关键词: 大地电磁, 二维反演, TM极化模式, 反演剖面长度, 有效反演深度

Abstract: Magnetotelluric sounding method(MT),the most important geophysical means of detecting the crust and upper mantle electrical structure,is more and more widely used.The study of the inversion depth of MT(the effective detection depth) is relatively rare,and the previous view believed that the depth of effective detection was only in association with frequency.With a large number of the inversion results of two-dimensional vertical fault models,we find that the length of the inversion profiles also has an important impact on the result.In this paper we designed a set of vertical fault models with different fault slips.Focusing on the TM polarization mode,we studied the relationship between the length of the inversion profile and the result in detail.The results show that,for a certain depth of the target area,when the bandwidth of frequency is wide enough and the length of the density of the site is appropriate,the length of the inversion profile directly influences the quality of inversion results.If the length of the MT inversion profile is short,the results cannot respond to target depth correctly,and if the length is appropriate,the results may be good.The study also found that,with the fault slip increasing,the length of the inversion profile also needs to increase,and there is a linear relationship between them.This conclusion has great significance both for the field observation and theoretical studies.

Key words: MT, 2D inversion, TM polarization mode, length of inversion profile, effective detection depth