Research And Application Of Extreme In The Electromagnetic Sounding

Magnetotelluric sounding (MT) and controlled source magnetotelluric sounding (CSAMT) electromagnetic exploration methods developed in recent decades, with its probing depth favored. MT sounding and CSAMT sounding apparent resistivity curve, the left branch (anterior branch) oscillation close to the upper layer resistivity (than the non-uniform earth, as the right end of the (low-frequency oscillation end) with a maximum amplitude of the oscillation peak the maximum absolute value of the resistivity curve is much smaller), in the past most people call it "false extrema.(Such as AAKaufman and GVKeller) called "extreme" and can also notice containing partially electrical information. The "false extrema contain comparative information about the geoelectric section not fake, false extrema In this paper, it is that the amplitude of the largest peak called "small extremal.This study is part of a study of the major instrument special WAN electromagnetic method of the National Natural Science Foundation of paper magnetotelluric sounding and controlled source electromagnetic sounding theory formula-based, two-story, three-and four-cross section, for example, programmed to calculate a range of different cross-section types, the apparent resistivity curves of different electrical parameters. By forward modeling, comparing, analyzing the relationship between the frequency of occurrence of the extremum curve characteristics, the magnitude of the margin, and section parameters and found that these characteristics of the small extremum contains information about the parameters of the geoelectric section. Simple ground structure (such as the two-story section), the asymptote (former support) and small extremal characterized under the left branch of the apparent resistivity curve, able to extract all the information about the profile parameters. Complex ground structure (such as three or more layer cross-section), according to the left branch of the apparent resistivity curve (former support) asymptote and small extremal characteristics, able to extract some parameters on the upper part of sectional provide strong constraints to extract all the cross-section information, to improve the accuracy and stability of interpretation. Specific methods of extraction of the above information is given.This article about the false extrema false, it should be called "extreme" point of view, about the characteristics of small extremal contains the geoelectric section rich view of the information and the specific method to extract the cross-section information, a new attempt.Make full use of the MT and CSAMT sounding apparent resistivity curve left branch (anterior branch) and small extremal characteristics, has a very important practical value and economic significance in the the electromagnetic exploration field work and the indoor explain. For simple electrically configured (e.g. Layer sectional), it is possible in a small observation (or observation) under conditions of low band of apparent resistivity curves obtained all the parameter information of the cross-sectional, greatly reducing the workload of the field observation and laboratory interpretation save time and cost, and improve work efficiency and economic benefits. For more complex ground structure (such as three or more layers sectional), in the absence of apparent resistivity the curve low frequency characteristics premise, the apparent resistivity curve left branch (anterior branch) and small extremal characteristics, more reliable and access to a number of cross-section upper information, provide strong constraints to obtain cross-section all information, reduce the unknown factors of inference and interpretation, and to improve the accuracy and stability of interpretation, save time and improve efficiency. Finally, compared to the explanations given by example with the previous geological cross-section and drilling control come to the satisfactory results of the explanations given by the extreme value characteristics.