Grounded electrical-source airborne transient electromagnetic (GREATEM) survey of Mount Bandai, north-eastern Japan

Toru Mogi; Ken’ichirou Kusunoki; Hideshi Kaieda; Hisatoshi Ito; Akira Jomori; Nobuhide Jomori; Youichi Yuuki

doi:10.1071/EG08115

RESEARCH ARTICLE

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Grounded electrical-source airborne transient electromagnetic (GREATEM) survey of Mount Bandai, north-eastern Japan

Toru Mogi ¹ ⁵ Ken’ichirou Kusunoki ² Hideshi Kaieda ² Hisatoshi Ito ² Akira Jomori ³ Nobuhide Jomori ³ Youichi Yuuki ⁴

+ Author Affiliations

- Author Affiliations

¹ Institute of Seismology and Volcanology, Hokkaido University, N10W8, Kita-ku, Sapporo 060-0810, Japan.

² Civil Engineering Research Laboratory, Central Research Institute of Electrical Power Industry, 1646 Abiko, Abiko City, Chiba Prefecture 270-1194, Japan.

³ NeoScience Co., 2-7-1, Ayumino, Izumi, Osaka 594-1157, Japan.

⁴ Geotechnical Center, Oyo Co., 2-61-5 Toro, Saitama 331-8688, Japan.

⁵ Corresponding author. Email: mogitisv@mail.sci.hokudai.ac.jp

Exploration Geophysics 40(1) 1-7 https://doi.org/10.1071/EG08115
Submitted: 9 September 2008 Accepted: 19 January 2009 Published: 27 February 2009

Abstract

Airborne electromagnetics (AEM) is a useful tool for investigating volcanic structures because it can survey large and inaccessible areas. Disadvantages include lower accuracy and limited depth of investigation. The Grounded Electrical Source Airborne Transient Electromagnetic (GREATEM) survey system was developed to increase the depth of investigation possible using AEM. The method was tested in a survey at Mount Bandai in north-eastern Japan. Mount Bandai is an andesitic stratovolcano that rises 1819 m above sea level. An eruption in July 1888 left a hoof-shaped collapsed wall in its northern crater and avalanche debris at its base. Previous surveys of Mount Bandai allow for comparisons of data on its structure and collapse mechanism as obtained by GREATEM and other geophysical methods. The results show resistive structures in recent volcanic cones and conductive structures in the collapsed-crater area. Conductive areas around the collapsed wall correspond to an alteration zone resulting from hydrothermal activity, supporting the contention that a major cause of the collapse associated with the 1888 eruption was hydrothermal alteration that structurally weakened the interior of the volcanic edifice.

Key words: airborne electromagnetics, collapsed wall, disaster mitigation, subsurface volcanic structure.

Acknowledgments

This study was performed under the project entitled ‘Integrated Disaster Prevention Using an Airborne Geophysical System,’ supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. The authors thank the members of the project committee, Prof. Y. Tanaka of Kyoto University, Dr Y. Fujimitsu of Kyushu University, and Mr T. Igarashi of Oyo Corporation, for their helpful discussions regarding the system design and survey results.

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