共查询到18条相似文献,搜索用时 703 毫秒
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本文提出一种通过测磁场确定面极化和体极化介质中二次极化电流的新方法.它与以往测电场的方法有所不同.当时域单向长脉冲激发电流通过面极化和体极化介质时,便在其表面和内部产生激发极化效应.在通电时间内和断电后的放电过程中,若极化介质内产生了二次极化电流,它必将在周围产生二次磁场.我们通过观测二次磁场可靠地确定了介质中二次电流的存在与否和量值大小以及矢量方向等重要内容.本文除给出一些实验结果外,还给出了实例.多年来,国内、外学者对体极化介质中二次极化电流的存在问题是有争议的,本文对此给出了具有充分说服力的实验结果,有利于统一这方面的认识. 相似文献
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根据分界面上稳定电流场的边界条件,解稳定电流场Laplace方程,给出椭球形分界面入射场、反射场及透射场的表达式,并导出圆柱形、球形分界面上入射角、反射角及透射角的关系式后,指出,只在少数特殊情况下三者才相等,对一般形状的大多数光滑连续分界面情况,它们是不相等的.其值取决于分界面的具体形状. 相似文献
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本文从麦氏方程出发,运用电流磁场的等效理论阐明了在磁电勘探中,当矿体的二次极化电流具有垂直对称轴分布时,在地表面及以上空间中任一点的磁异常场(H)均等于零。因而,具有任何垂直对称状电化学矿产模式(石油、天然气、地下水及金属矿床等)的磁电勘探法异常场线积分均不存在。此外,由于对各种形状和任何极化倾角的矿体情况,地表面上均无电流密度垂直分量(in)存在,故地表面上异常场线积分均为零(∮L H·dL=0)。因此,磁电勘探法不具备在地面上寻找此种矿产的物理前提。 本文还对倾斜极化球体和柱体的磁电勘探异常进行了计算,给出了主剖面上理论曲线的异常分布规律,指出了磁电异常的数量级。同时,还对井中磁电异常的分布规律给出了计算资料。为了对比,也对相应条件下的自然电场异常做了计算,指出了电场异常与磁场异常之间的不同特点及其对实际找矿的意义。 相似文献
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本文首先阐明负激电效应是客观存在的;然后用等效电阻率法导出地面上点源供电时的二次极化电位、电场强度、电流密度的表达式,并依此用线性滤波法对各种给定参数进行计算,依此对二次极化场的分布规律进行物理分析,对激电负效应给出直观的物理解释;最后,根据土槽模拟实验资料,证实了负激电效应的客观存在,反演数据也与实际情况相吻合。本文还得到二极装置和错层条件下的负激发极化效应。 相似文献
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由实验和理论给出了应力集中是如何影响钻孔周围速度场,以及速度场是如何影响偶极各向异性测量的。在低频率,偶极波主要易受远场应力的作用,即标准声波测井解释结果恰能得了最在应力方向。在高频率,偶极波主要受近场应力集中的影响,致命快速极化方向与最小构造应力的方向一致。这睦效应使得在快速极化方向和慢速极化方向测得的偶极波散曲线产季了交叉。根据宽频带偶极资料,偶极波散曲线交叉可被用作为应力诱发各向异性超过弱的 相似文献
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基于地下电流场的积分公式,离散化的二次电流场被分解为电性不连续界面上的一系列点电荷电场的代数和.单位正点电荷电场被引入作为空间扫描函数(SDS),积累电荷出现的概率(COP)函数定义为二次电流场与SDS的互相关.为对概率成像结果进行定量分析解释,提出了规范的积累电荷出现的概率(NCOP)函数.通过应用有限元算法对2D地电模型进行二次电流场合成,实现了二次电流场的多次叠加概率成像.结果表明对均匀半空间中赋存地质异常体的电性结构,概率成像方法对地下异常体的空间位置有较好的指示作用. 相似文献
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《地球物理学进展》2020,(2)
本文利用极化方法,提取和分析新疆区域2008—2017年拥有秒采样数据的乌鲁木齐、喀什、且末、温泉4个台站的垂直幅度极化值,分析极化值异常与新疆及其邻区2008年以来6级以上地震的关系.地磁场观测较容易受到高空电流体系等外源场的影响,为了分析外源场对极化值的影响,统计了2008—2017年共计64次磁暴期间的极化值,4个台站磁暴期间极化值都非常小,除了温泉台有1次大于2倍均方差之外,其余全部都小于各个台站的2倍均方差(极化值异常初始阈值为3倍均方差),同时通过计算出的极化值与K_p指数的相关系数可以看出,4个台站的相关系数都非常小(小于0.2),基本可以判断极化值在磁场扰动时应该表现为低值,而大量研究表明地震之前极化值会出现高值异常,因此基本排除了外源场对极化值的影响.2008—2017年共计93次5级以上地震,因各个台站背景噪声和仪器噪声以及构造背景差别较大,计算出的极化值幅度差别较大,各个台站极化值之间不具有可比性.结果表明:当各个台站的震中距相当时,震级越大,异常幅度越大.喀什台由于与多国交界,地质构造环境更为复杂,异常幅度等显示出更为复杂的特性,因此漏报等情况也较多. 相似文献
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本文首先指出经典粘性理论应适用于扇形边界低速风,接着论证了常用太阳风粘性数学表式的不正确性,导出了螺旋磁场中径向球对称强磁化等离子体流动的各种经典粘性表式,并证明了这些公式的合理性;最后讨论了常用太阳风经典粘性表式出错原因,估计了具有正确粘性公式的扇形边界低速太阳风粘性模式应有的结果。 相似文献
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In the theoretical part of the present paper, formulas have been analyzed for a magnetic dipole in a homogeneous and unbounded medium. The magnetic field is elliptically polarized in the region between the quasistatic zone and the far field. Since the position and the shape of the polarization ellipses depend on the complex wave number, k, it is possible to determine k by measuring the polarization ellipses. From k, the conductivity and the dielectric constant of the medium are easily calculated. The functions required for the measuring method have been computed and plotted in graphs. In the experimental part it was examined how far the theory may be applied to measurements of propagation through rock at frequencies ranging from 100-1000 kHz. These measurements showed that reasonably defined mean values of rock parameters can be given only if the deviations of the field from the theoretically expected field are not too high. These deviations have been named field distortions and have been examined by means of statistical methods (variance ratio tests). Gallery cavity and inhomogeneity or anisotropy of the medium account for these distortions. 相似文献
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通过对云南遥测地震台网2000年1月1日——2003年12月31日4年资料的分析, 使用剪切波分裂SAM综合分析方法,获得了云南地区10个数字地震台站的快剪切波偏振结果. 结果表明, 云南地区大部分台站的快剪切波偏振优势方向主要为近N——S或NNW方向; 位于活动断裂上的台站的快剪切波偏振优势方向与活动断裂的走向一致;与GPS主压应变方向一致,与区域主压应力方向基本一致;少数台站的快剪切波偏振较为复杂,或与活动断裂的走向及GPS主压应变方向不一致. 这样的台站总是位于几个断裂的交会处,反映了复杂的断裂背景和复杂的应力分布特征. 快剪切波偏振优势方向代表了原地最大主压应力方向,受到区域应力场和断裂分布等多种因素的控制. 相似文献
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B. S. RATHOR 《Geophysical Prospecting》1978,26(1):175-183
