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Aso Volcanological Laboratory, Faculty of Science, Kyoto University, Aso, Kumamoto, Japan
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- PublicationOpen AccessDrag-out effect of piezomagnetic signals due to a borehole: the Mogi source as an example(2007-02)
; ; ; ; ; ; ; ; ; ; ;Sasai, Y.; Disaster Prevention Division, Bureau of General Affairs, Tokyo Metropolitan Government, Tokyo, Japan ;Johnston, M. J. S.; US Geological Survey, Menlo Park, CA, U.S.A. ;Tanaka, Y.; Graduate School of Science, Kyoto University, Japan ;Mueller, R.; US Geological Survey, Menlo Park, CA, U.S.A. ;Hashimoto, T.; Graduate School of Science, Hokkaido University, Japan ;Utsugi, M.; Graduate School of Science, Kyoto University, Japan ;Sakanaka, S.; Faculty of Engineering and Resource Science, Akita University, Japan ;Uyeshima, M.; Earthquake Research Institute, The University of Tokyo, Japan ;Zlotnicki, J.; Observatoire de Physique du Globe de Clermont-Ferrand, France ;Yvetot, P.; Observatoire de Physique du Globe de Clermont-Ferrand, France; ; ; ; ; ; ; ; ; We show that using borehole measurements in tectonomagnetic experiments allows enhancement of the observed signals. New magnetic dipoles, which vary with stress changes from mechanical sources, are produced on the walls of the borehole. We evaluate such an effect quantitatively. First we formulate a general expression for the borehole effect due to any arbitrary source models. This is valid everywhere above the ground surface as well as within the cylindrical hole. A first-order approximate solution is given by a line of horizontal dipoles and vertical quadrupoles along the central axis of the borehole, which is valid above the ground surface and a slightly away (several tens of cm) from the top of the borehole. Selecting the Mogi model as an example, we numerically evaluated the borehole effect. It turned out that the vertical quadrupoles produce two orders of magnitude more intense magnetic field than the horizontal dipoles. The borehole effect is very local, i.e. detectable only within a few m from its outlet, since it is of the same order or more than the case without a borehole. However, magnetic lines of force cannot reach the ground surface from a deeper portion (>10 m) of a borehole.127 162 - PublicationOpen AccessGeomagnetic changes correlated with crustal movement in the north-eastern part of the Izu Peninsula, Japan(1997-03)
; ; ; ; ; ;Oshiman, N.; Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan ;Sasai, Y.; Earthquake Research Institute, University of Tokyo, Japan ;Honkura, Y.; Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo, Japan ;Ishikawa, Y.; Earthquake Research Institute, University of Tokyo, Japan ;Tanaka, Y.; Aso Volcanological Laboratory, Faculty of Science, Kyoto University, Aso, Kumamoto, Japan; ; ; ; After the 1989 sea-floor eruption off the east coast of Ito city, no remarkable activities of earthquake swarms were observed in the eastern part of the Izu Peninsula, Central Japan during the period from 1990 to 1992. However, a small swarm activity was again observed in January, 1993 and a remarkable one took place again in May-June 1993. Several months after the subsidence of the swarm activity, abrupt changes in the crustal movement in the inland of the peninsula were observed during the period from September 1993 to February 1994. At some continuous observation sites, well correlated changes in the geomagnetic total intensity were observed almost during the same period when the anomalous changes in the crustal movement were seen in the eastern part of the peninsula. The spatial patterns of negative changes of the total intensity in the northern half and positive ones in the south were seen in the north-eastern edge of the domed distribution of the upheaval. The changes in crustal movement and the geomagnetic field terminated when a small swarm activity occurred at the end of February 1994.148 666 - PublicationOpen AccessEvaluation of electric and magnetic field monitoring of Miyake-jima volcano monitoring of Miyake-jima volcanomonitoring of Miyake-jima volcano (Central Japan): 1995-1999(2001-04)
; ; ; ; ; ; ; ; ;Sasai, Y.; Earthquake Research Institute, University of Tokyo, Japan ;Zlotnicki, J.; Observatoire de Physique du globe de Clermont-Ferrand, Universitè Blaise Pascal et UMR6524, Aubiére cedex, France ;Nishida, Y.; Graduate school of science, Hokkaiodo University, Sappoto, Japan ;Uyeshima, M.; Earthquake Research Institute, University of Tokyo, Japan ;Yvetot, P.; Observatoire de Physique du globe de Clermont-Ferrand, Universitè Blaise Pascal et UMR6524, Aubiére cedex, France ;Tanaka, Y.; Volcano Research Center; Graduate Schoool of science, Kyoto University, Aso, Kumamoto, Japan ;Watanabe, H.; Earthquake Research Institute, University of Tokyo, Japan ;Takahashi, Y.; Earthquake Research Institute, University of Tokyo, Japan; ; ; ; ; ; ; full abstract in pdf130 452