Deep structure of the northeastern margin of the Parnaiba Basin, Brazil, from magnetotelluric imaging

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.     

郯庐断裂带中段(沂沭断裂带)电性结构研究与孕震环境

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.     

Integrated interpretation of the magnetotelluric and magnetic data from Mahallat geothermal field,Iran

Magnetotelluric (MT) and ground magnetic surveys were conducted on the Mahallat geothermal field situated in Markazi province, central Iran, as a primary part of the explorations and developments of a geothermal energy investigation program in the region. Mahallat region has the greatest geothermal fields in Iran. MT survey was performed in November 2011 on an 8 km profile crossing the hot springs with a total of 17 stations. The 2D inversion of the determinant MT data was performed using a 2D inversion routine based on the Occam approach. The 2D resistivity model obtained from the determinant data shows a low resistivity zone at 800-2000 m depth and a higher resistivity zone above the low resistivity zone, interpreted as geothermal reservoir and cap rock, respectively. It also revealed two major concealed faults which are acting as preferential paths for the circulation of hydrothermal fluids. To obtain more geophysical evidence, a ground magnetic survey with 5000 stations was also performed over an area of 200 km² around the MT profile. Magnetic measurements show a main positive anomaly of about +1000 nT over the study area, which could be interpreted as an intrusive body with the high magnetic susceptibility (i.e. mafic and ultramafic rocks) into the sedimentary host rocks. We interpret the body as the heat source of the geothermal system. Structural index and depth estimation of the anomaly indicate that the intrusive body is similar to a cylinder extending from about one kilometer depth down to greater depths. The results of MT and magnetic investigations indicate a geothermal reservoir which proves the preliminary geological observations to a great extent.     

Electrical Struture of the Crust in Manas Earthquake Area,Xinjiang,China

Magnetotelluric sounding data obtalned recently in Manas earthquake area were processed. Inthe result, curves of apparent resistivity, impedance Phase, skewness and optimum rotationangle versus period and the real magnetic induction vectors were obtained. Then the data ofall measuring points were interpreted by 2D automatic inversion. The result indicates thatalong the sounding profile the shallow crust can be divided into 5 segments and the deep crustcan be divided into 3 segments, with faults or deep-seated fault zones as the contactboundaries between them. The sedimentary cover along the profile extents down to depthabout 12 km in maximum and a low-resistivity body exists in the crust in southern section ofthe profile. The interpretation results are well consistent with geological and othergeophysical data. The Manas M7. 7 earthquake occurred near a contact zone where theelectrical structure of the crust sharply changes.     

新疆玛纳斯大震区地壳深部的电性结构

对玛纳斯大震区新近观测的大地电磁测深数据进行了处理,得到视电阻率曲线、阻抗相位曲线、二维偏离度、主轴方位角和地磁实感应矢量。然后对所有测点的资料进行了二维自动反演解释。结果表明,沿剖面的地壳浅部可划分为５个区段,沿剖面的深部可划分为３个区段,各区段的接触边界由断层或深断裂带组成。沿测线沉积盖层最大深度达１２ｋｍ左右;测线南段存在壳内低阻体。这些解释结果与地质及其它资料吻合较好。玛纳斯７．７级地震发生在地壳电性结构发生明显变化的接触带附近     

Magnetotelluric resistivity modeling for 3D characterization of geothermal reservoirs in the Western side of Mt. Aso, SW Japan

Geothermal reservoirs are usually located at a depth range of 2 to 5 km, so to efficiently utilize such resources an advanced prospecting method is needed to detect these deep geologic structures. This study aimed to three-dimensionally characterize geothermal reservoirs by a combination of Magnetotelluric (MT) survey, inversion analysis of apparent resistivity, and interpolation of the resistivity data obtained. The western side of Mt. Aso crater, southwest Japan, was chosen as the case study area. Three hot springs exist there and a fault is assumed to go in the direction connecting them. A MT survey was carried out at 26 sites and the data processed by a remote reference method to reduce artificial noises. Based on skewness and Mohr circle analyses of the impedance tensor, the local geologic structure at each site could be approximated as horizontally layered and therefore, a one-dimensional inversion analysis was applied to the MT raw data. The resultant resistivity column data were then interpolated by the three-dimensional optimization principle method. The resistivity distributions obtained clarified continuous conductors with especially low resistivity (less than 10 Ω·m) at the hot springs along the fault. Because the resistivity decreases largely with an abundance of clay minerals, the conductors could be considered to correspond with the cap rocks. Thus, two geothermal reservoirs, whose shapes were estimated to be pillar, were detected under the cap rocks in an elevation range of − 1000 to − 3000 m. By comparing the resistivity distributions with the temperature distributions based on fluid-flow calculations at a steady state using FEM, the validity of the location and dimension of the estimated reservoirs were confirmed.     

