【摘要】：大地電磁測深法(MT)是利用天然場源勘探地下電性結(jié)構(gòu)的一種頻率域地球物理勘探方法。與人工源電磁勘探方法相比,大地電磁測深法具有獨特的優(yōu)點,如施工方便、探測深度大、對低阻體反映靈敏等。目前大地電磁測深法主要應(yīng)用于深部礦產(chǎn)資源勘探、大地構(gòu)造研究、天然地震預(yù)報等領(lǐng)域。大地電磁測深反演直接影響其在各個領(lǐng)域的應(yīng)用效果。大地電磁反演存在多解性,加上電磁場在地下快速衰減,使深部分辨率降低。大地電磁約束反演的研究對于提高大地電磁反演精度、減小多解性,及廣泛應(yīng)用具有重要意義。本文回顧了大地電磁約束反演的研究現(xiàn)狀,推導(dǎo)、總結(jié)了大地電磁測深基本理論和約束反演基本理論。針對大地電磁反演中模型參數(shù)修改量的修正選取困難問題提出了基于約束條件修正模型參數(shù)修改量的約束反演方法。通過最小二乘約束反演方法,計算、分析對比了不同參數(shù)反演、不同約束方式及不同約束誤差限的反演效果。HKHKH型地電斷面不同計算結(jié)果表明:被約束層的反演效果得到提高,被約束層的反演效果提高的幅度與約束誤差限成反變關(guān)系;累層約束的層數(shù)越多,約束誤差限越小,對整體反演效果提高越顯著;總參數(shù)平均相對誤差與約束誤差限成正變關(guān)系。對下鄰層反演精度的提高幅度與約束誤差限成反變關(guān)系,但可能會降低無約束反演時已經(jīng)反演得較好的層位的反演結(jié)果。無約束反演時的層參數(shù)平均相對誤差越大,累層約束把該層約束后,對模型整體反演效果提高越顯著,反之亦然。累層約束反演情況下,參數(shù)總平均相對誤差與約束反演的累層層數(shù)成反變關(guān)系。研究結(jié)果表明:大地電磁約束反演可在一定程度上提高整體反演精度,有利于減少多解性。
[Abstract]:Magnetotelluric sounding (MT) is a frequency-domain geophysical method for the exploration of underground electrical structures using natural field sources. Compared with artificial source electromagnetic exploration method, magnetotelluric sounding method has unique advantages, such as easy construction, large detection depth, sensitive to low resistivity body, and so on. At present, magnetotelluric sounding is mainly used in deep mineral resources exploration, geotectonic research, natural earthquake prediction and other fields. Magnetotelluric sounding inversion directly affects its application in various fields. There are many solutions in magnetotelluric inversion and the fast attenuation of electromagnetic field in underground makes the deep resolution lower. The study of magnetotelluric inversion is of great significance for improving the precision of magnetotelluric inversion, reducing the multiplicity of solutions and its wide application. This paper reviews the research status of magnetotelluric constrained inversion, deduces the basic theory of magnetotelluric sounding and the basic theory of constrained inversion. In this paper, a constrained inversion method based on the modified model parameters is proposed to solve the difficult problem of modifying the parameters of the model in magnetotelluric inversion. Through the least square constrained inversion method, the inversion effects of different parameters inversion, different constraint ways and different constraint error limits are analyzed and compared. The results of different computation results of HKHKH type geoelectric section show that the inversion effect of the constrained layer is improved. The amplitude of the inversion effect of constrained layer is inversely related to the constraint error limit, the more layer constraints are, the smaller the constraint error limit is, and the more significant the inversion effect is to the whole inversion. The mean relative error of total parameter is positively correlated with the constraint error. The improvement of the inversion accuracy of the lower adjacent layer is inversely related to the constraint error, but it may reduce the inversion results of the unconstrained inversion. The larger the average relative error of the layer parameters in the unconstrained inversion is, the more significant the inversion effect of the model is when the layer is constrained by the layer constraint, and vice versa. In the case of constrained inversion, the total average relative error of parameters is inversely related to the cumulative layer number of constrained inversion. The results show that magnetotelluric constrained inversion can improve the whole inversion accuracy to some extent and reduce the multiplicity of solutions.
【學(xué)位授予單位】：長安大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：P631.325

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