用。模拟计算结果表明:(1)来自矿体深部的热液流体与经围岩加热的下渗海水的混合是造成TAG热液活动区硬石膏大量沉淀的重要原因;(2)在热液流体与海水的混合过程中,混合流体的化学性质和矿物沉淀情况在330~310℃上下发生了较大变化,330~310℃是一个特殊的温度区域;(3)利用数值计算结果探讨了TAG热液活动区不同区块(TAG-1,TAG-2和TAG-5等)的流体混合作用和热液活动过程。     

区域地下水污染调查取样点布设量化分配方法

在区域尺度、有限样品的地下水污染调查中,密度控制可以计算区域总样品数量,但取样点布设应综合考虑地质环境、人类活动等方面的差异性。目前,样点布设主要依赖技术人员经验,存在较强的不确定性,如何科学布设取样点是需要解决的一个科学问题。针对这个问题,文章基于实际工作创建了“区域预分配、单元再优选”的解决方法。在区域上,基于层次分析法构建量化分配模型,以背景控制因素和潜在污染因素建立分配因子组合,运用指数标度量化定性因子、标度函数计算定量因子,通过矩阵运算获取每个分配单元的样品预分配数量;在单元内,按照分段控制、条件优选的方法提高取样点针对性和代表性。利用构建的分配方法,以拉萨河流域地下水水质调查为案例进行了取样点布设分配应用,确定了各单元样品分配数量。结果表明:考虑背景控制和潜在污染的层次分析模型及量化计算平衡了拉萨河流域不同分配单元对样品的实际需求,解决了城关区面积小样品需求多、当雄县面积大样品需求少等问题;分段控制、条件优选的方法明确了分配单元内取样点选择依据。本方法的构建为地下水污染调查取样点布设提供了必要的方法支撑。     

潮水盆地铀成矿水文地球化学研究

在分析潮水盆地自然地理、地质背景及水文地质特征的基础上，对盆地铀成矿水文地球化学特征进行了探讨。结果表明：潮水盆地为-渗入型自流水盆地，其深层地下水中铀存在形式为UO2(CO3)n^2-2n。；从盆地边缘到盆地中心具有明显从氧化环境到还原环境的水文地球化学分带特征，水中铀经历了由溶滤迁移到还原沉淀的矿化过程；在盆地北缘的照壁山-白芨芨、阿右旗-陶家井地区，西南部的平易-平山湖地区具备十分有利的铀成矿条件和良好的铀成矿远景。     

氧化铬对铝型材厂碱蚀渣制备铝方柱石材料结构的影响

利用铝型材厂碱蚀渣为主要原料,采用二步煅烧工艺制备铝方柱石材料。探索二次煅烧温度对铝型材厂碱蚀渣制备铝方柱石材料相组成、结晶度、微观结构的影响,进而研究氧化铬对铝方柱石材料相组成、微观结构的影响。采用同步热分析、X射线衍射、扫描电镜及相关分析软件表征制备的铝方柱石材料的相组成和显微结构。结果表明：铝型材厂碱蚀渣中有大量可烧失成分,物料需要进行致密化处理,再经过1500℃煅烧后的铝方柱石材料结构中具有明显的铝方柱石条柱状结构,结晶度增大,铝方柱石相对含量达到91%。随着氧化铬加入量增加,结构中的铝铬酸钙相增加。当氧化铬加入量为2%时,试样中结晶相的结晶度最高,形成条柱状铝方柱石相与立方状铝铬酸钙相共存的结构。当氧化铬加入量4%时,试样中铝方柱石相几乎消失,结晶度降低。