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

Takeshi Nakamura, Hiroshi Takenaka, Sadaomi Suzuki

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2 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)1055-1062
Number of pages8
JournalEarth, Planets and Space
Issue number11
Publication statusPublished - 2005
Externally publishedYes


  • Aftershock region
  • Anisotropy
  • Cracks
  • S-wave splitting
  • Tottori-ken Seibu earthquake

ASJC Scopus subject areas

  • Geology
  • Space and Planetary Science


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