A model of the generation of electromagnetic emissions detected prior to earthquakes

Recent satellite and ground-based observations prove that during the formative period of earthquakes VLF/LF and ULF electromagnetic emissions are observed in seismogenic areas. This work offers an original model of self-generated electromagnetic oscillations of local segments of the lithospheric origins of the emissions. In the paper, the seismogenic area is considered to be an oscillatory-distributed system. This model simplifies physical analyses of the nonlinear effects and qualitatively explains the mechanisms that generate very low frequency electromagnetic waves in the period prior to an earthquake.     

感应-横向组合测井联合反演及多解性研究

电阻率测井反演问题解的局部收敛性和非唯一性增加了测井解释的难度，影响了实际的应用，把测量原理迥异的感应型和电流型测井结果联合起来反演，是减小这些影响的有效方法，利用经测井理论和反演技术，建立了适用感应－横向组合测井响应的联合演算法，研究了单一的横向测井反演的感应－横向联合反演的局部收敛性、非唯一性及解的偏差，结果表明，联合反演更有利于同时确定地层电阻率、侵入半径和侵入带电阻率，当初值地较大范围内变化时，反演结果均能在真值或真值附近收敛，改善了反演结果的局部收敛性，增加了反演结果的可信度，避免了差异较大乃至相互矛盾的解，现场实例证实了这一结论。     

水平井和大斜度井中的感应测井响应计算

感应测井受井斜影响十分严重，在水平井和大斜度井中，感应测井曲线几乎面目全非．水平井和大斜度井中感应测井响应的正演计算是正确认识这种复杂环境中感应测井响应特征的重要手段，是进行井斜环境影响校正的必要准备，是研究用感应测井曲线探测水平井井眼离最近界面距离的基础，同时也是感应测井理论的新发展．本文将论述水平井和大斜度井中感应测井响应正演计算的理论和方法；分析水平井、大斜度井中感应测井的响应特征     

Induction, adaptation and recovery of lysosomal integrity in green-lipped mussel Perna viridis

Biomarkers are generally applied to detect pollution in environmental monitoring. Such biological responses should accurately reflect the stress over time in a quantitative manner. As such, the initial and maximum responses induced by stress, as well as adaptation and recovery of these biomarkers, need to be fully understood or else erroneous false-negative or false-positive may be arrived. However, most of the biomarker studies only provided information on initially induced responses under different concentrations of toxicants, while biological adaptation and recovery were poorly known. In this study, the time required for induction, adaptation and recovery of lysosomal integrity in green-lipped mussel Perna viridis upon exposure to benzo[a]pyrene was investigated over a period of 62 days. Maximum induction occurred on day 6 when lysosomal integrity was significantly reduced by 51%, and no further change or adaptation was detected thereafter. When mussels were depurated in clean seawater after 18 days of exposure to benzo[a]pyrene, a gradual recovery was observed, with lysosomal integrity returning to its background level and showing a complete recovery after 20 days of depuration. Lysosomal integrity was significantly correlated with the body burden concentrations of benzo[a]pyrene and condition index of the mussels. The relatively fast induction (6 days) and recovery (20 days) without apparent adaptation suggested that lysosomal integrity in P. viridis can serve as a good biomarker in biomonitoring, as its response is not likely to generate both false-negative and false-positive results.     

基于CM4模型的中国大陆地区地磁场时空分布特征分析

本文利用第四代地磁场综合模型（Comprehensive Model 4,CM4）,计算了1982-2001年中国大陆地区同一经度链和同一纬度链上地磁台站的磁层源磁场及其感应场、电离层源磁场及其感应场的地磁北向分量X、东向分量Y、垂直分量Z的模型值,分析了各场源磁场随时间和空间的变化特征。结果表明:在时间上,经度链和纬度链台站的磁层源磁场及其感应场均呈现出11年和27天周期性变化。电离层源磁场及其感应场具有明显的季节变化,不同年份相同季节变化形态一致但幅度不同。在空间分布上,经度链和纬度链台站磁层源磁场及其感应场的年变化幅度呈现出不同变化特征,电离层源磁场及其感应场在经度链上变化特征不同,而纬度链台站的数值基本一致。日变化分析显示,磁静日和磁扰日期间,模型数据与台站实测数据变化一致性较好,相关性较高。     

A fast integral equation solver for 3D induction well logging in formations with large conductivity contrasts

