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Two electrical conductors beneath Kusatsu-Shirane volcano, Japan, imaged by audiomagnetotellurics, and their implications for the hydrothermal system
Earth, Planets and Space volume 58, pages1053–1059(2006)
Kusatsu-Shirane volcano, Japan, is known for its active phreatic eruptions. We have investigated its hydrothermal system by conducting audio-magnetotelluric soundings at 22 stations along a profile that extends across the volcano. The final two-dimensional model is characterized by two conductors. One is a 300- to 1000-m-thick conductor of 1–10 Ωm, which is located on the eastern slope and covered with 200-m-thick resistive layers of Kusatsu-Shirane lava and pyroclastics. This conductor indicates the presence of a Montmorillonite-rich layer of Pliocene volcanic rocks that may function both as an impermeable floor for the shallow fluid path from the peak to the hot springs to the east and as an impermeable cap for the deeper fluid path from the summit region to the foot of the volcano. The second conductor is found at a depth of 1–2 km from the surface, at the peak of the volcano, and its resistivity is as low as 1 Ωm or less. This low resistivity can be explained by fluids containing high concentrations of chloride and sulfate which were supplied from the magmatic gases. Micro-earthquakes cluster above this conductor, and the cut-off of the earthquakes corresponds to the top of the conductor. This conductor infers the presence of the fluid reservoir, and the upward release of these fluids from the reservoir through the conduit presumably triggers the micro-earthquakes at the peak area of the volcano. Crustal deformation modeling using GPS and leveling data of the past 10 years revealed that the center of the deflation coincides with the top of the second conductor, indicating that the fluid reservoir itself can be hosting the deformation.
Aizawa, K., R. Yoshimura, N. Oshiman, K. Yamazaki, T. Uto, Y. Ogawa, S. B. Tank, W. Kanda, S. Sakanaka, Y. Furukawa, T. Hashimoto, M. Uyeshima, T. Ogawa, I. Shiozaki, and A. Hurst, Hydrothermal System beneath Mt. Fuji volcano inferred from magnetotellurics and electric self-potential, Earth Planet. Sci. Lett., 235, 343–355, 2005.
Çağlar, İ. and T. İşseven, Two-dimensional geoelectrical structure of the Göynük geothermal area, northwest Anatolia, Turkey, J. Volcanol. Geotherm. Res., 134, 183–197, 2004.
Di Maio, R., P. Mauriello, D. Patella, Z. Petrillo, S. Piscitelli, and A. Siniscalchi, Electric and electromagnetic outline of the Mount Somma-Vesuvius structural setting, J. Volcanol. Geotherm. Res., 82, 219–238, 1998.
Fujita, K., Y. Ogawa, M. Ichiki, S. Yamaguchi, and Y. Makino, Audio frequency magneto-telluric survey of Norikura Volcano in central Japan, J. Volcanol. Geotherm. Res., 90, 209–217, 1999.
Geological Survey of Japan, Geological map of Japan, 1:200, 000, Nagano, 1998.
Geological Survey of Japan (ed.), Gravity CD-ROM of Japan, Ver. 2, Digital Geoscience Map P-2, Geological Survey of Japan, 2004.
Groom, R. W. and R. C. Bailey, Decomposition of magnetotelluric impedance tensor in the presence of local three-dimensional galvanic distortion, J. Geophys. Res., 94, 1913–1925, 1989.
Gunma Prefecture, Report on the geothermal survey around Kusatsu-Shirane volcano, 374 pp, 1989 (in Japanese).
Harvey, C. and P. Browne, Mixed-layer clays in geothermal systems and their effectiveness as mineral geothermometers, Proceedings World Geothermal Congress 2000, Kyushu-Tohoku, Japan, May 28–June 10, 1201–1204, 2000.
Hirabayashi, J., Formation of volcanic fluid reservoir and volcanic activity, J. Balneol. Soc. Jpn., 49, 99–105, 1999 (in Japanese with English abstract).
Hirabayashi, J., T. Ohba, and K. Nogami, Hydrothermal system of Kusatsu-Shirane volcano and Kirishima volcanic area inferred from geochemical observations, 53–62, in Magma prospecting present and future perspective, Proc. Disas. Prev. Res. Inst. Symp. (8K-6), Kyoto University, 1997 (in Japanese with English abstract).
Hiroshima, T., M. Komazawa, and T. Nakatsuka, Gravity map of Joshin-Etsu District (Bouguer anomalies), Gravity Map Series, no. 5, Geological Survey of Japan, 1994.
Kagiyama, T., H. Utada, and T. Yamamoto, Magma ascent beneath Unzen Volcano, SW Japan, deduced from the electrical resistivity structure, J. Volcanol. Geotherm. Res., 89, 35–42, 1999.
