本文選題：層狀各向異性介質(zhì)　切入點：阻抗張量　出處：《長安大學(xué)》2017年碩士論文

【摘要】：目前常規(guī)的大地電磁測深資料的正反演是基于各向同性介質(zhì)理論進行的,但是隨著人們認識不斷地加深,地下各向異性介質(zhì)逐漸引起人們的關(guān)注,越來越多的資料顯示,地殼和上地幔介質(zhì)是各向異性的。地下介質(zhì)的物理性質(zhì)如彈性、導(dǎo)電性、磁性、密度等都是各向異性的,然而大地電磁阻抗響應(yīng)函數(shù)對不同方向電導(dǎo)率很敏感,通過地表觀測大地電磁響應(yīng),再進行基于大地電磁各向異性理論反演,就能夠得到張量電導(dǎo)率。本文首先回顧了大地電磁各向異性正反演研究現(xiàn)狀,推導(dǎo)總結(jié)了大地電磁各向異性正演阻抗響應(yīng)解析表達式,不同于一維各向同性理論,層狀各向異性介質(zhì)阻抗是張量,即Z_(xx)、Z_(xy)、Z_(yx)、Z_(yy),且電導(dǎo)率張量一般具有對稱性,所以Z_(xx)=Z_(yy),Z_(xy)≠Z_(yx)。通過對兩層,三層,四層模型進行正演模擬,同時為了研究參數(shù)對正演結(jié)果的影響,對兩層模型逐一改變電阻率ρ_1、ρ_2、ρ_3,旋轉(zhuǎn)角度α_L、α_D、α_S得到:(1)輔助阻抗(Z_(xx)、Z_(yy)與主阻抗(Z_(xy)、Z_(yx)的數(shù)量級相差較大,因此輔助阻抗對地下介質(zhì)反應(yīng)程度比較低;(2)對阻抗進行參數(shù)靈敏度分析,阻抗對于某一層的各向異性角度,厚度最為靈敏,其次是電導(dǎo)率;(3) ρ_1、 ρ_2方向的電阻率對于正演結(jié)果影響同時存在的,而ρ_3基本不影響;(4)旋轉(zhuǎn)角度α_L,α_D, α_S同時影響正演的結(jié)果,因此ρ_(xy),ρ_(yx)對于不同方向電阻率的反應(yīng)是由電阻率和旋轉(zhuǎn)角度共同決定的。在各向異性正演理論的基礎(chǔ)上,通過阻尼最小二乘法進行全參數(shù)的反演,即對模型的三個方向電阻率,三個旋轉(zhuǎn)角度,以及厚度進行反演,同時舍棄輔助視電阻率,擬合兩個主視電阻率,選取合適的初始模型,得到了理想的反演結(jié)果。由于全參數(shù)反演模型的輸入?yún)?shù)比較多,反演結(jié)果受初始模型影響比較大。若初始模型選取不合適,則得不到合理的結(jié)果。因此在反演中,加入了可行方向法,一定程度上抑制了反演的多解性。通過對二層,三層,四層理論模型反演計算,反演結(jié)果與實際參數(shù)基本吻合,為了驗證程序的抗噪聲能力,將三層模型加入5%的噪聲反演,反演結(jié)果基本能與實際參數(shù)吻合。
[Abstract]:At present, the forward inversion of conventional magnetotelluric sounding data is based on the theory of isotropic medium, but with the deepening of people's understanding, the underground anisotropic media gradually attracts people's attention, and more and more data show that,The crust and upper mantle media are anisotropic.The physical properties of underground media such as elasticity, conductivity, magnetism and density are anisotropic. However, magnetotelluric impedance response function is sensitive to conductivity in different directions.Based on magnetotelluric anisotropy theory inversion, Zhang Liang conductivity can be obtained.In this paper, the present situation of magnetotelluric anisotropy forward and inverse modeling is reviewed, and the analytical expression of magnetotelluric anisotropic forward impedance response is deduced and summarized. Different from one-dimensional isotropic theory, the impedance of layered anisotropic medium is Zhang Liang.Therefore, the secondary impedance has a relatively low degree of response to the underground medium.) the impedance is the most sensitive to the anisotropic angle of a certain layer, and the thickness of the impedance is the most sensitive.Secondly, the resistivity of 蟻 _ 1, 蟻 _ s _ 2 direction has a simultaneous effect on the forward result, while 蟻 _ s _ 3 has no effect on the rotation angle 偽 _ L, 偽 _ S _ D, 偽 _ S simultaneously affects the result of forward modeling, while 蟻 _ s _ 3 has no effect on the rotation angle of 偽 _ L, 偽 _ S _ D, 偽 -S simultaneously.Therefore, the response of 蟻 _ S _ XY _ x to resistivity in different directions is determined by both resistivity and rotation angle.On the basis of anisotropic forward modeling theory, the damping least square method is used to inverse all parameters, that is, inversion of three directions resistivity, three rotation angles and thickness of the model, at the same time giving up the auxiliary apparent resistivity.Fitting the two principal apparent resistivity and selecting the appropriate initial model, the ideal inversion results are obtained.Due to the large number of input parameters of the full parameter inversion model, the inversion results are greatly affected by the initial model.If the initial model is not suitable, there is no reasonable result.Therefore, the feasible direction method is added to the inversion, which to some extent inhibits the multi-solvability of the inversion.In order to verify the anti-noise ability of the program, the inversion results of the two-layer, three-layer and four-layer theoretical models are basically consistent with the actual parameters. In order to verify the anti-noise ability of the program, 5% noise inversion is added to the three-layer model, and the inversion results are basically consistent with the actual parameters.
【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】：2017
【分類號】：P631.325

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