Results of electromagnetic sounding with JASC submarine cable

We present the results of long-term deep geoelectric studies using the JASC (Japan Sea Cable) submarine communication cable in the region of the Sea of Japan. In the 2D inversion of the amplitude and phase’s apparent resistivity curves and the frequency dependences of the tipper, we invoked the geological and geophysical information about the region and on-shore electromagnetic observations to fit the model to the observations. The resulting geoelectrical cross section of the region of the Sea of Japan along the JASC cable obtained in this way agrees well with the experimental data. The upper part of the section contains a conductive block beneath the bottom of the Central basin of the Sea of Japan at a depth of 10–40 km, a fault submerging below the continent in the marginal part and a deep fault in the continental region. In the lower portions of the cross section, the high-resistivity block interrupts the continuity of the horizontal conductive layers beneath the Yamato Uplift, and the conductive bottom part of the geoelectric cross section submerges under the continent. In the continental segment of the cross section, there is a large block with reduced electric resistivity, which is located between the conductive layers at a depth interval of 200–560 km. We analyze the characteristic features of the geoelectric cross section and the deep section imaged by seismic tomography in the region of the Sea of Japan.     

鄂尔多斯盆地西缘构造带北段深部电性结构

在横跨鄂尔多斯盆地西缘构造带北段的查甘池—银川—五湖洞约200 km长的东西向剖面上,进行了67个测点的大地电磁探测.使用“远参考道”和Robust技术处理数据.分析了各测点视电阻率、阻抗相位、二维偏离度、电性主轴方位角、磁实感应矢量等参数,采用NLCG二维反演方法对TE和TM两种模式的数据进行了二维反演.得到的二维电性结构表明,沿剖面查汗断裂带、贺兰山东缘断裂带和黄河断裂带是明显较大型电性边界,为超壳断裂带,而三关口断裂带深部延深不大.沿剖面阿拉善地块、贺兰山褶皱带、银川断陷盆地和鄂尔多斯地块具有明显不同的深部电性结构特征.阿拉善地块内部除浅表电阻率较低外,以下到深度约50 km都表现为高电阻特性.贺兰山褶皱带电性结构复杂,电阻率高低相间.银川盆地具有上宽下窄最深达约8 km低阻层,具有断陷盆地特征.鄂尔多斯地块具有低-高-低的深部电性结构特征,成层性较明显.     

滇西龙陵地区地壳电性结构及其对大瑞铁路地质选线影响研究

高黎贡山地处印度板块与欧亚板块碰撞缝合带附近的横断山脉南段,是大理一瑞丽铁路(大瑞线)的必经之地,地形起伏大、构造复杂、活动性强,高黎贡山隧道作为全线控制性工程之一,其地质选线的最大困难就是对隧道深部构造环境的了解,特别是缺少对与地热、地震等联系紧密的深部地质构造的认识.为此,本文以大地电磁方法为手段,以高黎贡山隧道为主要研究对象,通过对滇西龙陵地区高黎贡山隧道越岭段两条大地电磁剖面数据的处理解释对研究区的地壳电性结构特征进行了勘探研究.结合区域地质构造特征与主要工程地质问题之间关系的分析,根据隧道主要断层地质条件设计了三维垂直断层模型,利用三维有限元开展正演模拟研究发现,测点点距、位置与横向分辨率密切相关,点距越密,分辨率越高,测点位于断层在地表投影位置能有效提高分辨率.采用大地电磁阻抗张量分解技术对两条剖面上各测点的二维偏离度和电性走向进行了计算和分析,对剖面视电阻率和阻抗相位数据进行了二维NLCG联合反演研究,揭示了沿剖面的腾冲地块、龙陵一瑞丽断裂带及保山地块10 km深度的电性结构特征及相互关系.结果表明:剖面CD电性结构呈现区域构造的三分性,腾冲地块电性结构成层性较好,保山地块成层性较差,两者均以中高阻电性特征为主,中间夹龙陵一瑞丽断裂带,电性结构反映从3 km深度以下存在几乎近于直立延伸的低阻带,推测为班公湖一怒江缝合带滇西段丁青一怒江缝合带的反映;剖面AB共划分了6条与工程密切相关的深部隐伏断裂,结合地震地质、地表地质及龙陵地震深部背景研究,推测F7-3断裂为1975龙陵7.3级地震断裂;从地表黄草坝断裂开始向下延伸,有一条发育最大深度约为4 km的低阻通道,推测为地热断裂深循环通道,其与黄草坝断裂共同控制研究区地下热水的补给、径流和排泄条件,在高黎贡山隧道线位位置形成了一个相对低温通道,为隧道方案成立的关键工程地质条件.勘探结果表明:滇西龙陵地区地壳电性结构有效的反映了高黎贡山隧道深部隐伏断裂和地热断裂深循环通道等深部构造特征,为大瑞线隧道工程地质选线提供了深部地质背景依据.     

