转换函数和磁场振幅比的水平源场效应的数值计算研究
A NUMERICAL STUDY OF SOME HORIZONTAL SOURCE FIELD EFFECTS ON THE TRANSFER FUNCTIONS AND THE AMPLITUDE RATIOS IN GEOMAGNETIC INDUCTION INVESTIGATION
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摘要: 本文用三维有限差分法研究转换函数和磁场振幅比的某些源场效应,这些物理量常用于地震预报的研究工作。我们研究了几种水平均匀源场的情况,其中包括圆偏振的源场和极化方向不同的几种线性枞化源场。结果表明,即使在最简单的均匀水平源场的情况下,磁场振幅比肯定受源场变化的影响。然而,单台转换函数就不受均匀水平源场性质变化的影响。因此,转换函数随时间的变化适用于监测地震前兆,尤其适用于中低纬度地区,因该地区的源场垂直分量比较小。Abstract: The finite difference method for the 3-D case is used in this paper for studying the source field effect on the transfer functions and the amplitude ratios of geomagnetic fields, which are often used in the study of earthquake prediction. Several horizontal source field models are studied: in one case the field is assumed to be circularly polarized, and in other cases the field is assumed to be linearly polarized pointing to various directions. We show that, even in the simplest case where the source fields are uniform and horizontal, the amplitude ratio is definitely affected by variations of source fields. However, the single station transfer functions are not affected by changes in the nature of the uniform and horizontal source fields. Employing information on the time variations in transfer functions for monitoring the earthquake precursors is therefore meaningful, especially in the mid-or-low latitude locations where the vertical component of the inducing field is rather small.
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[6] Zhdanov, M. S,N. G. Golubev, V.V. Spichak, and 1v. M. Varentsov, The construction of effective methods for electromagnetic modelling, Geophyr. J. R. aszr. Soc., 1982, 68, 589——607
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[15] IIiblis, R. D. and F. W. Jones, The calculation of perturhation and induction arrows for a three——dimensional conductivity model, J. Cconaag, Ceoelecar., 1976, 28, 283——293.
[16] Chen, P. F. and 1'. C, W. Fung, Significance of the sign changing of the imaginary arrows in geomagnetic induction investigation, Gcophys. J. R, astr. Soc., 1985, 80, 257——263.[1] Bcamish, D., A geomagnetic precursor to the 1979 Carlisle earthquake, Geophys. J. R, astr. Soc.. 1982, 68,531——543.
[2] Honkura, Y. and S. Koyama, Observations of shortperiod geomagnetic variations at Nakaizu (1), Bull. Earthq. Rrr. Inst., Univ, Tokyo, 1978, 53, 925——930.
[3] Honkura, Y., Current research in earthquake prediction I, edited by T. Rikitake, 352——354, 1981, Center for Academic I'ublicatinns Japan, Tokyo
[4] witt——Taylor, C, R. and J. T. Weaver, On the finite difference solution of two——dimensional induction problems, Geophys. J. R. artr. Sac., 1976, 47, 375——396.
[5] Chen, P. F., On the finite difference metliod of threedimensional electromagnetic induction problem, Aila Ccaphysica Sinica, 1985, 28, 268——281.
[6] Zhdanov, M. S,N. G. Golubev, V.V. Spichak, and 1v. M. Varentsov, The construction of effective methods for electromagnetic modelling, Geophyr. J. R. aszr. Soc., 1982, 68, 589——607
[7] Weaver, J. T. and C. R. Brewitt——Taylor, Improved boundary conditions for the numerical solution of E——po——larization problems in geomagnetic induction, Geaphys. J. R. aszr. Sac., 1978, 54, 309——317.
[8] Gough, D. L, F, E. M. Lilley and M. W. McElhinny, A polarization——sensitive magnetic variation anomaly in South Australia, Nature, 1972, 239, 88——91.
[9] Jones, F. W., The perturbation of linearly and circularly polarized geomagnetic fields by a non——symmetric twoisland structure at three periods, J. Geomag. Geoelecar., 1974, 26, 295——310.
[10] Rokityansky, I, L, Geoelectromagnetic Investigation of the Earth's Crust and Mantle, 381, 1982, Springer—— Verlag, Berlin.
[11] Parkinson, W. D. and B. A. Hobbs, Conditions for the geomagnetic induction relatinnsliip, Phys. Earth Ylanra Intrr., 1979, 19, 5——6.
[12] Lilley, F. E. M. and D. J, Bennett, Linear relationship in geomagnetic variation studies, Phys. Earth Planet Into., 197.1, 7, 9——14.
[13] Frazer, R. A., W, J. Duncan and A. R. Collar, Elementary Matrices, 1947, Cambridge University Press,London,Parkinson, W. D., Directions of rapid geomagnetic fluctuations. ueophys. J. R. astr. Soc., 1959, 2, 1——14.
[14] Reddy, I. K., D. Rankin and R. J. Phillips, Three——dimensional modelling in magnetotalluric and magnetic variational sounding, Geophys. J. R. astr. Sac., 1977, S1, 313——325.
[15] IIiblis, R. D. and F. W. Jones, The calculation of perturhation and induction arrows for a three——dimensional conductivity model, J. Cconaag, Ceoelecar., 1976, 28, 283——293.
[16] Chen, P. F. and 1'. C, W. Fung, Significance of the sign changing of the imaginary arrows in geomagnetic induction investigation, Gcophys. J. R, astr. Soc., 1985, 80, 257——263.
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