The expressions for quasi-static electromagnetic fields of a horizontal electrical dipole placed on the surface of a polarizable half-space have been derived for low and high values of induced polarization parameter and presented along with numerical results. It has been observed that the polarity of the mutual impedance function is negative for low values and positive for high values of the induced polarization parameter in the entire time domain, whereas the induced voltage function is positive for low values of induced polarization parameter and becomes negative for high values. In the case of low values of induced polarization parameter the transient electromagnetic field in the beginning increases with time, later on it starts to decay with time. The present study shows that the decay rate of electromagnetic field is highly dependent upon the induced polarization parameter. In the light of the present study the conductivity of the polarizable medium may be determined more accurately. 相似文献
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An ML4.7 earthquake occurred on February 2,2012 in Liaoning Gaizhou (40.56°N,122.36°E),since then,small earthquakes are frequent in this area,and until now the seismic activity does not stop,several earthquakes with magnitude larger than 4.0 have occurred.As of October 30,2014,1223 earthquakes have happened in the Gaizhou area,including 934 earthquakes with the magnitude ML1.0~1.9,247 with the magnitude ML2.0~2.9 and 45 with the magnitude ML3.0~3.9.Meanwhile,earthquakes are continuously active in Haicheng area where the MS7.3 earthquake happened in 1975,and there are over 1100 earthquakes (ML ≥ 1.0) having occurred since the Gaizhou earthquake swarm activity.Because the polarization direction of the fast shear wave is very sensitive to the variation of the principal stress environment,the shear wave splitting parameter can reflect the regional stress state and the local structural features,especially effective for the analysis of small-scale stress environment characteristics.So based on the seismic activities of the two earthquake clusters,this study analyzes the characteristics of shear-wave splitting in Gaizhou-Haicheng area.Preliminary results show that predominant polarization direction of fast shear-waves in the old earthquake region of Haicheng is stable,consistent with the direction of regional stress field.Due to presence of active fault below the Gaixian station (GAX),the predominant polarization direction of fast shear-waves is more complicated.There are two predominant polarizations,consistent respectively with Jinzhou Fault strike which is below the station and the maximum principal stress direction in this area.In addition,Gaizhou earthquake swarm activity increased after December 22,2013,and after the time node,the predominant polarization direction of fast shear-waves in Gaixian station is SEE,which is close to the predominant polarization direction of fast shear-waves in Yingkou station,at the same time consistent with the maximum principal stress direction of this region.Thus it can be inferred,the enhanced activity of Gaizhou earthquake swarm since December 22,2014 may be related to local enhancement of regional stress.In addition,the average time-delays of slow waves in station YKO and GAX show that there are no obvious changes before and after the time point of December 22,2013,which is different greatly with the previous related researches on the variation of slow wave time-delays,and there is no possibility that the Gaizhou earthquake swarm evolved into foreshock sequences from current preliminary results.We should do more work to study the details of the time delay variation of shear wave splitting parameter. 相似文献
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本文对磁激发极化法当前存在的几个探矿理论问题进行了讨论,指出了某些著作中的错误及不完善之点,提出了作者的观点,给出了新的理论公式和异常剖面曲线以及某些条件下的室内模型实验结果和野外实际资料。 相似文献
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西格尔(H.O.Seigel)从理论计算得到导电颗粒含量为25%的极化球体有最大异常,因此认为:激发极化法只宜于寻找中等浸染程度的矿体,对于含量很高的矿体或良导致密型矿体,激发极化法是不行的。据称这种“饱和效应”的理论得到野外结果的证实。 本文根据我国激发极化法在良导致密型矿体上大都能获得明显视极化率异常的事实,说明西格尔的“饱和效应”理论与事实不符。本文认为良导致密型极化体不存在“饱和效应”问题,激发极化法对它们的勘探也是有效的。可能由于西格尔把低含量理论公式,不计条件地推导到高含量、甚至良导矿体,因此他的结论是错误的。本文最后讨论了电阻率因素对浸染型球体视极化率强度的影响。 相似文献