Geophysical greenfield exploration in the permo‐carboniferous Saar–Nahe basin—The Wiesbaden Geothermal Project,Germany

Structurally bound upwelling and outflowing hot fluids in the city of Wiesbaden suggest an interesting geothermal potential at the northern margin of the permo‐carboniferous Saar–Nahe basin, Germany. The Saar–Nahe basin in the Wiesbaden area was previously not a target for intensive geophysical prospecting of the deep underground. We present an exploration concept to investigate potential geothermal reservoirs near Wiesbaden for heat and power production. The acquired geophysical exploration data give new insights into the local geometry and internal structure of the Saar–Nahe basin. The exploration combines a wide range of methods, including the analysis of data, a dense grid gravity survey, as well as two‐dimensional and three‐dimensional seismic surveys. The resulting data, which for the first time reveal the deep structure of the Mainz and Saar–Nahe basins near Wiesbaden down to a depth of c. 4,000 m, show that the Saar–Nahe basin is strongly segmented and contains deep‐reaching active faults. Combining these information with numerical models of the stresses in the fault system and of the temperature distribution in the exploration area, a promising drilling target has been identified, which promise high permeability at a low risk of induced or triggered seismicity.     

Exploration of geothermal structure in Puga geothermal field, Ladakh Himalayas, India by magnetotelluric studies

To understand the crustal electric structure of the Puga geothermal field located in the Ladakh Himalayas, wide band (1000 Hz–0.001 Hz) magnetotelluric (MT) study have been carried out in the Puga area. Thirty-five MT sites were occupied with site spacing varying from 0.4 to 1 km. The measurements were carried out along three profiles oriented in east–west direction. After the preliminary analysis, the MT data were subjected to decomposition techniques. The one-dimensional inversion of the effective impedance data and the two-dimensional inversion of the TE (transverse electric) and TM (transverse magnetic) data confirm the presence of low resistive (5–25 Ω m) near surface region of 200–300 m thick in the anomalous geothermal part of the area related to the shallow geothermal reservoir. Additionally, the present study delineated an anomalous conductive zone (resistivity less than 10 Ω m) at a depth of about 2 km which is possibly related to the geothermal source in the area. A highly resistive basement layer separates the surface low resistive region and anomalous conductive part. The estimated minimum temperature at the top of conductive part is about 250 °C. The significance of the deeper conductive zone and its relation to the geothermal anomaly in the area is discussed.     

Topography of the Moho and earth crust structure beneath the East Vietnam Sea from 3D inversion of gravity field data

The Moho depth, crustal thickness and fault systems of the East Vietnam Sea (EVS) are determined by 3D interpretation of satellite gravity. The Moho depth is calculated by 3D Parker inversion from residual gravity anomaly that is obtained by removing the gravity effects of seafloor and Pre-Cenozoic sediment basement topographies from the free air anomaly. The 3D inversion solution is constrained by power density spectrum of gravity anomaly and seismic data. The calculated Moho depths in the EVS vary from 30–31 km near the coast to 9 km in the Central Basin. A map of the lithosphere extension factor in the Cenozoic is constructed from Moho and Pre-Cenozoic sediment basement depths. The fault systems constructed by the maximum horizontal gradient approach include NE-SW, NW-SE, and N-S oriented faults. Based on the interpretation results, the EVS is sub-divided into five structural zones which demonstrated the different characteristics of the crustal structure.     

Joint inversion of long‐offset and central‐loop transient electromagnetic data: Application to a mud volcano exploration in Perekishkul,Azerbaijan

