2-D Versus 3-D Magnetotelluric Data Interpretation

In recent years, the number of publications dealing with the mathematical and physical 3-D aspects of the magnetotelluric method has increased drastically. However, field experiments on a grid are often impractical and surveys are frequently restricted to single or widely separated profiles. So, in many cases we find ourselves with the following question: is the applicability of the 2-D hypothesis valid to extract geoelectric and geological information from real 3-D environments? The aim of this paper is to explore a few instructive but general situations to understand the basics of a 2-D interpretation of 3-D magnetotelluric data and to determine which data subset (TE-mode or TM-mode) is best for obtaining the electrical conductivity distribution of the subsurface using 2-D techniques. A review of the mathematical and physical fundamentals of the electromagnetic fields generated by a simple 3-D structure allows us to prioritise the choice of modes in a 2-D interpretation of responses influenced by 3-D structures. This analysis is corroborated by numerical results from synthetic models and by real data acquired by other authors. One important result of this analysis is that the mode most unaffected by 3-D effects depends on the position of the 3-D structure with respect to the regional 2-D strike direction. When the 3-D body is normal to the regional strike, the TE-mode is affected mainly by galvanic effects, while the TM-mode is affected by galvanic and inductive effects. In this case, a 2-D interpretation of the TM-mode is prone to error. When the 3-D body is parallel to the regional 2-D strike the TE-mode is affected by galvanic and inductive effects and the TM-mode is affected mainly by galvanic effects, making it more suitable for 2-D interpretation. In general, a wise 2-D interpretation of 3-D magnetotelluric data can be a guide to a reasonable geological interpretation.     

采用等效弹簧边界分析埋地管线在沉陷情况下的反应

场地的不均匀沉陷是导致埋地管线破坏重要原因之一.到目前为止,国内外对沉陷区埋地管线的反应分析甚少.为了真实地分析管线在沉陷情况下的反应,通过引入一个非线性弹簧,作为分析埋地管线在沉陷情况下反应的边界条件,以代替远处直线段管线的变形,将管线模拟成四节点薄壳单元,土介质简化为弹塑性弹簧,采用线性位移加载来模拟土体的沉陷作用,对有限元模型进行计算分析.通过实例计算,得出了管线的控制力,找出了管线的控制截面,为沉陷区埋地管线的设计提供一定的理论依据.     

位场曲化平积分方程的迭代解

提出了位场曲化平的新方法. 给定观测曲面S上的位场、S对下方水平面P的相对高程,确定P上的位场. 利用由P向上延拓到S的积分式,建立这两个面上位场及相对高程三者所满足的方程,它是第一类Fredholm积分方程. 用Fourier逆变换式把这一空间域积分式化为波数域积分式,再由指数函数的Taylor展开进一步化为级数式. 积分方程的解采用逐次逼近法迭代计算,即用S上的位场观测值作为P上位场的初始迭代值,用导出的级数式求得S上的位场计算值、由S上的位场观测值与计算值之差校正P上的位场,多次迭代,直到满足迭代终止准则. 我们还给出该积分方程的波数域迭代计算方法. 模型算例表明,重力异常曲化平的均方差和磁异常曲化平的均方差分别为0.0008 mGal和0.0019 nT,在主频为2.26 GHz的笔记本电脑运行,2048×2048数据量,计算时间是975 s. 野外磁场实际资料处理也证实这种方法的有效性.     

不同温压条件下蛇纹岩和角闪岩中波速与衰减的各向异性

在实验室中研究了蛇纹岩和角闪岩样品在不同温压条件下的纵、横波速度和Q值．这两种岩样对应的主要组成矿物叶蛇纹石和普通角闪石都具有很强的晶格优选方位（LPO）．随着围压的增加,波速和Q值均增大,但是在相互正交的三个方向上（垂直或平行于层理面及线理方向）增大的速度并不相同,这与微裂隙的逐渐闭合密切相关．在600MPa的围压下升高温度直到600℃以上,由于微裂隙的热扩张受到约束,波速和Q值下降幅度很小．观测到的波速和Q值的各向异性具有不同的机理,波速各向异性主要与定向分布的微裂隙和主要矿物的LPO等构造因素有关;高围压下纵波Q值各向异性与速度各向异性正好相反,可能是由于形成层理面的定向排列的平板状矿物晶体沿不同方向边界之间接触程度不同造成的．     

ICT切片重构模型的剖切及应用

在ICT切片重构模型的可视化中,为了分析重构模型的任意截面形状,并且观察该截面的内部结构,需要对重构模型进行剖切.本文针对剖切提出一种简单方法,该方法利用剖切面对重构模型所在的立方体图像空间进行剖切,生成交点集合,然后将空间剖切平面映射到二维图像平面上,最后计算空间剖切平面图像的灰度值,得到剖面图像.通过剖面图像,可以直观地看到内部结构形状,为后续无损检测奠定基础.     

