Journal of geomagnetism and geoelectricity最新文献_第3页

Noise reduction in electromagnetic time series to improve detection of seismic-induced signals 电磁时间序列降噪以提高地震感应信号的检测

Journal of geomagnetism and geoelectricity Pub Date : 1997-11-20 DOI: 10.5636/JGG.49.1257

J. Larsen

引用次数: 11

Repeated Self-Potential Profiling of Izu-Oshima Volcano, Japan 日本伊豆大岛火山的重复自我电位分析

Journal of geomagnetism and geoelectricity Pub Date : 1997-11-20 DOI: 10.5636/JGG.49.1267

T. Ishido, T. Kikuchi, N. Matsushima, Y. Yano, S. Nakao, M. Sugihara, T. Tosha, S. Takakura, Y. Ogawa

{"title":"Repeated Self-Potential Profiling of Izu-Oshima Volcano, Japan","authors":"T. Ishido, T. Kikuchi, N. Matsushima, Y. Yano, S. Nakao, M. Sugihara, T. Tosha, S. Takakura, Y. Ogawa","doi":"10.5636/JGG.49.1267","DOIUrl":"https://doi.org/10.5636/JGG.49.1267","url":null,"abstract":"Between March 1989 and March 1994, annual self-potential (SP) surveys were carried out on Izu-Oshima, a small volcanic island. A terrain-related SP distribution of about -1 mV per meter of elevation was observed outside the caldera in all five surveys. Inside the caldera, SP increases from about -350 mV to near 0 mV (relative to the coastline) as the summit crater is approached, although negative anomalies of small spatial extent are manifest. Self-potential inside the caldera decreased by about 100 mV between the March 1989 and the March 1990 surveys, which appears to be correlated with a significant decline in the degassing rate from the summit crater. After 1990, the SP distribution is quite steady along the entire survey line which extends from the west coast through the southern part of the caldera, and ends east of Ura-sabaku. Recently a postprocessor has been developed to calculate space/time distributions of electrokinetic potentials resulting from histories of underground conditions (pressure, temperature, salt concentration, flowrate etc.) computed by multiphase multi-component unsteady geothermal reservoir simulations (Ishido and Pritchett, 1996). We applied this postprocessor to a simple two-dimensional model of hydrothermal activity in a volcanic island. The low potentials in areas of high elevation are reproduced in the model, and are caused by downflow of meteoric waters. The high potential centered at the summit crater is found to be produced by upflows of volcanic gas and vapor which diminish meteoric water downflow near the volcanic conduit.","PeriodicalId":156587,"journal":{"name":"Journal of geomagnetism and geoelectricity","volume":"61 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129284644","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 47

Migration versus inversion in electromagnetic imaging technique 电磁成像技术中的偏移与反演

Journal of geomagnetism and geoelectricity Pub Date : 1997-11-20 DOI: 10.5636/JGG.49.1415

M. Zhdanov, P. Traynin

{"title":"Migration versus inversion in electromagnetic imaging technique","authors":"M. Zhdanov, P. Traynin","doi":"10.5636/JGG.49.1415","DOIUrl":"https://doi.org/10.5636/JGG.49.1415","url":null,"abstract":"One of the most challenging problems in electromagnetic (EM) geophysical methods is developing fast and stable methods of imaging inhomogeneous underground structures using EM data. In our previous publications we developed a novel approach to this problem, using EM migration. In this paper we demonstrate that there is a very close connection between the method of EM migration and the solution of the conventional EM inverse problem. Actually, we show that migration is an approximate inversion. It realizes the first iteration in the inversion algorithm, based on the minimization of the residual field energy flow through the profile of observations. This new theoretical result opens a way for formulating a new imaging condition. We compare this new imaging condition with the traditional one, obtained for simplified geoelectrical models of the subsurface structures. This result also leads to the construction of a solution of the inverse EM problem, based on iterative EM migration in the frequency domain, and gradient (or conjugate gradient) search for the optimal geoelectrical model. However, the authors have found that in the framework of this method, even the first iteration, based on the migration of the residual field, generates a reasonable geoelectrical image of the subsurface structure.","PeriodicalId":156587,"journal":{"name":"Journal of geomagnetism and geoelectricity","volume":"39 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116487529","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 15

The resistivity structure around the hypocentral area of the Ebino earthquake swarm in Kyushu district, Japan 日本九州地区埃比诺地震群震源周围的电阻率结构

Journal of geomagnetism and geoelectricity Pub Date : 1997-11-20 DOI: 10.5636/JGG.49.1279

T. Goto, N. Oshiman, N. Sumitomo

引用次数: 2

Studies of the Georesistivity Structure in the Central Part of the Northeastern Japan Arc. 日本东北弧中部地电阻率结构研究。

Journal of geomagnetism and geoelectricity Pub Date : 1997-11-20 DOI: 10.5636/JGG.49.1601

