1-D DC Resistivity Modeling and Interpretation in Anisotropic Media Using Particle Swarm Optimization

We examine the one-dimensional direct current method in anisotropic earth formation. We derive an analytic expression of a simple, two-layered anisotropic earth model. Further, we also consider a horizontally layered anisotropic earth response with respect to the digital filter method, which yields a quasi-analytic solution over anisotropic media. These analytic and quasi-analytic solutions are useful tests for numerical codes. A two-dimensional finite difference earth model in anisotropic media is presented in order to generate a synthetic data set for a simple one-dimensional earth. Further, we propose a particle swarm optimization method for estimating the model parameters of a layered anisotropic earth model such as horizontal and vertical resistivities, and thickness. The particle swarm optimization is a naturally inspired meta-heuristic algorithm. The proposed method finds model parameters quite successfully based on synthetic and field data. However, adding 5 % Gaussian noise to the synthetic data increases the ambiguity of the value of the model parameters. For this reason, the results should be controlled by a number of statistical tests. In this study, we use probability density function within 95 % confidence interval, parameter variation of each iteration and frequency distribution of the model parameters to reduce the ambiguity. The result is promising and the proposed method can be used for evaluating one-dimensional direct current data in anisotropic media.     

金属大棚对周口台地电阻率干扰定量分析

周口地电阻率观测2015年出现异常变化,因异常期间该台场地存在较多干扰源。为正确评价该次异常,在电测深结果的基础上建立三维数值模型,采用有限元数值计算,定量评估该台测区周围金属蔬菜大棚等干扰源对地电阻率观测的影响量。结果表明:金属大棚可能是周口台本次地电阻率异常的主要影响因素。     

Self‐convection of floating heat sources: A model for continental drift

Abstract

Two models of floating heat sources are studied. In the first model the motion of two line heat sources constrained to float at an arbitrary depth in a viscous fluid is determined in the limit of small convection velocities. It is found that the sources drift apart and at great separation attain a constant velocity proportional to the square root of the heat flux. The second model is a floating block heat source, presumed to be very long compared to its depth. It is found to exhibit periodic excursions between the end walls of the fluid container with the same dependence of velocity on heat flux as the line sources. A series of experiments are described which exhibit various features of the theory. The numerical values found when the theory is applied to the earth suggest that the idealized flows may be useful in the interpretation of continental drift.     

降雨对昌黎台地电阻率的干扰分析

昌黎台地电阻率受降雨影响明显, 降雨量越大, 地电阻率下降幅度越大, 两者存在良好的线性关系。 基于昌黎台电测深资料反演的水平层状均匀介质结果, 建立地表薄层电性结构变化模型, 通过影响系数理论定性分析降雨对地电阻率的即时效应, 研究结果显示降雨主要是通过改变地表介质含水量和电性结构造成地电阻率变化的。 利用褶积滤波法定量模拟降雨对地电阻率的短期影响过程, 可以较好去除降雨对地电阻率的即时影响和滞后响应。     

地球横向不均匀结构对地表以及空间固定点同震重力变化的影响

本文提出一个新算法,用来高精度计算三维不均匀地球模型中地震位错引起的地表以及空间固定点同震重力变化.具体地说,我们首先把实际三维不均匀地球分解成球对称地球模型和对应的横向不均匀增量,分别进行计算,二者对应的计算结果分别称为球对称解和三维响应.由于球对称解可直接利用球对称地球模型位错理论计算得到,本文的目标是计算三维响应即地球的横向不均匀结构对同震重力变化的影响.然后,我们把三维响应再分为震源的响应和地球横向不均匀结构的响应,它们可分别借助对震源函数的扰动以及对平衡方程式的变分求解.本文推导出六个特殊点源位错引起的地表以及空间固定点同震重力变化计算公式(一个垂直走滑位错,两个相互垂直的倾滑位错,三个开裂位错),对这些公式进行适当组合就可以计算任意位置任意类型位错产生的同震重力变化,对应的计算公式同步给出.接着,依据36阶P波速度模型,我们利用岩石试验经验关系式推导出三维S波速度模型,密度模型,位场模型以及重力模型.最后,利用上述三维模型,本文计算出三种典型类型的点源位错产生的同震重力变化,结果显示三维响应与位错类型,震源深度都有关系,其最大响应占球对称解的0.5%左右,且在所有影响因素中S波速度模型影响最大.数值结果同时表明,三维响应中震源的响应与地球横向不均匀构造的响应处于同一量级.本文给出的地表和空间固定点同震重力变化计算公式可分别高精度解析地表重力和卫星重力观测数据(GRACE、GOCE等),提高大地测量数据理论解析水平.     

