共查询到18条相似文献，搜索用时 171 毫秒
1.
《地球物理学进展》2016,(6)
受计算机硬件水平限制,大地电磁(MT)三维反演难以在实际中推广应用,MT数据解释仍以二维反演为主.地质构造具有一定的二维性特征,但不同的地质构造走向往往不同、MT测线无法与每个构造的走向垂直,这使得实际MT数据并不满足严格的二维反演条件.因此,有必要开展大地电磁测深二维反演对"准二维"地质构造的适应性研究.本文设计三个理论地电模型,通过三维正演计算获得各测点大地电磁响应,以此模拟实际观测数据.对MT数据进行相位张量分析,结果表明设计的地电模型主要表现为二维性特征.利用非线性共轭梯度(NLCG)反演算法对理论MT数据进行二维反演研究,重点讨论了测线方向、电性主轴旋转策略及反演模式选择,对反演结果的影响.对比分析反演结果,得到如下认识:1.测线方向对反演结果影响较小;2.电性主轴旋转角度对反演结果影响较大;3.TE+TM联合模式及单独TM模式的反演效果较好.研究结果表明:当一条测线下方在横向与纵向上存在走向不同的多个异常体时,对整条剖面分测点、分频段进行电性主轴旋转,反演所得结果最可靠. 相似文献
2.
局部畸变问题曾经困扰大地电磁资料反演解释几十年,大地电磁三维数值模拟技术的发展为剖析局部畸变特点和得到可靠的反演成像结果提供了技术基础。本文采用三维数值模拟成像方法对典型三维局部畸变模型进行模拟分析。三维数值模拟结果显示:电场分量垂直电性分界面的极化模式视电阻率曲线(对应二维情况下TM模式)在穿越低阻异常体界面时,曲线会先上移后下移,而在穿越高阻异常体界面时,曲线会先下移后上移,这与电性分界面处积累面电荷产生的二次电场有关。三维模型中XY模式、YX模式视电阻率和相位在三维异常体附近的水平变化是呈现近似垂向对称的,该现象与电场垂直跨越电性界面时视电阻率的变化规律是吻合的,当测线分别沿X方向和Y方向展布时,三维情况下的XY和YX模式分别对应二维情况下的TM模式。低阻小异常体对区域构造响应的畸变影响比高阻小异常体要严重。低阻小异常体对二维区域响应的两种极化模式视电阻率和相位都有非常明显的畸变影响,相比较而言对TE模式的畸变要大于TM模式,因此我们在做二维反演解释时,可优先考虑拟合TM模式数据。位于小异常体中心上方测点的三维畸变响应虽然与对应真实二维区域响应的差异比较大,但可以等效于某种二维模型响应,这种由局部畸变造成的假二维响应在实际野外数据的解释中是需要注意的。 相似文献
3.
针对大地电磁二维反演中TE、TM极化模式的选择问题,设计了多个二维、三维模型进行了正演计算,从数据对比和反演结果对比两方面入手,分析研究了三维模型和二维模型响应数据的差异、反演中极化模式的选择、以及三维模型数据的二维反演近似等问题.研究结果表明:在三维模型条件下,利用二维模型进行反演时,TE模式对模型的二维的近似程度要求远高于TM模式;当三维结构影响较明显时,利用TM模式数据进行二维反演比利用TE模式或利用TE+TM模式联合反演都更合理,反演结果中的虚假结构明显减少;对于TM模式,相位受三维畸变影响较小,视电阻率较大,所以二维反演中可适当加大相位的权;对于实测数据的二维反演,应优先考虑采用TM模式数据进行二维反演,其次是TM+TE模式,一般不要单独采用TE模式. 相似文献
4.
