Unified approach to amplitude attenuation and coda excitation in the randomly inhomogeneous lithosphere

A unified model is proposed for explaining the frequency dependent amplitude attenuation and the coda wave excitation on the basis of the single scattering process in the randomly inhomogeneous lithosphere. Adopting Birch's law and a direct proportion between density and wave velocity, we statistically describe the inhomogeneous medium by one random function characterized by the von Karman autocorrelation function. We calculate the amplitude attenuation from the solid angle integral of scattered wave energy on the basis of the Born approxiimation after subtracting the travel-time fluctuation effect caused by slowly varying velocity inhomogeneities. This subtraction is equivalent to neglect energy loss by scattering within a cone around the forward direction. The random inhomogeneity of the von Karman autocorrelation function of order 0.35 with the mean square fractional fluctuation of 7.2×10^–3 1.3×10^–2 and the correlation distance of 2.15.1 km well explains observed backward scattering coefficientg and the ratioQ _P ^–1 /Q _S ^–1 , and observed and partially conjecturedQ _S ^–1 for frequencies between 0.5 Hz and 30 Hz.     

An investigation of upper mantle heterogeneity beneath the Archaean and Proterozoic crust of western Canada from Lithoprobe controlled-source seismic experiments

Observations of upper mantle reflectivity at numerous locations around the world have been linked to the presence of a heterogeneous distribution of rock types within a broad layer of the upper mantle. This phenomenon is observed in wide-angle reflection data from Lithoprobe's Alberta Basement Transect [the SAREX and Deep Probe experiments of 1995] and Trans-Hudson Orogen Transect [the THoRE experiment of 1993]. SAREX and Deep Probe image the Archaean lithosphere of the Hearne and Wyoming Provinces, whereas THoRE images the Archaean and Proterozoic lithosphere of the Trans-Hudson Orogen and neighbouring areas.Finite-difference synthetic seismograms are used to constrain the position and physical properties of the reflective layer. SAREX/Deep Probe modelling uses a 2-D visco-elastic finite-difference routine; THoRE modelling uses a pseudospectral algorithm. In both cases, the upper mantle is parameterized in terms of two media. One medium is the background matrix; the other is statistically distributed within the first as a series of elliptical bodies. Such a scheme is suitable for modelling: (1) variations in lithology (e.g., a peridotite matrix with eclogite lenses) or (2) variations in rheology (e.g., lenses of increased strain within a less strained background).The synthetic seismograms show that the properties of heterogeneities in the upper mantle do not change significantly between the two Lithoprobe transects. Beneath the Trans-Hudson Orogen in Saskatchewan, the layer is best modelled to lie at depths between 80 and 150 km. Based on observations from perpendicular profiles, anisotropy of the heterogeneities is inferred. Beneath the Precambrian domains of Alberta, 400 km to the west, upper mantle heterogeneities are modelled to occur between depths of 90 and 140 km. In both cases the heterogeneous bodies within the model have cross-sectional lengths of tens of kilometers, vertical thicknesses less than 1 km, and velocity contrasts from the background of − 0.3 to − 0.4 km/s. Based on consistency with complementary data and other results, the heterogeneous layer is inferred to be part of the continental lithosphere and may have formed through lateral flow or deformation within the upper mantle.     

Structural and nutritional heterogeneity of riparian vegetation in Patagonia (Argentina) in relation to seasonal grazing by sheep

Riparian meadows of southern Patagonia are temporally and spatially heterogeneous habitats. They are thought to play a key role in regulating the dynamics of arid grazed steppes of the region. We conducted a 2-year study with sheep to determine the influence of two grazing conditions (deferment and spring grazing) on structural and nutritional parameters of three vegetation types apparently associated with a soil moisture gradient in a riparian meadow in southern Santa Cruz (Argentina). Spring deferment allowed forage accumulation in very moist and intermediate vegetation types by the beginning of the summer and had no detrimental impact on forage quality. Deferment had no effect on biomass accumulation of the drier vegetation type at our study site. Structural attributes of the vegetation appeared to affect spatial grazing patterns of sheep. Soil-related patchiness, rather than sheep grazing, appeared to control vegetation structure and nutritional value. The proportion of more mesic plant communities in riparian habitats of Patagonia could determine the outcome of plant–animal interactions in these systems. Practical recommendations of grazing capacity in paddocks, or more theoretical considerations of ecosystem dynamics of the Patagonian steppes need to explicitly consider the internal patchiness of riparian habitats.     