THE NON-LINEAR INVERSION OF SEISMIC WAVEFORMS CAN BE PERFORMED EITHER BY TIME EXTRAPOLATION OR BY DEPTH EXTRAPOLATION1

The classical aim of non-linear inversion of seismograms is to obtain the earth model which, for null initial conditions and given sources, best predicts the observed seismograms. This problem is currently solved by an iterative method: each iteration involves the resolution of the wave equation with the actual sources in the current medium, the resolution of the wave equation, backwards in time, with the current residuals as sources; and the correlation, at each point of space, of the two wavefields thus obtained. Our view of inversion is more general: we want to obtain a whole set of earth model, initial conditions, source functions, and predicted seismograms, which are the closest to some a priori values, and which are related through the wave equation. It allows us to justify the previous method, but it also allows us to set the same inverse problem in a different way: what is now searched for is the best fit between calculated and a priori initial conditions, for given sources and observed surface displacements. This leads to a completely different iterative method, in which each iteration involves the downward extrapolation of given surface displacements and tractions, down to a given depth (the‘bottom’), the upward extrapolation of null displacements and tractions at the bottom, using as sources the initial time conditions of the previous field, and a correlation, at each point of the space, of the two wavefields thus obtained. Besides the theoretical interest of the result, it opens the way to alternative numerical methods of resolution of the inverse problem. If the non-linear inversion using forward-backward time propagations now works, this non-linear inversion using downward-upward extrapolations will give the same results but more economically, because of some tricks which may be used in depth extrapolation (calculation frequency by frequency, inversion of the top layers before the bottom layers, etc.).     

宽带高频电磁场数据反演方法研究

采用非线性最小二乘法结合蒙特卡罗法,实现宽带高频电磁场椭圆极化率数据的精确反演,确定地下层状介质的真实电阻率和介电常数.反演结果表明,对于均匀半空间和二层介质模型,最小二乘法能够很好地实现反演,而对于三层或更多层的介质,首先利用蒙特卡罗法确定拟合初始模型,再进行最小二乘反演,能够避免收敛到局部极小值,提高了反演的稳定性.为了加速正演响应函数的计算和迭代的速度,采用高密度采样的线性滤波算法,大大加快了该精确反演方法的速度.针对如覆盖区地质填图和土壤调查等大面积确定地质体性质的应用,本文还给出了一种近似反演方法（相位矢量图法）,能够快速获取视电阻率和视介电常数,不仅可以为应用提供有用的基础信息,而且可作为精确反演方法的初始模型.     

CENTRAL FREQUENCY SOUNDING IN SHALLOW ENGINEERING AND HYDRO-GEOLOGICAL PROBLEMS*

The paper deals with the early stages of development of a convenient form of electromagnetic induction method of sounding referred to as ‘Central Frequency Sounding’ and abbreviated as CFS. The method is introduced as a rapid and useful technique for investigation of shallow engineering and hydro-geological problems. Sets of theoretical two-layer master curves, suitable for interpretation of field data involving measurement of the vertical magnetic component of the field induced at the center of a loop placed on a two-layer earth, have been presented. The approximate but reasonably accurate solutions for a two-layer earth of any arbitrary resistivity contrast have been considered for the purpose and expressed in a form suitable for computation. The computed results have been presented in sets of curves useful for interpretation of field data.     

Effects of Earth’s Lateral Inhomogeneous Structures on Coseismic Gravity Changes

Based on the perturbation method, we present a new method to study the effects of Earth’s laterally inhomogeneous structures on coseismic gravity changes caused by dislocations within a 3-D heterogeneous spherical earth model. We describe this method by six independent dislocations: A vertical strike-slip, two vertical dip-slips perpendicular to each other, and three tensile openings on three perpendicular planes. We derived the calculation formulae for the six independent dislocations. A combination of the six independent dislocations is useful to compute the effects on coseismic gravity changes resulting from an arbitrary seismic source at an arbitrary position.     

