起伏地形和随机噪声对大地电磁相位张量的影响研究

The Research on the Influence of Topography and Random Noise on Magnetotelluric Phase Tensor

在大地电磁测深中,当浅地表存在小尺度的局部异常体时,在其附近的测点会产生电场畸变,导致观测阻抗和区域阻抗之间产生较大的偏差,进而给资料处理和解释带来较大的困难。各种阻抗张量分解方法的本质也就是要消除局部异常体所导致的畸变,获得准确的区域构造信息。相位张量以其不受局部电场畸变影响和无需对地下介质构造作任何假设的优点得到了广泛的应用。本文介绍了相位张量的基本理论,并利用数值模拟的方式讨论了起伏地形和随机噪声对相位张量的影响。研究结果表明:起伏地形对相位张量的影响较小,利用相位张量可以获得可靠的区域构造信息,例如地下介质的维性信息和二维区域构造走向等;而随机噪声会导致其产生较大畸变,特别是对于低频数据,此时相位张量所反映的构造信息将出现较大的偏差。

When there is a small local abnormal body near the surface in the magnetotellu- ric, the sites near the body will produce electromagnetic field distortion, and cause the de- viation between observation impedance and regional impedance, thus bring greater difficul- ties for data processing and interpretation. The essence of the various decompositions of MT impedance tensor is to eliminate the local distortion caused by abnormal body and ob- tain accurate regional structure information. The phase tensor has been wildly used, be- cause it is not affected by the local galvanic distortion and don＇t need any assumption for the regional structure. In this paper, the basic theory of phase tensor is introduced and the in- fluence of topography and random noise is discussed. The results show that the topography has less effect on phase tensor, and reliable information of the regional structure can be ob-rained by phase tensor, such as dimensionality and regional structural trend. But the ran- dom noise can produce serious distortion, especially for the lower frequency data, so the in- formation reflected by phase tensor will have a larger deviation.