煤矿水害多源信息预测方法研究

基于MAPGIS平台,用Visual C＋＋对其进行二次开发,研制了煤矿水害多源信息预测系统.通过对地震、电法、水文地质等多源数据进行处理后,在MAPGIS系统下进行成图、配准和空间定量分析,建立了预测模型.用该系统对煤矿实际资料进行了处理,结果表明其预测结果较传统方法更为准确.     

碳酸盐岩油藏流动单元研究方法探讨

流动单元研究对于提高油田采收率具有很大的实际意义，该项研究在砂岩油藏研究中已取得较大进展．对于缝洞型碳酸盐岩油藏由于成因、岩性和岩石结构构造、成岩后生作用、构造断裂作用、溶蚀作用等多因素对储集空间的影响，使已有的流动单元概念及研究技术方法难于应用．针对缝洞型碳酸盐岩地质特征，论证了碳酸盐岩储层渗流屏障的存在及其类型．提出区别于砂岩油藏的缝洞型碳酸盐岩储层流动单元的概念．说明各类动态资料对油藏储层流动单元研究较为重要．提出了研究思路和方法，包括：油藏压力趋势分析法、井间生产干扰分析法、流体性质差异分析法、井间干扰试井法．并结合塔河油田实际资料。进行了初步分析．     

Numerical Calculation of Equivalent Cell Permeability Tensors for General Quadrilateral Control Volumes

A new method for upscaling fine scale permeability fields to general quadrilateral-shaped coarse cells is presented. The procedure, referred to as the conforming scale up method, applies a triangle-based finite element technique, capable of accurately resolving both the coarse cell geometry and the subgrid heterogeneity, to the solution of the local fine scale problem. An appropriate averaging of this solution provides the equivalent permeability tensor for the coarse scale quadrilateral cell. The general level of accuracy of the technique is demonstrated through application to a number of flow problems. The real strength of the conforming scale up method is demonstrated when the method is applied in conjunction with a flow-based gridding technique. In this case, the approach is shown to provide results that are significantly more accurate than those obtained using standard techniques.     

地震前兆时空非均匀性指标Cv值的实验检验

在双向加载条件下，对两种构造和介质不同的岩石标本进行变形实验，测量了标本表面不同部位的应变．在此基础上，利用王晓青和陈学忠等提出的描述地震前兆非均匀分布的参量————Cv值，分析了标本变形失稳过程中应变异常的分布，以期从实验角度检验Cv值方法并探讨其物理意义．研究表明，Cv值的变化与岩石变形特征的变化有关，是描述前兆分布非均匀性的一种有效指标；Cv值在失稳发生前先异常上升，然后下降，并在Cv值恢复过程中或恢复后伴随着失稳事件的发生．因此，Cv值是一种有效的预报指标．      

基于遥感数据的常熟市耕地资源数量动态变化分析

采用RS和GIS技术，对常熟市1984—2001年间土地利用进行调查，获得了1984、1992、1999、2001年四个时期的土地利用状况及其变化资料。通过多时期对比分析发现：1984—1992年，居民点工矿占用耕地、耕地变成水域和耕地变成交通用地，分别占耕地转出总面积的56．7％、36．6％和5．4％。1992—1999年上述各项则分别占耕地转出总面积的47．3％、45．7％和7．0％。1999——2001年分别占耕地转出总面积的2．4％、95．6％和1．3％。1999年以后农村农业结构调整已经成为耕地面积减少的主要原因，应通过制定区域农业中长期发展规划和法规进行宏观调控。     

应用MORPAS系统证据权重法进行多源信息成矿预测——以澜沧江南段地区为例

在分析了成矿预测的特点并在对澜沧江南段铜多金属的成矿规律深入研究的基础上,利用MORPAS系统抽取构置了来自地质异常场、成矿异常场和矿化异常场等多源信息的16个预测变量;把研究区划分为2.5 km×2.5 km大小的1334个统计单元,利用证据权重法的数学模型对研究区铜多金属矿产进行预测;圈定了3级成矿远景区;研究表明证据权法用于成矿预测方法简单,结果可靠性较高;利用MORPAS系统进行成矿预测可以提高工作的效率和精确度.