Name : UTADA,  Hisashi
            Position : Professor
            Division/Center : Ocean Hemisphere Research Center
            Research area : Geoelectromagnetism
 

Research:

       Main interest of my research group is studying the structure and dynamics of the Earth's deep interior by electromagnetic methods.
       For that purpose, we are carrying out long-term observations of electric and magnetic field variations in the Pacific area under the
       Ocean Hemisphere Network Project. Our electromagnetic observation consists of an array of magnetometer site on the Pacific islands
       and a submarine cable network to measure the electrical potential variations over oceanic distances.

       Data of these field variations involve the effect of electromagnetic induction of the earth due to geomagnetic field fluctuations of
       external origin. Analysis of thus obtained time series data in the period range of several hours to several days leads us the three
       dimensional (3-D) image of the electrical conductivity distribution in the mantle. To solve the electromagnetic induction in the 3-D
       heterogeneous earth, my group is developing an accurate computer code based on an integral equation method of 3-D electromagnetic
       scattering problem.

       Time variations of longer than a year are mostly reflecting the secular variations originated in the outer core. Our effort in geomagnetic
       observations will assist in having a better spatial resolution of the secular variations in the Pacific area where only a few geomagnetic
       observatories have so far been operating. However, my group's research is unique because of the electric field measurement. We
       have shown that observation and analysis of the electric field will provide us information of the toroidal magnetic field near the
       core-mantle boundary (CMB) that can never be obtained by the geomagnetic measurements. This will give a strong constraint on the
       geodynamo process. My group also studies the problem of electromagnetic core-mantle coupling on the basis of observation and
       analysis of the electromagnetic data.

       In addition to the above work, I am carrying out cooperative programs to study the deep crustal electrical structure in the volcanic and
       seismically active areas to get useful knowledge on the physical process of crustal activities. Various kinds of survey methods such
       as Magnetotelluric (MT), Time-domain Electromagnetic (TDEM) and Network-MT methods are employed depending on different
       environments and different scale length of the target.

Publications:

Shimizu, H., and H. Utada, Ocean Hemisphere Geomagnetic Network: its instrumental design and perspective for long-term geomagnetic observations in the Pacific, Earth Planets Space, 51, 917--932, 1999.

Yamaguchi, S., Y. Kobayashi, N. Oshiman, K. Tanimoto, H. Murakami, I. Shiozaki, M.Uyeshima, H. Utada, and N. Sumitomo, Preliminary report on regional resistivity variation inferred from the Network-MT investigation in the Shikoku district, southwestern Japan, Earth Planets Space, 51, 193--203, 1999.

Ichiki, M., M. Mishina, T. Goto, N. Oshiman, N. Sumitomo, and H. Utada, Magnetotelluric investigations for the seismically active area in Northern Miyagi Prefecture, northeastern Japan, Earth Planets Space, 51, 351--361, 1999.

Kagiyama, T., H. Utada, and T. Yamamoto, Magma ascent beneath Unzen Volcano, SW Japan, deduced from the electrical resistivity structure, J. Volcan. Geotherm. Res., 89, 35--42, 1999.

Evans, L., P. Tarits, A. D. Chave, A. White, G. Heinson, J. H. Filloux, H. Toh, N. Seama, H. Utada, J. R. Booker, and M. J. Unsworth, Asymmetric Electrical Structure in the Mantle Beneath the East Pacific Rise at 17°S, Science, 286, 5440, 752--756, 1999.

Utada, H., M. Neki, and T. Kagiyama, A study of annual variations in the geomagnetic total intensity with special attention to detecting volcanomagnetic signals, Earth Planets Space, 52, 91--103, 2000.

Utada, H., and H. Munekane, On galvanic distortion of regional three-dimensional magnetotelluric impedances, Geophys. J. Int., 140, 2, 385--398, 2000.

Ogawa, T., and H. Utada, Electromagnetic signals related to incidence of a teleseismic body wave into a subsurface piezoelectric body, Earth Planets Space, 52, 4, 253--260, 2000.

Joseph, E.J., H. Toh, H. Fujimoto, R.V. Iyengar, B.P. Singh, H. Utada, and J. Segawa, Seafloor electromagnetic induction studies in the Bay of Bengal, Marine Geophys. Res., 21, 1--21, 2000.

Ogawa, T, and H. Utada, Coseismic piezoelectric effects due to a dislocation 1. An analytic far and early-time field solution in a homogeneous whole space, Phys. Earth Planet. Inter., 121, 273--288, 2000.