The effect and application of "false extreme" in frequency-domain electromagnetic sounding

In frequency-domain sounding, "false extreme" phenomenon often appears in the apparent resistivity curve. Previous investigations focused on the subject without considering strata information containing in false Extreme. The use of false extreme effect is a new attempt to explain data. This paper analyzes the effect of false extreme value and its physical mechanism. The buried depth of subsurface structure of the North China coal has been determined using false extreme effect in apparent resistivity curve. Firstly, get the electromagnetic sounding curves corresponding to the false extreme effect over the borehole. Then, according to borehole logs, obtain the correlation coefficient between frequency points corresponding to the false extreme effect and burial depth of coal seam. Finally, based on the correlation coefficient, the buried depth of coal seam in entire survey area is evaluated. This method has been applied in northern area of Taiyuan, Shanxi, and achieved good results.