【摘要】 本文是“地震的感应磁效应(一)——三维电磁感应的数值理论”一文的继续。首先从理论和实际计算两个方面证明了三维电磁感应数值方程解的唯一性、收敛性和稳定性,从而充实了作为研究地壳、上地幔电性结构横向不均匀性理论基础的“三维数值方法”。作为这一理论方法的实际应用,文中对不同源场周期和具有不同埋藏深度的三维电导率异常体进行了模拟计算,以研究地震感应磁效应的大小、空间分布特征和频率特性。模拟计算结果表明,对于周期从数秒到数分钟的地磁短周期变化,若电导率异常体的线度与5至7级地震的震源体积大体相当,其电导率较原背景电导率高近一个量级,其感应磁效应主要特征为:在异常体正上方,地面磁场的水平分量变化最大,相对变化量约30％;在异常体于源场方向一致的两侧,垂直分量变化最大,相对变化量约40—50％。因此,观测短周期地磁场的异常变化,有可能是监测地震孕育过程地下电性变化的一种试验途径。但由于上述异常强度在空间上衰减迅速,所以观测必须接近震源区,这对测点的选择是个不利的因素。更多还原

【Abstract】 The numerical theory of the three-dimensional electromagnetic induction is a powerful tool in studying the seismo-magnetic induction effect, as well as the lateral inhomogeneity of the electrical structure in the earth’s crust and upper mantle. The complete numerical equations were established in our preceding paper[1]. In this paper we first show both theoretically and numerically the uniqueness, convergency and stability of the solution of these equations under definite conditions. Secondly, some model calculations are carried out for various periods of source field and burying depths of local anomalous bodies to study the space-distribution and frequency characteristics of the seismomagnetic induction effect. Under the assumptions that the dimension of the anomalous body corresponds approximately to the source dimension of an earthquake of magnitude 5-7, and that its conductivity is ten times as large as the normal value, the results for source period of a few seconds to a few minutes show that the largest anomaly, relative variation about 30%, of the horizontal component takes place in the central part above the anomalous body, and that the largest anomaly, relative variation 50%, of the vertical component takes place at the two sides perpendicular to the direction of the source field. Therefore, observing the anomalies of short period variations of the field might be a promising approach to monitoring conductivity variations associated with earthquake process. The anomalous intensity of the seismo-magnetic effect, however, decreases quite rapidly with distance, so that the observing sites have to be near the earthquake source region; and this brings about the difficulty for their arrangement in advance.更多还原