《地球物理学进展》2016,(3)
应用CSAMT方法进行标量测量时,一般要求测线沿垂直构造走向的方向布测.在实际测量的时候由于地表条件复杂经常出现无法判断地下构造走向的情况,例如,在长白山地区进行CSAMT测量,由于表面覆盖有玄武岩无法判断地下构造走向,对得到的标量数据进行一维、二维反演处理时无法判断哪种反演方式的结果更准确.鉴于此,建立三维地质模型,应用CSAMT三维正演程序进行数值模拟.研究测线与构造走向平行,呈45°及垂直三种情况下的一维、二维反演,对结果做比较分析.实验结果表明,测线平行构造走向时,一维、二维反演结果近似;测线与构造走向呈45°或垂直时,二维反演结果比一维反演结果对异常体的形状,大小,埋深及电性参数反演的更准确. 相似文献
5.
九瑞矿集区作为全国重点整装勘查区之一,深部找矿工作一直是研究重点和热点.本文在综合分析研究区区域地质资料、对典型地层和岩石标本进行电阻率参数测试和统计分析的基础上,利用研究区面积性AMT数据进行三维电性结构研究.为获得AMT最佳反演参数,选择一条典型AMT剖面开展二维非线性共轭梯度(NLCG)反演,进而总结出利用TM极化模式数据、拉格朗日乘子等于3的二维反演方案.综合利用地质、钻探和电性特征对全区23条AMT剖面进行二维约束反演,并将所有测线的电阻率反演结果三维网格化,得到了研究区的三维电性结构.最后,我们通过对三维电性结构的综合分析,确定研究区地下地层、岩体展布、断裂构造分布特征以及基底起伏情况.与已知矿床对比,我们发现浅部北西断裂与北东向区域性深部断裂交汇处、基底隆起凹槽边缘以及岩体边缘为成矿有利区. 相似文献
6.
交错模型指的是由几组走向不同的线性构造（近似二维）在空间（纵向、横向）上组合而成的模型.对于电性结构，交错模型表现为纵向或横向上的构造存在电性主轴方位的变化.从构造维性的角度来看，交错模型是一种由二维模型组合而成的特殊的三维模型，直接对其进行大地电磁二维反演，不易获得可靠的反演结果.本文针对交错模型的特点，提出分频段-分区段反演方案.该方案首先需要借助于阻抗张量成像技术，在频率域确定组成交错模型的各线性构造的电性主轴，然后，针对不同的频段、区段，选择对应电性主轴的数据进行反演，通过初始模型的构建将不同电性主轴方位的反演结果对接起来.本文通过三维理论模型的研究，系统展示了分频段-分区段反演的全过程，归纳得到：在分频段反演时先做低频段反演，在分区段反演时先做二维性更不显著一侧的反演.最后，本文将这一技术用于郯庐断裂带中南段一条实测剖面的反演中，其结果与常规二维反演结果相比较，深部的信息更为丰富，且与其他已有地质、地球物理结果的可对比性更好，表明在构造复杂地区，大地电磁分频段-分区段二维反演具有较高的模型分辨率和可靠性. 相似文献
7.
穿过郯庐断裂带中段（沂沭断裂带,36°N）所做的大地电磁测深（MT）剖面长约150km.使用Robust技术和远参考道大地电磁方法处理观测数据.通过分析视电阻率、阻抗相位、Swift二维偏离度和区域走向,定性确定测区的电性结构.二维反演解释中选择非线性共轭梯度（NLCG）方法,使用TE、TM两种模式资料联合反演,沿剖面的二维电性结构显示：自西向东,鲁西隆起、郯庐断裂带、胶莱坳陷及鲁东隆起4个电性区块分别对应,鲁东和鲁西隆起区为高阻,郯庐断裂带电性结构复杂,高、低阻相间,胶莱坳陷为低阻（高导）区.沿MT剖面附近曾发生3个地震,其震源区处在电性变化剧烈部位,并在震源区附近存在高导体. 相似文献
8.
佳木斯地块及东缘是中国东北地区的重要地质构造单元. 为探测该地区地壳深部结构与构造关系，沿桦南—饶河实施了240 km的大地电磁测深的探测研究. 采用光滑模型二维反演方法对桦南—饶河大地电磁剖面的探测数据进行了二维反演和综合地球物理解释. 研究结果揭示了研究区断面域的电性结构：(1)剖面西段具有稳定的高阻特征且具有稳定的岩石圈厚度（约90km），在十几公里深度范围存在壳内高导层，该区段对应佳木斯地块. (2)剖面中部具有明显的电性梯度带，该梯度带反映了佳木斯地块的东界位置及其深部的结构形态. (3)剖面东段电性特征揭示了佳木斯地块以东区段浅部为逆冲推覆体，深部为多个高阻块体和低阻条带相间的电性结构，这些高阻块体可能为早期俯冲的岩石圈残片. 相似文献
9.
