La crue torrentielle du Bez (Hautes-Alpes,Briançonnais), 24 juillet 1995

Résumé

À la suite d’un violent orage, une lave torrentielle d’un volume supérieur à 100 000 m³ s’est répandue sur le cône de déjection du torrent du Bez, provoquant des dégâts considérables aux infrastructures. Les observations réalisées durant l’événement et les investigations menées dans le bassin versant nous permettent de mieux comprendre le déclenchement de cette lave. Le flot boueux marquant le début de l’événement a été en grande partie alimenté par les ravinements affectant le haut du bassin versant. La lave à blocs qui a suivi s’est nourrie quant à elle des dépôts morainiques recouvrant la rive gauche du torrent, dans la partie inférieure du bassin versant. Au lendemain de la crue, on pouvait observer deux grandes entailles d’une profondeur maximale de 15 m. L’instabilité des berges qui en résultait a alors été rapidement enrayée par d’importants travaux de terrassements et d’enrochements. © Elsevier, Paris     

改进的PS探测方法及其应用

提出一种改进的永久散射体PS(Persistent Scatterer)探测方法,首先基于时序SAR影像的振幅信息,利用振幅和振幅离差指数双阈值法获取PS候选点,然后根据干涉相位空间相关性,对所有候选点进行相位稳定性分析,筛选出既满足雷达反射强度高、又符合散射稳定性要求的真实PS点,最后基于所选PS点提取形变信息。选取上海市局部区域作为实验区,以16幅TerraSAR-X(TSX)影像为数据源,进行PS探测和形变信息提取。结果表明,相比于已有的PS探测方法,本文方法能够更准确、可靠地识别出时序SAR影像中的PS点。形变结果显示,研究区域内最大沉降速率为-51mm/a,平均沉降速率为-15.8mm/a,以水准实测数据进行检核,验证了基于改进的PS探测方法进行地表形变信息提取结果的可靠性。     

PSI技术在地表形变监测中的应用研究

基于时序SAR影像准确识别PS是永久散射体合成孔径雷达干涉(PSI)技术建模及形变信息提取中最为关键的问题之一。本文提出了一种改进的PS探测算法,它是基于时序SAR影像的振幅信息,利用振幅和振幅离差指数双阈值法获取PS候选点,对所有候选点进行相位稳定性分析,筛选出既满足雷达反射强度高、又符合散射稳定性要求的真实PS点,并基于所选PS点提取形变信息。实验结果表明,相比于已有PS探测方法,本文所提出的方法能够更准确、可靠地识别出时序SAR影像中的PS目标,进而提高了PSI形变探测结果的精度和可靠性。     

储层岩石流动电位频散特性的数学模拟

利用储层岩石流动电位的频散特性评价复杂储层已经成为勘探地球物理领域关注的热点,但是目前还没有形成基于储层岩石储渗特性及电化学性质的具有普遍指导意义的理论方法和数学模型.本文利用微观毛管理论,通过随时间谐变条件下渗流场和电流场的耦合模型,建立了描述储层岩石流动电位频散特性的数学方法,定量分析了频率域储层岩石动态渗透率、动电耦合系数和流动电位耦合系数随储层岩石孔隙度、溶液浓度和阳离子交换量的变化规律.研究结果表明:储层岩石流动电位频散特性是储层流体惯性力与流体黏滞力相互作用的结果.储层岩石孔隙度越大,储层维持流体原有运动状态的能力越大,临界频率越小;储层岩石的溶液浓度和阳离子交换量对临界频率没有影响.储层岩石的孔隙度越大,流体流动能力越强,流动电位各耦合系数的数值越大;溶液浓度越小或阳离子交换量越大,孔隙固液界面的双电层作用越强,各耦合系数的数值越大.     

Practical modified scheme of linear shallow-water equations for distant propagation of tsunamis

A simple but practical numerical model describing a distant propagation of tsunamis is newly proposed by introducing an additional term to the existing modified scheme. The numerical dispersion of the proposed model is manipulated to replace the physical dispersion of the linear Boussinesq equations without any limitation. The new model developed in this study is applied to propagation of a Gaussian hump over a constant water depth and the predicted free surface displacements are compared with available analytical solutions. A very reasonable agreement is observed.     

