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Lateral inhomogeneity deduced from 3-D magnetotelluric modeling around the hypocentral area of the 1984 Western Nagano Prefecture earthquake, central Japan

Abstract

Earthquake swarms have been observed since 1976 in the southeastern region of Mt. Ontake, where the 1984 Western Nagano Prefecture earthquake (M6.8) occurred. Most earthquake swarm activities show a dense distribution in a narrow area and at shallow depths. We have carried out forward 3-D magnetotelluric modeling for the data set observed around the focal region of the earthquake swarms. An initial 3-D image was constructed based on previous 2-D magnetotelluric analysis results. The resistivity structure shows remarkable lateral inhomogeneity: a low resistivity zone is located at shallow depth around the center of the study area and the low resistivity zone is surrounded by a high resistive structure and its shape is about a 4-km cube. This feature agrees well with the distribution of the degree of water saturation deduced from seismic information. Hypocenters of recent seismicity are distributed around an area between the resistivity boundary and the relatively high-resistance region. This fact strongly suggests that earthquakes in the study area are triggered by fluid (water) in the crust.

References

  • Gamble, T. D., W. M. Goubau, and J. Clarke, Magnetotellurics with a remote magnetic reference, Geophysics, 44, 53–68, 1979.

    Article  Google Scholar 

  • Garcia, X., J. Ledo, and P. Queralt, 2D inversion of 3D magnetotelluric data: The Kayabe dataset, Earth Planets Space, 51, 1135–1142, 1999.

    Article  Google Scholar 

  • Geological Survey of Japan (GSJ), Geological Map of Japan 1:1,000,000, 3rd Edition, CD-ROM version, Digital Geo-science Map G-1, 1995.

  • Glover, P. W. J., P. J. Hole, and J. Pous, A modified archie’s law for two conducting phases, Earth Planets. Sci. Lett., 180, 369–383, 2000.

    Article  Google Scholar 

  • Groom, R. W. and R. C. Bailey, Decomposition of magnetotelluric impedance tensors in the presence of local three-dimensional galvanic distortions, J. Geophys. Res., 94, 1913–1925, 1989.

    Article  Google Scholar 

  • Hori, S., H. Aoki, and T. Ooida, Focal mechanisms of the earthquake swarm southeast of Mt. Ontake, Central Honshu, Japan, Zisin, 35, 162–169, 1982 (in Japanese with English abstract).

    Google Scholar 

  • Horiuchi, S. and The members of the 1986 Joint Seismological research in Western Nagano Prefecture, Hypocenter locations by a dense network, J. Phys. Earth, 40, 313–326, 1992.

    Article  Google Scholar 

  • Iio, Y., R. Ikeda, K. Omura, Y. Matsuda, Y. Shiokawa, M. Takeda, and D. Uehara, Conductivity structure of seismogenic region in the western Nagano Prefecture, BUTSURI-TANSA, 53, 56–66, 2000 (in Japanese with English abstract).

    Google Scholar 

  • Inamori, T., S. Horiuchi, and A. Hasegawa, Location of mid-crustal reflectors by a reflection method using aftershock waveform data in the focal area of the 1984 Western Nagano Prefecture Earthquake, J. Phys. Earth, 40, 379–393, 1992.

    Article  Google Scholar 

  • 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.

    Article  Google Scholar 

  • Kimura, J. and T. Yoshida, Magma transport system beneath Norikura volcanic chains, Gekkan Chikyu (Earth Monthly), 18, 97–103, 1996 (in Japanese).

    Google Scholar 

  • Ledo, J., C. Ayala, J. Pous, P. Queralt, A. Marcuello, and J. A. Munoz, New geophysical constraints on the deep structure of the Pyrenees, Geophys. Res. Lett., 27, 1037–1040, 2000.

    Article  Google Scholar 

  • Mackie, R. L., T. R. Madden, and P. E. Wannamaker, Three-dimensional magnetotelluric modeling using difference equations-theory and comparisons to integral equation solutions, Geophysics, 58, 215–226, 1993.

    Article  Google Scholar 

  • Mitsuhata, Y., Y. Ogawa, M. Mishina, T. Kono, T. Yokokura, and T. Uchida, Electromagnetic heterogeneity of the seismogenic region of 1962 M6.5 Northern Miyagi Earthquake, northeastern Japan, Geophys. Res. Lett., 28, 4371–4374, 2001.

