地球物理学报  2010, Vol. 53 Issue (3): 469-478   PDF    
地球电磁法研究新进展-"第19届国际地球电磁感应学术研讨会"专辑
赵国泽1 , NikolayPalshin2 , 黄清华3     
1. 中国地震局地质研究所, 北京 100029;
2. Geophysical Fields Laboratory, Shirshov Institute of Oceanology, RAS, 36 Nakhimov Av., Moscow 117997 Russia;
3. 北京大学地球与空间科学学院地球物理学系, 北京 100871
Recent advances of geo-electromagnetic methods-preface to the special issue on "The 19th International Workshop on Electromagnetic Induction in the Earth"
ZHAO Guo-Ze1, Nikolay Palshin2, HUANG Qing-Hua3     
1. Institute of Geology, China Earthquake Administration, Beijing 100029, China;
2. Geophysical Fields Laboratory, Shirshov Institute of Oceanology, RAS, 36 Nakhimov Av., Moscow 117997 Russia;
3. School of Earth and Space Sciences, Peking University, Beijing 100871, China
1 About the workshop

Geo-electromagnetic methods are of particular importance in geophysics. They are used for studying the conductivity structure from the Earth's surface to deep mantle as well as space environment using natural and/or artificial electric, magnetic and electromagnetic (EM) fields.

The biennial workshops, International Workshop on Electromagnetic Induction in the Earth, sponsored by the Working Group-2 of the International Association of Geomagnetism and Aeronomy (IAGA) aim at presentation and exchange of newly obtained achievements in geoelectromagnetic science. They have taken place in different locations all over the world. The first workshop was held in Edinburgh, U. K. in 1972. The 19th International Workshop on Electromagnetic Induction in the Earth (simply named as "Beijing EM Workshop" below) was held from Oct. 23 to Oct. 29, 2008 in Beijing. It was organized by Geo-electromagnetic Committee of the Chinese Geophysical Society. It attracted 480 participants including 155 young researchers and students from 43 countries from all major continents of the world, which is the overwhelming record in the history of these induction workshops. The 235 delegates came from outside China representing research institutes, universities and the industrial sector. A total of 387 abstracts including 131 extended abstracts were contributed to Beijing EM Workshop, 238 of which were submitted by delegates outside China. Here are selected topics extensively explored by the participants, in the form of oral and poster presentations and discussion sessions. A total of 57 contributions were presented in ten oral sessions and 330 posters were presented throughout the workshop.

Beside the main workshop, a Pre-Workshop and Post-Workshop were organized. The Pre-Workshop took place n Being from 20 to 22 October, 2009. It consisted of five tutorial courses given by Igor Rokityansky, Weerachai Siripunvaraporn, George Jiracek, Ivan Varentsov and Saurabh Verma, which were based on the concept of EM methods, data processing, 3-D modelling and inversion, new development of EM methods etc. About 80 people, including 32 from outside China, attended this Pre-Workshop.

The Post-Workshop on Deep Structure and Dynamics of Himalaya-Tibet and the Wenchuan Strong Earthquake was held in Chengdu University of Technology in Sichuan province, from 31 October to 3 November, 2008. About 50 people attended this meeting. A number of the Pos-Workshop participants joined a trip to visit the Wenchuan earthquake area.

The special ssues have been published on 16 workshops of past 19 workshops for papers presented at the workshops. No special issues for other 3 workshops have been published because similar special issues were published in relative years corresponding to the IUGG or IAGA assembly. Some of the workshops have published two special issues on the workshops and on the review papers respectively, like Beijing EM workshop. A total of 37 special issues have been published for electro-magnetic methods since 1972, which are in Phys. Earth Planet. Int./Surveys in Geophysics/J. Geomagn. Geoelectr./Earth, Planets and Space/ Acta Geodaet. Geophys. and Montanist. Acad. Set Hung./Advances Earth Planet. Sci/Pure Appl. Geophys./J. Geophys. Res., /J. Geophys./J. Appl. Geophys./Geophysical Surveys/Acta Geolo-gica/Chinese Journal of Geophysics[1, 2].

2 Achievements of EM Research and Application 2.1 Outlines

Over the last decade, significant advances have been made in data acquisition, processing, and modelling techniques for geo-electromagnetic and magneotelluric (MT) ields. EM methods have been applied increasingly to investigate the Earth's crust and upper mantle structures and geodynamics, to detect hydrocarbon reservoirs and mineral resources and geothermal water, to image the nearsurface structures for engineering and environmental purposes and to monitor earthquakes and other geo-hazards. The scientitic programme of the Beijing EM Workshop was divided into ten sessions including a special session for workshop-host country (China), which are as follows.

(1) EM and integrated geophysical studies of the Earth:

Part Ⅰ: Near surface applications, including environmental and engineering studies;

Part Ⅱ: Crustal and mantle studies, including regions with seismic and volcanic activity.

(2) Laboratory studies of electrical properties of rock activity.

(3) Special session on EM exploration in China.

(4) Applied EM methods for hydrocarbon, geothermal and mineral exploration.

(5) 2D/3D modelling and inversion of EM data, including joint inversion techniques.

(6) Marine EM studies.

(7) Theoretical aspects of EM exploration, including data processing, response function analysis and distortion analysis.

(8) Global induction studies using satellite and ground EM data.

(9) Potpourti Session: instrument development, natural source field studies, and new projects.

The session"Crustal and mantle studies, including regions with seismic and volcanic activity"attracted the largest number of papers. EM and MT sounding methods provide valuable information on the Earth's electrical conductivity and this parameter is extremely sensitive to geodynamic processes including temperature increase, partial melting, phase transition and excess pressure. The papers reported on the conductivity structures of continent-continent collisions around the Tibet plateau. Recent MT studies have delineated abroad zone of mid-crustal low resistivity that could represent a zone of large scale crustal flow extending from eastern and northeastern Tibet to southeatt Asia which may be a combination of partial melts and aqueous fluids. The crustal flow layer is estimated to be involved in uplitt and shortening of the Tibet plateau and tt may have also played a role in the Wenchuan Ms8.0 Earthquake on May 12, 2008, in Sichuan Province, China. A special invited review repott by Zhang Peizhen et al presented the new research on the tectonics and deep structure of Wenchuan Ms8.0 Earthquake.