Mud volcanism is commonly observed in Azerbaijan and the surrounding South Caspian Basin. This natural phenomenon is very similar to magmatic volcanoes but differs in one considerable aspect: Magmatic volcanoes are generally the result of ascending molten rock within the Earth's crust, whereas mud volcanoes are characterised by expelling mixtures of water, mud, and gas. The majority of mud volcanoes have been observed on ocean floors or in deep sedimentary basins, such as those found in Azerbaijan. Furthermore, their occurrences in Azerbaijan are generally closely associated with hydrocarbon reservoirs and are therefore of immense economic and geological interest. The broadside long‐offset transient electromagnetic method and the central‐loop transient electromagnetic method were applied to study the inner structure of such mud volcanoes and to determine the depth of a resistive geological formation that is predicted to contain the majority of the hydrocarbon reservoirs in the survey area. One‐dimensional joint inversion of central‐loop and long‐offset transient electromagnetic data was performed using the inversion schemes of Occam and Marquardt. By using the joint inversion models, a subsurface resistivity structure ranging from the surface to a depth of approximately 7 km was determined. Along a profile running perpendicular to the assumed strike direction, lateral resistivity variations could only be determined in the shallow depth range using the transient electromagnetic data. An attempt to resolve further two‐dimensional/three‐dimensional resistivity structures, representing possible mud migration paths at large depths using the long‐offset transient electromagnetic data, failed. Moreover, the joint inversion models led to ambiguous results regarding the depth and resistivity of the hydrocarbon target formation due to poor resolution at great depths (>5 km). Thus, 1D/2D modelling studies were subsequently performed to investigate the influence of the resistive terminating half‐space on the measured long‐offset transient electromagnetic data. The 1D joint inversion models were utilised as starting models for both the 1D and 2D modelling studies. The results tend to show that a resistive terminating half‐space, implying the presence of the target formation, is the favourable geological setting. Furthermore, the 2D modelling study aimed to fit all measured long‐offset transient electromagnetic Ex transients along the profile simultaneously. Consequently, 3125 2D forward calculations were necessary to determine the best‐fit resistivity model. The results are consistent with the 1D inversion, indicating that the data are best described by a resistive terminating half‐space, although the resistivity and depth cannot be determined clearly.     

3D upper crustal density structure of the Deccan Syneclise,Central India

A constrained 3D density model of the upper crust along a part of the Deccan Syneclise is carried out based on the complete Bouguer anomaly data. Spectral analysis of the complete Bouguer gravity anomaly map of the study region suggests two major sources: short wavelength anomalies (<100 km) caused primarily due to the density inhomogeneities at shallow crustal level and long wavelength anomalies (>100 km) produced due to the sources deeper than the upper crust. A residual map of the short wavelength anomalies is prepared from the complete Bouguer anomaly using Butterworth high‐pass filter (100 km cut‐off wavelength). Utilizing the constraints from deep resistivity sounding, magnetotellurics and deep seismic sounding studies, 2.5D density models have been generated along 39 profiles of this region. The mismatch between the calculated response of the a priori 2.5D model with the residual (short wavelength) gravity anomalies is minimized by introducing high‐density intrusive bodies (≥2.81 g/cm³) in the basement. With these 2.5D density models, the initial geometry of our 3D density model, which includes alluvium, Deccan trap, Mesozoic sediment and high‐density intrusive bodies in the basement up to a depth of 7 km (upper crust), is generated. In the final 3D model, Deccan trap extends from 200 m to nearly 1700 m below the 90–150 m thick Quaternary sediment. Further down, the sub‐trappean Mesozoic sediment is present at a depth range of 600–3000 m followed by the basement. The derived 3D density model also indicates six intrusive bodies of density 2.83 g/cm³ in the basement at an average depth of about 4–7 km that best fits the residual gravity anomaly of the study area.     

A radio magnetotelluric study to evaluate the extents of a limestone quarry in Estonia

Electromagnetic signals from distant radio transmitters in the frequency range 15–250 kHz were measured to model an electrical resistivity structure beneath 7 profiles in the vicinity of the Karinu limestone quarry in Estonia with the aim to map the extent of the economically exploitable limestone. The resistivity models from a 2D inversion of determinant resistivity and phase values using an Occam type of regularization contained reasonably accurate information about the geometry, namely depth to the top and the bottom of the target high‐resistivity limestone. The resistivity models correlated well with existing geological evidences as well as information from closely located boreholes. However, the sharp lithological boundaries seen in the boreholes were not resolved exactly in the resistivity models. This is probably because of the smoothing regularization used in the inversion process. Combined use of borehole data together with resistivity models resulted in two major geological interpretations; a) towards the western part of the existing limestone quarry there is a NNW to NS striking fault, covered by post‐glacial sediments, b) a potential cost‐effective exploitable area containing high quality highly resistive limestone is located south of the existing quarry. This case study shows the applicability of the reasonably fast radio magnetotelluric (RMT) method for the exploration of near‐surface resources.     

