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大地电磁(Megnetotelluric,简称MT)测深数据子库是中国岩石圈三维结构数据库所属子库之一。本文阐述了结合GIS技术开发大地电磁测深数据库管理系统的必要性。讨论了新型大地电磁测深数据库及基于GIS平台的数据库管理系统的总体设计思想。在分析原ACCESS大地电磁测深数据库所存在问题的基础上,建立新的MT数据库实体-关系模型,并进一步把原有的MT数据库改造为SQL Server 2000数据库;同时,开发了基于GIS的MT数据库管理系统。本文介绍了基于GIS的MT数据库管理系统所具有的功能。 相似文献
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如何得到快速稳定的反演结果和更清晰的地质体分界面等问题仍然是当前MT反演研究的一个重点.为了解决反演结果不能得到清晰的电性分界面的问题,本文在前人研究的基础上,基于OCCAM反演以及突出尖锐边界反演的思想,结合最小支撑梯度泛函,构建了新的反演目标函数,并利用共轭梯度法优化目标函数,实现了一种光滑模型与尖锐边界结合的MT二维反演方法.模型实验证明了该方法的准确性,通过与已发表的相关反演方法的结果进行比较,证明了该方法在光滑稳定的基础上可突出对尖锐电性边界的刻画.对广东徐闻地区的实测MT资料进行了处理,表明了该方法的适用性和效果. 相似文献
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由于人工源电磁探测效果与收发距离有一定关系,本文首先分析了收发距离为零的中心回线源瞬变电磁法（Transient Electromagnetic Method,TEM）视电阻率定义和算法特点,回溯了从圆形回线到矩形的修正式中心回线装置的发展过程;概述了从中心回线发展到接地导线源短偏移瞬变电磁（Short-Offset TEM,SOTEM）理论上的可行性;列举了将LOTEM（Long-Offset TEM）从数倍于探测深度的观测区推进到近源区后的探测实例.对于频率域人工源电磁法,介绍了起源于MT（Magneto-Telluric）的CSAMT（Controlled Source Audio-frequency Magneto-Telluric）与电磁频率测深法不同发展道路.电磁频率测深将观测区从远区推进到了中区;广域电磁法通过全区视电阻率新定义不仅提高了解释精度,而且将传统CSAMT远场观测模式推进到中区探测模式;最后指出,如能采用新的点微元假设计算方法,可有望分离自有场和辐射场,实现频域电磁近源探测. 相似文献
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目前大地电磁(MT)测深资料反演主要基于各向同性介质,但随着MT实际应用的需要,各向异性研究已逐渐引起关注.我们采用广泛应用的广义逆法对一维MT水平层状各向异性介质模型反演进行了探索性研究,并实现了MT全张量响应(即所有的阻抗张量的视电阻率和相位)的一维各向异性反演.理论模型试验表明,无论理论观测值中是否含有噪声,这种方法都能够较好地恢复真实模型,验证了其正确性和有效性.将此方法用于MT实测资料时,能够同时拟合4对视电阻率和阻抗相位曲线,说明本方法可以用于实测资料的处理解释,具有一定的实用价值. 相似文献
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基于网格精度、形成系统方程的方式、边界条件以及预条件线性算子等,文中对大地电磁（MT）有限差分数值解作了对比.对不同网格剖分方式下的三个均匀半空间模型的一维MT响应对比显示,在降低首层厚度的同时保持层间厚度变化在合理范围可以同时提高主场和辅助场的精度.在利用正常中心网格法（主场和辅助场都定义在单元顶面的中心）计算二维（2-D）TM模式响应时,应该从Maxwell一次差分方程开始组建二次差分方程,这样可以更充分考虑模型电阻率的变化.在对边界值如何影响数值解的测试表明,仅仅提高一维（1-D）边界值的精度对提高2-D MT有限差分数值解的精度是有限的.线性算子对提高MT解的效率十分重要,简单的对比进一步表明合适的预条件再配合好的线性算子（如文中求解2-D MT时所采用的DILU-BICGSTAB方法）不仅可以加速收敛,而且可以降低迭代次数. 相似文献
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消除噪声干扰对大地电磁测深资料的影响是大地电磁(MT)工作中的首要问题.基于结构风险最小化原则的支持向量机能够解决小样本情况下非线性函数拟合的通用性和推广性问题,是求复杂的非线性拟合函数的一种有效技术.本文首先介绍了ε-SVR(ε不敏感损失函数—支持向量机回归)的原理及SVR相关参数的选择,在此基础上,利用该算法对大地电磁测深实测资料进行回归处理,并与当前常用的去噪方法(Robust变换结合人工筛选)进行对比,结果表明ε-SVR算法可以较好地消除MT测深曲线所受噪声影响,提高工作效率.同时给原始数据加入10%噪声,并利用该算法对加噪后的数据进行回归处理,加噪前后拟合结果的绝对误差的均方差为9.454,相对误差的均方差为1.61%,证明该模型具有良好的泛化能力和稳健性. 相似文献
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首次采用高精度、全自动、数字化、含有电磁场5个分量的 MT 测量系统,在中国西北祁连山中段进行剖面式 MT 监测中,获得了较为真实的青海共和7.0级地震(1990年4月)的临震电磁幅射前兆信息.使用全定量化的频谱分析新方法,并且综合剖面多次复测资料,在时间-空间的双度坐标上跟踪分析.结果指出,大震临震电磁幅射前兆谱的特征主要有:(1)呈传导电流为主的同步电场干扰型;(2)频谱分布的窄带性(0.5—20s);(3)振幅的奇异性(电场干扰脉冲幅值为正常值的10~2数量级);(4)一定程度上显示孕震源的方向性;(5)幅射的间发性(临震3天中出现3个高峰时段).更为有意义的是:在高峰期至发震时刻之间约有48小时的相对平静间歇,此间观测者就能够在现场迅速响应,作出临震预报的判据.MT 监测所获得的临震电磁幅射信息主要是传导电流,而地下较为普遍存在的壳内高导层可能为该传导电流回路提供了良好的通道,便于被较远的 MT 监测点所接收. 相似文献
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Three-dimensional (3D) magnetotelluric (MT) surveys have been performed in Jeju, the largest volcanic island in Korea to figure out any possible structures or potential anomaly for remnant deep geothermal resources. Various approaches have been applied to interpret MT data observed in Jeju. MT dataset shows generally simple stratigraphy of four layers, though contains the severe static and the sea-effects. In our previous works, the induction vectors and 3D inversion results have commonly indicated the existence of a conductive anomaly in central parts of the island, beneath Mt. Halla. The 3D inversion dealt the static shifts as inversion parameters. The Jeju MT dataset, however, still contains the effect of conductive sea water surrounding the island.The sea-effect on MT impedance can be represented as a distortion tensor and excluded from the Jeju MT dataset by an iterative sea-effect correction. In this study, 3D inversion incorporating static shift parameterization was conducted using MT dataset corrected using 1D resistivity model obtained from