"Applied EM methods for hydrocarbon, geothermal and mineral exploration" and "2D/3D modelling and inversion of EM data" were also large sessions. Nowadays, EM surveys are often carried out in complex tectonic zones and in regions with rough topography required by study target, which are challenges to modeling and interpretation of the EM data and require development of EM techniques. Recently tremendous advances have been made in numerical modeling of EM fields. In order to improve the accuracy of numerical methods and to obtain reliable geological models, some new approaches have been presented, e. g., the improved finite-difference and finite-element discretization techniques, 3D small-bin MT acquisition techniques, direct 3D EM modeling, MT, TEM, CSAMT (AMT), CSEM, DC and IP as well integrated interpretation methods combining other geophysical parameters. Some exploration examples were presented at the work-shop.

A new sub-discipline of geophysics called "biogeophysics"was one of the hot topics at the Beijing EM workshop. Apaper tilted"Geophysical Signatures of Microbial Activity"by Estella Atekwana provided an overview of this new field. Subsurface microbes are able to alter physical and chemical properties of geologic media through mineral dissolution and precipitation as well as through biofilm formation and the interaction with host media. Such microbially-induced changes in physical and chemical properties of geological media may be detected by using geophysical methods. Examples of studies that investigated biosignatures in geophysical data were reported.

The most recent advances on the laboratory electrical conductivity measurement on mantle minerals were reposted at Beijing EM workshop. The electrical conductivity signature of several mantle phase transformations, with the most important ones at 410 km, 520 km, 660 km and D, r have implications for electromagnetic induction studies. It was also shown that the high conductive layer at the top of the asthenosphere (60~100 km depth) could be explained by the presence of partial melting.

2.2 Papers in this issue

Thirty two papers are cited in this issue which involve main parts of the focus topics in Beijing EM workshop. Some research results can also be found from another special issue of the work-shop[2~7].

1 Electromagnetic methods in earthquake monitoring and prediction

Zhao et al (2010)[8] introduced the most new experiments using Control Source Extremely Low Frequency (CSELF) electromagnetic technique in 2009 indicating its great potential in earthquake monitoring. Zhao et al (2010)[9] recorded the impending signal called as the HRT precursor wave before Wenchuan Ms8.0 earthquake (12th/May/2008) using a new PS100 system at a station. Ren et al (2010)[10] introduced an analytical regularization method to deal with the high-frequency instability problem in numerical smulation of seismoelectric wave-fields in multilayered porous media. Gao et al[11] analysed the observed data such as ELF before and after Wenchuan Ms8.0 earthquake at the Hanwang station 320 km to the epicenter and found that the electric and magnetic anomalies on the frequency band (0.5~39 Hz) during the main and its aftershocks ttmes are greaterthanthose in normal timesby1~5 orders of magnitude. Tang et al[12] compared the electromagnetic data at stations Hanwang and Chouziba with the seismic data for 15 events indicating that the coseismic signal of aftershocks exists on all electric and magnetic components at two sites and they arrived at the same ttme but not at the earthquake generation tme. Huang et al[13] investigated the possible inlluences in numerical smula-tion of selectivity phenomena of seismic electric signal (SES), based on 3D finite element method (FEM).

Tan et al[14] studied the features and mechanism of the tidal geo-electrical fields based on the data of 100 geoelectrical observatories in China continent indicating that the tidal geoelectrical field can be divided into the TGF-A of approximate sine wave and the TGF-B of approximate echelon wave. Zhou et al[15] analyzed GPS data at 25 stations and showed that positive anomalies of Vertical Total Electron Content (VTEC) in the afternoon of May 3 and on May 9 were probably the ionospheric precursors of Wenchuan Ms8.0 earthquake. Zhang et al[16] mvestigated the data recorded by DEMETER for 15 days in a relative quiet geomagnetic around the M8.6 Sumatra earthquake on 28 March 2005 and found ionospheric perturbations in many parameters such as the electric field and plasma parameters in the equatorial area before the event.

2 Magnetotelluric method and deep sounding

Veeraswamy et al[17] made a MT sounding along a profile crossing Lesser and Higher Himalayas in the northern part of Indian plate and a 2D model shown that the close proximity of the resistive Rampur window of the Lesser Himalaya on the eastern side of the Chail thrust region and the basement ridges on the western side of the Chail thrust region would have contributed to the northward turn of MBT and associated thrust belts (Kangra reentrant). Wan et al[18] studied MT data along the profiles in the eastern Tibetan plateau. A2-D modeling with consideration of topography was carried out and showed that an up-ward arched high conductive layer (HCL) existed in the crust of both KDG and DLSb, but not in SCb, which maybe a partial mett with some quantity satt fluid. The relationship between the HCL and the seismisity was discussed. Wang et al[19] investigated the deep structure in western margin of the Ordos basin using MT method and found there were four blocks named as Alax block, Helanshan fold zone, Yinchuan basin and Ordos block from west to east. The Alax block is of high resistivity and the Ordos block is characterized by layering electric structure in the crust. Zhang et al[20] analyzed MT data along 150 km long profile across the central Tan-Lu fault zone using 2D inversion and found that it was composed of four electrical sections and the foci of three strong earthquakes located in the significantly heterogeneous regions of the crust with existence of high conductivity bodies nearby. Szarka et al[21] suggested a possible additional source of geomagnetic and crustal conductivity anomalies: the so-called second-order magnetic phase transition in the Earth's crust, namely a significant enhancement of the magnetic susceptibility near the Curie (Néel) depth and applied t in explanation on an unrealistic high resistivity and extremely thick layer in the crust.