基于小波包分解的地层吸收补偿

在分析地震反射波勘探信号小波包分解特性的基础上,提出了基于小波包分解的地层吸收补偿方法．如果没有地层吸收,浅层反射波和深层反射波具有相同的振幅谱而相位谱相差一线性相位．如果把地震记录分成不同的频段,不同频段对于时间的能量分布关系具有相似性,即对所有频段的深层反射的能量与同一频段浅层反射能量之比应该相同;只是不同频段的绝对能量大小不一样．由于地层的吸收造成各频段能量对时间的分布不同,如果给这些频段乘以时变权使各频段能量对时间的分布相同,就起到了对地层吸收的补偿作用．该方法首先用小波包对地震勘探信号进行分频,然后根据地层吸收的特点,在每一个频段上分别提取每一个时间点的吸收系数并用其倒数加权每一个小波包系数,再用加权后的小波包系数重构地震反射波记录消除地层吸收．该方法适合Ｑ值未知的情况,对变Ｑ和常Ｑ都能适应．从实际应用效果看,该方法能很好的补偿地层的吸收。     

Simple equations guide high-frequency surface-wave investigation techniques

We discuss five useful equations related to high-frequency surface-wave techniques and their implications in practice. These equations are theoretical results from published literature regarding source selection, data-acquisition parameters, resolution of a dispersion curve image in the frequency–velocity domain, and the cut-off frequency of high modes. The first equation suggests Rayleigh waves appear in the shortest offset when a source is located on the ground surface, which supports our observations that surface impact sources are the best source for surface-wave techniques. The second and third equations, based on the layered earth model, reveal a relationship between the optimal nearest offset in Rayleigh-wave data acquisition and seismic setting—the observed maximum and minimum phase velocities, and the maximum wavelength. Comparison among data acquired with different offsets at one test site confirms the better data were acquired with the suggested optimal nearest offset. The fourth equation illustrates that resolution of a dispersion curve image at a given frequency is directly proportional to the product of a length of a geophone array and the frequency. We used real-world data to verify the fourth equation. The last equation shows that the cut-off frequency of high modes of Love waves for a two-layer model is determined by shear-wave velocities and the thickness of the top layer. We applied this equation to Rayleigh waves and multi-layer models with the average velocity and obtained encouraging results. This equation not only endows with a criterion to distinguish high modes from numerical artifacts but also provides a straightforward means to resolve the depth to the half space of a layered earth model.     

点源两层大地三维地电模型视电阻率边界元解

本文用两层均匀大地人工点源作用下的空间电位分布作为基本解，导出了下伏基岩中陷含三维地质体情况下，关于电位的边界积分方程组，用边界单元法解积分方程求得地表电位，从而求得了一定装置下的视电阻率。本文方法的独特优点是积分只须在异常体边界面上进行了测线可以沿任意方向。用联剖法计算了均匀半空间下含球形异常体的ρｓ曲线，所得结果与其他学者用解析方法所求得的结果一致。用中间梯度法计算下层基岩中含有一长方体，测线     

Current and voltage source induced polarization transients: a comparative consideration

The article discusses the excitation of transient induced polarization responses using current and voltage sources. The first method has found a wide application in induced polarization surveys and—directly or indirectly—in the theory of the induced polarization method. Typically, rectangular current pulses are injected into the earth via grounding electrodes, and decaying induced polarization voltage is measured during the pauses between pulses. In this case, only the secondary field is recorded in the absence of the primary field, which is an important advantage of this method. On the other hand, since the current injected into the ground is fully controlled by the source, this method does not allow studying induced polarization by measuring the current in the transmitter line or associated magnetic field. When energising the earth with voltage pulses, the measured quantity is the transient induced polarization current. In principle, this method allows induced polarization studies to be done by recording the transmitter line current, the associated magnetic field, or its rate of change. The decay of current in a grounded transmitter line depends not only on the induced polarization of the earth but also on the polarization of the grounding electrodes. This problem does not occur when induced polarization transients in the earth are excited inductively. A grounded transmitter line is a mixed‐type source; hence, for a purely inductive excitation of induced polarization transients, one should use an ungrounded loop, which is coupled to the earth solely by electromagnetic induction.     