3-D Magnetotelluric Exploration of Tenerife Geothermal System (Canary Islands,Spain)

The resistivity structure of the Tenerife geothermal system has been determined by the 3-D inversion of data from different magnetotelluric surveys. In this paper, the ocean and topography effects on the magnetotelluric data were investigated by constructing a 3-D conceptual geoelectrical model of the island. The study showed that these effects should be taken into account in order to obtain a reliable subsurface model of the island. Data from 148 sites were used during three-dimensional inversion. The most interesting feature in the final geoelectrical model of the geothermal system is a low resistivity structure (<10 Ωm) above the resistive core of the system. The low resistivity structure has been interpreted as a hydrothermal clay alteration cap typically generated in the conventional geothermal systems. The resistivity model has been correlated with a recent seismic velocity model, showing that a low resistivity structure surrounds an area with high P wave velocity and medium–high resistivity. This medium–high resistivity area can be associated with a slowly solidified magma and, therefore, with a hotter part of the geothermal system.     

Analysis of Deformation Characteristic and Uplift Mechanism in Longgang Volcanoes,Jilin

吉林龙岗火山区是第四纪活动火山,具有潜在喷发危险。通过GNSS和水准资料分析区域三维地壳运动,得出2011—2019年相对欧亚板块水平运动以东南向为主,速度＜10 mm/a。敦化-密山断裂以东受日本2011年“3·11地震”影响强烈,现以拉张运动为主;近年来水准资料揭示火山区垂直运动以隆升为主。2014—2019年的InSAR资料显示隆升集中在靖宇一带。结合MT剖面反演得到的深部电性结构,龙岗火山区西侧高阻体分布在深度18 km以上,金龙顶子火山下方最浅。中部为早期喷发形成的火山,下方高阻体分布在深度40 km以上,东侧抚松一带分布在深度约20 km以上,地壳范围内的高阻结构表明岩浆已固结。高阻结构层可分辨出断层两侧电阻的差异性。高阻体下方存在大规模低阻结构,推测为中下地壳岩浆系统。金龙顶子火山深度10 km以下的低阻结构可能为岩浆通道,并与中下地壳岩浆系统相连。东侧区域岩浆平均深度约30 km,相对较浅。龙岗火山区幔源物质的上涌及间断性的向上运移引起地壳隆升及地震活动。     

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.     

长白山天池火山岩浆系统分析

针对外媒报道长白山天池火山在近2年内有可能喷发的言论,在长白山天池火山区布测了一条长度约为103 km的二维大地电磁测深观测剖面,对火山区深部电性结构进行探测研究.由于研究区内不明来源的电磁干扰非常强,对数据采用了远参考处理、Robust处理、Rhoplus分析、张量阻抗分解和基于一维层状介质电阻率与相位互算方法等先进处理技术,获取到一批在强干扰区质量较为可靠的电磁数据,利用数据计算分析了长白山天池火山区二维构造走向和感应矢量特征,采用NLCG二维反演技术对资料进行了二维反演解释,并将反演结果与前人探测结果进行了对比分析.探测结果表明:在天池火山口下方存在明显的直立型岩浆通道,岩浆通道在下方约5~8 km位置形成关闭;在火山口下方往北方向附近,在埋深位置约7 km深处存在一个明显的低阻异常体,电阻率小于10 Ωm,且与岩浆通道对接,推测其可能是地表浅部发育的岩浆囊;在长白山山门附近C07-C09号测点之间和C04-C05号测点之间,在埋深约7~17 km深处发现近直立型低阻带,低阻带与下方低阻体直接相连,推测低阻带内赋存有活动的岩浆;随着埋深的增加,从天池火山口南部约20 km位置往北方向,在埋深13~30 km之间壳内广泛发育明显的低阻异常体,推测其可能是活动的岩浆囊.反演结果与前人探测结果整体电性特征相似,但又局部不同.     

四川大足-福建泉州深部地电特征

根据四川大足-福建泉州剖面的大地电磁测深结果,划分了低阻的中新生界、高阻的三叠系-古生界以及相对低阻的浅变质的元古界板溪群等;了解了一些岩体的底界深度,推断沅麻盆地5 km以下出现岩脉群. 武陵山重力梯度带附近,中下地壳至上地幔岩石层有很高的电阻率,它和梯度带的形成有关.华南褶皱系普遍存在壳内高导层,它和爆破地震所反映的壳内低速层的位置相近. 深部电性证明,华蓥山断裂带、茶陵断裂带和福安-南靖断裂带等是深、大断裂带. 上地幔岩石层在横向上具有不同的电阻率.软流层深度自西向东由120-150kin变化到76km,衡阳以东最深可达240km. 由软流层变化及断裂分布,认为扬子准地台和华南褶皱系两大构造单元的分界位于茶陵-永兴断裂附近.