Xiao et al[22] studied and compared the 3D finite difference forward modeling results focusing on the grid resolution, ways to form system matrix, boundary conditions and preconditioning linear solvers and indicated that the accuracy of both the primary and auxiliary fields increased when the thickness of the first row decreased and could not greatly be enhanced by increasing the accuracy of the 1-D boundary values only. Zhang et al[23] investigated sharp boundary inversion through introducing a diagonal gradient support into the objective function to improve the presentation of oblique geo-electrical interface and found that this new algorithm was stable and practical.

3 EM methods for near surface applications

Massoud et al[24] described TEM sounding and GEM profiling applied at Hawara archeological area, Egypt to investigate the subsurface water and its effect on the archeological targets. Integrated interpretation indicates that the agricultural activities and the flooding irrigation are the main sources for the water that invades the subsurface section at this area and the subsurface water level is at variable depths ranging from 2 to 7 m. Weng et al[25] introduced a new method to compute the transient electromagnetic (TEM) response for a large rectangular loop over layered earths by spanning the large loop using fictitious squares. Yang et al[26] researched the full-space apparent resistivity interpretation technique in mine transient electromagnetic method in order to enhance the applicability and effect for mine transient electromagnetic data.

Saraev et al[27] introduced the application of AMT method in diamond provinces of Yakut and Archangelsk, Russia, and indicated that Kimberlite pipe clusters are confined along the borders of local conductive zones within the kmberlite fields which is prone of the heightened fracturing and kimberlite magma penetration. Wang et al[28] simulated 3D CSAMT electromagnetic fields of a conductive dyke with a conductive overburden using 3D contraction integral equation (CIE) method and showed that the most effective configuration of the transmitter was in the case when the direction of the grounded-wire transmitter was along the strike of dyke. The detectability of the conductive dyke was also investigated. Qin et al[29] studied the influencing factors on the SLF electromagnetic exploration including the relationships between the nature electromagnetic field and the time as well as between the sensor orientation and the artificial electromagnetic interference, and influence of weather conditions on the data.

Qiang et al. [30] studied the electrode combination of 3D tunnel DC focused method and worked out three kinds of electrode combinations: four-point power source, fivepoint power source and ninepoint power source with calculating the spacial potential distributions of the three kinds of electrode systems by 3D FEM. Lu et al[31] introduced an algebraic multigrid (AMG) method used to solve finite difference linear equations which were derived from 3D DC resistivity modelling and became more efficient as the number of 3D grid nodes increased. Tang et al[32] presented an adaptive finite-element technique for 2. 5-D DC resistivity modelling with unstructured triangulation in the discretizaiton of arbitrary complex models and showed that, the elements near the source points were highly refined to eliminate the singularity during the adaptive process. Tang et al[33] introduced 3D DC resistivity forward modeling by finite and infinite element coupling method in order to alleviate the computational burden and speed up inversion. Li et al[34] studied three-dimensional FEM modeling of point source borehole-ground electrical potential measurements where the computational region was titled and meshes were designed to undulate with the topography.

4 Marine and helicopter-borne EM methods

Li et al[35] investigated airwave effects on time domain (or transient) responses in shallow water environments, the frequency domain, marine controlled source electromagnetic (CSEM) method for detecting thin hydrocarbon reservoirs. The airwave arrives earlier in shallow water and later in deep water environments and it occurs at different time than the signals traveling through the deep resistor, which show that CSEM is a great potential method. Zhu et al[6] discussed the Conductivity Depth Imaging (CDI) of ttme domain helicopter-borne electromagnetic data based on neural network. CDI obtained by artificial neural network is much closer to the true model than that by lookup table method, especially for resistive layers. Li et al[37] studied 1-D forward and inverse for airborne transient electromagnetic method with new Hankel filters.

5 Laboratory studies and global induction studies

Zhang et al[8] investigated the electrical conductivity of enstatite up to 20 GPa and 1600 K in the laboratory. The experimental results demonstrate that small polaron is the dominant mechanism in the high temperature regions, while proton is in charge of the low temperature regions and that a pressure induced phase transition from enstatite to ringwoodite under pressure of 20 GPa. Asimopolos et al[39] applied the spectral and wavelet analyses to the geomagnetic data at Kakioka and Vernadsky observatories and discussed the advantages and disadvantages of Fourier Transform and Wavelet Transform.

3 Abundant Activities

In addition to the scientific program, there were a number of social events during the workshop. The participants and accompanying persons were invited to visit the Forbidden City, the Great Wall, the new Olympic village for a quick look at the Bird's nest, Water cube, etc. A ping-pong (table tennis) friend-ship match was held between the international and Chinese teams. A dance performance was given for the participants; a talented group of professional artists from the Art College of Yangtze University in Huber Province came to Beijing just for this event. Many delegates and colleagues were not stingy at all to use the prose words "Beijing EM Olympics" for Beijing EM workshop. In order to encourage interactions between the delegates, the activities mentioned above were free.

The year 2008 was an unusual year when the Wenchuan Ms8.0 Earthquake on May 12 in Sichuan province shocked the large part of the main continent of China and the Olympic Games were held in August 2008 in Beijing. Beijing EM workshop was just held in this year. The Local Organizing Committee and IAGA I-2 group are grateful to the all participants for their attending the Beijing EM workshop. It is expected that we will meet again in future workshops in Giza, Egypt, in September 2010, and Darwin, Australia, in late July and early August 2012.

