Estimation of Site Effects in Beijing City

— For the realistic modeling of the seismic ground motion in lateral heterogeneous anelastic media, the database of 3-D geophysical structures for Beijing City has been built up to model the seismic ground motion in the City, caused by the 1976 Tangshan and the 1998 Zhangbei earthquakes. The hybrid method, which combines the modal summation and the finite-difference algorithms, is used in the simulation. The modeling of the seismic ground motion, for both the Tangshan and the Zhangbei earthquakes, shows that the thick Quaternary sedimentary cover amplifies the peak values and increases the duration of the seismic ground motion in the northwestern part of the City. Therefore the thickness of the Quaternary sediments in Beijing City is the key factor controling the local ground effects. Four zones are defined on the base of the different thickness of the Quaternary sediments. The response spectra for each zone are computed, indicating that peak spectral values as high as 0.1 g are compatible with past seismicity and can be well exceeded if an event similar to the 1697 Sanhe-Pinggu occurs.     

2003年淮河流域大水期间体积降水量的研究

针对 2 0 0 3年梅雨期淮河流域大水提出了体积降水量的概念及其计算方法 ,在计算出淮河流域和其各子流域逐日和总体积降水量的基础上 ,将体积降水量与水文站的水位和流量进行了对比分析。结果表明 :水位对累计体积降水量有较好的即时响应 ,流量对体积降水量有较好的延迟响应。另外 ,讨论了流域体积降水量的预报问题 ,用国内外数值天气预报产品和中央气象台指导预报产品 ,进行了流域体积降水量预报试验 ,并对预报结果进行了检验分析。结果表明 :在目前天气预报水平条件下 ,利用数值天气预报和中央气象台业务预报产品制作体积降水量是可行的 ,能够延长洪水预报的预见期 ;而且 ,数值天气预报产品在预报体积降水量方面有明显的优势 ,因此可以直接利用数值天气预报产品进行体积降水量的客观预报 ,为防汛工作提供重要的依据。     

河流调整中的熵、熵产生和能耗率的变化

河流是一个真正的开放系统,而不是孤立系统或封闭系统。运用经典热力学和非平衡态热力学基本原理,分析研究了河流调整中的熵、熵产生和能耗率的变化。指出:熵和熵产生是两个不同的概念;最小熵产生原理等价于最小能耗率原理;冲积河流在调整过程中遵循最小熵产生原理或最小能耗率原理,而不是最大熵原理。     

澜沧江中游某崩塌堆积体变形空间效应研究

某崩塌堆积体范围内布置有公路、缆机平台、电站进水口等重要建筑物。其变形稳定性直接影响到治理工程设计、施工安全以及电站的运行。因此，文章在对其环境地质条件、物质结构、形成机制分析的基础上，对其变形空间效应作系统的地质分析；并建立了相应的三维地质力学模型，应用FLAC-3D快速拉各朗日差分程序对其空间变形特征进行了详细的分析。结果表明：收口转向及变形收敛特征使得堆积体下部形成一个“支撑拱”，从而阻碍了上部堆积体向下部的变形与位移，利于堆积体的稳定；同时，三维数值模拟结果也表明：堆积体的变形具有明显的空间效应。其位移矢量表现出一定的收敛性，且变形主要分布在1360～1650m高程；变形方式表现出一定的分区特征，表现出后缘压缩固结，中部滑移，前缘受阻压缩的位移特征。纵向具有明显的收口效应；横向上比较来看，也存在变形受阻的收口特征；收口范围主要集中在1330～1440m高程范围。     

A brief comparison of lava flows from the Deccan Volcanic Province and the Columbia-Oregon Plateau Flood Basalts: Implications for models of flood basalt emplacement

The nature and style of emplacement of Continental Flood Basalt (CFB) lava flows has been a matter of great interest as well as considerable controversy in the recent past. However, even a cursory review of published literature reveals that the Columbia River Basalt Group (CRBG) and Hawaiian volcanoes provide most of the data relevant to this topic. It is interesting to note, however, that the CRBG lava flows and their palaeotopographic control is atypical of other CFB provinces in the world. In this paper, we first present a short overview of important studies pertaining to the emplacement of flood basalt flows. We then briefly review the morphology of lava flows from the Deccan Volcanic Province (DVP) and the Columbia-Oregon Plateau flood basalts. The review underscores the existence of significant variations in lava flow morphology between different provinces, and even within the same province. It is quite likely that there were more than one way of emplacing the voluminous and extensive CFB lava flows. We argue that the establishment of general models of emplacement must be based on a comprehensive documentation of lava flow morphology from all CFB provinces.     

