海拉尔盆地中-上地壳电性结构特征研究

本文通过对横穿海拉尔盆地的一条长约222km的北西—南东向大地电磁测深剖面数据的定性分析及二维定量反演解释,首次获得了海拉尔盆地高精度大范围的电性结构图.海拉尔盆地中-上地壳电性结构纵向上具有典型的分层特性,总体可分为四层,即低阻层-高阻层-低阻层-高阻层,而横向上又具有分块特点.海拉尔盆地边缘及内部分布的众多断裂将盆地划分为隆起与坳陷相间的格局,并发现盆地内部坳陷区也存在有小规模凸起,每一构造单元内部电性结构各具特点.海拉尔盆地中-上地壳低阻层底面最深达28km,通常在6~16km之间,但厚度变化不大,在4~10km之间,且隆起区与坳陷区底面埋深差别较大.据电性结构模型推测出两条新断裂F8和F9,且断裂F9规模较大,为基底断裂.中-上地壳的低阻层可能在一定程度上控制着海拉尔盆地内油气田的分布格局.     

宁夏海原大震区西安州—韦州剖面大地电磁探测与研究

对穿过宁夏海原大震区西安州(N36.5°,E105.5°)北至同心县韦州(N37.28°,E106.48°)的大地电磁测深剖面，采用远参考道大地电磁方法进行测量和资料处理，得到高精度的数据如视电阻率、阻抗相位、二维偏离度、最佳主轴方位角等. 依据这些数据，对测区的电性结构进行了定性分析和二维定量反演解释. 结果表明，沿剖面可以分成5个电性区块，与西、南华山隆起(Ⅰ)、兴仁堡—海原盆地(Ⅱ)、中卫—清水河盆地(Ⅲ)、中宁—红寺堡盆地(Ⅳ)和鄂尔多斯西缘带(Ⅴ)对应，各区块的边界由大断裂构成. 地表到深度10km左右，西、南华山隆起和鄂尔多斯西缘带呈高阻特性，兴仁堡—海原、中卫—清水河、中宁—红寺堡三个盆地的电阻率较低且呈盆地凹陷形状，盆地基底显示为西南深东北浅的簸箕状起伏形态，基底最深约为8km. 西、南华山隆起、中卫—清水河盆地和鄂尔多斯西缘带的下地壳为“正常”电阻率结构. 兴仁堡—海原和中宁—红寺堡盆地的下地壳上部为“异常”低电阻率带. 1920年的海原大震区存在明显的电性结构差异，震区西南侧和上部区域为相对高阻，东北侧和下部区域为相对低阻.     

Induction studies with satellite data

The natural variations of the Earth's magnetic field of periods spanning from milliseconds to decades can be used to infer the conductivity-depth profile of the Earth's interior. Satellites provide a good spatial coverage of magnetic measurements, and forthcoming missions will probably allow for observations lasting several years, which helps to reduce the statistical error of the estimated response functions.Two methods are used to study the electrical conductivity of the Earth's mantle in the period range from hours to months. In the first, known as the potential method, a spherical harmonic analysis of the geomagnetic field is performed, and the Q-response, which is the transfer function between the internal (induced) and the external (inducing) expansion coefficients is determined for a specific frequency. In the second approach, known as the geomagnetic depth sounding method, the C-response, which is the transfer function between the magnetic vertical component and the horizontal derivative of the horizontal components, is determined. If one of these transfer functions is known for several frequencies, models of the electrical conductivity in the Earth's interior can be constructed.This paper reviews and discusses the possibilities for induction studies using high-precision magnetic measurements from low-altitude satellites. The different methods and various transfer functions are presented, with special emphasis on the differences in analysing data from ground stations and from satellites. The results of several induction studies with scalar satellite data (from the POGO satellites) and with vector data (from the Magsat mission) demonstrate the ability to probe the Earth's conductivity from space. However, compared to the results obtained with ground data the satellite results are much noisier, which presumably is due to the shorter time series of the satellite studies.The results of a new analysis of data from the Magsat satellite indicate higher resistivity in oceanic areas than in continental areas. However, since this holds for the whole range of periods between 2 and 20 days, this difference probably is not caused purely by differences in mantle conductivity (for which one would expect less difference for the longer periods). Further studies with data from recently launched and future satellites are needed.     