More on the evolution of bed material waves in alluvial rivers

Sediment waves or pulses can form in rivers following variations in input from landslides, debris flows, and other sources. The question as to how rivers cope with such sediment inputs is of considerable practical interest. Experimental, numerical and field evidence assembled by the authors suggests that in mountain gravel‐bed streams, such pulses show relatively little translation, instead mostly dispersing in place. This research has recently been the subject of discussion. In particular it has been suggested that (a) the equations of flow and sediment mass balance used in the analyses, and in most other morphodynamic analyses, require correction; (b) the dominance of dispersion appears only because the hyperbolic nature of the governing equations has not been adequately considered; and (c) the sediment transport equation used in the analyses does not lead to generalizable results. Here we suggest that (a) the relations for mass balance do not require the indicated correction; (b) the hyperbolic nature of the governing equations does not preclude the result of dispersion dominating translation in mountain streams; and (c) the general behaviour of an appropriate hyperbolic model of sediment waves (pulses) includes the relative roles of dispersion and translation, and is not affected by the precise choice of a sediment transport relation (as long as the choice is reasonable for the case in question). Copyright © 2005 John Wiley & Sons, Ltd.     

A Practical Method for Accurate Measurement of Trace Level Fluorine in Mg‐ and Fe‐Bearing Minerals and Glasses Using Electron Probe Microanalysis

Fluorine plays an important role in magmatic and hydrothermal processes, but due to its low abundance in geological samples determining F is difficult by electron probe microanalysis. By using a W‐Si multi‐layered pseudocrystal as the diffraction crystal instead of thallium acid phthalate (TAP), count rates were considerably higher, which however introduced spectral interferences between FKα and FeLα and MgKβ lines when normal integral mode is applied. In this study, we developed a protocol using a W‐Si multi‐layered pseudocrystal for measuring accurately trace level F in both minerals and glasses. First, we used differential mode with an optimised PHA (pulse height analysis) setting in signal processing, instead of normal integral mode, which completely eliminated the second‐order MgKβ line. Second, the overlap of the first‐order FeLα on FKα peak, which cannot be filtered by modifying the PHA setting, was calibrated quantitatively using F‐free minerals and silicate glasses. Applying this two‐step method, F was determined in a number of reference glasses, as well as in glasses synthesised from powders of the rock reference materials AC‐E, GS‐N and DR‐N. Our data are consistent within error with F concentrations determined by other methods, demonstrating the reliability of this method.     

川西海相气田高含硫天然气集输装置泄漏快速模拟方法

川西气区已经开发多年,海相气藏的开发已经成为气田发展的必然趋势。川西海相气井中高含H2S,高含硫集输装置发生泄漏事故将引发毒性气体扩散,毒性气体会对周围一定距离的公众造成损害。本文通过分析川西人口密集区高含硫天然气泄漏扩散分布规律,对高斯扩散模型参数选取方法进行优化,设计了一种快速分析评价方法,形成一套针对集输管道含硫天然气、净化厂脱硫装置含H2S天然气泄漏的扩散模拟程序,实现对气体泄漏扩散后果的快速模拟。以彭州1井为例,模拟分析不同地形参数条件下集输管线、净化厂脱硫装置发生泄露后在风速0.5 m/s、1.5 m/s时的扩散模拟情况,及泄漏扩散后硫化氢浓度1 000 ppm、100 ppm所能到的最远安全距离,为确定公众防护距离评价提供决策支持。     

Significant Difference in Dimming Magnitude Between Urban and Rural Regions in China and Its Implication for Surface Temperature

The climatology and long term trends of sunshine duration (SSD), total cloud amount (TCC) and surface temperature are studied based on surface observations at 84 stations across China from 1961 to 2009. These stations were classified into metropolis, large city, small city and rural station based on their populations and specific station locations. Difference in SSD and its implication for surface temperature among four station categories are analyzed. Different SSD decreasing rates among four station categories were found. The maximum decreasing rate occurred at metropolis stations (-89.2 h per decade) and the minimum rate occurred at rural station (-54.1 h per decade). TCC also showed a negative trend. The correlation coefficients between decadal variability of SSD and TCC were significantly positive, which implied that the dimming during this period was apparently not explained by TCC. Among all station categories, the maximum temperatures (Tmax) showed a similar positive trend, however, the minimum temperatures (Tmin) increased much faster at urban stations than at rural stations. This suggested that the faster decline of SSD at urban stations could partly dampen the effect of urban heat island on Tmax.