Acknowledgment

The Local Organizing Com-mittee and IAGA I-2 group are most grateful for their generous financial and logistical support to many international and Chinese organizations, institutions and universities and enterprises, among them the China Earthquake Administration (CEA), the Chinese Geophysical Society (CGS), the National Science Foundation of China (NSFC), the China National Petroleum Corporation (CNPC), the China Petroleum and Chemical Corporation (SINOPEC), the China Geological Survey (CGS), NSF of USA, IAGA, Chinese Academy of Science (CAS), Yangtze University, Jilin University, China University of Geoscience, South China University, Chengdu University of Technology, the Beijing Ouhualian Science and Technology Ltd. (BOST), Phoenix in Canada, KMS Technologies in USA, Metronix in Germany, IERP in Russian, Tierra Tecnica in Japan and Schlumberger in USA and so on. Thanks to the financial support from above organizations a total of 74 people from 22 different countries received a financial support to attend Beijing EM workshop. Most of the support was given to students or postdoctoral fellows/junior scientists.

Finally, we, as Guest Editors, thank the members referees for their careful and constructive reviews as well as the editors Chinese Journal of Geophysics, for their help and advice during the preparing process for publication. We also greatly appreciate the valuable help from Yasuo Ogawa, Ian Ferguson, Toivo Korja, George Jiraceck, Saurabh Verma, Martyn Unsworth, Li Yuguo and other members of IAGA I-2 group and colleagues in calling for paper and writing materials.

We cherish the memory of Professor Ulrich Schmucker. Prof. Ulrich Schmucker was one of the pioneers in using electromagnetic induction effects to probe the Earth's conductivity and was the only person who had been to all workshops from the very first one in 1972. Prof. Schmucker visited China many times and educated a lot of researchers including some from China. Prof. Schmucker had a deep feeling on both EM work-shop and Chinese colleagues. Despite suffering from cold, he decided to fly to Beijing to attend the Beijing EM workshop. His illness worsened suddenly and unexpectedly he died on the 4th day of the workshop to the dismay and shock of his colleagues. A particular assembly was organized for the colleagues to express their heartfelt condolences and memories at workshop. Let us follow his way to promote the development of EM methods and strengthen the scientific exchange.

1 研讨会概况

地球电磁法是地球物理学的重要方法, 它是通过观测自然的和人工产生的电场、磁场或电磁场研究自地表到地幔深处的电性结构和空间环境.

由IAGA -2工作组主办的两年一届的"国际地球电磁感应学术研讨会"的目的是展示和交流各种电磁方法的最新研究成果和前沿研究课题.每次研讨会的举办地点经过竞争和选举确定, 1972年在Edinburgh, U. K.举行了第1届研讨会.2008年10月23~29日在北京举行的是"第19届国际地球电磁感应学术研讨会"(以下简称"北京电磁研讨会"), 是由中国地球物理学会地球电磁专业委员会组织和承办.本次会议的参加人数、论文和报告数目都是创纪录的.有来自世界各大陆43个国家的480名代表出席会议, 其中境外代表 235人, 主要是来自研究机构、大学和企业的专家、学者和学生.会议接收和编人文集的摘要共387篇, 其中境外238篇, 详细摘要131篇, 并通过口头报告、张贴和讨论会等形式进行深人交流.大会报告57篇, 其中综述报告6篇, 其余330篇在会议其间用展版形式全程展示.

除了主会议外, 组织委员会还分别举办了会前会和会后会.会前会于2008年10月20~22日在北京举行, 邀请Igor Rokityansky, Weerachai Siripunvaraporn, George Jiracek, Ivan Varentsov和Saurabh Verma5位专家就地球电磁法的基本理论、电磁资料处理、三维正反演和电磁法新技术和未来发展趋势等进行专门讲座, 80多人(含境外32人)出席了会议.

会后会于2008年10月31日到11月3日在成都理工大学举行, 会议主题是喜玛拉雅一青藏高原深部结构和动力学以及汶川大地震, 50多位国内外代表出席会议, 会后组织参观了汶川地震区.

第1届到第19届研讨会中, 除了有3届在相应年份由IUGG或IAGA出版了地球电磁专辑外, 其余16届都出版了专门的会议专辑, 有的会议既出版会议专辑, 也出版综述报告专辑.自1972年来, 共出版了37册地球电磁法专辑, 出版专辑的刊物包括: Phys. Earth Planet. Int. /Surveys in Geophysics/J. Geomagn. Geoelectr. /Earth, Planets and Space/Acta Geodaet.Geophys.and Montanist.Acad. Sci. Hung. / Advances Earth Plantt. Sci/PAGEOPH/J.Geophys. Res., /J. Geophys. /J. Applied Geophys. / Geophysical Surveys/ ActaGeologica/Chinese Journal of Geophysics等[1, 2]

2 学术成就 2.1 概述

过去十多年来, 大地电磁等地球电磁法在数据采集、数据处理和正反演等方面取得非常明显的进步, 应用领域越来越广, 涉及地壳上地幔结构和动力学研究、石油和矿产资源以及地热和地下水勘探、工程和环境应用探查、地震等自然灾害的监测和预测等各个方面.北京电磁研讨会共设10个专题, 并首次为承办国(中国)设置了专门的专题, 它们是:

(1)地球电磁法和综合地球物理研究.

Ⅰ:近地表应用, 包括环境与工程研究.

Ⅱ:地壳上地幔结构和地震、火山研究.

(2)岩石电学性质的实验研究.

(3)中国电磁探测, 包括地震、能源和资源等.

(4)石油、地热以及矿床勘探中的应用电磁法.

(5)电磁数据的2D/3D正反演, 包括联合反演技术

(6)海洋电磁研究.

(7)电磁勘探的理论研究, 包括数据处理、响应函数分析、畸变分析等.

(8)基于卫星和地面数据的全球电磁研究.

(9)综合专题:仪器开发、天然场源研究、新计划等.