基于无人机摄影的地震形变场测量技术研究

采用当前方法测量地震形变场时,不能有效去除地震图像中存在的噪声,得到的测量结果与实际结果之间的误差较大,存在抗干扰性差和测量精准度低的问题。提出基于无人机摄影的地震形变场测量技术,对无人机摄影得到的主图像和辅图像做配准处理,采用SAR处理器处理图像数据,得到干涉图。利用SUSAN算法检测干涉图的边缘,通过K均值方法划分模板区域中存在的特征值类别,根据划分结果得到干涉图的相关参数和噪声区域,结合非线性扩散方法和SUSAN算法完成干涉图的去噪处理,依据基线估计去除干涉图中存在的平地效应,利用网络流算法完成相位解缠,获得地形相位值,绘制地震形变图,完成地震形变场的测量。实验结果表明,所提方法的抗干扰性强、测量精准度高。     

Efficiency of base isolation systems in structural seismic protection and energetic assessment

This paper concerns the seismic response of structures isolated at the base by means of High Damping Rubber Bearings (HDRB). The analysis is performed by using a stochastic approach, and a Gaussian zero mean filtered non‐stationary stochastic process is used in order to model the seismic acceleration acting at the base of the structure. More precisely, the generalized Kanai–Tajimi model is adopted to describe the non‐stationary amplitude and frequency characteristics of the seismic motion. The hysteretic differential Bouc–Wen model (BWM) is adopted in order to take into account the non‐linear constitutive behaviour both of the base isolation device and of the structure. Moreover, the stochastic linearization method in the time domain is adopted to estimate the statistical moments of the non‐linear system response in the state space. The non‐linear differential equation of the response covariance matrix is then solved by using an iterative procedure which updates the coefficients of the equivalent linear system at each step and searches for the solution of the response covariance matrix equation. After the system response variance is estimated, a sensitivity analysis is carried out. The final aim of the research is to assess the real capacity of base isolation devices in order to protect the structures from seismic actions, by avoiding a non‐linear response, with associated large plastic displacements and, therefore, by limiting related damage phenomena in structural and non‐structural elements. In order to attain this objective the stochastic response of a non‐linear n‐dof shear‐type base‐isolated building is analysed; the constitutive law both of the structure and of the base devices is described, as previously reported, by adopting the BWM and by using appropriate parameters for this model, able to suitably characterize an ordinary building and the base isolators considered in the study. The protection level offered to the structure by the base isolators is then assessed by evaluating the reduction both of the displacement response and the hysteretic dissipated energy. Copyright © 2003 John Wiley & Sons, Ltd.     

Influence of natural radioactivity on creep rate

Steady-state creep in the earth's mantle is controlled by the diffusion coefficient and by the distances traveled by defects between sources and sinks. In this paper, we investigate the role played by additional vacancies created by natural radioactivity. According to recent studies, bombardment of solids by energetic particles can act as a perturbation. The resulting strain rate is proportional to the rate of vacancy creation and, contrary to ordinary creep mechanisms, is only weakly dependent on the temperature and the energy necessary to create those vacancies; it is independent of the grain size. The strain rate is of the same order of magnitude as the diffusion mechanism but smaller than the dislocation-climb rate by two to three orders of magnitude. Consequently, the strain rate produced by natural radioactivity does not play a major role in the observed rate of deformation, although it could constitute a lower limit to the creep rate and act as a regulatory mechanism. Furthermore, being less strongly affected by temperature and the vacancy-formation energy than are the other mechanisms, it is also less strongly affected by depth.     

基于遗传算法和统计学的电阻率测深二维反演研究

本文介绍了一种以遗传算法和统计学为基础的反演方法,该方法利用一维反演结果的统计学特征确定地层电性结构并设计初始模型,使用遗传算法修改模型,经过二维有限单元法正演达到拟合误差最小,从而完成电阻率测深数据的二维反演.这个方法的优点在于不需要解大型线性方程组,降低计算量,先判断地层电性结构,反演后给出用地电断面表示的直观的解释结果.理论模型试算和模型实验证明该方法效果较好.     

