Skip to main content


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

Spatiotemporal distribution of very-low frequency earthquakes in Tokachi-oki near the junction of the Kuril and Japan trenches revealed by using array signal processing


We have developed a signal-processing method for array data recorded at densely and widely distributed tiltmeter stations in Japan and analyzed the data recorded during the last 5 years. Filtered seismograms were analyzed to detect coherent seismic waves and estimate the epicenters. In order to identify very-low frequency earthquakes (VLFEs) with only low-frequency energies only, we selected only events not listed in the earthquake catalogue provided by the Japan Meteorological Agency from all of the detected events. The epicenters of the obtained VLFEs were estimated to be distributed not only along the Nankai Trough, where the events occurred on the reverse faults in the well-developed accretionary prism, but also in Tokachi-oki without accretion. This result suggests that even in such a region, VLFEs can occur on a shallower portion of the plate boundary than the seismogenic region of ordinary earthquakes and/or in a deformed area of the overriding plate along the subduction zone without accretion.


  1. Dominguez, S., S. E. Lallemand, J. Malavieille, and R. von Huene, Upper plate deformation associated with seamount subduction, Tectonophysics, 293, 207–224, 1998.

  2. Earthquake Research Committee, Long-term evaluation of earthquakes along the Kuril trench,, The Headquarters for Earthquake Research Promotion, 2003.

  3. Ito, Y. and K. Obara, Dynamic deformation of the accretionary prism excites very low frequency earthquakes, Geophys. Res. Lett., 33, L02311, doi:10.1029/2005GL025270, 2006.

  4. Ito, Y., H. Matsubayashi, H. Kimura, T. Matsumoto, Y. Asano, and S. Sekiguchi, Spatial distribution for moment tensor solutions of the 2003 Tokachi-oki earthquake (Mw = 7.9) and aftershocks, Earth Planets Space, 56, 301–306, 2004.

  5. Ito, Y., K. Obara, K. Shiomi, S. Sekine, and H. Hirose, Slow earthquakes coincident with episodic tremors and slow slip events, Science, 315, 503–506, 2007.

  6. Miyazaki, S., P. Segall, J. Fukuda, and T. Kato, Space-time distribution of afterslip following the 2003 Tokachi-oki earthquake: Implications for variations in fault zone frictional properties, Geophys. Res. Lett., 31, L06623, doi:10.1029/2003GL019410, 2004.

  7. Moore, G., T. Shipley, P. Stoffa, D. Karig, A. Taira, S. Kuramoto, H. Tokuyama, and K. Suyehiro, Structure of the Nankai Trough accretionary zone from multichannel seismic reflection data, J. Geophys. Res., 95, 8753–8765, 1990.

  8. Neidell, N. S. and M. T. Taner, Semblance and other coherency measures for multichannel data, Geophysics, 36, 482–497, 1971.

  9. Obara, K., Nonvolcanic deep tremor associated with subduction in southwest Japan, Science, 296, 1679–1681, 2002.

  10. Obara, K. and Y. Ito, Very low frequency earthquakes excited by the 2004 off the Kii peninsula earthquakes: A dynamic deformation process in the large accretionary prism, Earth Planets Space, 57, 321–326, 2005.

  11. Obara, K., Y. Haryu, Y. Ito, and K. Shiomi, Low frequency events occurred during the sequence of aftershock activity of the 2003 Tokachi-Oki earthquake; a dynamic process of the tectonic erosion by subducted seamount, Earth Planets Space, 56, 347–351, 2004.

  12. Obara, K., K. Kasahara, S. Hori, and Y. Okada, A densely distributed high-sensitivity seismograph network in Japan: Hi-net by National Research Institute for Earth Science and Disaster Prevention, Rev. Sci. Inst., 76, 021301, doi:10.1063/1.1854197, 2005.

  13. Park, J. O., T. Tsuru, S. Kodaira, P. R. Cummins, and Y. Kaneda, Splay fault branching along the Nankai subduction zone, Science, 297, 1157–1160, 2002.

  14. Press, W. H., S. A. Teukolsky, W. T. Vetterling, and B. P. Flannery, Numerical recipes: The art of scientific computing FORTRAN version, 702 pp., Cambridge Univ. Press, Cambridge, 1989.

  15. Scholz, C. H., Earthquakes and friction laws, Nature, 391, 37–42, 1998.

  16. von Huene, R. and R. Culotta, Tectonic erosion at the front of the Japan Trench convergent margin, Tectonophysics, 160, 75–90, 1989.

  17. Wessel, P. and W. H. F. Smith, New, improved version of the Generic Mapping Tools released, Eos Trans. AGU, 79, 579, 1998.

  18. Yagi, Y., Source rupture process of the 2003 Tokachi-oki earthquake determined by joint inversion of teleseismic body wave and strong ground motion data, Earth Planets Space, 56, 311–316, 2004.

  19. Yamazaki, T. and Y. Okamura, Subducting seamounts and deformation of overriding forearc wedges around Japan, Tectonophysics, 160, 207–229, 1989.

Download references

Author information



Corresponding author

Correspondence to Youichi Asano.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Asano, Y., Obara, K. & Ito, Y. Spatiotemporal distribution of very-low frequency earthquakes in Tokachi-oki near the junction of the Kuril and Japan trenches revealed by using array signal processing. Earth Planet Sp 60, 871–875 (2008).

Download citation

Key words

  • Very-low frequency earthquake
  • array signal processing
  • subduction
  • Tokachi-oki