Electromagnetometry at the sea floor

  • Jiro Segawa
  • Hiroaki Toh


Electromagnetometry at the sea floor has been developed over the last two decades taking advantage of the progress of positioning and acoustic technology in marine region. In spite of its risks and costs, electromagnetometry at the sea floor has significantly contributed to the study of conductivity anomalies through direct observations of electromagnetic variations at the sea floor. Some of the fruitful results of the ocean bottom observations around Japan as well as data processing of sea floor electromagnetic measurements are reviewed. Future problems in electromagnetometry at the sea floor are also discussed. In conclusion, the importance of establishing semipermanent electromagnetic observatories at the sea floor is emphasized.


Electromagnetometry sea floor electromagnetic variations conductivity anomaly 


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  1. Asakawa E, Utada H and Yukutake T 1988 Application of Sompi spectral analysis to the estimation of the geomagnetic transfer function;J. Geomagn. Geoelectr. 40 447–463Google Scholar
  2. Bindoff N L, Lilley F E M and Filloux J H 1988 A separation of ionospheric and oceanic tidal components in magnetic fluctuation data;J. Geomagn. Geoelectr. 40 1445–1467Google Scholar
  3. Chave A D and Filloux J H 1984 Electromagnetic induction fields in the deep ocean off California: Oceanic and ionospheric sources;Geophys. J. R. Astron. Soc. 77 143–171Google Scholar
  4. Cheesman S J, Edwards R N and Chave A D 1987 On the theory of sea-floor conductivity mapping using transient electromagnetic systems;Geophysics 52 204–217CrossRefGoogle Scholar
  5. Cox C 1980 Electromagnetic induction in the oceans and inferences on the constitution of the Earth;Geophys. Surv. 4 137–156CrossRefGoogle Scholar
  6. Edwards R N, Law L K, Wolfgram P A, Nobes D C, Bone M N, Trigss D F and Delaurier J M 1985 First results of the MOSES experiment: sea-sediment conductivity and thickness determination, Bute Inlet, British Columbia, by magnetometric offshore electrical sounding;Geophysics 50 153–160CrossRefGoogle Scholar
  7. EMSLAB Group 1988 The EMSLAB electromagnetic sounding experiment;Eos 69 98–99Google Scholar
  8. Filloux J H 1967 An ocean bottom, D-component magnetometer;Geophysics 32 978–987CrossRefGoogle Scholar
  9. Filloux J H 1980a Observation of very low frequency electromagnetic signals in the ocean;J. Geomagn. Geoelectr. 32 (suppl. I) SI 1-SI 12Google Scholar
  10. Filloux J H 1980b Magnetotelluric soundings over the northeast Pacific may reveal spatial dependence of depth and conductance of the asthenosphere;Earth Planet. Sci. Lett. 46 244–252CrossRefGoogle Scholar
  11. Hermance J F 1973 Processing of magnetotelluric data;Phys. Earth Planet. Inter. 7 349–364CrossRefGoogle Scholar
  12. Honkura Y 1974 Electrical conductivity anomalies beneath the Japan arc;J. Geomagn. Geoelectr. 26 147–171Google Scholar
  13. Kaneko Y, Oshima S and Honkura Y 1988 Conductivity anomaly beneath Ryukyu arc; Programme and Abstracts, Society of Geomagnetism and Earth Planetary Space Sciences, Japan (in Japanese)Google Scholar
  14. Kumuzawa M 1985 Physics of the earth and planet interiors; Lecture Note, Geophysical Institute, University of TokyoGoogle Scholar
  15. Ogawa Y, Yukutake T and Utada H 1986 Two-dimensional modelling of resistivity structure beneath the Tohoku district, northern Honshu of Japan by a finite element method;J. Geomagn. Geoelectr. 38 45–79Google Scholar
  16. Rikitake T 1969 The undulation of an electrically conductive layer beneath the islands of Japan;Tectonophysics 7 257–264CrossRefGoogle Scholar
  17. Rikitake T and Honkura Y 1985Solid earth geomagnetism (Tokyo: Terra Sci. Pub. Co.) Vol 5, 384 ppGoogle Scholar
  18. Sasai Y 1968 Spatial dependence of short-period geomagnetic fluctuations on Oshima Island (2);Bull. Earthq. Res. Inst. Univ. Tokyo 46 907–926Google Scholar
  19. Segawa J, Kasuga T and Yukutake T 1981 Preliminary test on a three-component ocean bottom magnetometer;J. Geod. Soc. Jpn 27 293–251Google Scholar
  20. Shiozaki I, Nogi Y, Yamaguchi S, Ohkubo A, Ichikita T, Yaskawa K, Fujiwara S and Sumitomo N 1988 Preliminary report on co-operative investigations of electrical resistivity structure beneath the Chugoku and Shikoku districts of Japan; Programme and Abstracts, Society of Geomagnetism and Earth, Planetary and Space Sciences, Japan (in Japanese)Google Scholar
  21. Traits P and Honkura Y 1988 Sea effects on geomagnetic variations in the Japanese islands; Programme and Abstracts, Society of Geomagnetism and Earth, Planetary and Space Sciences, Japan (in Japanese)Google Scholar
  22. Tatsumi Y 1989 Migration of fluid phases and genesis of basalt magmas in subduction zones;J. Geophys. Res. 94 4697–4707CrossRefGoogle Scholar
  23. Toh H, Fujimoto H and Segawa J 1988 A seafloor geomagnetic observation across the northern Izu-Bonin ridge; Programme and Abstracts, Society of Geomagnetism and Earth, Planetary and Space Sciences, Japan (in Japanese)Google Scholar
  24. Utada H, Hamano Y and Yukutake T 1986 A two-dimensional conductivity model across central Japan;J. Geomagn. Geoelectr. 38 447–473Google Scholar
  25. Utada H 1987A direct inversion method for two-dimensional modelling in the geomagnetic induction problem; PhD thesis, University of TokyoGoogle Scholar
  26. Yamano M 1986Heat flow studies of the circum-Pacific subduction zones; PhD thesis, University of TokyoGoogle Scholar

Copyright information

© Indian Academy of Sciences 1990

Authors and Affiliations

  • Jiro Segawa
    • 1
  • Hiroaki Toh
    • 1
  1. 1.Ocean Research InstituteThe University of TokyoTokyoJapan

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