二维大地电磁资料的偏移

MIGRATION OF 2-D MAGNETOTELLURIC DATA

本文采用反射映像(即U/D成像)原理对大地电磁资料进行成像,将地面观测的波场分解成上行波和下行波,并分别向下延拓,利用上、下行波的时间一致性原理确定地下电性界面的位置.对TE和TM模式的MT响应分别处理可以得到两个深度剖面,两剖面的一致性便为实际反射界面的最佳估计.理论和实际资料的计算表明,MT偏移技术是比较有效的,它可获得地下界面直观的映像.和常规MT反演方法相比较,该方法具有算法简单等优点,并且还能获得表示地下地质构造真实映像的MT深度剖面.

In this paper we make use of the principle of reflector mapping (i.e. U/D imaging principle) to image MT data. That is, the MT wavefield observed on the surface of the earth can be resolved into upgoing and downgoing waves, they are extrapolated downward by the phase-shift method or the phase-shift plus interpolation (PSPI) method. Conductivity interfaces of the medium could be found by using the time coincidence of the upgoing and downgoing waves. Two depth sections are obtained by processing TE and TM modes separately, the best estimate of the actual reflector position is the location of the coincidence of the two sections. The synthetic and real data examples show that the migration technique of MT data presented here is very effective. It is able to obtain the visual image of subsurface interfaces. As compared with the conventional 2-D inversion, this procedure is more simple in calculation and can a+-tain the MT depth section, which gives the true picture of the subsurface geologic structure.