Goldstein, N E

Hoversten, G M

Morrison, H F

Mozley, E

Wilt, M

English

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Lawrence Berkeley National LaboratoryLBL PublicationsTitleA Comparison of Electromagnetic and Magnetotelluric SurveysPermalinkhttps://escholarship.org/uc/item/9rm80922AuthorsMorrison, H FGoldstein, N EHoversten, G Met al.Publication Date1979-05-01Copyright InformationThis work is made available under the terms of a Creative Commons Attribution License, available at https://creativecommons.org/licenses/by/4.0/eScholarship.org Powered by the California Digital LibraryUniversity of California.. ·.; . ..., .j .!..; .J , . " To be presented at the 49th International Meeting, Society of Exploration Geophysicists, New Orleans, LA, November 4-8, 1979 A COMPARISON OF ELECTROMAGNETIC AND MAGNETOTELLURIC SURVEYS H. F. Morrison, N. E. Goldstein, G. M. Hoversten, M. Wilt and E. Mozley May 1979 Prepared for the U. S. Department of Energy under Contract W-7405-ENG-48 For Reference Not to be taken from this room {)C-fo6 ~ LBL-9267 Abstract LEGAL NOTICE This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the United States Department of Energy, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights. DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or the Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of California. ~ :~ 0 \.J LBL-9267 A COMPARISON OF ELECTROMAGNETIC AND MAGNETOTELLURIC SURVEYS H.F. Morrison*. N.E. Goldstein+, G.M. Hoversten*, M. Wilt+, E.Mozley* Inductive frequency domain electromagnetic soundings have been conducted at three magnetotelluric sounding sites on the flanks of Mt. Hood, Oregon. The transmitter was a horizontal loop trans.mitter with a moment of "-10 6 amp turns meter2 ; a SQUID magnetometer and portable digital signal averager were used at the receiver. Separations of up to 1.5 km, and frequencies between 0.3 and 100 Hz were used. The MT soundings were conducted with the new remote reference scheme and data were taken in the .03 to 10 Hz band. The strong radial flow patterns of the volcanics permit first order modeling of the MT data with 2 dimensional models at the three sites. At two of the sites a confined conductor at about 500 meters underneath a resistive upper section is evident; however,detailed modeling is certainly made difficult by obvious three dimensional and topographic effects. Model studies show that the depth to the conductor is underestimated by MT in th.is case. The em soundings, each with several receiver sites, yield remarkably consistent interpretations of a conductor of 15-25 ohm meter at 500-540 meters depth at both sites. Model studies in this case clearly show that the depth estimates are not as biased by the confined nature of the conductor as are the MT resQlts. The em data were i'nterpreted in terms of amplitude and phase, in a joint inversion, for a two layer model. Orientation errors of the receiver were removed by numerically rotating the orthogonal receiver sensor to minimize the radial field component at low frequencies. Inversion on the ellipticity of the magnetic field, which is rotation independent, yielded the same models. Despite large moments and long averaging time the S/N ratio at frequencies lower than .3 Hz was poor. A new scheme has been devised using a remote reference natural field noise cancellation system that should lower the low frequency cut off by at least one decade. *University of California, Berkeley, Department of Materials Science and Mineral Engineering, Engineering Geoscience Group, Berkeley CA. 94720 +Lawrence Berkeley Laboratory, Eatth Sciences Divi~ion, University of California, Berkeley, CA. 94720 Abstract submitted to the 49th International Meeting, Society of Exploration Geophysicists, New Orleans, 4-8 Nov. 1979 J .j .1 ) This report was done with support from the Department of Energy. Any conclusions or opinions expressed in this report represent solely those of the author(s) and not necessarily those of The Regents of the University of California, the Lawrence Berkeley Laboratory or the Department of Energy. Reference to a company or product name does not imply approval or recommendation of the product by the University of California or the U.S. Department of Energy to the exclusion of others that may be suitable. .. ~ . ,....... TECHNICAL INFORMATION DEPARTMENT LAWRENCE BERKELEY LABORATORY UNIVERSITY OF CALIFORNIA BERKELEY, CALIFORNIA 94720 . (_, 

A Comparison of Electromagnetic and Magnetotelluric Surveys

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A Comparison of Electromagnetic and Magnetotelluric Surveys

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