十个专题中"地壳上地幔结构和地震、火山研究"专题吸引了最多的论文.地球导电性对地球内部的升温、部分熔融、岩石相变和超高压等的异常灵敏性,使电磁法探测为地球动力学研究提供了许多有价值的信息.例如,多篇文章报道了青藏高原等碰撞带的电性结构,指出青藏高原东部和东南部中地壳普遍存在部分熔融和流体混合的低阻层,并向亚洲东南方向运动,导致青藏高原的上隆和地壳缩短,并可能诱发了5·12四川汶川8级强震的发生.特邀张培震等报告了汶川地震和深部结构的地质和地球物理的综合研究结果.

"石油、地热以及矿床勘探中的应用地电磁方法"和"电磁数据的2D/3D正反演"专题也吸引了大量的文章.由于实际需要,电磁探测经常在构造复杂、地形起伏剧烈的地区进行,给资料解释提出了严重的挑战,促使电磁模型技术也取得巨大的进步.为了改进数值方法的精度和得到可靠的地质模型,发展了一些新的技术,例如,改进的有限差分和有限元模型剖分技术、三维密集单元数据采集技术、各种电磁法的三维模型技术、MT、TEM、CSAMT (AMT)、CSEM、DC和IP等以及结合其他地球物理参数的综合解释技术等.一些成功的研究实例也在会上报告或展示.

一个新的地球物理学分支"生物地球物理学"成为这次会议的热点课题之一.地下微生物通过矿物溶解、沉淀和生物膜建造及其与环境介质的相互作用改变了地球介质的物理化学性质,这些微生物诱发的环境物理化学性质的改变可以被地球物理方法探查到,并已经取得了关于地球物理数据中微生物信号的研究实例.

关于地幔矿物电导率的实验室测量,报告了最有意义的几个地幔相转换界面,它们是410km (撖榄石向瓦兹利石)、520km (瓦兹利石向林伍德石)、660 km (林伍德石向钙钛矿和镁方铁矿)和D"(钙钛矿向后钙钛矿)深度的界面.在软流圈顶部(60~100 km)高导层可以用部分熔融的存在予以解释.

2.2 论文简介

本专辑的32篇论文涉及到研讨会报告或展版的大部分内容的最新进展,一些成果也在本次会议的另一个专辑的论文中予以介绍[2~7].根据32篇论文的内容,将其分为以下五个部分.

1 地震预测监测电磁法

赵国泽等[8]介绍了被认为是在地震预测监测中最有发展应用潜力的大功率人工源极低频电磁技术(CSELF)最新的试验成果.Zhao等[8]介绍了利用新一代高精密度地电测量PS-100系统,记录到汶川8. 0级地震等的前兆异常现象.RenH X等[10]介绍了一种能有效克服层状孔隙介质震电波场数值模拟中存在的高频不稳定性问题的解析处理方法.高曙德等[11]通过分析陇南汉王地震台ELF观测数据,发现与汶川主震和余震对应的电磁场功率谱比正常月份大1~5个数量级.汤吉等[12]通过对比研究,发现汶川地震的强余震期间大地电磁场时间序列变化与地震波序列到时有很好的对应性,而不对应发震时刻.黄清华等[13]通过三维有限元数值模拟,讨论了地震电信号选择性现象的可能原因以及数值模拟的一些可能影响因素.谭大诚等[14]研究了潮汐地电场特征及机理,基于一百个地电场台站的数据,将潮汐地电场分为近正弦形的TGF-A型和近梯形的TGF-B型.Zhou等[15]通过分析25个GPS台站数据,认为5月3日下午和5月9日的垂向电子总含量(VTEC)的正异常可能是汶川地震的电离层前兆.Zhang等[16]分析了2005年3月28日苏门答腊发生8. 6级地震前后15天的DEMETER卫星观测数据,发现电场和等离子体等多个参量地震前的扰动现象.

2 大地电磁和深部探测

Veeraswamy等[17]通过在印度板块北部地形起伏较大的喜马拉雅山地区大地电磁研究,指出主边界带及逆冲带的突然向北转弯是由于Chal逆冲带东侧的推挤和西侧的基底脊柱联合作用的结果.万战生等[18]在青藏高原东边缘大地电磁剖面的研究表明,在康滇地轴和大凉山地块地壳中存在向上拱起的高导层,推测与含流体的岩石部分熔融有关,讨论了电性结构和地震活动性的关系.王鑫等[19]在鄂尔多斯盆地西缘的大地电磁研究表明,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不同的地壳电性结构特征,其中阿拉善地块为高阻特性,鄂尔多斯地块具有成层性结构.张继红等[2°]通过对穿过郯庐断裂带中段大地电磁测深剖面的研究,指出沿剖面的电性结构可分成4段,发现3次历史强震震源区位于剧烈的电性变化的部位.Szarka等[21]提出了一种可能导致地磁和地壳电导率异常的来源:地壳中的二级磁相变,即居里(尼尔)面深度附近磁化率的显著提高.

Xao等[22]利用三维数值模拟方法计算对比发现,模型第一层的网格厚度的减小可提高主场和辅助场的精度,一维边界条件的精度对计算结果影响不大,采用适当的线性解法可明显改善叠代算法的收敛状况.Zhang等[23]通过引人对角梯度支撑,研究了倾斜电性分界面等二维大地电磁尖锐边界反演问题.

3 浅层电磁法

Massoud等[24]介绍了利用TEM和地面电磁法(GEM)在埃及Hawara遗址区(包括Hawara金字塔)的地下水探测结果,发现农业灌溉是浸人到地下的水的主要来源,深度在2~7 m之间.Weng等[25]针对矩形大定源层状模型,提出了将大定源用较少的有限大小方形回线叠加的瞬变电磁响应计算方法.杨海燕等[26]研究了矿井瞬变电磁法全空间视电阻率的解释方法,以更好地圈定低阻异常范围.