the iterative scheme. Reasonably reconstructed images are obtained through the 3D inversion and using the MT dataset with sea-effect correction. The inversion result still shows the conductive anomaly in a similar depth. RMS misfits converged to a lower value than that of inversion using MT data before the sea-effect correction. From the fact, it is highly possible that the conductive anomaly is not an artifact but a real underground structure. Further investigation about the anomaly including exploration drilling is needed to see if it is from a fracture containing conductive sea water or related to the old volcanic activities. 相似文献
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Deep structure of the northeastern margin of the Parnaiba Basin, Brazil, from magnetotelluric imaging 总被引：1，自引：0，他引：1
The magnetotelluric (MT) method has been applied to the determination of the deep resistivity structure of the northeastern margin of the Parnaiba Basin. Transient electromagnetic (TEM) and MT data were collected in early 1999 along a 95 km long N–S line, extending from the coast across the projected subcrop position of a discontinuous fault found to the west of the study area that is believed to be a possible basin‐bounding fault. The MT data were processed to yield the TE‐ and TM‐mode responses and then corrected for static shift using central‐loop and single‐loop TEM data, respectively. Regularized 2D MT inversion was subsequently undertaken using a structured initial model with the near‐surface constrained by TEM inversion results. As a consistency check, we performed another set of 2D inversions using different smooth initial models. The various optimal 2D inversion models show clearly the presence of a major basement trough, over 2 km deep, located about 70 km from the coast. We interpret it as possibly marking the main basin margin and suggest that it may have implications for groundwater resource development in the area. 相似文献
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V. A. Kuznetsov 《Izvestiya Physics of the Solid Earth》2010,46(2):165-172
Pathways of further development of the dynamic correction technique suggested by E. Fainberg are discussed. This technique allows the correction of magnetotelluric (MT) and magnetovariational (MV) data distorted by subsurface irregularities within a broad range of frequencies beyond the static shift interval. This paper addresses new algorithms for the dynamic correction of tensor MT and MV response functions. Moreover, experiments on the dynamic correction of MT and MV data calculated for models containing heterogeneities in sedimentary cover and infinite or half-infinite conductive crustal prism are described. Model experiments show that the dynamic correction can ensure sufficient accuracy of the input data for the reliable solution of the inverse problem of magnetotellurics. 相似文献
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复杂地形、地质条件的大地电磁数据解释容易出现假象,采用三维正演技术模拟地形和地表不均匀体的背景响应,对实测数据阻抗相位不变量进行校正,实现更准确的定性分析;对三维异常体模型的合成数据进行一维、二维多参数反演试算,以确定地形剧变区选择反演技术的最佳方案.合成数据的试反演结果显示一维反演水平切片假异常较多,二维反演能压制测向假异常,但不能压制走向的假异常,水平切片多出现测向条带.使用本文提出的阻抗相位不变量校正法扣除地形、地表背景响应,结合一维、二维反演,能使实际资料解释成果更加可靠. 相似文献
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本文针对Groom-Bailey分解法在消除地表电性不均匀体对MT数据的畸变效应时存在的问题引入遗传算法,对基于传统线性最优化方法的GB分解算法进行改进,提出基于遗传算法的大地电磁阻抗张量分解方法.通过对理论合成数据以及三维/二维模型正演数据的分解试验,并且对青藏高原北缘阿尔金断裂地区实际MT数据进行分解处理,证明了基于遗传算法的GB分解能够更加有效地校正三维/二维情况下近地表三维电性不均匀体所造成的畸变影响.最后,在已有算法基础上,研究了基于遗传算法的多频率GB分解算法和MT数据静校正算法,并通过实际MT数据的处理证明了这些算法的有效性. 相似文献
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Max A. Meju 《Geophysical Prospecting》2005,53(4):463-479