Study on displacement field generated by aftershocks in Landers earthquake fault zone and its adjacent areas

Introduction The displacement field produced by earthquake can be measured on the Earth surface. The displacement field variation with time can be used to study lots of geodynamics parameters such as the Earth′s viscosity structure (Nur and Mavko, 1974; Sun et al, 1994; Deng et al, 1998), after-slip distribution (Shen et al, 1994; Reilinger et al, 2000), etc. Furthermore, earthquake also pro-duces lots of aftershocks, which have nearly the same focal mechanism as the main shock (e.g. Hard…     

核电厂设计地震动评定中的构造法和概率法结果比较

剖析和比较了地震危险性分析方法(综合概率法)和地震构造法的结果,认为,不能简单将构造法的结果作为概率法的上限,也不能确定在10-4的概率水平上,概率法结果就比构造法结果大,因此评定核电厂极限安全地震应同时使用构造法、概率法和其它方法,并取各种结果的最大值     

兰德斯地震断层面及其附近余震产生的位移场研究

根据兰德斯(Landers)地震断层面及其附近余震目录计算这些余震产生的位移场, 并与根据兰德斯地震破裂面滑动分布计算的主震产生的位移场进行对比. 结果表明, 断层面及其附近余震产生位移场的方向与主震大体一致, 余震破裂总体来看是继承性的. 余震产生的位移场达厘米量级, 足可以被GPS观测所捕获. 在利用地震震后随时间变化位移场研究地球粘性结构、 地震震后滑动分布等地球物理问题时, 扣除余震产生的位移场可以最大限度地减小反演结果的不确定性, 得到符合实际的结果.      

苏05井数字化水位雨荷效应的处理与改正

根据苏05井水位受降雨影响具有滞后“记忆”效应的特点,利用褶积滤波方法,对苏05井水位的雨荷效应进行处理和改正。处理结果表明,井水位与固体潮理论值的相关系数由处理前的0．24l上升为改正后的0．65l,达到未受降雨影响的水平,因此对于受降雨影响严重的井孔水位进行降雨量的改正是有效而又极其必要的。     

在SeisDps实时系统中用零点、极点计算ML的过程

在SeisDps地震处理软件的实时系统中,不是用系统的幅频特性计算震级ML,而是利用台站的零点、极点和增益,将记录的数字地震波形仿真成伍德-安德森地震仪记录的波形,计算具有3 大优点的ML震级,本文主要介绍用零点、极点和增益计算ML的过程。     

电离层预报模型研究

当利用无线电电磁波进行远程通信、卫星导航时,传递信号要受到电离层的影响,因此,对电离层中电子含量的研究显得特别重要.虽然国际上有几种电离层的电子含量预报模型,但其预报只能精确到电子含量的50%～60%.本文提出了一种新的电离层电子含量预报方法:即用球谐函数对IGS(国际GPS服务)所给出的离地面450 km高的球面上的每一网点的电离层电子含量进行拟合,对不同的时间所得到的拟合系数所形成的时间序列用时间序列分析理论中的ARMA(p,q)模型进行预报,从而实现全球的电离层电子含量预报.利用本方法对2004年和2005年IGS所给电离层电子含量资料在地理框架中做了分析预报,5天内电子含量预报相对精度在90%左右.     

On the meridional circulation and balance of momentum in the Southern Ocean of POP

 The circulation of the Southern Ocean is studied in the eddy-resolving model POP (Parallel Ocean Program) by an analysis of zonally integrated balances. The TEM formalism (Transformed Eulerian Mean) is extended to include topography and continental boundaries, thus deviations from a zonally integrated state involve transient and standing eddies. The meridional circulation is presented in terms of the Eulerian, eddy-induced, and residual streamfunctions. It is shown that the splitting of the meridional circulation into Ekman and geostrophic transports and the component induced by subgrid and Reynolds stresses is identical to a particular form of the zonally integrated balance of zonal momentum. In this balance, the eddy-induced streamfunctions represent the interfacial form stresses by transient and standing eddies and the residual streamfunction represents the acceleration of the zonal current by density fluxes in a zonally integrated frame. The latter acceleration term is directly related to the surface flux of density and interior fluxes due to the resolved and unresolved eddies. The eddy-induced circulation is extremely vigorous in POP. In the upper ocean a shallow circulation, reversed in comparison to the Deacon cell and mainly due to standing eddies, appears to the north of Drake Passage latitudes, and in the Drake Passage belt of latitudes a deep-reaching cell is induced by transient eddies. In the resulting residual circulation the Deacon cell is largely cancelled and the residual advection of the zonal mean potential density is balanced by diapycnal eddy and subgrid fluxes which are strong in the upper few hundred meters but small in the ocean interior. The balance of zonal momentum is consistent with other eddy-resolving models; a new aspect is the clear identification of density effects in the zonally integrated balance. We show that the wind stress and the stress induced by the residual circulation drive the eastward current, whereas both eddy species result in a braking. Finally, we extend the Johnson–Bryden model of zonal transport to incorporate all relevant terms from the zonal momentum balance. It is shown that wind stress and induction by the residual circulation carry an eastward transport while bottom form stress and the stress induced by standing eddies yield westward components of transport. Received: 26 June 2001 / Accepted: 2 November 2001     