横过松嫩地块东缘和佳木斯地块西缘的大地电磁测深剖面揭示了两块体结合带附近的深部电性结构.本文对剖面测点做了标准化数据处理,并对二维偏离度、构造走向进行了计算和分析,采用非线性共轭梯度(NLCG)二维反演方法对TM模式的数据进行了反演,获得了该剖面的地壳、上地幔电性结构模型,划分出三个典型构造单元:松嫩地块东缘、碰撞拼合带和佳木斯地块西缘.研究结果表明,研究区上地壳基本呈高阻特征,可能为岩浆岩,代表其经历了多期次岩浆作用,而松嫩地块东缘和佳木斯地块西缘的中下地壳的高导体可能与地幔物质的上涌有关;拼合带下方存在西倾的高导体和高阻体,可能是佳木斯地块向西俯冲到松嫩地块下方的构造遗迹;研究区可能发生了拆沉作用,与之伴随的地幔物质上涌可能是后期伸展作用的一个动力. 相似文献
10.
横跨大兴安岭与海拉尔盆地和松辽盆地结合地带的大地电磁测深剖面揭示了盆山构造的深部电性结构.剖面西起海拉尔盆地东缘,向东延伸穿过大兴安岭中部,一直到达松辽盆地西缘.本文对剖面测点的二维偏离度、构造走向等进行了计算和分析,采用非线性共轭梯度(NLCG)二维反演方法对TM模式的数据进行了反演,获得了该剖面的地壳、上地幔电性结构模型,划分出三个典型构造单元:海拉尔盆地、大兴安岭和松辽盆地.研究结果表明,海拉尔盆地东缘和松辽盆地西缘浅部都呈低阻特征,但松辽盆地西缘深部电性结构比较复杂,而大兴安岭整体呈高阻特征.海拉尔盆地东缘可能属于兴安块体,松辽盆地西缘与大兴安岭接触关系复杂.海拉尔盆地东缘岩石圈厚度约为110km,大兴安岭岩石圈厚度约为110~150km.大兴安岭上地壳基本呈高阻特征,可能为多次叠置的岩浆岩,代表大兴安岭经历了多期次岩浆作用;中下地壳横向存在较大范围低阻体,可能反映了大兴安岭地壳内部非刚性的特点;残存在岩石圈地幔的高阻异常,说明其下地壳可能发生过拆沉作用.大兴安岭与松辽盆地结合带存在一个岩石圈尺度的西倾低阻带,向下延伸到岩石圈底部,可能是早期松嫩地块向兴安地块俯冲并以软碰撞形式拼合的构造遗迹. 相似文献
11.
Application of 2D magnetotelluric methods in a geological complex area, Xinjiang, China 总被引：2，自引：0，他引：2
Qibin Xiao Xinping CaiGuanghe Liang Xingwang XuBaolin Zhang 《Journal of Applied Geophysics》2011,75(1):19-30
Magnetotelluric (MT) data along two profiles were collected in Tulargen Cu-Ni mining area, Xinjiang, China. The MT profiles, crossing the known ore-bearing magmatic body, are interpreted to have further understanding of the ore-bearing magmatic bodies' stretch and shape in depth, and to evaluate the prospect in the mining area. The values of phase sensitivity skewness indicate a contaminated two-dimensional (2D) structure (there exist local three-dimensional (3D) structures at shallow level) over 3D structures. G-B decomposition of the impedance tensors indicates the dominant geoelectrical strike in survey area is in East-West direction. To obtain reliable electrical structures, four different 2D inversion codes as REBOCC, NLCG, OCCAM, and ABIC are adopted, inversions of a synthetic 3D model using these codes indicate TM data are more suitable to invert the electrical structures along the profiles in Tulargen Cu-Ni mining area, while TE and TE + TM inversions can be used to verify the transverse variation of electrical structures at shallow level. The 2D electrical structures show high-resistivity basement covered by relatively low-resistivity strata in the mining area, the conductive anomalies are imbedded in the upper covers. The known ore-bearing magmatic body is coincided with the positions of two conductive anomalies in both profiles at shallow level; its extension at depth is deduced according to the shapes of the anomalies. Other conductive anomalies, isolated and existing only at limited depth as the known ore-bearing magmatic body, are presumed of good prospect. 相似文献
12.