Surface cracks—geomorphological indicators for late Quaternary halotectonic movements in Northern Germany

Loading and unloading effects of the Scandinavian Ice Sheet triggered halotectonic movements in Northern Germany. We present newly detected geomorphological features—termed surface cracks—which indicate a relation between ice sheet-induced salt movement and surface processes. As a part of the Central European Basin System, numerous Zechstein salt structures are abundant in the North German Basin. On the basis of high-resolution digital terrain data, more than 160 surface cracks were mapped in Northern Germany, which were grouped into 30 clusters. Almost all of the surface cracks occur above the top regions of Zechstein salt structures. The surface cracks can be several kilometres long, up to more than 20 m deep and more than 100 m wide. The comparison of the shape of the salt structures and the orientation of the cracks reveals a geometric dependency, indicating that the cracks preferably occur near the crest margins of the salt structures. Furthermore, 3D seismic data from two sites show that subsurface faults originating from salt movement exist beneath the surface cracks. We interpret the cracks as surface ruptures due to ice sheet-induced halotectonic movements. The cracks occur in a variety of Quaternary sediments and landforms. This indicates that widespread halokinetic movements occurred in the region after the last (Weichselian) deglaciation and likely before the thawing of the permafrost, possibly in a time frame from c. 30–20 ka until c. 15 ka.     

The Structure of the Muya Basin of the Baikal Rift Based on the Interpretation of Archival Vertical Electrical Sounding Data

Izvestiya, Physics of the Solid Earth - Abstract—Results of the interpretation of the archival vertical electrical sounding data from the Muya Basin of the Baikal Rift Zone are presented....     

Deep electromagnetic sounding of the lithosphere in the eastern Baltic (fennoscandian) shield with high-power controlled sources and industrial power transmission lines (FENICS experiment)

The paper addresses the technique and the first results of a unique experiment on the deep tensor frequency electromagnetic sounding, the Fennoscandian Electrical conductivity from results of sounding with Natural and Controlled Sources (FENICS). In the experiment, Energy-1 and Energy-2 generators with power of up to 200 kW and two mutually orthogonal industrial 109- and 120-km-long power transmission lines were used. The sounding frequency range was 0.1–200 Hz. The signals were measured in the Kola-Karelian region, in Finland, on Svalbard, and in Ukraine at distances up to 2150 km from the source. The parameters of electric conductivity in the lithosphere are studied down to depths on the order of 50–70 km. A strong lateral homogeneity (the one-dimensionality) of a geoelectric section of the Earth’s crust is revealed below depths of 10–15 km. At the same time, a region with reduced transverse crustal resistivity spread over about 80 000 square kilometers is identified within the depth interval from 20 to 40 km. On the southeast the contour of the anomaly borders the zone of deepening of the Moho boundary down to 60 km in Central Finland. The results are compared with the AMT-MT sounding data and a geodynamic interpretation of the obtained information is carried out.     

StudyofCurieisothermalsurfaceinSichuanBasinandtheseismicareaonitswesternmar┐gin

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Recent studies of time variations of natural electromagnetic fields in Scotland

A series of geomagnetic induction studies has been undertaken in Scotland since 1973. It includes the operation of two geomagnetic arrays, one over northern Scotland and the other over southern Scotland, subsequent individual station and small-scale geomagnetic array studies, and three sets of magnetotelluric soundings which traverse Scotland from the Lewisian Foreland to the English border. The problems associated with the interpretation of induction data from an island located in the subauroral region are discussed qualitatively and the manner in which both coast and source field effects can be accounted for, is described. The geomagnetic deep sounding data (GDS) from all the observation sites have been collated, and examples of hypothetical event contour maps and traverses across the Great Glen and of individual events from the northern array are presented. They indicate that significant lateral variations in electrical conductivity structure within the crust and upper mantle are associated with the major geological faults in the region. Examples of the results of the magnetotelluric soundings are also presented, together with an outline of the procedure used for one- and two-dimensional modelling. Models of the geo-electric structure in both northern and southern Scotland have been obtained. These show distinctive features which are compatible with the qualitative interpretation of the magnetovariational data. For example, the major granitic blocks are highly resistive while regions of relatively low resistivity exist at upper crustal depths near the Great Glen, Highland boundary and Southern Uplands faults. A zone of low resistivity exists at lower crust-uppermost mantle depths throughout much of the region, the lowest value occurring under the Southern Uplands.     

