永胜6.0级地震的余震S波分裂研究

利用云南永胜 6 0级地震的余震资料对该区S波分裂进行了研究。结果表明 ,快速横波偏振方向有两个优势取向 :N2 0°W和N6 0°W ,前者与区域主压应力方向一致 ,后者则为永胜地震主破裂方向。可以认为 ,永胜地震的S波分裂是应力作用的EDA裂隙与发震破裂隙共同作用的结果。延迟时间在 2～ 2 0ms km范围内变化 ,整个时段的平均值为 7 0ms km。与以前许多学者的研究结果比较 ,本文的结果与之在量级上是比较相符的     

周期性层状介质中超声波传播的实验研究

实验研究了韵律层结构和超声波探测频率对弹性波波速和波形的影响。实验中所使用的超声波频率为 2 4 0kHz ,韵律层由不同厚度的钢板和有机玻璃板构成。研究表明 ,当λi/di<4 (i=1 ,2 ) (λi 为超声波在介质i中传播时的波长 ,di 为韵律层中介质i的厚度 )时 ,韵律层的波速近似等于 2种介质的时间平均速度 ;当λi/di>5 (i=1 ,2 )时 ,其速度开始显著地降低 ,并趋向于有效介质波速的Reuss下限 (VRp)。韵律层的结构对于透射波的波形有显著的影响。特别是当λi/di 接近于 6时 ,透射波波形非常简单 ,并且其透射波的振幅显著地降低。因此波形简单并不一定对应着简单的介质结构。由于弹性波在韵律层中的传播速度以及波形与探测频率有关 ,因此在利用地震测深结果分析岩石圈结构 ,推断其物质组成时应该充分考虑地震测深频率和地壳结构对分析结果的影响     

2003年7～9月固原地电阻率异常变化分析

针对固原台视电阻率2003年7月出现的趋势上升变化,在环境、气候调查的基础上,利用水平层状介质模型反演固原台电性分层结构,计算了降雨量和地下水对其视电阻率的影响,认为大量降雨和地下水上升造成了该台视电阻率的上升。     

中国北方兴蒙地区叠合盆地砂岩型铀成矿特征及勘查方法综述

中国北方兴蒙地区发育多个中大型叠合盆地,盆地内均发现大型、特大型铀矿床,且最近又有许多新的找矿突破。兴蒙地区叠合盆地在铀成矿及勘查方法等方面具有很多共性。研究发现,铀成矿作用受特定的构造样式和构造演化阶段控制,有利的沉积相主要发育于盆地发展的坳陷期,局部为断陷期,在断陷期和断坳转换期形成了盆地内铀成矿的还原介质,在挤压隆升剥蚀期,构造反转、地层掀斜剥蚀形成剥蚀窗口,有利于含矿流体的运移。盆地内铀成矿作用的类型为:①潜水、潜水-层间和层间氧化作用;②同沉积成矿;③构造热事件叠加成矿;④多种流体混合作用成矿。根据这些成矿特征,盆地内的铀矿勘查可通过以下方式进行:①铀源体可通过源-汇系统进行厘定;②成矿流场和成矿通道通过反转抬升剥蚀窗口和有利沉积相厘定;③沉积建造、油气逸散场可利用其物性特征(电性、放射性等)进行厘定。地质及物化探方法组合可有效地完成上述勘查。     

多孔介质界面对重非水相液体迁移过程影响的图像法研究

重非水相液体(dense nonaqueous phase liquid,DNAPL)污染土壤和地下水的问题已引起广泛关注,研究其在不同粒径多孔介质及其界面的运移特征形态是确定污染区域、修复治理土壤和地下水环境的前提。文章通过室内试验研究多孔介质界面对DNAPL运移与分布特性的影响。首先在二维砂槽上进行DNAPL污染物的入渗试验,试验过程中用数码相机拍照,将DNAPL扩散过程以图像的形式记录下来;然后用AutoCAD对图片进行处理,绘制出DNAPL迁移过程的锋面变化图。结果表明:DNAPL入渗过程中,迁移主要受到重力作用与毛细作用的控制,毛细作用力随着介质粒径的增大逐层减小,重力作用逐渐起主导作用使污染物入渗速度逐层增大;介质结构影响DNAPL的迁移形态,介质粒径逐层增大,DNAPL污染物的渗流面与指进扩散宽度逐层减小,扩散方式由面状变为指状;在不同粒径介质界面介质结构发生突变时,DNAPL迁移锋面线曲率也相应变大,此时DNAPL的迁移呈现“凸”型特征,另外,不同的界面横向扩散的滞留宽度不同,随着介质粒径的增大,界面的横向扩散宽度相对变短。     