APPLYING 3D INVERSION OF SINGLE-PROFILE MAGNETOTELLURIC DATA TO IDENTIFY THE SHADE AND YUNONGXI FAULTS 
下载免费PDF全文
下载免费PDF全文 JIANG Feng CHEN Xiao-bin DONG Ze-yi CUI Teng-fa LIU Zhong-yin WANG Pei-jie 《地震地质》2019,41(6):1444-1463
Many synthetic model studies suggested that the best way to obtain good 3D interpretation results is to distribute the MT sites at a 2D grid array with regular site spacing over the target area. However, MT 3D inversion was very difficult about 10 years ago. A lot of MT data were collected along one profile and then interpreted with 2D inversion. How to apply the state-of-the-art 3D inversion technique to interpret the accumulated mass MT profiles data is an important topic. Some studies on 3D inversion of measured MT profile data suggested that 2D inversions usually had higher resolution for the subsurface than 3D inversions. Meanwhile, they often made their interpretation based on 2D inversion results, and 3D inversion results were only used to evaluate whether the overall resistivity structures were correct. Some researchers thought that 3D inversions could not resolute the local structure well, while 2D inversion results could agree with the surface geologic features much well and interpret the geologic structures easily. But in the present paper, we find that the result of 3D inversion is better than that of 2D inversion in identifying the location of the two local faults, the Shade Fault(SDF)and the Yunongxi Fault(YNXF), and the deep structures.
In this paper, we first studied the electrical structure of SDF and YNXF based on a measured magnetotelluric(MT) profile data. Besides, from the point of identifying active faults, we compared the capacity of identifying deep existing faults between 2D inversion models and 3D models with different inversion parameters. The results show that both 2D and 3D inversion of the single-profile data could obtain reasonable and reliable electrical structures on a regional scale. Combining 2D and 3D models, and according to our present data, we find that both SDF and YNXF probably have cut completely the high resistivity layer in the upper crust and extended to the high conductivity layer in the middle crust. In terms of the deep geometry of the faults, at the profile's location, the SDF dips nearly vertically or dips southeast with high dip angle, and the YNXF dips southeast at depth. In addition, according to the results from our measured MT profile, we find that the 3D inversion of single-profile MT data has the capacity of identifying the location and deep geometry of local faults under present computing ability. Finally, this research suggests that appropriate cell size and reasonable smoothing parameters are important factors for the 3D inversion of single-profile MT data, more specifically, too coarse meshes or too large smoothing parameters on horizontal direction of 3D inversion may result in low resolution of 3D inversions that cannot identify the structure of faults. While, for vertical mesh size and data error thresholds, they have limited effect on identifying shallow tectonics as long as their changes are within a reasonable range. 3D inversion results also indicate that, to some extent, adding tippers to the 3D inversion of a MT profile can improve the model's constraint on the deep geometry of the outcropped faults. 相似文献
13.
