Piezomagnetic fields produced by dislocation sources

Tectonomagnetic modeling based on the linear piezomagnetic effect is reviewed with special attention to dislocation models. Stacey's scheme was the prototype for such modeling, as proposed in his first seismomagnetic calculations in 1964. The linear piezomagnetic law is presented, in which the stress-induced magnetization is expressed as a linear combination of stress components. The Gauss law for magnetic field and the Cauchy-Navier equation for static elastic equilibrium are combined through linear piezomagnetism and the Hooke law to yield the basic equation for piezomagnetic potential. A representation theorem for its solution is given by surface integrals of the displacement and its normal derivative over the strained body.A Green's function method is developed to compute the piezomagnetic field produced by a dislocation surface in an elastic half-space. Volterra's formula for piezomagnetic potential is derived by modifying Stacey's scheme for tectonomagnetic modeling. The Green's functions for the problem are called elementary piezomagnetic potentials, which are defined as potentials produced by elementary dislocations. Special consideration is required to construct the elementary piezomagnetic potentials, because the stress field around a point dislocation has a singularity of orderr ^–3. The integral representing elementary piezomagnetic potentials is not uniformly convergent. Owing to inappropriate convergency, the Green's functions obtained in an earlier study led to a puzzling outcome. Revised Green's functions give consistent results with those obtained so far by numerical integrations. Generally the piezomagnetic field produced by dislocation sources is weak in the case of a homogeneous earth model. Two enhancement effects for piezomagnetic signals are suggested: one due to inhomogeneous magnetization and the other via bore-hole observations.     

净化处理构造磁观测数据的多道约束维纳滤波法

本文提出一种能净化处理流动地磁观测所得的总强度数据的多道约束维纳滤波法。它只要求对测网中各测点进行一次总强度F、磁偏角D和磁倾角I的绝对测量,使其满足所需的约束条件,便能利用附近地磁台同时段的三分量数据精确地拟合得出各测点在各观测期间的三分量值。这样,就可算出相邻两点间总强度差矢量的大小和方向,排除地磁内、外源场的干扰。进而再利用该台的三分量扰动场数据,通过同样的滤波运算,可先后获得相邻两点间跟构造应力作用有关的感应场与剩余场。以台距为144～455公里的北京、静海、昌黎和红山四个地磁台的144个分量数据进行检验,结果表明:(1)各分量的拟合值与真值之差的标准差分别为σ_X=1.22～2.65nT,σ_Y=1.16～3.97nT,σ_Z=1.18～2.32nT,σ_F=1.18～2.34nT;(2)拟合值的均值与真值的均值之差则很小。X_f-X_o和Z_f-Z_o都是零,Y_f-Y_o=-0.2～-0.3nT,F_f-F_o=0.2～0.3nT;(3)所算出的总强度差矢量之均值的大小和方向与真值的几乎完全相等;(4)感应场不足1nT,远远小于剩余场。