自適應(yīng)有限元法的大地電磁二維各向異性正反演
本文選題:大地電磁法 切入點:二維反演 出處:《石油地球物理勘探》2016年04期 論文類型:期刊論文
【摘要】:電性各向異性廣泛存在于地殼和上地幔范圍內(nèi),對觀測電磁場有不可忽視的影響。大地電磁法能夠探測大范圍深部電性結(jié)構(gòu)并反映其各向異性特征,但目前關(guān)于該方法各向異性二維正反演的研究還有待加深。利用基于非結(jié)構(gòu)網(wǎng)格的自適應(yīng)有限元法求解對角各向異性情況下大地電磁正演控制方程,既有利于起伏地形和復(fù)雜地質(zhì)構(gòu)造的建模,又便于模擬包含多種尺寸結(jié)構(gòu)的地電模型;網(wǎng)格的自動細(xì)化可避免人為網(wǎng)格劃分導(dǎo)致的計算誤差并可提高計算效率。反演算法則采取了經(jīng)典模型空間Occam策略,使得模型的搜索過程非常穩(wěn)定,能在較少迭代次數(shù)內(nèi)獲得合理的反演結(jié)果。對經(jīng)典四層層狀模型和二維各向異性塊體模型進(jìn)行了正演模擬試算,并分別與一維準(zhǔn)解析解、二維有限差分?jǐn)?shù)值解結(jié)果進(jìn)行對比,驗證了正演算法的準(zhǔn)確性;最后對一復(fù)雜海底起伏各向異性模型進(jìn)行了反演試算,反演結(jié)果準(zhǔn)確反映了各向異性異常體的存在,并成功地還原了真實模型的主要電性特征。
[Abstract]:The electrical anisotropy exists widely in the crust and upper mantle and has an important influence on the observation of electromagnetic field. The magnetotelluric method can detect the electrical structure in a wide range of depth and reflect its anisotropic characteristics. However, the research on anisotropic two-dimensional forward and inverse modeling of this method needs to be deepened. An adaptive finite element method based on unstructured meshes is used to solve the magnetotelluric forward control equations under diagonal anisotropy. It is not only beneficial to the modeling of undulating terrain and complex geological structure, but also convenient to simulate the geoelectric model with various sizes. The automatic mesh thinning can avoid the error caused by artificial mesh generation and improve the computational efficiency. The inversion algorithm adopts the classical model space Occam strategy, which makes the search process of the model very stable. Reasonable inversion results can be obtained in fewer iterations. The forward simulation of the classical four layer model and the two dimensional anisotropic block model is carried out, and the results are compared with the results of one dimensional quasi analytical solution and two dimensional finite difference numerical solution, respectively. The accuracy of the forward algorithm is verified, and the inversion of a complex seafloor undulating anisotropic model is carried out. The inversion results accurately reflect the existence of anisotropic anomaly and successfully restore the main electrical characteristics of the real model.
【作者單位】: 中國地質(zhì)大學(xué)地球物理與空間信息學(xué)院地球內(nèi)部多尺度成像湖北省重點實驗室;中國海洋大學(xué)海洋地球科學(xué)學(xué)院;
【基金】:國家自然科學(xué)基金項目(41274077,41474055) 湖北省自然科學(xué)基金項目(2015CFA019)聯(lián)合資助
【分類號】:P631.325
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