A simple scaling relationship is shown to facilitate comparison, correlation and integration of data recorded using the common experimental configurations in electrical and electromagnetic depth sounding. Applications of the scheme to field data from typical geological and landfill environments show that it is robust and, where transient electromagnetic (TEM) data are available, enables easy identification and quantification of electrical static shift (galvanic distortion) in magnetotelluric and direct current (DC) sounding curves. TEM‐based procedures are suggested for both the direct removal of static shift in DC sounding curves and effective joint data inversion with the most‐squares criterion in the presence of static shift. A case study of aquifer characterization using sounding data from borehole sites in the Vale of York in England shows that static shift is a common problem in this glacial‐covered terrain and demonstrates the effectiveness of the proposed joint DC‐TEM inversion strategy in handling distorted soundings. 相似文献
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George R. Jiracek 《Surveys in Geophysics》1990,11(2-3):163-203
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Gyesoon Park Seokhoon Oh Heuisoon Lee Jung-Ho Kim Byung-Doo Kwon 《Journal of Applied Geophysics》2011,73(3):232-242
To enhance the spatial resolution, two types of complementary integration methods were developed using gravity and magnetotelluric (MT) data. The first method involves the enhancement processing of gravity vertical resolution using MT data. This is called a layer density correction (LDC) process which makes the density distribution more sensitive to geologic structure. The second method involves the spatial expansion processing of MT data using the enhanced gravity data. In this process, non-linear indicator transformation (NLIT) and simple kriging with varying local means (SKlm) methods were employed. The assumptions are that while the results are analyzed by different physical properties, each method senses the same underlying geologic structure and thus there is a relationship among the physical properties. The proposed geostatistical integration methods were tested using synthetic models and field data. The experiment illustrates that the integration method proposed in this study can provide improved structures. The method integrates constructively the gravity information having a wider spatial distribution and the MT information having higher vertical resolution. 相似文献
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研究了基于矢量有限元方法的大地电磁带地形三维反演算法并开发了三维反演计算程序代码.在大地电磁场正演数值模拟方面,采用并行直接稀疏求解器PARDISO且无需进行散度校正的快速正演方案,对典型地形模型,在中等规模计算条件下,与双共轭梯度法(BICG)计算结果比较,发现PARDISO比BICG快10倍以上;通过理论模型试算,并与前人的有限元法计算结果对比,验证了带地形三维正演计算程序的正确性.在反演方面,本研究基于共轭梯度方法编写了大地电磁带地形三维反演代码,为了避免直接求取雅可比矩阵,将反演中的雅可比矩阵计算问题转为求解两次“拟正演”问题,进而将PARDISO的快速正演方案应用于“拟正演”问题的求解,以提高反演计算效率.利用开发的反演算法对多个带地形地电模型的合成数据进行了三维反演,反演结果能很好地重现理论模型的电性结构,验证了本文开发的三维反演算法的正确性和可靠性.最后,利用该算法反演了某矿区大地电磁实测数据,反演得到的三维电性结构清晰地反映了研究区的地电特征,将反演结果与该区已有地质资料结合进行解释,应用效果明显,进一步验证了本文算法的有效性. 相似文献
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M. S. Zhdanov V. I. Dmitriev A. V. Gribenko 《Izvestiya Physics of the Solid Earth》2010,46(8):655-669
The problem of quantitative three-dimensional interpretation of the magnetotelluric (MT) data ranks among the most difficult
problems in electromagnetic (EM) geophysics. Our paper presents a new rigorous numerical method for MT inversion, based on
the integral equations technique. An important feature of the proposed method is the calculation of the Frechet derivative
with the aid of a quasi-analytical approximation with an inhomogeneous background. This approach simplifies the algorithm
of inversion and requires only a single forward modeling on each iteration. We have also developed a method for a joint inversion
of MT and magnetovariational (MV) data. We show in the present paper that the joint inversion of MT impedances and the Wiese-Parkinson
vectors can automatically allow for the static shift in the observed data, which is caused by the geoelectric inhomogeneities
contained in the near-surface layer. 相似文献