三维地电模型数值模拟中视电阻率真假异常特征分析

本文概要介绍了三维数值模拟中双网格系统的剖分方法,并通过几种典型模型的有限单元法三维数值模拟计算（网格单元电导率分块均匀、电位三线性变化）,充分揭示了对称四极电阻率测深法三维地电模型视电阻率真假异常的分布规律,分析了产生真假异常的原因,并研究了真异常的形态与引起真异常的地质体位置的关系。     

Solutions of the inherent problem of the equivalence in direct current resistivity and electromagnetic methods through global optimization and joint inversion by successive refinement of model space

The problem of equivalence in direct current (DC) resistivity and electromagnetic methods for a thin resistive and conducting layer is well‐known. Attempts have been made in the past to resolve this problem through joint inversion. However, equivalence still remains an unresolved problem. In the present study, an effort is made to reduce non‐uniqueness due to equivalence using global optimization and joint inversion by successive refinement of the model space. A number of solutions derived for DC resistivity data using very fast simulated annealing global inversion that fits the observations equally well, follow the equivalence principle and show a definite trend. For a thin conductive layer, the quotient between resistivity and thickness is constant, while for a resistive one, the product between these magnitudes is constant. Three approaches to obtain very fast simulated annealing solutions are tested. In the first one, layer resistivities and thicknesses are optimized in a linear domain. In the second, layer resistivities are optimized in the logarithmic domain and thicknesses in the linear domain. Lastly, both layer resistivities and thicknesses are optimized in the logarithmic domain. Only model data from the mean models, corresponding to very fast simulated annealing solutions obtained for approach three, always fit the observations. The mean model defined by multiple very fast simulated annealing solutions shows extremely large uncertainty (almost 100%) in the final solution after inversion of individual DC resistivity or electromagnetic (EM) data sets. Uncertainty associated with the intermediate resistive and conducting layers after global optimization and joint inversion is still large. In order to reduce the large uncertainty associated with the intermediate layer, global optimization is performed over several iterations by reducing and redefining the search limits of model parameters according to the uncertainty in the solution. The new minimum and maximum limits are obtained from the uncertainty in the previous iteration. Though the misfit error reduces in the solution after successive refinement of the model space in individual inversion, it is observed that the mean model drifts away from the actual model. However, successive refinement of the model space using global optimization and joint inversion reduces uncertainty to a very low level in 4–5 iterations. This approach works very well in resolving the problem of equivalence for resistive as well as for conducting layers. The efficacy of the approach has been demonstrated using DC resistivity and EM data, however, it can be applied to any geophysical data to solve the inherent ambiguities in the interpretations.     

Geographers in the U.S. Government in Washington,DC, during World War II

Geographers in Washington, DC, during World War II and the agencies in which they worked are recalled through the naming of geographers engaged in wartime work during this seminal period in the development of the geography profession in the United States. The five agencies then employing the largest number of geographers were the Research and Analysis Branch of the Office of Strategic Services, the Topographic Branch of the Military Intelligence Division of the War Department, the Board of Economic Warfare (later the Foreign Economic Administration), the Board on Geographic Names, and the Office of the Geographer, Department of State. The impacts of this period on individual geographers, the professional organization of geographers, cartography, higher education, and the government are suggested.     

综合物探方法在铝土矿勘查中的应用

区域地层为较稳定的沉积岩层,中二叠系梁山组含铝岩系广泛分布于区域上向斜构造内,为铝土矿的找矿奠定了物质基础.区内车盘向斜构造控制着铝土矿的分布,使探矿工作成为可能.由于铝土矿无明显的磁性、密度差异等物性特征,铝土矿的地球物理勘探仍然是盲区,单一的地球物理方法难以提取出其异常特征.本文阐述了综合利用音频大地电磁法(AMT)和直流电测深(DC)两种物探方法在沉积岩中查找铝土矿,并获得良好的效果.音频大地电磁测深法可以提供大尺度的岩性分布特征.直流电测深能准确的划分出地下介质层位的电阻率分布,且对细小异常的分辨能力强.据地质资料推测,目标矿层铝土矿位于石灰岩与砂泥岩分界面中.AMT能划分出分界面,但难以识别覆存其中的目标矿体,利用DC可查出该异常.结合钻孔资料可以验证异常,同时对比进行物探数据的处理和解释,这样的组合勘探方法对于深部找矿及后期的开发是行之有效的.     