Saraev等[27]介绍了把AMT技术成功地应用于金刚石矿的勘探中的实例.Wang等[28]用压缩积分方程法模拟了导电薄层下的3D导电岩脉的CSAMT电磁场响应,指出最有效的源的位置是把发射源沿岩脉的走向放置,并研究了导电岩脉的可探测性.秦其明等[29]利用北京大学两口地热井连续5天的超低频(SLF)电磁场观测数据,研究了电磁信号随时间的变化特点和工频信号及降雨对观测信号的影响.

强建科,阮百尧等[30]对三维坑道直流聚焦法超前探测的电极组合做了研究,给出了四点、五点和九点电源布极方式研究结果.Lu等[31]介绍了利用代数多重网格方法求解三维直流电法有限差分线性方程组的方法,提高了计算精度和效率.Tang等[32]研究了用于非结构化网格2. 5-D直流电阻率的一种自适应有限元数值模拟方法和任意复杂模型的网格剖分问题.汤井田等[33]为解决传统有限元截断边界所引起的问题,介绍了一种新的三维直流电阻率有限元-无限元耦合数值模拟方法.李长伟等[34]研究了点源场井地电位测量的三维有限元正演模拟,以实现起伏地形和倾斜井情形下的正演计算.

4 海洋和航空电磁法

Li等[35]研究了空气波对浅海条件油气藏薄层探测瞬变电磁法中频率域可控源电磁方法(CSEM)的影响,显示了海洋电磁法(CSEM)的巨大应用价值和潜力.朱凯光等[36]研究了基于神经网络的时间域直升机探测的电导率深度成像技术(CDI).李永兴等[37]采用新的汉克尔变换系数,优化了航空瞬变电磁法一维正反演研究.

5 岩石实验和地磁场

Zhang等[38]通过1600 K和20GP温压条件下实验室测量的顽火辉石电导率指出,在高温区以小极化子导电机制为主,在低温区以质子导电为主,是压力(20GPa)诱发了顽火辉石向林伍德石的相变. Asimopolos等[39]基于频谱和小波分析等方法,分析了Kakioka和Vernadsky地磁台2007年的数据,讨论了上述方法在地磁资料处理中的优缺点.

3 丰富的交流活动

除学术活动外,会议还组织与会代表参观了八达岭长城、故宫和鸟巢、水立方,组织了中外代表参与的乒乓球友谊赛,并邀请长江大学艺术团在联欢晚会上表演了精彩的文艺节目.与会代表纷纷表示,本次会议内容丰富多彩,达到了学术和多种交流的目的,堪称“北京电磁奥林匹克”

2008年是不平凡的一年,5月12日四川汶川8级大地震的发生震动了中国的大部分地区,北京奥林匹克运动会的成功举行向世界展示了正在发展中的东方大国的风采,北京电磁研讨会正是在这一年举行的.会议组委会和IAGA 1-2工作组非常感谢并欢迎所有出席会议的各国代表,并期盼2010年和2012年分别在埃及Giza和澳大利亚Darwin再次相聚.

致谢

研讨会得到了国际和国内40多个组织、研究机构、大学和企业的大力支持,它们是中国地震局、中国地球物理学会、国家自然科学基金委员会、中国石油天然气总公司、中国石油化工股份有限公司、中国地质调查局、中国科学院、长江大学、吉林大学、中国地质大学、中南大学、成都理工大学以及欧华联科技有限公司、美国基金会、IAGA、加拿大凤凰地球物理公司、美国KMS、德国Metronix、俄罗斯IERP、日本TierraTecnica和Schlumberger等.会议组委会和IAGA 1-2工作组对于上述等单位的支持表示诚挚的感谢.正是由于他们的支持,使得来自22个国家的74位青年科技工作者、青年学生和资深专家在会议的资助下如期参加会议.

作为本专辑的客座编辑,我们特别感谢地球物理学报编辑部工作人员在论文编辑过程中的指导和帮助.感谢各位审稿专家在百忙中付出的认真而辛勤的劳动,使本专辑达到较高的水平,并及时出版.感谢Yasuo Ogawa, Ian Ferguson, Toivo Korja, George Jiraceck, SaurabhVerma, Martyn Unsworth, LiYuguo等许多IAGA 1-2工作组成员和许多国内外同行在专辑征稿和资料提供等各方面给予的支持和帮助.

缅怀UlrichSchmucker教授 德国UlrichSch-mucker教授是电磁感应研究的开拓者之一,是惟一一位参加了1972年来所有研讨会的著名学者. Schmucker教授曾多次访问我国,并培养了包括来自中国的众多科学工作者.Schmucker教授对电磁研讨会和中国同行都怀有深厚的感情,尽管他已经身患感冒,但仍坚持要亲临北京的会议现场.在会议期间他的病情突然加重,他的意外去世使他的同事们无比震惊.会议期间,组织了专门的哀思会表达对Schmucker教授的哀悼和怀念.让我们沿着Ulrich Schmucker教授的足迹,为推动地球电磁学的发展,促进国际交流而继续努力.

