大地电磁资料精细处理和二维反演解释技术研究(六)——交错模型的大地电磁二维反演

交错模型指的是由几组走向不同的线性构造（近似二维）在空间（纵向、横向）上组合而成的模型.对于电性结构，交错模型表现为纵向或横向上的构造存在电性主轴方位的变化.从构造维性的角度来看，交错模型是一种由二维模型组合而成的特殊的三维模型，直接对其进行大地电磁二维反演，不易获得可靠的反演结果.本文针对交错模型的特点，提出分频段-分区段反演方案.该方案首先需要借助于阻抗张量成像技术，在频率域确定组成交错模型的各线性构造的电性主轴，然后，针对不同的频段、区段，选择对应电性主轴的数据进行反演，通过初始模型的构建将不同电性主轴方位的反演结果对接起来.本文通过三维理论模型的研究，系统展示了分频段-分区段反演的全过程，归纳得到：在分频段反演时先做低频段反演，在分区段反演时先做二维性更不显著一侧的反演.最后，本文将这一技术用于郯庐断裂带中南段一条实测剖面的反演中，其结果与常规二维反演结果相比较，深部的信息更为丰富，且与其他已有地质、地球物理结果的可对比性更好，表明在构造复杂地区，大地电磁分频段-分区段二维反演具有较高的模型分辨率和可靠性.

Refined processing and two-dimensional inversion of Magnetotelluric (MT) data(VI): Two-dimensional magnetotelluric inversion based on the staggered model

The staggered model refers to a combination of several groups of linear structures (approximately two-dimensional) in space (vertical and horizontal directions). For electrical structures, the staggered model is characterized by variations of the geo-electrical strike in longitudinal or transverse directions. From the viewpoint of structural dimension, the staggered model is a special three-dimensional model made up of two-dimensional models, which is not easy to obtain reliable inversion results by two-dimensional Magnetotelluric (MT) inversion directly. Considering such characteristics, a sub-band and sub-segment inversion scheme is proposed in this work, in which the geo-electrical strikes of the linear structures are determined in the frequency domain by means of impedance tensor imaging. Then, the data of the corresponding strikes are selected for different frequency bands and segments, and the inversion results of different strikes are connected to each other through the construction of the initial models. In this paper, the whole process of sub-band and sub-segment inversion is demonstrated by a theoretical three-dimensional model. The results show that the inversion for low frequency band data should be performed at first in sub-band inversion, and in sub-segment inversion the segments with weak two-dimensionality are inverted in advance. This technique is applied to the inversion of a measured profile in the middle and southern sections of the Tanlu fault zone. The result is compared with the conventional two-dimensional inversion results, which shows that the new method permits to reveal more abundant information at depth, consistent with existing geological and geophysical results from previous work. It is shown that the two-dimensional MT inversion of sub-band and sub-segment has higher resolution and reliability in areas with complicated structures.