基于双金属球三维电场探空仪的一次雷暴云内电荷结构观测研究

本文自主研制性能稳定的双金属球三维电场探空仪,并结合气象探空仪等构建了雷暴电场-气象综合探空系统,实现了雷暴云内三维电场及温度、湿度的同步测量.2019年夏季对华北平原地区雷暴开展穿云观测,并结合地面大气电场、雷达回波、变分多普勒雷达分析系统(VDRAS)反演的动力场等资料进行综合研究,首次给出该地区雷暴云内的电场和电荷结构分布特征.对2019年8月7日发生的一次中尺度对流系统电场探空发现,在雷暴减弱阶段,其弱回波区内存在5个极性交替的电荷区:4.4~5.6 km之间的上部正电荷区(0℃附近)、3.6~4.4 km之间的中部负电荷区和1.0~3.6 km之间的下部正电荷区,此外在1 km下方有一个负极性电荷区,雷暴云顶附近5.7~6.9 km之间为一个弱负极性屏蔽电荷区.其中,中部负电荷区和下部正电荷区由多个不同强度、不同厚度的电荷层构成.此外,电场探空系统在中部负电荷区高度范围内经历的上升—下沉—再次上升的往返探空数据表明,雷暴云内动力环境复杂,电荷结构分布相似但又有所差异,反映了实际雷暴云内电荷分布的时空不均匀性和复杂性.     

陕西地区单台Z／H地磁测深研究

应用陕西地磁台网Ｓｑ资料和单台Ｚ／Ｈ地磁测深法对陕西地区地下电导率分布进行了研究，结果表明，理想代换导体视探ｈ约为５００ＫＭ，电导率σ为０．０７ｓ／ｍ（周期为１２小时），且存在２５０ＫＭ和７００ＫＭ深度附近的高导层，感应比例尺度实部Ｃ＾１ｒｅａｌ和Ｃ＾２ｒｅａｌ及内外场之比│Ｑ＾１│和│Ｑ＾２│似有１１年周期变化。各台测定的结果相当接近，和其他方法测定的范围结果基本一致。用冬夏季静日均值结果较春秋     

Electrical investigation in the Chaîne des Puys (France)

Numerous geologists have studied the structure of the Chaîne des Puys, our knowledge of which has recently been enlarged by geophysical research. Some of the hypotheses concerning its structure at average depth had to be checked, and so in 1975 the National Institute for Astronomy and Geophysics (I.N.A.G.) provided the necessary support for such work.An anomaly of the electrical conductivity was clearly apparent, both from the magnetotelluric method in a wide range of frequencies as well as from more classical methods (electrical sounding) or from newer methods such as differential magnetic sounding.It has been proved that the structure, which is believed to be responsible for this anomaly of conductivity, is quite different from other inferred structures which result from the interpretation of magnetic data only. However, although the coexistence of these different structural elements is not impossible, heat-flow measurements and geochemical studies do not support the assumption of an active magma chamber (a few kilometres deep).     

Electromagnetic studies of global geodynamic processes

The deep electromagnetic sounding (DES) technique is one of the few geophysical methods, along with seismology, gravity, heat flow, which may be use to probe the structure of the Earth's mantle directly. The interpretation of the DESs may provide electrical conductivity profiles down to the upper part of the lower mantle. The electrical conductivity is extremely sensitive to most of the thermodynamic processes we believe are acting in the Earth's mantle (temperature increases, partial melting, phase transition and to a lesser extent pressure). Therefore, in principle, results from DES along with laboratory measurements could be used to constrain models of these processes.The DES technique is reviewed in the light of recent results obtained in a variety of domains: data acquisition and analysis, global induction modeling and data inversion and interpretation.The mechanisms and the importance of surface distortions of the DES data are reviewed and techniques to model them are discussed. The recent results in terms of the conductivity distribution in the mantle from local and global DES are presented and a tentative synthesis is proposed.The geodynamic interpretations of the deep conductivity structures are reviewed. The existence of mantle lateral heterogeneities in conductivity at all scales and depths for which electromagnetic data are available is now well documented. A comparison with global results from seismology is presented.     

Subglacial Meltwater Recharge in the Dongkemadi River Basin,Yangtze River Source Region

Glaciers on the Tibetan Plateau play an important role in the local hydrological cycle. However, there are only few studies on groundwater in the alpine basins in the Tibetan Plateau which considered the effects of glaciers. Glaciers are extensively distributed in the Dongkemadi River Basin, which is a representative alpine basin in the Yangtze River source region. This study focuses on building a numerical groundwater flow model with glaciations using HydroGeoSphere (HGS) to simulate subglacial meltwater recharge to groundwater in the Dongkemadi River Basin in response to future climate changes. Effects of hydraulic conductivity, precipitation, and temperature on subglacial meltwater recharge to groundwater were discussed. Glacier changes in the future 50 years were predicted under different climate change scenarios. Results show that: (1) the average thickness of the glacier will change significantly; (2) the simulated rate of annual mean subglacial meltwater recharge to groundwater is 4.58 mm, which accounts for 6.33% of total groundwater recharge; and (3) hydraulic conductivity has the largest influence on subglacial meltwater recharge to groundwater, followed by temperature and precipitation. Results of this study are also important to sustainable water resource usage in the Yangtze River source region.     