参考文献
[1] MT-Net.http://www.dias.ie/mtnet/main/index.html.2009
[2] Korja T, Zhao G. Preface to the Special Issue on "The 19~(th) Electromagnetic Induction Workshop". Surv Geophys , 2010. DOI:10.1007/s10712-009-9092-0
[3] Ralph-Uwe Börner. Numerical modelling in geo-electromagnetics:advances and challenges. Surv Geophys , 2010. DOI:10.1007/s10712-009-9087-x
[4] Unsworth M. Magnetotelluric studies of active continent-continent collisions. Surv Geophys , 2010. DOI:10.1007/s10712-009-9086-y
[5] He Z X, Hu W B, Dong W B. Petroleum electromagnetic prospecting advances and case studies in China. Surv Geophys , 2010. DOI:10.1007/s10712-009-9093-z
[6] Yoshino T. Laboratory electrical conductivity measurement of mantle minerals. Surv Geophys , 2010. DOI:10.1007/s10712-009-9084-0
[7] Estella A Atekwana, Eliot A Atekwana. Geophysical signatures of microbial activity at hydrocarbon contaminated sites:a review. Surv Geophys , 2010. DOI:10.1007/s10712-009-9089-8
[8] 赵国泽, 王立凤, 汤吉, 等. 地震监测人工源极低频电磁技术(CSELF)新试验. 地球物理学报 , 2010, 53(3): 479–486. Zhao G Z, Wang L F, Tang J, et al. New experiments of CSELF electromagnetic method for earthquake monitoring. Chinese J.Geophys. (in Chinese) , 2010, 53(3): 479-486. DOI:10.3969/j.issn.0001-5733.2010.03.002
[9] Zhao Y L, Zhao B R, Qian W, et al. HRT precursor wave and its mechanism. Chinese J.Geophys. , 2010, 53(3): 487-505. DOI:10.3969/j.issn.0001-5733.2010.03.003
[10] Ren H X, Huang Q H, Chen X F. Analytical regularization of the high-frequency instability problem in numerical simulation of seismoelectric wave-fields in multi-layered porous media. Chinese J.Geophys. , 2010, 53(3): 506-511. DOI:10.3969/j.issn.0001-5733.2010.03.004
[11] 高曙德, 汤吉, 杜学彬, 等. 汶川8.0级地震前后电磁场的变化特征. 地球物理学报 , 2010, 53(3): 512–525. Gao S D, Tang J, Du X B, et al. The change characteristics of electromagnetic field before to after Wenchuan Ms8.0 earthquake. Chinese J.Geophys. (in Chinese) , 2010, 53(3): 512-525. DOI:10.3969/j.issn.0001-5733.2010.03.005
[12] 汤吉, 詹艳, 王立凤, 等. 汶川地震强余震的电磁同震效应. 地球物理学报 , 2010, 53(3): 526–534. Tang J, Zhan Y, Wang L F, et al. Electromagnetic coseismic effect associated with aftershock of Wenchuan Ms8.0 earthquake.. Chinese J.Geophys. (in Chinese) , 2010, 53(3): 526-534. DOI:10.3969/j.issn.0001-5733.2010.03.006
[13] 黄清华, 林玉峰. 地震电信号选择性数值模拟及可能影响因素. 地球物理学报 , 2010, 53(3): 535–543. Huang Q H, Lin Y F. Numerical simulation of selectivity of seismic electric signal and its possible influences. Chinese J.Geophys. (in Chinese) , 2010, 53(3): 535-543. DOI:10.3969/j.issn.0001-5733.2010.03.007
[14] 谭大诚, 赵家骝, 席继楼, 等. 潮汐地电场特征及机理研究. 地球物理学报 , 2010, 53(3): 544–555. Tan D C, Zhao J L, Xi J L, et al. A study on feature and mechanism of the tidal geoelectrical field. Chinese J.Geophys. (in Chinese) , 2010, 53(3): 544-555. DOI:10.3969/j.issn.0001-5733.2010.03.008
[15] Zhou Y Y, Wu Y, Qiao X J, et al. Anomalous variations of ionospheric VTEC before Ms8.0 Wenchuan earthquake. Chinese J.Geophys. , 2010, 53(3): 556-566. DOI:10.3969/j.issn.0001-5733.2010.03.009
[16] Zhang X M, Liu J, Shen X H, et al. Ionospheric perturbations associated with the M8.6 Sumatra earthquake on 28 March 2005. Chinese J.Geophys. , 2010, 53(3): 567-575. DOI:10.3969/j.issn.0001-5733.2010.03.010
[17] Veeraswamy K, Abdul Azeez K K, Basava S, et al. Electrical structure across Lesser and Higher NW Himalaya, India. Chinese J.Geophys. , 2010, 53(3): 576-584. DOI:10.3969/j.issn.0001-5733.2010.03.011
[18] 万战生, 赵国泽, 汤吉, 等. 青藏高原东边缘冕宁-宜宾剖面电性结构及其构造意义. 地球物理学报 , 2010, 53(3): 585–594. Wan Z S, Zhao G Z, Tang J, et al. The electrical structure of the crust along Mianning-Yibin profile in the eastern edge of Tibetan plateau and its tectonic implications. Chinese J.Geophys. (in Chinese) , 2010, 53(3): 585-594. DOI:10.3969/j.issn.0001-5733.2010.03.012
[19] 王鑫, 詹艳, 赵国泽, 等. 鄂尔多斯盆地西缘构造带北段深部电性结构. 地球物理学报 , 2010, 53(3): 595–604. Wang X, Zhan Y, Zhao G Z, et al. Deep electric structure beneath the northern section of the western margin of the Ordos basin. Chinese J.Geophys. (in Chinese) , 2010, 53(3): 595-604. DOI:10.3969/j.issn.0001-5733.2010.03.013
[20] 张继红, 赵国泽, 肖骑彬, 等. 郯庐断裂带中段(沂沭断裂带)电性结构研究与孕震环境. 地球物理学报 , 2010, 53(3): 605–611. Zhang J H, Zhao G Z, Xiao X B, et al. Analysis of electric structure of the central Tan-Lu fault zone (Yi-Shu fault zone, 36°N) and seismogenic condition. Chinese J.Geophys. (in Chinese) , 2010, 53(3): 605-611. DOI:10.3969/j.issn.0001-5733.2010.03.014
