Skip to main content


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

Article metrics

  • 239 Accesses

  • 2 Citations


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.


  1. Ben-Menahem, A. and S. J. Singh, Seismic Waves and Sources (2nd edition), 1102 pp., Dover, New York, 2000.

  2. Booth, D. C. and S. Crampin, Shear-wave polarizations on a curved wavefront at an isotropic free-surface, Geophys. J. Roy. Astr. Soc., 83, 31–45, 1985.

  3. Bowman, J. R. and M. Ando, Shear-wave splitting in the upper-mantle wedge above the Tonga subduction zone, Geophys. J. Roy. Astr. Soc., 88, 25–41, 1987.

  4. Buchbinder, G. G. R., Shear wave splitting and anisotropy from the aftershocks of the Nahanni Northwest Territories, earthquakes, J. Geophys. Res., 95, 4777–4785, 1990.

  5. Cochran, E. S., J. E. Vidale, and Y. G. Li, Near-fault anisotropy following the Hector Mine earthquake, J. Geophys. Res., 108, 2436, doi:10.1029/2002JB002352, 2003.

  6. Crampin, S., Seismic wave propagation through a cracked solid: polarization as a possible dilatancy diagnostic, Geophys. J. Roy. Astr. Soc., 53, 467–496, 1978.

  7. Crampin, S., The fracture criticality of crustal rocks, Geophys. J. Int., 118, 428–438, 1994.

  8. Crampin, S., R. Evans, B. Üçer, M. Doyle, J. P. Davis, G. V. Yegorkina, and A. Miller, Observations of dilatancy-induced polarization anomalies and earthquake prediction, Nature, 286, 874–877, 1980.

  9. Evans, R., Effects of the free surface on shear wavetrains, Geophys. J. Roy. Astr. Soc., 76, 165–172, 1984.

  10. Fukuyama, E., W. L. Ellsworth, F. Waldhauser, and A. Kubo, Detailed fault structure of the 2000 western Tottori, Japan, earthquake sequence, Bull. Seism. Soc. Am., 93, 1468–1478, 2003.

  11. Gledhill, K. R., Evidence for shallow and pervasive seismic anisotropy in the Wellington region, New Zealand, Geophys. Res., 96, 21503–21516, 1991.

  12. Hickman, S., R. H. Sibson, and R. Bruhn, Introduction to special section: Mechanical involvement of fluids in faulting, J. Geophys. Res., 100, 12831–12840, 1995.

  13. Hudson, J. A., Wave speeds and attenuation of elastic waves in material containing cracks, Geophys. J. Roy. Astr. Soc., 64, 133–150, 1981.

  14. Kaneshima, S., Origin of crustal anisotropy: Shear wave splitting studies in Japan, J. Geophys. Res., 95, 11121–11133, 1990.

  15. Li, Y. G., Shear wave splitting observations and implications on stress regimes in the Los Angeles basin, California, J. Geophys. Res., 101, 13,947–13,961, 1996.

  16. Li, Y. G., J. E. Vidale, K. Aki, F. Xu, and T. Burdette, Evidence of shallow fault zone strengthening after the 1992 M 7.5 Landers, California, earthquake, Science, 279, 217–219, 1998.

  17. Mamada, Y. and H. Takenaka, Strong attenuation of shear waves in the focal region of the 1997 Northwestern Kagoshima earthquakes, Japan, Bull. Seism. Soc. Am., 94, 464–478, 2004.

  18. Mizuno, T., K. Yomogida, H. Ito, and Y. Kuwahara, Spatial distribution of shear wave anisotropy in the crust of the southern Hyogo region by borehole observations, Geophys. J. Int., 147, 528–542, 2001.

  19. Nakamura, T., H. Takenaka, A. Watanabe, Y. Fujii, and S. Suzuki, Aftershock observation in the focal region of the 2000 Western Tottori earthquake, Sci. Repts., Dept. Earth and Planet. Sci., Kyushu Univ., 21, 49–59, 2002 (in Japanese with English abstract).

  20. O’Connell, R. J. and B. Budiansky, Seismic velocities in dry and saturated cracked solids, J. Geophys. Res., 79, 5412–5426, 1974.

  21. Ohmi, S. and K. Obara, Deep low-frequency earthquakes beneath the focal region of the Mw 6.7 2000 Western Tottori earthquake, Geophys. Res. Lett., 29, doi:10.1029/2001GL014469, 2002.

  22. Ohmi, S., K. Watanabe, T. Shibutani, N. Hirano, and S. Nakao, The 2000 Western Tottori Earthquake—Seismic activity revealed by the regional seismic networks—, Earth Planets Space, 54, 819–830, 2002.

  23. Oshiman, N., Conductivity structure beneath the western part of Japan, Earth Monthly, 38, 82–90, 2002 (in Japanese).

  24. Saiga, A., Y. Hiramatsu, T. Ooida, and K. Yamaoka, Spatial variation in the crustal anisotropy and its temporal variation associated with the moderate size earthquake in the Tokai region, central Japan, Geophys. J. Int., 154, 695–705, 2003.

  25. Shih, X. R. and R. P. Meyer, Observation of shear wave splitting from natural events: South moat of Long Valley Caldera, California, June 29 to August 12, 1982, J. Geophys. Res., 95, 11179–11195, 1990.

  26. Sibson, R. H., Implications of fault-valve behavior for rupture nucleation and recurrence, Tectonophysics, 211, 283–293, 1992.

  27. Tadokoro, K. and M. Ando, Evidence for rapid fault healing derived from temporal changes in S wave splitting, Geophys. Res. Lett., 29, doi:10. 1029/2001GL013644, 2002.

  28. Tadokoro, K., M. Ando, and Y. Umeda, S wave splitting in the aftershock region of the 1995 Hyogo-ken Nanbu earthquake, J. Geophys. Res., 104, 981–991, 1999.

  29. Udias, A., Principles of Seismology, Cambridge University Press, Cambridge, 475 pp., 1999.

  30. Ueno, H., S. Hatakeyama, T. Aketagawa, J. Funasaki, and N. Hamada, Improvement of hypocenter determination procedures in the Japan Meteorological Agency, Quart. J. Seism., 65, 123–134, 2002 (in Japanese with English abstract).

  31. Umeda, Y., The 2000 western Tottori earthquake, Earth Planets Space, 54, 3–4, 2002.

  32. Utsu, T., Seismology (3rd edition), Kyoritsu Shuppan, Tokyo, 376 pp., 2001 (in Japanese).

  33. Watanabe, A., H. Takenaka, Y. Fujii, and H. Fujiwara, Seismograph orientation at K-NET observatories (2): Oita Prefecture, Zisin, 53, 185–192, 2000 (in Japanese with English abstract).

  34. Zhang, Z. and S. Y. Schwartz, Seismic anisotropy in the shallow crust of the Loma Prieta segment of the San Andreas fault system, J. Geophys. Res., 99, 9651–9661, 1994.

  35. Zhao, D. and T. Mizuno, Crack density and saturation rate in the 1995 Kobe earthquake region, Geophys. Res. Lett., 26, 3213–3216, 1999.

  36. Zhao, D., H. Tani, and O. P. Mishra, Crustal heterogeneity in the 2000 western Tottori earthquake region: effect of fluids from slab dehydration, Phys. Earth Planet. Inter., 145, 161–177, 2004.

Download references

Author information

Correspondence to Takeshi Nakamura.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

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) doi:10.1186/BF03351884

Download citation

Key words

  • Anisotropy
  • S-wave splitting
  • cracks
  • aftershock region
  • Tottori-ken Seibu earthquake