Deep structure of Western Yakutia from magnetotelluric soundings

Analysis of magnetotelluric (MT) sounding studies in western Yakutia showed that amplitude curves are strongly affected by the regional distribution of electrical conductivity heterogeneities of the sedimentary cover, while phase curves are distorted to a lesser extent. The distribution of the longitudinal conductance in the sedimentary cover is constructed, and MT fields and resistivity and phase curves are modeled. Based on combined analysis of experimental and model data and results of inversion of corrected curves, an interpretation of main anomalies of MT fields is given and a regional crustal anomaly of the electrical conductivity is discovered.     

Interpretation of the short period variations in geomagnetic anomalies of Shaanxi region

1BriefintroductionoftheanomaliesofshortperiodgeomagneticvariationsinShaanxiAtemporarymeasurementprofilecomposedofmeasurementsitesofShiquan,Foping,Banfangzi,Zhouzhi,Wugong,Qianling,BinxianandNingxian,whichisbasicalalongnorth-southdirectionfromShiquaninthesouthernpartofShaanxitoNingxianinGansu,wassetupandsimultaneousobservationofthree-componentgeomagneticshortperiodvariationswereperformedateightsitesduringSeptemberof1996.Observationalresultsshowthatthereisareversalaxisofgeomagneticverticalv…     

基于电性结构模型的青藏高原东缘上地幔热结构研究

研究青藏高原东缘地区的深部物质结构对于理解青藏高原的隆升及扩张机制具有重要的科学意义.本文将青藏高原东缘实测大地电磁测深剖面反演所得的岩石圈电性结构模型与高温高压岩石物理实验测得的上地幔矿物和熔融体导电性定量关系相结合,通过Hashin-Shtrikman(HS)边界条件建立上地幔电导率与温度、熔融百分比等参数的定量关系,在此基础上计算得到了青藏高原东缘上地幔热结构及熔融百分比分布模型.研究结果表明在青藏高原东缘地区通过大地电磁测深方法所探测到的上地幔低阻体可以解释为由高温作用所产生的局部熔融区域.其中,松潘—甘孜地块上地幔高导体对应的温度介于1300～1500℃之间,熔融百分比可高达10%,支持前人将松潘—甘孜地块内部的低阻体解释为局部熔融的观点.龙门山断裂带以东、四川盆地西缘的上地幔高导体温度介于1200～1400℃之间,熔融百分比介于1%～5%左右,表明扬子克拉通的西缘可能正在经历一定程度的活化作用.龙门山断裂带下方的上地幔高阻体温度介于1100℃附近,基本没有发生局部熔融,具有较冷的刚性块体特征,与该区域频发的地震活动相吻合.四川盆地东部的扬子上地幔温度介于800～900℃之间,没有发生局部熔融,符合古老稳定的克拉通块体的基本特征.     

A regional strategy for geothermal exploration with emphasis on gravity and magnetotellurics

As part of the resource evaluation and exploration program conducted by Los Alamos Scientific Laboratory for the national Hot Dry Rock (HDR) Geothermal Program, a regional magnetotelluric (MT) survey of New Mexico and Arizona is being performed. The MT lines are being located in areas where the results of analysis of residual gravity anomaly maps of Arizona and New Mexico, integrated with other geologic and geophysical studies indicate the greatest potential for HDR resources.The residual gravity anomalies are derived by applying the concept of predicting gravity anomalies from topography. This can be accomplished by employing reductions similar to those used in some isostatic investigations, in which a regional topographic surface is used as the Bouguer reduction datum. The datum is derived by comparison of various harmonics of Bouguer anomalies and elevations of stations. Topography can be used to predict Bouguer anomalies because of isostatic compensation; the resultant anomalies can be considered high frequency residual anomalies or isostatic anomalies corrected for regional compensation. Such maps have been produced for Arizona, New Mexico, west Texas, and Chihuahua, Mexico.The main objective of the MT project is to produce a regional geoelectric contour map of the pervasive deep electrical conductor within the crust and/or upper mantle beneath the Colorado Plateau and the adjacent Basin and Range Province and Rio Grande Rift. The MT survey consists of 200 sites along several long profiles with site spacing of 15–20 km. Pre-existing available MT data are being integrated with the new data. After the data are processed, a one-dimensional inversion is applied to the sounding curve and used as a starting point for 2-D modeling. Such a project and ultimate map will be of major value in studying the regional geophysics and tectonics of the southwest United States as they now apply to HDR resources in particular and geothermal resources in general.Electrical conductivity anomalies of large areal extent are of particular interest in geothermal exploration. Correlation analysis of large conductive anomalies with other geophysical, geological, and geotectonic data is being performed. Preliminary analysis of the data has suggested several major regions of anomalously shallow high electrical conductivity. Among these is the Aquarius area of northwest Arizona which is the site of a longwavelength residual anomaly low, which when modeled and correlated with other geophysical data can be shown to be possibly related to low density and high temperature in the crust at depths of 20 km or less. Preliminary analysis of MT data indicates the possible existence of a mid-crustal high electrical conductivity anomaly in this same region.     