基于行波分离的VTI介质逆时偏移

现阶段,各向同性介质假设已经不能满足复杂地质构造条件下的成像需求,忽略介质各向异性影响会使速度估计不准确,成像精度降低。为此,笔者从VTI介质一阶速度—应力方程出发,利用Poynting矢量特性对地震波进行方向行波分离,得出了基于上下行波分离的互相关成像条件,并将其应用在复杂VTI介质中。通过层状模型和SEG/EAGE岩丘模型测试验证了该算法的有效性以及在成像上的优越性;另外,当偏移速度不准确时,本文方法仍能够有效压制偏移噪声,成像质量更佳。     

饱和非均质介质中PCE的运移分布与修复研究

重非水相液体(DNAPLs)泄漏进入土壤-地下水环境成为长期污染源,给人类健康及生态环境带来严重威胁。将四氯乙烯(PCE)作为特征污染物,通过二维砂箱实验探究饱和非均质介质中PCE的运移分布,及Tween 80溶液对PCE的去除效果。采用透射光法监测运移与修复过程,定量评估PCE的修复效率。结果表明,由于PCE无法克服毛细压力,在低渗透性介质上方聚积污染池;由于拉断效应,PCE在运移路径上以离散状形式存在。离散状PCE与Tween 80溶液的有效接触面积大,易被优先溶解去除,控制着修复效率。Tween 80溶液对离散状PCE修复效果显著,可作为有效的修复溶剂选用。     

Analysis of solute transport with a hyperbolic scale-dependent dispersion model

An empirical hyperbolic scale-dependent dispersion model, which predicts a linear growth of dispersivity close to the origin and the attainment of an asymptotic dispersivity at large distances, is presented for deterministic modelling of field-scale solute transport and the analysis of solute transport experiments. A simple relationship is derived between local dispersivity, which is used in numerical simulations of solute transport, and effective dispersivity, which is estimated from the analysis of tracer breakthrough curves. The scale-dependent dispersion model is used to interpret a field tracer experiment by nonlinear least-squares inversion of a numerical solution for unsaturated transport. Simultaneous inversion of concentration-time data from several sampling locations indicates a linear growth of the dispersion process over the scale of the experiment. These findings are consistent with the results of an earlier analysis based on the use of a constant dispersion coefficient model at each of the sampling depths.     

Flow and transport through two-dimensional isotropic media of binary conductivity distribution. Part 2: NUMERICAL simulations and comparison with theoretical results

In the present part the results of numerical simulations of flow and transport in media made up from circular inclusions of conductivity K that are submerged in a matrix of conductivity K ₀, subjected to uniform mean velocity, are presented. This is achieved for a few values of =K/K ₀ (0.01, 0.1 and 10) and of the volume fraction n (0.05, 0.1 and 0.2). The numerical simulations (NS) are compared with the analytical approximate models presented in Part 1: the composite elements (CEA), the effective medium (EMA), the dilute system (DSA) and the first-order in the logconductivity variance (FOA). The comparison is made for the longitudinal velocity variance and for the longitudinal macrodispersivity. This is carried out for n<0.2, for which the theoretical and simulation models represent the same structure of random and independent inclusions distribution. The main result is that transport is quite accurately modeled by the EMA and CEA for low , for which _L is large, whereas in the case of =10, the EMA matches the NS for n<0.1. The first-order approximation is quite far apart from the NS for the values of examined . This material is based upon work supported by the National Science Foundation under Grant No. 0218914. Authors also wish to thank the Center of Computational Research, University at Buffalo for assistance in running numerical simulations.     

Random domain decomposition for flow in heterogeneous stratified aquifers

We study two-dimensional flow in a layered heterogeneous medium composed of two materials whose hydraulic properties and spatial distribution are known statistically but are otherwise uncertain. Our analysis relies on the composite media theory, which employs random domain decomposition in the context of groundwater flow moment equations to explicitly account for the separate effects of material and geometric uncertainty on ensemble moments of head and flux. Flow parallel and perpendicular to the layering in a two-material composite layered medium is considered. The hydraulic conductivity of each material is log-normally distributed with a much higher mean in one material than in the other. The hydraulic conductivities of points within different materials are uncorrelated. The location of the internal boundary between the two contrasting materials is random and normally distributed with given mean and variance. We solve the equations for (ensemble) moments of hydraulic head and flux and analyze the impact of unknown geometry of materials on statistical moments of head and flux. We compare the composite media approach to approximations that replace statistically inhomogeneous conductivity fields with pseudo-homogeneous random fields. This work was performed under the auspices of the US Department of Energy (DOE): DOE/BES (Bureau of Energy Sciences) Program in the Applied Mathematical Sciences contract KC-07–01–01 and Los Alamos National Laboratory under LDRD 98604. This work made use of STC shared experimental facilities supported by the National Science Foundation under Agreement No. EAR-9876800. This work was supported in part by the European Commission under Contract No. EVK1-CT-1999–00041 (W-SAHaRA).