Skip to main content

Advertisement

We’d like to understand how you use our websites in order to improve them. Register your interest.

Shear-wave anisotropy beneath the Ryukyu arc

Abstract

We have investigated regional shear-wave splitting beneath the Ryukyu arc in order to clarify the mantle flow beneath the Ryukyu arc and compare it with the extension of the Okinawa Trough. The splitting of regional shear waves (direct S) in the central and southern Ryukyu arc regions was analyzed in terms of fast-polarization direction and delay time using data from 11 short-period stations and two broadband seismic stations. The events occurred at depths ranging between 45 and 217 km, and the magnitude of the events ranged from 2.8 to 5.2. In general, the orientations of fast polarization were found to parallel to the strike of the Ryukyu Trench, with average delay times of 0.25–0.56 s. Specifically, the orientation of fast polarization was parallel to the direction of the extension in the south Ryukyu arc, suggesting that the direction of mantle flow is parallel to the extension in the south Okinawa Trough. However, the orientation of fast polarization was oblique to the direction of extension in the central Ryukyu arc, indicating that the mantle flow beneath the central Ryukyu arc is not parallel to the extension of the central Okinawa Trough. Based on these results, we suggest that the difference between the direction of the mantle flow and that of the lithosphere extension induces extensional strain with a simple shear component, which in turn causes oblique rifting in the central Okinawa Trough.

References

  1. Ando, M., Y. Ishikawa, and F. Yamazaki, Shear-wave polarization anisotropy in the upper mantle beneath Honshu, Japan, J. Geophys. Res., 88, 5850–5864, 1983.

    Article  Google Scholar 

  2. Audoine, E., M. K. Savage, and K. Gledhill, Seismic anisotropy from local earthquakes in the transition region from a subduction to a strike-slip plate boundary, New Zealand, J. Geophys. Res., 105, 8013–8033, 2000.

    Article  Google Scholar 

  3. Fouch, M. J. and K. M. Fischer, Mantle anisotropy beneath Northwest Pacific subduction zones, J. Geophys. Res., 101, 15987–16002, 1996.

    Article  Google Scholar 

  4. Fournier, M., O. Fabbri, J. Angelier, and J.-P. Cadet, Regional seismicity and on-land deformation in the Ryukyu arc: implications for the kinematics of opening of the Okinawa Trough, J. Geophys. Res., 106, 13751–13768, 2001.

    Article  Google Scholar 

  5. Jung, H. and S. Karato, Water induced fabric transitions in olivine, Science, 293, 1460–1463, 2001.

    Article  Google Scholar 

  6. Kimura, M., Y. Wang, and H. Yagi, Submarine geo-structure and tectonics in the Ryukyu arc, Chishitu News, 543, 24–38, 1999 (in Japanese).

    Google Scholar 

  7. Kubo, A. and E. Fukuyama, Stress field along the Ryukyu Arc and the Okinawa Trough inferred from moment tensors of shallow earthquakes, Earth Planet. Sci. Lett., 210, 305–316, 2003.

    Article  Google Scholar 

  8. Letouzey, J. and M. Kimura, Okinawa Trough genesis: Structure and evolution of a back-arc basin developed in a continent, Mar. Pet. Geol., 2, 111–130, 1985.

    Article  Google Scholar 

  9. Liu, X., K. C. McNally, and Z.-K. Shen, Evidence for a role of the downgoing slab in earthquake slip partitioning at oblique subduction zones, J. Geophys. Res., 100, 15351–15372, 1995.

    Article  Google Scholar 

  10. Long, M. D. and R. D. van der Hilst, Shear wave splitting from local events beneath the Ryukyu arc: Trench-parallel anisotropy in the mantle wedge, Phys. Earth Planet. Inter., 155, 300–312, 2006.

    Article  Google Scholar 

  11. Marson-Pidgeon, K., M. K. Savage, K. Gledhill, and G. Stuart, Seismic anisotropy beneath the lower half of the North Island, New Zealand, J. Geophys. Res., 104, 20277–20286, 1999.

    Article  Google Scholar 

  12. Nakamura, M., Crustal deformation in the central and southern Ryukyu Arc estimated from GPS data, Earth Planet. Sci. Lett., 217, 389–398, 2004.

    Article  Google Scholar 

  13. Nakamura, M. and S. Kaneshiro, Determination of subducted Philippine Sea plate in the Nansei islands deduced from hypocenter data, Bull. Sci., Univ. Ryukyus, 70, 73–82, 2000.

    Google Scholar 

  14. Okada, T., T. Matsuzawa, and A. Hasegawa, Shear-wave polarization anisotropy beneath the north-eastern part of Honshu, Japan, Geophys. J. Int., 123, 781–797, 1995.

    Article  Google Scholar 

  15. Peyton, V., V. Levin, J. Park, M. Brandon, J. Lees, E. Gordeev, and A. Ozerov, Mantle flow at a slab edge: seismic anisotropy in the Kamchatka region, Geophys. Res. Lett., 28, 379–382, 2001.

    Article  Google Scholar 

  16. Seno, T., S. Stein, and A. E. Gripp, A model for the motion of the Phillipine Sea plate consistent with NUVEL-1 and geological data, J. Geophys. Res., 98, 17941–17948, 1993.

    Article  Google Scholar 

  17. Sibuet, J.-C., S.-K. Hsu, C.-T. Shyu, and C.-S. Liu, Structural and kinematic evolution of the Okinawa trough backarc basin, in Backarc Basins: Tectonics and Magmatism, edited by B. Taylor, pp. 343–378, Plenum, New York, 1995.

    Google Scholar 

  18. Sibuet, J.-C., B. Deffontaines, S.-K. Hsu, N. Thareau, J.-P. Le Formal, C.-S. Liu, and ACT party, Okinawa trough backarc basin: Early tectonic magmatic evolution, J. Geophys. Res., 103, 30245–30267, 1998.

    Article  Google Scholar 

  19. Smith, G. P., D. A. Wiens, K. M. Fischer, L. M. Dorman, S. C. Webb, and J. A. Hildebrand, A complex pattern of mantle flow in the Lau backarc, Science, 292, 713–716, 2001.

    Article  Google Scholar 

  20. Zhang, S. and S. Karato, Lattice preferred orientation of olivine aggregates deformed in simple shear, Nature, 375, 774–777, 1995.

    Article  Google Scholar 

Download references

Author information

Affiliations

Authors

Corresponding author

Correspondence to Mamoru Nakamura.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Nakamura, M., Yamamoto, A. Shear-wave anisotropy beneath the Ryukyu arc. Earth Planet Sp 61, 1197–1202 (2009). https://doi.org/10.1186/BF03352972

Download citation

Key words

  • S-waves
  • wave splitting
  • seismic anisotropy
  • Ryukyu arc
  • Okinawa Trough