Y. Fujinawa, N. Kawakami, T. Asch, M. Uyeshima, Y. Honkura

{"title":"Studies of the Georesistivity Structure in the Central Part of the Northeastern Japan Arc.","authors":"Y. Fujinawa, N. Kawakami, T. Asch, M. Uyeshima, Y. Honkura","doi":"10.5636/JGG.49.1601","DOIUrl":"https://doi.org/10.5636/JGG.49.1601","url":null,"abstract":"Wideband magnetotelluric measurements were conducted along three traverses in the central Tohoku district of the northeastern Japan arc. These data provide independent constraints for understanding seismo-tectonics and geology where the Pacific plate subducts beneath the Eurasian plate. Smooth two-dimensional models of the data acquired along the three transects were obtained using the Generalized Rapid Relaxation Inversion algorithm. Modeling suggest that the area can be reasonably treated as two-dimensional with the structural direction being north-south in agreement with the strikes of geological units. The three 2-D models correlate well with the regional geological morphology in the central part of the Tohoku district which is divided by three high altitude regions. The resistivity profiles indicate two clear conductive anomalies in the Central Basin Range and in the Kitakami, Abukuma river regions that show considerable variability in each of the three 2-D models. Boundaries of conductive bodies correlate well with mapped faults, including those of pre-Tertiary age. The northernmost cross section is more complex possibly because of the presence of Quaternary volcanoes and an active geothermal source area in the vicinity.","PeriodicalId":156587,"journal":{"name":"Journal of geomagnetism and geoelectricity","volume":"42 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127425658","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 5

Fast and stable two-dimensional inversion of magnetotelluric data 大地电磁资料二维快速稳定反演

Journal of geomagnetism and geoelectricity Pub Date : 1997-11-20 DOI: 10.5636/JGG.49.1469

P. D. Lugão, O. Portniaguine, M. Zhdanov

{"title":"Fast and stable two-dimensional inversion of magnetotelluric data","authors":"P. D. Lugão, O. Portniaguine, M. Zhdanov","doi":"10.5636/JGG.49.1469","DOIUrl":"https://doi.org/10.5636/JGG.49.1469","url":null,"abstract":"The two-dimensional (2-D) magnetotelluric (MT) inverse problem still poses difficult challenges in spite of efforts to develop fast and efficient methods for its solution. In this paper, we present a new approach for the solution of overparameterized cases based on regularization theory and full 2-D, quasi-analytic, calculation of the Frechet derivatives. For the forward solution we use a fast and efficient finite difference formulation to the solution of the MT equations in both transverse electric (TE) and transverse magnetic (TM) modes based on the balance method. The Frechet derivative matrix is obtained as a solution to simple forward and back substitution of the LU decomposed matrix of coefficients from the forward problem utilizing the principle of reciprocity. Magnetotelluric data is usually contaminated by noise, so that its inverse problem is ill-posed. In order to constrain the solution to a set of acceptable models, Tikhonov regularization is applied and yields a regularized parametric functional. The regularized conjugate gradient method is then utilized to minimize the parametric functional. Results of inversion for a set of synthetic data and for a set of CSAMT data from Kennecott Exploration show that the method yields models which are physically and geologically reasonable for both synthetic and real data sets.","PeriodicalId":156587,"journal":{"name":"Journal of geomagnetism and geoelectricity","volume":"27 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114300813","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 21

13th Workshop on Electromagnetic Induction in the Earth 第十三届地球电磁感应研讨会

Journal of geomagnetism and geoelectricity Pub Date : 1997-11-20 DOI: 10.5636/JGG.49.1255

Y. Honkura, Y. Ogawa

引用次数: 6

Modeling of non-stationary electrokinetic effect in a conductive crust 导电地壳中非稳态电动力学效应的模拟

Journal of geomagnetism and geoelectricity Pub Date : 1997-11-20 DOI: 10.5636/JGG.49.1317

O. Majaeva, Y. Fujinawa, M. Zhitomirsky

引用次数: 9

EM Induction in Elongated Conductors Normal to a Coastline with Application to Geomagnetic Measurements in Nigeria 垂直于海岸线的细长导体的电磁感应及其在尼日利亚地磁测量中的应用

Journal of geomagnetism and geoelectricity Pub Date : 1997-11-20 DOI: 10.5636/JGG.49.1401

J. Chen, H. W. Dosso, S. Kang

引用次数: 4

Local galvanic distortions in the central part of north-eastern Japan. (Part 1) 日本东北部中部的局部电流畸变。(第1部分)

Journal of geomagnetism and geoelectricity Pub Date : 1997-11-20 DOI: 10.5636/JGG.49.1387

N. Kawakami, Y. Fujinawa, T. Asch, S. Takasugi

{"title":"Local galvanic distortions in the central part of north-eastern Japan. (Part 1)","authors":"N. Kawakami, Y. Fujinawa, T. Asch, S. Takasugi","doi":"10.5636/JGG.49.1387","DOIUrl":"https://doi.org/10.5636/JGG.49.1387","url":null,"abstract":"Wide-band (20, 000 Hz to 0.002 Hz) magnetotelluric (MT) observations have been conducted since 1990 in the central part of the Tohoku district in the northeastern part of Japan to investigate the deep electrical resistivity structure. MT data were obtained on three east-west-trending MT transects about 140 km long and separated by about 20 km. In this paper we investigate three-dimensional galvanic distortions on the three transects using the Groom-Bailey tensor decomposition technique. We have focused on the regional strike direction and are not considering static shifts in the data. The decomposition method worked well at most sites but failed at some sites suggesting considerable regional three-dimensionality there. We found that the north-northwest to south-southeast direction is the predominant regional strike. This direction coincides with the regional geological strike being nearly perpendicular to the subduction direction of the Pacific plate. The induction vectors are generally in agreement with the regional strike direction deduced by the decomposition method on the southernmost line, but they deviate systematically on northernmost and middle lines suggesting conductivity contrasts in these areas.","PeriodicalId":156587,"journal":{"name":"Journal of geomagnetism and geoelectricity","volume":"32 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133648754","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 6