《Journal of Applied Geophysics》2006,58(3):218-231
This study deals with two-dimensional (2D) inversions of synthetic and observed radiomagnetotelluric (RMT) data on typical buried conductive waste sites in Europe, and with the practical aspects of different inversion algorithms. In the inversion calculations, we used smoothing and L2-norm stabilizers and compared the results. The resolution of the geometry of the highly conductive waste site, in particular, was investigated. In the inversion with the L2-norm stabilizer, we used the least-squares solution with singular value decomposition (LSSVD) and conjugate gradient (CG), whereas only the conjugate gradient solver was used in the 2D-inversion with the smoothing stabilizer. The inversion results of the synthetic data showed a better resolution of the geometry of the highly conductive waste site when a L2-norm stabilizer was applied in the inversion; in particular, a better detection of the bottom of the waste deposit was achieved. Additional model studies were carried out using synthetic RMT data in order to investigate the 2D inversion of RMT data observed on a 3D structure; these studies showed that the use of TM mode data yields a better resolution of the structure than joint inversion of TE and TM modes.2D inversions of RMT data on a waste site near Cologne showed that the inversion of the TM mode could resolve well the geometry, especially the bottom of the waste site, if information about the background conductivity structure was available. In this case study, inversion with the L2-norm stabilizer produced a sharper image of the waste site than inversion with the smoothing stabilizer, as indicated also by the inversion study that used synthetic data. 相似文献
14.
G. Michael Hoversten 《Geophysical Prospecting》1996,44(6):935-961
Hydrocarbon exploration in the Papuan fold belt is made extremely difficult by mountainous terrain, equatorial jungle and thick karstified Miocene limestones at the surface. The high-velocity karstified limestones at or near the surface often render the seismic technique useless for imaging the subsurface. In such areas magnetotellurics (MT) provides a valuable capability for mapping subsurface structure. The main structural interface which can be mapped with MT, due to the large electrical contrast, is the contact between the resistive Darai limestone and the underlying conductive sediments of the Ieru Formation. In some areas the base of the Darai can be mapped with reasonable accuracy by fitting 1D models to the observed MT data. However, in many cases where 2D and 3D effects are severe, 1D interpretations can yield dramatically incorrect results. Numerical and field data examples are presented which demonstrate the severity of the 1D errors and the improvements in accuracy which can be achieved using a 2D inverse solution. Two MT lines over adjacent anticlines, both with well control and seismic data, are used to demonstrate the application of 1D and 2D inversions for structural models. In both cases the seismic data provide no aid in the interpretations. The example over the Hides anticline illustrates a situation where 1D inversion of either TE or TM mode provides essentially the same depth to base of Darai as 2D inversion of both TE and TM. Both models provide base Darai depth estimates which are within 10% of that measured in the well. The example over the Angore anticline illustrates the inadequacy of 1D inversion in structurally complex geology complicated by electrical statics. The TE mode fits a 1D Darai thickness of 800 metres while the TM mode fits a 1D Darai thickness of 3500 metres, bracketing the thickness of 2450 metres observed in the well. The final 2D inversion model provides a depth estimate of 2250 metres. Four MT lines along the Angore anticline have been interpreted using 2D inversion. A high degree of correlation exists between lineaments observed on an airborne radar image and zones of low resistivity within the high-resistivity material interpreted as Darai limestone. These low-resistivity zones are interpreted as fault zones. Three-dimensional modelling has been used to simulate 3D statics in an otherwise 2D earth. These data were used to test the Groom-Bailey (GB) decomposition for possible benefits in reducing static effects and estimating geoelectric strike in the Papua New Guinea (PNG) field data. It has been found that the GB decomposition can provide improved regional 2D strike estimates in 3D contaminated data. However, in situations such as PNG, where the regional 2D strike is well established and hence can be fixed, the GB decomposition provides apparent resistivities identical to those simply rotated to strike. 相似文献
15.
Introduction Ready and Renkin (1971) were the first to make the research on anisotropy problems in magnetotellurics (MT). The progress in the research is not evident because it is more complex and difficult than isotropic problems. Now, the one-dimensional (1D) anisotropy problems in MT have been well solved, while for the two-dimensional (2D) cases, the numerical solutions have only been obtained for some particular conditions (Ready and Renkin, 1975). As to the three-dimensional (3D) ani… 相似文献
16.