Mathematical simulation and experimental studies of the shugo mud volcano

This paper considers the theoretical and experimental principles of a monitoring system for mud volcanoes using powerful vibroseismic sources. A mathematical method has been developed to simulate magma chambers of arbitrary geometry with allowance for deep-seated faults near the volcano, overlapping layers, etc. Results are reported from calculations of the seismic field for the source zone of the Shugo mud volcano. Mathematical modeling served as a basis to develop a technique of vibroseismic sounding using powerful controlled sources yielding a force of 40–100 tons on the ground. For the first time in the history of observations on mud volcanoes, two mud volcanoes on land have been subjected to active vibroseismic sounding. These are the Akhtanizovskii and Shugo volcanoes in the Taman’ mud-volcanic province. The results of experimental investigations are reported. Numerical simulation has helped refine the earth model in the Shugo area, which was previously derived from vibroseismic sounding data.     

三维电阻率测深数据Zohdy近似反演方法

Zohdy方法近似反演三维电阻率测深数据。正演计算采用有限单元法。反演初始模型由测量视电阻率数据给出。通过比较实测视电阻率值和预测模型计算的视电阻率值对数差来修改模型网格电阻率．为了解决任意电极距测深数据的反演,采用大、小双网格剖分。大网格反映地下电性分布情况。小网格用于实际有限元正演计算．在电阻率调整公式中加入一个迭代系数,能够加快收敛速度．并对加5％随机噪声的模型理论视电阻率测深断面数据进行反演,得到的电阻率分布与模型电阻率基本一致．     

一种模拟随机数字地层模型的方法

介绍了一种利用计算机生成随机数字地层模型的方法。此方法根据给定的地层厚度及参数统计特性．按截尾正态分布进行随机抽样构建随机分层结构,并对各分层参数随机赋值,完成随机模型的构筑。用此方法可以很容易地在计算机上生成大量符合某种统计特性的随机数字层状地层模型,从而可以在这些模型上进行感兴趣的仿真模拟研究。为展示这一方法的应用,生成了10个第四系随机层状模型,并在这些模型上进行了地震SH波的地震动放大效应数字模拟实验。结果发现随机模型的响应无论在形态特点还是幅值上都与均值模型的响应显著不同,表明用不完全准确的参数模型模拟估计场址地震动响应时必须充分考虑到参数不准导致的误差。     

Analogue model measurements for a horizontal magnetic dipole embedded within a conducting medium

The validity of an analogue model method employing a horizontal magnetic dipole source situated within a conducting layer for the cases of a poorly conducting model earth and a highly conducting model ocean is studied by comparing model magnetic field measurements with theoretical calculations. The model is then used to study one example for each case; the response of a conducting cylinder simulating an ore body embedded in the earth, and the response of a conducting wedge simulating a shelving ocean.     

2001年地球物理学的一些进展

简要回顾了2001年地球物理学的一些进展。指出在用地球系统科学研究整个地球的结构、演化和动力学过程中，地球物理学作为地球科学中主要提供地球内部信息和资料的学科，将成为地球系统科学研究的一个重要内容。讨论了现在的地球和空间科学研究以及环境监到等地球物理技术在反恐怖活动以及在国家军事方面的重要意义及应用。在21世纪能源危机日益严重的情况下，中国急需进行油气资源的二次创业，而天然气水合物研究是能源研究的一个新方向。     

地形变场与现代地壳垂直运动及地震活动关系初探(Ⅰ)——地形变场的计算方法和物理意义

地震与地壳形变有着密切的关系 ,但台站地倾斜资料空间连续性不好 .为此在场分析的基础上 ,利用逐步订正法将地倾斜观测资料内插到 1°× 1°的经纬度网格点 ,引入曲面总曲率的概念计算格点上的Gauss曲率 ,并推广到格点化的有限区域上得到表征曲面形态和变形强度的地表形变场 .结果表明 :该方法可以合理地弥补资料不连续的缺陷 ,并在地表形变场上捕捉到一些关键的地表形变特征 ,如地凸区、地凹区、鞍形场等 .为地震分析和预报中如何拓展和利用大范围时空信息提供了一种有益的思路 .