Kasaya, T., N. Oshiman, N. Sumitomo, M. Uyeshima, Y. Iio, and D. Uehara, Resistivity structure around the hypocentral area of the 1984 Western Nagano Prefecture earthquake in central Japan, Earth Planets Space, 54, 107–118, 2002.
Kikawada, Y., T. Oi, T. Honda, T. Ossaka, and H. Kakihara, Lanthanoid abundances of acidic hot spring and crater lake waters in the Kusatsu-Shirane volcano region, Japan, Geochem. J., 27, 19–33, 1993.
Kumagai, H., B. A. Chouet, and M. Nakano, Temporal evolution of a hydrothermal system in Kusatsu-Shirane Volcano, Japan, inferred from the complex frequencies of long-period events, J. Geophys. Res., 107(B10), 2236, doi:10.1029/2001JB000653, 2002.
Kurasawa, T., Problem with the drilling of geothermal well in the south of Mt. Kusatsu-Shirane, Gunma Prf., J. Japan Geothermal Energy Assoc, 30, 1–23, 1993 (in Japanese with English abstract).
Makino, M., S. Watanabe, T. Sumita, and Y. Ogawa, Microgravity Survey in the vicinity of the Kusatsu-Shirane Summit, report on the 4th joint observation of Kusatsu-Shirane volcano, 69–80, 2004 (in Japanese).
Manzella, A., G. Volpi, A. Zaja, and M. Meju, Combined TEM-MT investigation of shallow-depth resistivity structure of Mt Somma-Vesuvius, J. Volcanol. Geotherm. Res., 131, 19–32, 2004.
Matsushima, N., H. Oshima, Y. Ogawa, S. Takakura, H. Satoh, M. Utsugi, and Y. Nishida, Magma prospecting in Usu volcano, Hokkaido, Japan, using magnetotelluric soundings, J. Volcanol. Geotherm. Res., 109(4), 263–277, 2001.
Mizuhashi, S., Geothermal system of Kusatsu-Shirane volcano inferred from the volatile mass flux, Master thesis, Tokyo Institute of Technology, 69 pp., 2004 (in Japanese).
Mori, T., J. Hirabayashi, K. Nogami, and S. Onizawa, A new seismic observation system at the Kusatsu-Shirane volcano, Bull. Volcanol. Soc. Japan, Ser. 2, 51, 41–47, 2006 (in Japanese with English abstract).
Müller, A. and V. Haak, 3-D modeling of the deep electrical conductivity of Merapi volcano (Central Java): integrating magnetotellurics, induction vectors and the effects of steep topography, J. Volcanol. Geotherm. Res., 138(3–4), 205–222, 2004.
Murakami, M., A. Kagawa, A. Yamada, H. Satoh, M. Yokokawa, T. Kimura, T. Kawamoto, K. Mori, and A. Suzuki, A deflation source beneath Kusatsu-Shirane volcano inferred from repeated campaign measurements of GPS and precise leveling, 4th Joint Observation of Kusatsu-Shirane Volcano, 31–36, 2004 (in Japanese).
Nakano, M., H. Kumagai, and B. A. Chouet, Source mechanism of long-period events at Kusatsu-Shirane Volcano, Japan, inferred from waveform inversion of the effective excitation functions, J. Volcanol. Geotherm. Res., 122, 149–164, 2003.
Ogawa, Y., On two-dimensional modeling of magnetotelluric field data, Surv. Geophys., 23(2–3), 251–273, 2002.
Ogawa, Y. and Y. Honkura, Mid-crustal electrical conductors and their correlations to seismicity and deformation at Itoigawa-Shizuoka Tectonic Line, Central Japan, Earth Planets Space, 56, 1285–1291, 2004.
Ogawa, Y. and S. Takakura, CSAMT measurement across the 1986 C Craters of Izu-Oshima Island, Japan, J. Geomag. Geoelectr., 42, 211–224, 1990.
Ogawa, Y. and T. Uchida, A two-dimensional magnetotelluric inversion assuming Gaussian static shift, Geophys. J. Int., 126, 69–76, 1996.
Ogawa, Y., S. Takakura, and T. Soya, Wideband magnetotelluric measurements across Izu-Oshima volcano, J. Geomag. Geoelectr., 44, 561–566, 1992.
Ogawa, Y., N. Matsushima, H. Oshima, S. Takakura, M. Utsugi, K. Hirano, M. Igarashi, and T. Doi, A resistivity cross-section of Usu volcano, Hokkaido, Japan, by audiomagnetotellurics soundings, Earth Planets Space, 50, 339–346, 1998.
