【作者】 余年；

【导师】 王绪本；

【作者基本信息】 成都理工大学 ， 信号与信息处理， 2008， 硕士

【摘要】 本文采用先进的资料处理与解释技术对龙门山大地电磁(MT)剖面资料进行了分析,研究得到较为可信的龙门山构造带中段地壳电性结构。结合前人的地质研究成果等,发挥大地电磁方法的优势,针对龙门山构造带的龙门山地壳结构、盆山耦合关系等热点问题进行了探讨和研究。文章首先详细介绍了龙门山剖面工作情况,该剖面南起中江,经龙门山穿过松潘,进入若尔盖到达禄曲,跨越了川西前陆盆地、龙门山构造带、松潘-甘孜褶皱带和西秦岭造山带等,并对大地电磁资料处理的流程进行了简要介绍。重点对剖面进行定性解释研究。通过张量阻抗旋转确定了区域构造走向,由分析结果得到剖面的最佳方位角为北西-南东向,与剖面的布置方向大致相同;采用Mohr圆分析法对全部49个测点进行分析,得到了二维偏离角和各向异性角,结论是剖面整体表现为二维性,其中龙门山构造带三维性和各向异性表现均较强;阻抗的二维偏离度也可以得出类似的结论;通过二维有限元对断裂模型正演模拟,总结出倾子资料特征规律,对实测倾子分析发现相对电阻率反演结果,其对断裂构造的反映更细致、信息更丰富;通过曲线类型和视电阻率、相位断面图特征分析,了解了主要构造的电性特点,为剖面的电性解释提供了基础。对反演模式的选择,二维反演的基本理论等问题进行了讨论,并就几种常用反演方法进行了比较,考察了它们对初始模型的依赖程度、收敛的稳定性、反演效果的优劣等问题,采用了非线性共轭梯度(NLCG)反演技术和TE+TM联合模式,对沿剖面的资料进行了反演得到了剖面的地壳二维电性结构。以龙门山构造带为重点,介绍了剖面沿线主要构造的地层、断裂等基本地质情况,并结合定性分析的结果,分析剖面的二维电性结构,再次证明龙门山逆冲推覆构造的存在,清楚地揭示四川盆地表现为下部高阻上部低阻层的二元结构,揭示了松潘-甘孜褶皱带浅部存在较高的高阻带,深部为低阻带的低-高-低的电性结构特征;并对剖面中主要断裂的位置和产状作出了说明。最后,结合此次大地电磁剖面对汶川地震进行简单的分析,并结合其他资料得出了龙门山构造带表现为逆冲推覆构造和汶川地震震源浅的结论,对剖面经过的余震区的震源深度进行探讨,发现其余震震源深度位置均约为10km左右,与大地电磁剖面揭示的深度大致相同。更多还原

【Abstract】 This paper analysed the Magnetotelluric sounding(MT) profile data of Longmen Mountain with advanced data-processing technique, we provide rather reliable electrical structure of the crust mantle in the middle section of Longmen Mountain structural belt. Combining with the basic geology and using the advancement of MT, we discussed and did research on the hot issues of the Longmenshan crustal structure and on Basin-mountain Coupling of Longmenshan structural belt.The article first detailed the work of Longmen Mountain profile,the profile from Zhongjiang in the South, through Longmen Mountain and Songpan, accessed Ruoergai block, arrived in Luqu,Gansu, crossover foreland basin of Sichuan Basin, Longmenshan structural belt, fold belt of Songpan-Ganzi and West Qinling Orogen, and summary introduced the data processing of MT.Secondly, we focused on qualitative analysis of profile. By the rotation of tensor impedance, we certained regional structural trend of profile, Results from the analysis the best azimuth is NW-SE, roughly the same direction of the layout of the profile; All 49 points were analyzed with Mohr circle analysis method, obtained angle of deviation and angle of nonisotropy of two-dimensional, concluded that the overall performance of the two-dimensional, and Longmen Mountain has strong performance of 3D and nonisotropy; Form the two dimension degree of deviation of impedance, we can have the same conclusion of Mohr circle analysis method;made a forward simulation of tilted fault model by using two-dimension simulation programme, summed up the characteristics of tipper, by analysis of the actual tipper, it is obvious that, in comparison of inversion result of resistivity, data of tipper reflect more detailedly to fault structure with more information; by analysis of curve, apparent resistivity, phase, understand the major electrical structure features, provides a basis of the interpretation of the electrical structure. Thirdly, we discussed the inversion model and two-dimensional inversion of the basic theory, compared several commonly inversion methods, study the issues such as the dependency of initial model, the stability of convergence ,the superior and inferior of inversion results, used the Non-liner conjugate gradient method and TE&TM combined mode for two-dimensional inversion, and obtain the two-dimensional electrical structure of the crust of the profile.Fourthly, we focus on Longmenshan structural belt, introduced the basic geological conditions of main structure’s layer and fault along the profile,with qualitative analysis of the results, analysis two-dimensional electrical structure of the crust, once again proves the existence of thrust tectonic of Longmen Mountain, clearly reveals the dual structure of the high resistance in lower part and the low resistance in upper part of Sichuan basin, reveals that there have resistive bed in superficial part and low resistance zone for the deep of Songpan-Ganzi fold belt, electrical characteristics of Low-High-Low; and made a note of the location and attitude of major fault.Finally, combined with MT profile, we do a simple analysis of Wenchuan earthquake ,with other information can have the conclusion of thrust tectonic and the focal depth of Wenchuan earthquake is very low, and discuss the aftershock zone of the focal depth, found that focal depth of aftershock were about 10km,it is the same as MT profile reveals.更多还原