一种波速结构的两步优化反演策略

借助虚拟反演思路,通过对各种遗传算子不同匹配方式的比较研究,指出了对于频散曲线反演浮点数编码与轮盘赌选择的匹配方式离线性能最好,提出了一种两步优化反演策略.该两步策略利用浮点数编码、轮盘赌选择、浮点数均匀交换与变异算子匹配组成基本遗传算法框架,在此框架基础上施加免疫启发策略和免重复计算加速策略,多次运行,对每次运行结果继续施加模拟退火算法使其至少达到局部最优,最后取得最优解.免疫启发策略充分利用最佳个体的信息加速进化进程,通过对每代的最佳个体施加一服从标准正态分布的随机数来加强对邻近区域的局部搜索,通过标准差的调整也兼顾了对邻近区域以外区域的搜索,将局部搜索和全局搜索有机地结合起来,同时还最大限度地降低了对遗传算法自身进化进程的干扰;免重复计算策略大大减少了正演计算次数,节约了计算成本,提高了反演效率.两步反演策略避免了多次平均法的缺陷,提高了反演结果的稳定性和精度,降低了非惟一性.     

三维三分量CSAMT法有限元正演模拟研究初探

首先从麦克斯韦方程出发,用伽里金方法推导了三维三分量CSAMT法的有限元方程.在研究过程中,认识到加入散度条件的必要性,在公式中强加了散度条件,提高了解的完备性.其次将成功应用于二维线源频率域电磁法有限元模拟中的两种技术推广到三维中,一是边界条件统一采用一阶吸收边界,使线源产生的电磁波在边界上按波的传播规律被吸收,以降低平面波假设造成的影响;二是总体系数矩阵的存储,用两个二维数组分别记录总体系数矩阵的非零元素及其在总体结点编号中所处的位置,使总体系数矩阵的存储量达到最小的同时,物理意义明确,迭代求解时迅速简便.最后用均匀半空间模型进行了验证.     

PNN测井方法的蒙特卡罗模拟结果研究

PNN（脉冲中子-中子）测井是利用He-3管记录热中子时间谱,通过获取地层宏观吸收截面来确定含水饱和度的方法.本文利用蒙特卡罗方法（MCNP-4C）模拟了不同地层水矿化度、孔隙度、饱和度和井眼等条件下的热中子时间谱,研究了地层宏观吸收截面与地层水矿化度的关系,从理论上确定PNN测井适合的地层水矿化度范围约为10～100 g/L,在地层水矿化度为50 g/L时适于测井的孔隙度下限约为10%.井眼流体不同,地层的热中子计数率不同,但对地层宏观吸收截面影响较小.利用远近探测器热中子计数比值可以确定孔隙度,并提出了根据不同岩性和饱和度的地层宏观吸收截面与孔隙度的交会图来评价骨架、含水饱和度以及确定油层、水层和气层的方法.PNN测井方法在低地层水矿化度、低孔隙度地层比其他方法具有优势.     

Numerical simulation of ground flow caused by seismic liquefaction

Flow failure of sandy subsoil induced by seismic liquefaction is known to cause significant damage to structures. It is induced not only by the dynamic forces exerted by seismic acceleration but also by the static gravity force in consequence of the topography of the ground. The ground flow may sometimes continue after the end of the seismic loading and finally the ground is significantly deformed to cause a failure.This paper numerically predicts the magnitude of flow that could occur when soil liquefaction continues for a sufficiently long period. It is considered that liquefied soil behaves like a viscous liquid, and hence, ground flow is governed by the principle of minimum potential energy. In the calculation, liquefied sand is assumed to be a viscous liquid that deforms in undrained conditions with its volume remaining constant. To consider the non-linearity due to large displacement, the updated Lagrangian method is used to solve the equation of motion. The Newmark β method is employed to calculate the time history of the ground motion. Finally, a simulation using this calculation method shows that the proposed method gives reasonable results for the conditions indicated.