电磁测深法视电阻率定义问题的研究

本文首先提出电法勘探中视电阻率定义的基本原则,并以此为依据讨论了MT法、TEMS法及FEMS法中各种视电阻率定义的优缺点,提出了改进办法.研究发现,MT法利用面阻抗实部或在时间域中给出的视电阻率是很有效的定义方法,能很好地区分良导层,而面阻抗虚部定义的视电阻率效果最差.对TEMS法来说,利用视电阻率全区定义较通常的远区或近区近似定义更有效.研究还表明,由磁场时间导数定义的全区视电阻率有时出现多解性甚至无解,而利用磁场本身定义的视电阻率是很有效的.对FEMS法,进行了类似的全区视电阻率定义问题讨论,虽然取得的结果不如TEMS法理想,但比起目前常用的大、小感应数条件下定义的视电阻率响应还是有一定效果.文中对电磁测深法中出现的视电阻率响应曲线的假极值效应进行了物理解释.

A STUDY OF THE DfYINITION OF APPARENTRESISTIVITY IN ELECTROMAGNETIC SOUNDING

This paper puts forward the basic principle for definition of apparentresistivity in electrical prospecting, and on such a basis discusses merits anddemerits of various sorts of apparent resistivity definition in MT, TEMS andFEMS methods with some suggestions for improvement made. Studies showthat in MT method the apparent resistivity defined by using real part ofplane impedance or given in time domain is very effective, which can wellrecognize the good conductive layer, while the apparent resistivity defined byusing imaginary part of plane impedance yields the worst result. So far asTEMS method is concerned, the whole-region definition of apparent resistivityis more effective than distant-region or nearby-region approximate definition.Studies also reveal that the whole-region apparent resistivity defined by timederivative of magnetic field sometimes has multi-solutions or even nosolution,whereas the apparent resistivity defined by magnetic field itseif is quiteeffective. For FEMS method, similar discussion is also made concerning thedefinition of whole-region apparent resistivity, and the result obtained, thoughnot so ideal as the result of TEMS method, is somewhat better than the appa-rent resistivity response defined under the condition of commonly-used largeand small induction values. This paper has made physical interpretation of thefalse extremum effect of apparent resistivity response curve that appears inelectromagnetic sounding method.