Numerical simulation and inversion of MT fields in the 3D electric conductivity model of the Vesuvius volcano

Possibilities for three-dimensional (3D) magnetotelluric (MT) sounding of local objects contained in the Earth’s crust are estimated in a case study of the magma chamber of the Vesuvius volcano. Stochastic inversion of the model MT data by the Markov Chain Monte Carlo (MCMC) method has shown that the most efficient approach is not simultaneous but successive estimation of the geometry and the depth of the anomaly and the assessment of the conductivity distribution within the anomalous region. A zone of equivalence is revealed between the a priori estimate of the depth of the anomalous zone and the a posteriori distribution of electric conductivity within it. Based on the present estimation and previous results, an algorithm for determination of the parameters of local crustal anomaly is proposed.     

中国海—西太平洋典型剖面(南幅)揭示的微陆块-窄洋盆构造格局

基于编制最新地学成果图件的需要,我们整合了最新地质、地球物理资料成果,运用最新的技术方法,开展了中国海—西太平洋地区典型剖面的编制工作.典型剖面(南幅)主要集成了南海地区近年来获得的广角地震探测资料,运用重-磁-震联合反演方法,结合拖网、钻井、地热、地质剖面等,以块体构造学说为编图思想编制而成.典型剖面(南幅)从华南以NNW-SSE向直抵苏拉威西海,穿过了多个构造单元,包括3个陆缘-离散地块区(华南块体—南海北部陆缘、中沙地块、礼乐—北巴拉望地块)、4个海盆区(西北次海盆、中央海盆、苏禄海盆、苏拉威西海盆)、2个俯冲-岛弧区(卡加延脊、苏禄脊),这些构造单元一起构成了西太平洋边缘独特的"微陆块-窄洋盆"构造格局.自古特提斯向欧亚大陆之下俯冲以来,该区域经历了复杂的构造演化过程.在形成这种构造格局的过程中,地壳处在不断消亡和生成的动态循环之中,同时构造应力也处在动态变化之中.通过对区域地球动力学的综合分析,认为这种微陆块-窄洋盆构造格局的形成,很大程度上是由于其位于三大板块交接的独特区域,以及受区域内复杂而丰富的俯冲作用的影响和制约.通过典型剖面编制工作,推动了中国海—西太平洋区域内大地...     

Corrections for near surface effects: Decomposition of the magnetotelluric impedance tensor and scaling corrections for regional resistivities: A tutorial

This paper primarily examines the effects of small-scale or near-surface conductivity inhomogeneities on the magnetotelluric (MT) impedance tensor. These effects cause three different types of distortion results. (1) The well-knownstatic shifts of sounding curves. (2) When the underlying regional setting is two-dimensional then the two regional impedances are mixed in an arbitrary coordinate system. Thus the level and shape of each sounding curve is distorted as are the phases. (3) At sufficiently high frequencies these effects generate anomalous magnetic fields that in turn alter the background phases.This tutorial first explores the usefulness of various MT tensor analysis techniques to overcome the problem of phase mixing and to recover regional information in the presence of local geological noise. Synthetic and experimental data are considered. A sequence ofa priori models of increasing complexity are described. The use of appropriate decompositions of the MT tensor each with an increasing number of parameters is emphasised. In a second part, phase mixing and static shifts are examined from a synoptic view. Some static shift removal techniques that can be used in conjunction with the decomposition are discussed. This paper is not a review but rather an investigation of a few methods that the authors have found useful with field data.