Ogawa, Y., H. M. Bibby, T. G. Caldwell, S. Takakura, T. Uchida, N. Matsushima, S. L. Bennie, T. Tosha, and Y. Nishi, Wide-band magnetotelluric measurements across the Taupo Volcanic Zone, New Zealand—preliminary results, Geophys. Res. Lett., 26, 3673–3676, 1999.
Ogawa, Y., M. Mishina, T. Goto, H. Satoh, N. Oshiman, T. Kasaya, Y. Takahashi, T. Nisitani, S. Sakanaka, M. Uyeshima, Y. Takahashi, Y. Honkura, and M. Matsushima, Magnetotelluric imaging of fluid in the interpolate earthquake zone, NE Japan back arc, Geophys. Res. Lett., 28, 3741–3744, 2001.
Ogawa, Y., S. Takakura, and Y. Honkura, Resistivity structure across Itoigawa-Shizuoka tectonic line and its implications for concentrated deformation, Earth Planets Space, 54, 1115–1120, 2002.
Ohba, T., Geothermal system of Kusatsu-Shirane volcano, in Volcanic Structure in the Shallow Part and Volcanic Fluid, Proc. Disas. Prev. Res. Inst. Symp.(12K-3), Kyoto Univ., 161–168, 2002 (in Japanese).
Ohba, T., J. Hirabayashi, and K. Nogami, Water, heat and chloride budgets of the crater lake, Yugama, at Kusatsu-Shirane volcano, Geochem. J., 28, 217–231, 1994.
Ohba, T., J. Hirabayashi, and K. Nogami, D/H and 18O/16O ratios of water in the crater lake at Kusatsu-Shirane volcano, Japan, J. Volcanol. Geotherm. Res., 97, 329–346, 2000.
Ohwada, M., T. Ohba, J. Hirabayashi, K. Nogami, K. Nakamura, and K. Nagao, Interaction between magmatic fluid and meteoric water, inferred from 18O/16O and 36Ar/H2O ratios of fumarolic gases at the Kusatsu-Shirane volcano, Japan, Earth Planets Space, 55, 105–110, 2003.
Oskooi, B., L. B. Pedersen, M. Smirnov, K. Arnason, H. Eysteinsson, A. Manzella, and the DGP Working Group, The deep geothermal structure of the Mid-Atlantic Ridge deduced from MT data in SW Iceland, Phys. Earth Planet. Inter., 150, 183–195, 2005.
Ossaka, J. and J. Hirabayashi, Clay minerals in volcanic ejecta, J. Mine. Soc. Jpn., 15, 223–228, 1981 (in Japanese with English abstract).
Pellerin, L., J. M. Johnston, and G. W. Hohmann, A numerical evaluation of electromagnetic methods in geothermal exploration, Geophysics, 61, 121–130, 1996.
Sano, Y., J. Hirabayashi, T. Oba, and T. Gamo, Carbon and helium isotopic ratios at Kusatsu-Shirane Volcano, Japan, Appl. Geochem., 9, 371–377, 1994.
Takeda, T., H. Sato, T. Iwasaki, N. Matsuta, S. Sakai, T. Iidaka, and A. Kato, Crustal structure in the northern Fossa Magna region, central Japan, modeled from refraction/wide-angle reflection data, Earth Planets Space, 56, 1293–1299, 2004.
Todaka, N., C. Akasaka, T. Xu, and K. Pruess, Reactive Geothermal Transport Simulation to Study the Formation Mechanism of Impermeable Barrier between Acidic and Neutral Fluid Zones in the Onikobe Geothermal Field, Japan, LBNL-52493, Lawrence Berkeley National Laboratory, University of California, Berkeley, 37 pp, 2003.
Uchida, T., Reservoir structure of the Sengan geothermal field interpreted from the resistivity data, J. Geotherm. Res. Soc. Japan, 12, 1–21, 1990 (in Japanese with English abstract).
Ucok, H., I. Ershaghi, and G. Olhoeft, Electrical resistivity of geothermal brines, J. Petrol. Technol., 32(4), 717–727, 1980.
Uto, K., Y. Hayakawa, S. Aramaki, and J. Ossaka, Geological map of Kusatsu-Shirane volcano, Geological Survey of Japan, 1983 (in Japanese)
Yamazaki, A., M. Churei, S. Tsunomura, and S. Nakajima, Analysis of the variation of geomagnetic total force at Kusatsu-Shirane volcano: the remarkable changes in the geomagnetic total force in 1990 and the estimated thermal demagnetization model, Mem. Kakioka Mag. Obs., 24(2), 53–66, 1992 (in Japanese with English abstract).
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Nurhasan, Ogawa, Y., Ujihara, N. et al. Two electrical conductors beneath Kusatsu-Shirane volcano, Japan, imaged by audiomagnetotellurics, and their implications for the hydrothermal system. Earth Planet Sp 58, 1053–1059 (2006) doi:10.1186/BF03352610