M. Bastani A. Savvaidis L.B. Pedersen T. Kalscheuer 《Journal of Applied Geophysics》2011,75(2):180-195
In order to gain a better understanding of the geometry of surface faults, five Controlled Source/Radio Magnetotelluric (CSRMT) profiles were measured across the Volvi basin, 45 km northeast of the city of Thessaloniki in Greece. The data were collected in two frequency ranges: a) 1–12.5 kHz using a remotely controlled double horizontal magnetic dipole transmitter (CSAMT measurements), and b) 15–250 kHz using the signal from distant radio transmitters (RMT measurements). The transition from the RMT band to the CSAMT band was smooth and continuous allowing us to combine both datasets for plane-wave modeling. The surface geology shows a predominantly 2D structure, and therefore we planned the survey into profiles perpendicular to the geological strike. We have used a 2D interpretation tool to model the data in TE, TM, TE + TM and determinant modes. Using a 4% error floor on the impedance, 2D resistivity models from inversion of the determinant data provide lower RMS data fits (4.2 and 1.2 for resistivity and phase, respectively) compared to the combined TE + TM data (4.4, 2.8, overall resistivity and phase, respectively). 2D inversion of the measured tensor data shows a sharp change in the depth to the top of resistive gneiss–schist basement that is overlain by a less resistive overburden at southern basin flanks. The change in depth to the bedrock is clearly seen in all 2D models along the measured profiles suggesting the existence of normal faults with strike directions of NE–SW to E–W. The 2D electrical resistivity models suggest that the bedrock deepens towards south-west. The resistivity models are also compared with the existing borehole information in the area and show a reasonable correlation. For example the sharp change of depth to the bedrock towards the center of the basin as seen in the resistivity models are also confirmed by the borehole data. 相似文献
17.
Three‐dimensional modelling of magnetotelluric data to image Sehqanat hydrocarbon reservoir in southwestern Iran 下载免费PDF全文
下载免费PDF全文 A detailed magnetotelluric survey was conducted in 2013 in the Sehqanat oil field, southwestern Iran to map the geoelectrical structures of the sedimentary Zagros zone, particularly the boundary between the Gachsaran Formation acting as cap rock and the Asmari Formation as the reservoir. According to the electrical well logs, a large resistivity contrast exists between the two formations. The Gachsaran Formation is formed by tens to hundreds of metres of evaporites and it is highly conductive (ca. 1 Ωm–10 Ωm), and the Asmari Formation consists of dense carbonates, which are considerably more resistive (more than 100 Ωm). Broadband magnetotelluric data were collected along five southwest–northeast directed parallel lines with more than 600 stations crossing the main geological trend. Although dimensionality and strike analysis of the magnetotelluric transfer functions showed that overall they satisfied local 2D conditions, there were also strong 3D conditions found in some of the sites. Therefore, in order to obtain a more reliable image of the resistivity distribution in the Sehqanat oil field, in addition to standard 2D inversion, we investigated to what extent 3D inversion of the data was feasible and what improvements in the resistivity image could be obtained. The 2D inversion models using the determinant average of the impedance tensor depict the main resistivity structures well, whereas the estimated 3D model shows significantly more details although problems were encountered in fitting the data with the latter. Both approaches resolved the Gachsaran–Asmari transition from high conductivity to moderate conductivity. The well‐known Sehqanat anticline could also be delineated throughout the 2D and 3D resistivity models as a resistive dome‐shaped body in the middle parts of the magnetotelluric profiles. 相似文献
18.
This paper presents a short theoretical summary of the series expansion-based 2.5D combined geoelectric weighted inversion (CGWI) method and highlights the advantageous way with which the number of unknowns can be decreased due to the simultaneous characteristic of this inversion. 2.5D CGWI is an approximate inversion method for the determination of 3D structures, which uses the joint 2D forward modeling of dip and strike direction data. In the inversion procedure, the Steiner’s most frequent value method is applied to the automatic separation of dip and strike direction data and outliers. The workflow of inversion and its practical application are presented in the study. For conventional vertical electrical sounding (VES) measurements, this method can determine the parameters of complex structures more accurately than the single inversion method. Field data show that the 2.5D CGWI which was developed can determine the optimal location for drilling an exploratory thermal water prospecting well. The novelty of this research is that the measured VES data in dip and strike direction are jointly inverted by the 2.5D CGWI method. 相似文献