Skip to main content


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

Subsurface structure and faulting of the Median Tectonic Line, southwest Japan inferred from GPS velocity field


The Median Tectonic Line (MTL) is the longest arc-parallel fault system in southwest Japan whose right-lateral strike-slip is related to oblique subduction of the Philippine Sea plate (PH). We constructed a dense Global Positioning System network along a 200 km-long traverse line across the MTL in 1998 to estimate deep fault structure and slip distribution. Horizontal velocities were determined at 65 sites through campaign measurements and show crustal shortening in the direction of the plate convergence. Using multi-rectangular segments and depth-dependent coupling at the plate interface, we calculate and remove elastic deformation caused by the PH subduction. The residual velocity field shows right-lateral strike-slip block motion of about 5 mm/yr across the MTL, consistent with geological estimates. However, the block boundary does not coincide with the surface trace of the MTL, being displaced 20–30 km to the north. The residual velocity field is reproduced by a model with a 35–45° northwarddipping fault plane, full locking of the upper portion to a depth of 15 km, and steady slip of 5 mm/yr below. GPS results are supported by imaging of an inclined fault plane revealed by seismic profiling and currently low activity of shallow earthquakes.


  1. Hyndman, R., K. Wang, and M. Yamano, Thermal constraints on the seismogenic portion of the southwestern Japan subduction thrust, J. Geophys. Res., 100, 15,373–15,392, 1995.

    Article  Google Scholar 

  2. Ito, T., T. Ikawa, S. Yamakita, and T. Maeda, Gently north-dipping Median Tectonic Line (MTL) revealed by recent seismic reflection studies, southwest Japan, Tectonophys., 264, 51–63, 1996.

    Article  Google Scholar 

  3. Matsu’ura, M., D. D. Jackson, and A. Cheng, Dislocation model for aseismic crustal deformation at Holister, California, J. Geophys. Res., 91, 12,661–12,674, 1986.

    Article  Google Scholar 

  4. Miyazaki, S. and K. Heki, Crustal velocity field of southwest Japan: Subduction and arc-arc collision, J. Geophys. Res., 106, 4305–4326, 2001.

    Article  Google Scholar 

  5. Okano, K. and S. Kimura, Crustal movements in and around Shikoku, southwest Japan associated with great Nankai earthquakes, J. Seism. Soc. Japan, 49, 361–374, 1996 (in Japanese).

    Google Scholar 

  6. Onishi, M., T. Ikawa, T. Matsuoka, T. Kawamura, T. Echigo, M. Orito, T. Ito, N. Hirata, T. Iwasaki, E. Kurashimo, and H. Sato, Deep seismic reflection experiment with a highly dense array of seismograms near the Median Tectonic Line, Shikoku, Japan, Abstr. 1999 Fall Meeting of the Seismological Society of Japan, P107, 1999.

  7. Ozawa, T., T. Tabei, and S. Miyazaki, Interplate coupling along the Nankai Trough off southwest Japan derived from GPS measurements, Geophys. Res. Lett., 26, 927–930, 1999.

    Article  Google Scholar 

  8. Research Group for Active Faults of Japan, Active Faults in Japan: Sheet Maps and Inventories, Univ. of Tokyo Press, 437 pp., 1991 (in Japanese).

  9. Sagiya, T. and W. Thatcher, Coseismic slip resolution along a plate boundary megathrust: The Nankai Trough, southwest Japan, J. Geophys. Res., 104, 1111–1129, 1999.

    Article  Google Scholar 

  10. Savage, J. C., A dislocation model of strain accumulation and release at a subduction zone, J. Geophys. Res., 88, 4984–4996, 1983.

    Article  Google Scholar 

  11. Tsuji, H., Y. Hatanaka, T. Sagiya, and M. Hashimoto, Coseismic crustal deformation from the 1994 Hokkaido-Toho-Oki earthquake monitored by a nationwide continuous GPS array in Japan, Geophys. Res. Lett., 22, 1669–1672, 1995.

    Article  Google Scholar 

  12. Tsutsumi, H. and A. Okada, Segmentation and Holocene surface faulting on the Median Tectonic Line, southwest Japan, J. Geophys. Res., 101, 5855–5871, 1996.

    Article  Google Scholar 

  13. Wang, K., Stress-strain ‘paradox’, plate coupling, and forearc seismicity at the Cascadia and Nankai subduction zones, Tectonophys., 319, 321–338, 2000.

    Article  Google Scholar 

Download references

Author information



Corresponding author

Correspondence to Takao Tabei.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Tabei, T., Hashimoto, M., Miyazaki, S. et al. Subsurface structure and faulting of the Median Tectonic Line, southwest Japan inferred from GPS velocity field. Earth Planet Sp 54, 1065–1070 (2002).

Download citation


  • Fault Plane
  • Plate Interface
  • Block Motion
  • Nankai Trough
  • Residual Velocity