Relationship between solar radiation and the development and morphology of small cirque glaciers (Maladeta Mountain massif, Central Pyrenees, Spain)

Abstract Spatial and temporal variations in radiative fluxes influence glacier mass‐balance in mountain areas. The primary goal of this study was to assess differences in solar radiation on three glacial cirques located in the Maladeta Mountain massif (Central Spanish Pyrenees), and analyse their implications on glacier development and morphology. A quantitative approach is adopted to obtain the values of solar radiation (direct, diffuse and global radiation), combining several field data parameters (measured at 55 control‐points) with the solar radiation modelling package Ecosim. The data obtained confirm that the morphologies of the glacial bodies developed in the three cirques have a good correlation with the spatial variation on solar radiation inputs, favouring also the conservation (Aneto and Coronas cirques) or total vanishing (Llosás cirque) of the glacial remnants analysed here. The study shows how strongly in this Alpine‐Mediterranean context solar radiation — firstly as a function of latitude and time of year, and locally as a function of topographic slope, aspect and shadowing — controls the mass‐balance and the spatial distribution of melting in small glaciers, having an effect on the development of their morphologies.     

Channel adjustments of the lower Trinity River,Texas, downstream of Livingston Dam

Channel cross‐sectional changes since construction of Livingston Dam and Lake Livingston in 1968 were studied in the lower Trinity River, Texas, to test theoretical models of channel adjustment, and to determine controls on the spatial extent of channel response. High and average flows were not significantly modified by the dam, but sediment transport is greatly reduced. The study is treated as an opportunistic experiment to examine the effects of a reduction in sediment supply when discharge regime is unchanged. Channel scour is evident for about 60 km downstream, and the general phenomena of incision, widening, coarsening of channel sediment and a decrease in channel slope are successfully predicted, in a qualitative sense, by standard models of channel response. However, there is no consistent channel response within this reach, as various qualitatively different combinations of increases, decreases or no change in width, depth, slope and roughness occur. These multiple modes of adjustment are predicted by the unstable hydraulic geometry model. Between about 60 km and the Trinity delta 175 km downstream of the dam, no morphological response to the dam is observed. Rather than a diminution of the dam's effects on fluvial processes, this is due to a fundamental change in controls of the fluvial system. The downstream end of the scour zone corresponds to the upstream extent of channel response to Holocene sea level rise. Beyond 60 km downstream, the Trinity River is characterized by extensive sediment storage and reduced conveyance capacity, so that even after dam construction sediment supply still exceeds transport capacity. The channel bed of much of this reach is near or below sea level, so that sea level rise and backwater effects from the estuary are more important controls on the fluvial system than upstream inputs. Copyright © 2005 John Wiley & Sons, Ltd.     

Analysis of the environmental sensitivities of a typical dynamic epikarst system at the Nongla monitoring site, Guangxi, China

Nongla, a typical karst dynamic system (KDS) monitoring site, is located at Nongla Village, Mashan County, Guangxi, China. The data from a Greenspan CTDP300 multichannel data logger indicates that the KDS is highly sensitive to environmental changes. Multi-day and diurnal physico-chemical composition of epikarst spring water is quite different under different climatic conditions. During a day with no rainfall, water temperature and air temperature have similar variations. Electrical conductivity (EC) has good positive correlation with pH value and water temperature. During rainstorms, the physico-chemical composition of the spring water is initially strongly effected by dilution, pH and EC drop rapidly. However, half to one hour later, EC returns to normal and the CO₂ effects will be the dominant physical effect. This is due to the high fissure rates and high permeability in the epikarst zone. Dilution effects were observed during the entire rainstorm event,whereas, it only acts during the earliest period of light rain. Therefore, it is necessary to examine the water–rock–CO₂ combination as a whole system to explain the hydrochemical behavior of epikarst processes.     

植被覆盖地表主动微波遥感反演土壤水分算法研究

主动微波遥感监测土壤水分具有全天时、全天候并对地物有一定的穿透能力等特点,突破了传统测量方法和光学遥感获取土壤水分的局限。文中在分析植被对微波信号影响的基础上,总结了当前国内外基于主动微波遥感监测植被覆盖地表土壤水分的原理和方法,指出利用,宋朝景“水-云模型”从总的极化雷达后向散射中去除植被影响后,能够改进后向散射系数和土壤含水量之间的关系。最后利用ENVISAT ASAR数据,结合实地采样获得的土壤含水量数据拟合两者之间的关系,结果表明农作物覆盖地表土壤水分变化的估算算法还需要进一步发展和改进以提高反演精度。     

Geotechnical Properties of Low Calcium and High Calcium Fly Ash

In this paper, a comparative study has been made for physical and engineering properties of low calcium and high calcium Indian fly ash. The grain size distribution of fly ash is independent of lime content. Fly ash particles of size >75 μm are mostly irregular in shape whereas finer fractions are spherical for low calcium fly ash. For high calcium fly ash, chemical and mineralogical differences have been observed for different size fractions. Compared to low calcium fly ash, optimum moisture content is low and maximum dry density is high for high calcium fly ash. Optimum moisture content is directly proportional and maximum dry density is inversely proportional to the carbon content. The mode and duration of curing have significant effect on strength and stress–strain behavior of compacted fly ash. The gain in strength with time for high calcium fly ash is very high compared to that of low calcium fly ash due to presence of reactive minerals and glassy phase.