Simulation of induction logging responses in formations with large conductivity contrasts is an important but challenging problem due to the singularity of a linear system caused by large contrasts. Also, three‐dimensional (3D) analysis of complex geophysical structures usually encounters high computational demands. In this paper, a pre‐corrected fast Fourier transform (pFFT)‐accelerated integral equation method is applied to overcome these difficulties. In the approach, the entire formation is included in the solution domain. The volume integral equation is set up in the region based on the fact that the total field is the summation of the excitation field and the secondary field. The emitted field by the transmitter coil (treated as a magnetic dipole) is regarded as the excitation of the system. Then the method of moments (MoM) is used to solve the integral equation. To reduce the high computational requirements of the MoM, the pFFT method is used to speed up the solution of the matrix equation and reduce the memory requirement as well. The resultant method is capable of computing induction logging problems involving large and complex formations. For problems with high conductivity contrasts, the solution of the matrix equation usually converges very slow or even fails to converge due to the large condition number of the coefficient matrix. To overcome this difficulty, an incomplete LU pre‐conditioner is used to significantly speed up the convergence of the matrix equation, thus further reducing the computation time. Numerical results show that the present method is efficient and flexible for 3D simulation of induction logging and is specifically superior for problems with high conductivity contrasts.     

Recordings and occurrence of geomagnetically induced currents in the Finnish natural gas pipeline network

A project implemented to study the effects of space weather on the Finnish natural gas pipeline was started in August 1998. The aims of the project were (1) to derive a model for calculating geomagnetically induced currents (GIC) and pipe-to-soil (P/S) voltages in the Finnish natural gas pipeline, (2) to perform measurements of GIC and P/S voltages in the pipeline and (3) to derive statistical predictions for the occurrences of GIC and P/S voltages at different locations in the pipeline network.GIC and P/S voltage were recorded at a compressor station. The GIC measurement was made with two magnetometers, one right above the pipe, and another at the Nurmijärvi Geophysical Observatory about 30 km southwest. The largest GIC since November 1998 has been 30 A. The P/S voltage recording was stopped in May 1999, but GIC is still measured.GIC statistics were derived based on the recordings of the geomagnetic field at Nurmijärvi. The geoelectric field was calculated by using the plane wave model. This field was input to the general pipeline model resulting in the distribution of currents and P/S voltages at selected points in the pipeline. As could be expected, the largest P/S voltage variations occur at the ends of the pipeline network, while the largest GIC flow in the middle parts.     

东太平洋Juan de Fuca板块的磁变研究

作为EMSLAB电磁感应国际合作计划的一部分,通过对海底观测的三分量变化地磁场的分析,构制了横跨Juan de Fuca洋脊、Juan de Fuca板块到板块俯冲带的三条地磁转换函数剖面,计算了各个测点的地磁场感应矢量。结果表明,Juan de Fuca板块的东、西两部分的浅部电性结构是有差异的,近海岸线的东区更导电;而深部电性结构是相对均匀的。这一结果与由大地电磁资料计算得到的二维模型剖面是一致的。     

陕西地区地磁湾扰异常

本文从频率域分析了陕西近年来记到的约十个地磁湾扰和磁扰。结果表明,渭河南北的垂直分量位相相反,水平分量也存在异常,源场极化方向和异常幅度有一走关系,同相和异相感应矢量指向渭河方向,这些都说明感应电流从渭河地堑下集中流过。据此推测在地壳下部或地幔上部存在一高导体。结合邻区地磁湾扰和其它短周期异常认为,这个高导体可向东西延伸上千公里长。     

Comparison between moving and stationary transmitter systems in induction logging

In a general treatment of the theory of induction logging, an exact integral representation has been obtained for the mutual impedance between a vertical dipole transmitter and a coaxial dipole receiver in a three layered earth. Based on this representation, a computer model has been devised using the traditional Slingram system of induction logging and the comparatively new Turam system, ignoring borehole effects. The model results indicate that due to its much larger response, the Turam system is in general preferable to the Slingram in mineral and groundwater investigations where formation conductivity much less than 1 S/m is generally encountered. However, if the surrounding media are conductive (more than 0.1 S/m), the Turam system suffers from large amplitude attenuation and phase rotation of the primary field caused by the conductive surrounding, and is less useful than the Slingram system which does not so suffer, unless the target bed is shallow. Because it is a more complex function of system parameters than the corresponding Slingram log, a Turam log can be conveniently interpreted only by the modern inverse method using a fast algorithm for the forward solution and a high speed digital computer.