    Article  Google Scholar 

  • Mizoue, M. and Y. Ishiketa, Detection of melting zone beneath fault area of the 1984 Western Nagano Prefecture Earthquake and beneath southeastern foot of Mt. Ontake, Gekkan Chikyu (Earth Monthly), 10, 700–705, 1988 (in Japanese).

    Google Scholar 

  • New Energy and Industrial Technology Development Organization (NEDO), Investigation report of the geothermal development promotion (Otaki area), No. 17, 1988.

  • Ogawa, Y. and T. Uchida, Two dimensional magnetotelluric inversion assuming Gaussian static shift, Geophys. J. Int., 126, 69–76, 1996.

    Article  Google Scholar 

  • 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 fluids in intraplate earthquakes zones, NE Japan back arc, Geophys. Res. Lett., 28, 3741–3744, 2001.

    Article  Google Scholar 

  • 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.

    Article  Google Scholar 

  • Saeki, T. and Y. Umeda, Shear-wave polarizations in the rupture region of the 1984 Western Nagano Prefecture Earthquake, Zisin, 41, 163–171, 1988.

    Google Scholar 

  • Sano, Y., Y. Nakamura, and H. Wakita, 3He/4He ratio anomalies associated with the 1984 Western Nagano Earthquake: Possibly induced by a diapiric magma, J. Geophys. Res., 91, 12291–12295, 1986.

    Article  Google Scholar 

  • Sano, Y., Y. Nishio, S. Sasaki, T. Gamo, and K. Nagao, Helium and carbon isotope systematics at Ontake Volcano, Japan, J. Geophys. Res., 103, 23863–23873, 1998.

    Article  Google Scholar 

  • Shichi, R., A. Yamamoto, A. Kimura, and H. Aoki, Gravimetric evidences for active faults around Mt. Ontake, central Japan: Specifically for hidden faulting of the 1984 Western Nagano Prefecture Earthquake, J. Phys. Earth, 40, 459–478, 1992.

    Article  Google Scholar 

  • Shuto, T. and T. Otsuka, Late Jurassic-earliest Cretaceous accretionary complex of the eastern Mino Terrane, central Japan: Radiolarian age and imbricate structure of the Misogawa Complex, J. Geol. Soc. Japan, 110, 67–84, 2004.

    Article  Google Scholar 

  • Takeda, J., Y. Iio, Y. Kobayashi, K. Yamamoto, H. Sato, S. Ohmi, H. Ito, R. Ikeda, and E. Yamamoto, The relationship between seismicity and fluid existing in the crust inferred from Vp/Vs Ratio, Zisin, 51, 419–430, 1999 (in Japanese with English abstract).

    Google Scholar 

  • Tanabe, S., Time variation in seismic reflector around Mt. Ontake, M. Sc. Thesis, Earth and Planetary Science, Kyoto Univ., 40 pp., 1996.

    Google Scholar 

  • Tank, S. B., Y. Honkura, Y. Ogawa, N. Oshiman, M. K. Tuncer, C. Celik, E. Tolak, and A. M. Isikara, Resistivity structure in the western part of the fault rupture zone associated with the 1999 Izmit earthquake and its seismogenic implication, Earth Planets Space, 55, 437–442, 2003.

    Article  Google Scholar 

  • Umeda, Y. and K. Ito, A model for the prediction of intraplate large earthquake growing in the inhomogeneous crust, Zisin, 50, 263–272, 1998 (in Japanese with English abstract).

    Google Scholar 

  • Yamada, N. and T. Kobayashi, Geology of the Ontakesan district, Geological Sheet Map at 1:50,000, Geological Survey. Japan, 136 p., 1988 (in Japanese with English abstract).

    Google Scholar 

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Correspondence to Takafumi Kasaya.

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Kasaya, T., Oshiman, N. Lateral inhomogeneity deduced from 3-D magnetotelluric modeling around the hypocentral area of the 1984 Western Nagano Prefecture earthquake, central Japan. Earth Planet Sp 56, 547–552 (2004). https://doi.org/10.1186/BF03352514

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  • DOI: https://doi.org/10.1186/BF03352514

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