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Strong S-wave anisotropy in the aftershock region of the 2000 Tottori-ken Seibu, Japan, earthquake (Mw6.6)

Earth, Planets and Space volume 57, pages 1055–1062 (2005)Cite this article

Abstract

The 2000 Tottori-ken Seibu earthquake (Mw6.6) occurred in Tottori prefecture, western Japan on October 6, 2000. We conducted aftershock observation and analyzed S-wave anisotropy using the aftershocks Mjma2.0 to 3.5 observed at two stations near the aftershock region. The fast S-waves are polarized to almost E-W direction, which corresponds to the P-axis direction of the mainshock. The delay time of the split S-waves ranges between 20 and 100 ms. The crack density inside and outside the aftershock area is estimated from the delay time. The distribution of crack density shows a strong spatial variation and depends on the ratio of the path length inside the aftershock region against the whole path length. Assuming a uniform distribution of anisotropy inside and outside the aftershock region, the crack densities inside and outside are 0.017 and 0.007, respectively. It thus seems probable that in the aftershock region the distribution of cracks is intensive and cracks are opened due to the presence of fluids in seismogenic layers. This considerable spatial variation of anisotropy between inside and outside the aftershock region suggests that the aftershock region may have different mechanical properties from the surrounding area.

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Author notes

  1. Sadaomi Suzuki

    Present address: Tono Research Institute of Earthquake Science, Yamanouchi Akeyo-cho 1-63, Mizunami, 509-6132, Japan

Authors and Affiliations

  1. Department of Earth and Planetary Sciences, Kyushu University, Hakozaki 6-10-1, Fukuoka, 812-8581, Japan

    Takeshi Nakamura, Hiroshi Takenaka & Sadaomi Suzuki

Authors
  1. Takeshi Nakamura
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  2. Hiroshi Takenaka
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  3. Sadaomi Suzuki
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Correspondence to Takeshi Nakamura.

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Nakamura, T., Takenaka, H. & Suzuki, S. Strong S-wave anisotropy in the aftershock region of the 2000 Tottori-ken Seibu, Japan, earthquake (Mw6.6). Earth Planet Sp 57, 1055–1062 (2005). https://doi.org/10.1186/BF03351884

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  • DOI: https://doi.org/10.1186/BF03351884

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