地震台站隔离式直流电源

在＂十一五＂新丰江数字地震台网的台站加密建设过程中,以AVR单片机为核心控制单元,设计了一套具有远程控制功能的隔离式直流电源,用于地震台站的设备供电,介绍了隔离式直流电源的系统特性、主要功能、系统架构及工作原理,重点阐述了该直流电源的隔离原理和功能实现,解决了野外仪器易受雷击的问题。     

大数据量地球物理测井绘图关键技术研究

在开发地球物理测井解释软件过程中,绘图所涉及的数据量很大,在绘图过程中要进行大量的比例运算、坐标转换及坐标映射等,特别是绘制巨幅、需要连续滚屏显示的声电成像测井图像,数据量和运算量更大,因此,就会经常出现内存不足、图形刷新速度过慢、图形重叠和闪烁等现象.在开发测井解释系统GeoWell过程中,采用内存映射文件、内存DC绘图、局部重绘等技术实现了大数据量巨幅测井图形的快速度、高质量绘制以及图形的连续滚动显示,提高了绘图效率,为微机环境下开发大数据量复杂测井绘图软件提供了技术参考.     

电法在基桩桩长检测中的应用

应用地下单点电极(或多点电极)与无穷远电极向地下供电产生电场分布的特点,通过检测地表电位差的分布,可以确定地下单点电极(或多点电极)的埋深,从而达到检测混凝土管桩桩长的目的.结合工程项目,对预应力管桩的实际桩长进行了检测,电测井测试对比检验说明检测是成功的.用电法检验工程桩桩长,弥补了低应变反射波法难于有效、精确检测多节预应力管桩实际桩长的困难局面,可有效发现工程质量隐患.     

井中震电效应的模拟实验研究Ⅰ:井液部分

在总结前人对震电效应理论和实验研究现状的基础上,指出了井中震电勘探的特殊性．利用自行设计的实验系统,实验考察了直流电场对井液声学性质的影响,并对实验现象做了机理探讨．发现：当使用小功率直流电源(32V,3A)对NaCl溶液(20000mg／L)施以直流电场时,与电流强度和作用时间有关的电解导致了溶液物理化学组分的变化,当OH^-取代Cl^-时,可以使溶液的声速和幅度增大,但同时出现的气体(H2、Cl2),特别是H2导致了“气泡幕”的发生,对声波能量(幅度)的影响是决定性的,实验结果和机理分析有助于丰富对井中震电勘探实验现象的认识．     

电测深法和电磁波CT法在采空区注浆加固效果检测中的综合应用

本文分别介绍了电测深法和电磁波层析成像方法,两种方法操作简单且能够详细反映采空区注浆加固效果。综合应用两种方法对铁路地下采空区加固效果进行检测,结果均表明了在线路的K0+278～K0+450段加固效果良好,两种检测方法检测结果具有一致性。证明将两种检测方法综合应用在采空区加固效果检测是合理的、可行的,为今后其他同类的检测效果提供了可借鉴的经验。     

中国广东电网的几次强磁暴影响事件

2001年以来,随着我国阳\|淮系统等多条500 kV长距离线路的相继建成投运,江苏上河、广东岭澳等地变压器多次发现不明原因的强烈振动和噪声增大事件.本文通过对2004年11月以来、十几次磁暴地磁数据与变压器中性点实测电流数据的比较,证明了干扰事件是磁暴在电网产生的地磁感应电流（GIC）所为;其中,2004年11月7日和10日磁暴在岭澳核电站引发的GIC最大值为47A和55.8A,大于直流输电单极运行时变压器中性点的直流电流水平,因此磁暴对岭澳核电站的瞬时影响比直流输电的影响大;监测数据表明广东电网的GIC水平高于阳淮输电系统的水平,初步分析认为与电网结构和海岸效应等因素有关.目前,举世瞩目的1000 kV特高压工程已开工建设,特高压线路的单位电阻最多是500 kV的二分之一,并且线路更长、规划规模大、且变压器采用单相变压器组结构,磁暴影响问题迫切需要研究.