[21] Szarka L, Kiss J, Prácser E, et al. The magnetic phase transition and geophysical crustal anomalies. Chinese J.Geophys. , 2010, 53(3): 612-621. DOI:10.3969/j.issn.0001-5733.2010.03.015
[22] Xiao Q B, Zhao G Z. Comparison of finite difference numerical solutions in magnetotelluric modelling. Chinese J.Geophys. , 2010, 53(3): 622-630. DOI:10.3969/j.issn.0001-5733.2010.03.016
[23] Zhang L L, Yu P, Wang J L, et al. A study on 2D magnetotelluric sharp boundary inversion. Chinese J.Geophys. , 2010, 53(3): 631-637. DOI:10.3969/j.issn.0001-5733.2010.03.017
[24] Massoud U, Abbas A M, Mesbah H S A, et al. Mapping of subsoil water level and its impacts on Hawara archeological site by transient and multi-frequency electromagnetic survey. Chinese J.Geophys. , 2010, 53(3): 638-645. DOI:10.3969/j.issn.0001-5733.2010.03.018
[25] Weng A H, Liu Y H, Chen Y L, et al. Computation of transient electromagnetic field from a rectangular loop over stratified Earths. Chinese J.Geophys. , 2010, 53(3): 646-650. DOI:10.3969/j.issn.0001-5733.2010.03.019
[26] 杨海燕, 邓居智, 张华, 等. 矿井瞬变电磁法全空间视电阻率解释方法研究. 地球物理学报 , 2010, 53(3): 651–656. Yang H Y, Deng J Z, Zhang H, et al. Research on full-space apparent resistivity interpretation technique in mine transient electromagnetic method. Chinese J.Geophys. (in Chinese) , 2010, 53(3): 651-656. DOI:10.3969/j.issn.0001-5733.2010.03.020
[27] Saraev A K, Antaschuk K M, Nikiforov A B, et al. Audiomagnetotelluric soundings for the diamond exploration. Chinese J.Geophys. , 2010, 53(3): 657-676. DOI:10.3969/j.issn.0001-5733.2010.03.021
[28] Wang R, Masashi Endo, Di Q Y, et al. The analysis of CSAMT responses of dyke embedded below conductive overburden. Chinese J.Geophys. , 2010, 53(3): 677-684. DOI:10.3969/j.issn.0001-5733.2010.03.022
[29] 秦其明, 李百寿, 崔容菠, 等. 地热井的天然源超低频电磁探测影响因素分析. 地球物理学报 , 2010, 53(3): 685–694. Qin Q M, Li B S, Cui R B, et al. Analysis of factors affecting natural source SLF electromagnetic exploration at geothermal wells. Chinese J.Geophys. (in Chinese) , 2010, 53(3): 685-694. DOI:10.3969/j.issn.0001-5733.2010.03.023
[30] 强建科, 阮百尧, 周俊杰. 三维坑道直流聚焦法超前探测的电极组合研究. 地球物理学报 , 2010, 53(3): 695–699. Qiang J K, Ruan B Y, Zhou Z J. Research on the array of electrodes of advanced focus detection with 3D DC resistivity in tunnel. Chinese J.Geophys. (in Chinese) , 2010, 53(3): 695-699. DOI:10.3969/j.issn.0001-5733.2010.03.024
[31] Lu J J, Wu X P, Spitzer K. Algebraic multigrid method for 3D DC resistivity modelling. Chinese J.Geophys. , 2010, 53(3): 700-707. DOI:10.3969/j.issn.0001-5733.2010.03.025
[32] Tang J T, Wang F Y, Ren Z Y. 25-D DC resistivity modeling by adaptive finite-element method with unstructured triangulation.. Chinese J.Geophys. , 2010, 53(3): 708-716. DOI:10.3969/j.issn.0001-5733.2010.03.026
[33] 汤井田, 公劲喆. 三维直流电阻率有限元-无限元耦合数值模拟. 地球物理学报 , 2010, 53(3): 717–728. Tang J T, Gong J Z. 3D DC resistivity forward modeling by finite-infinite element coupling method. Chinese J.Geophys. (in Chinese) , 2010, 53(3): 717-728. DOI:10.3969/j.issn.0001-5733.2010.03.027
[34] 李长伟, 阮百尧, 吕玉增, 等. 点源场井-地电位测量三维有限元模拟. 地球物理学报 , 2010, 53(3): 729–736. Li C W, Ruan B Y, Lü Y Z, et al. Three-dimensional FEM modeling of point source borehole-ground electrical potential measurements. Chinese J.Geophys. (in Chinese) , 2010, 53(3): 729-736. DOI:10.3969/j.issn.0001-5733.2010.03.028
[35] Li Y G, Constable S. Transient electromagnetic in shallow water:insights from 1D modeling. Chinese J.Geophys. , 2010, 53(3): 737-742. DOI:10.3969/j.issn.0001-5733.2010.03.029
[36] 朱凯光, 林君, 韩悦慧, 等. 基于神经网络的时间域直升机电磁数据电导率深度成像. 地球物理学报 , 2010, 53(3): 743–750. Zhu K G, Lin J, Han Y H, et al. Research on conductivity depth imaging of time domain helicopter-borne electromagnetic data based on neural network. Chinese J.Geophys. (in Chinese) , 2010, 53(3): 743-750. DOI:10.3969/j.issn.0001-5733.2010.03.030
[37] 李永兴, 强建科, 汤井田. 航空瞬变电磁法一维正反演研究. 地球物理学报 , 2010, 53(3): 751–759. Li Y X, Qiang J K, Tang J T. A research on 1-D forward and inverse airborne transient electromagnetic method. Chinese J.Geophys. (in Chinese) , 2010, 53(3): 751-759. DOI:10.3969/j.issn.0001-5733.2010.03.031
[38] Zhang B H, Wu X P, Xu J S, et al. Electrical conductivity of enstatite up to 20 GPa and 1600 K. Chinese J.Geophys. , 2010, 53(3): 760-764. DOI:10.3969/j.issn.0001-5733.2010.03.032
[39] Asimopolos L, Pestina A M, Asimopolos N S. Considerations on geomagnetic data analysis. Chinese J.Geophys. , 2010, 53(3): 765-772. DOI:10.3969/j.issn.0001-5733.2010.03.033