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Letter | Open | Published:

A precise hypocenter determination method using network correlation coefficients and its application to deep low-frequency earthquakes


A knowledge of the precise locations of deep low-frequency earthquakes (LFEs) along subduction zones is essential to be able to constrain the spatial extent of various slow earthquakes and the underlying physical processes. We have developed a hypocenter determination method that utilizes the summed cross-correlation coefficient over many stations, denoted a network correlation coefficient (NCC). The method consists of two parts: (1) an estimation of relative hypocenter locations for every pair of events by a grid search, and (2) a linear least squares inversion for self-consistent relative hypocenter locations for the initial centroid. We have applied this method to ten LFEs in the Tokai region, Japan. Statistically significant values of NCC indicate the relative locations for many pairs, which in turn determine the self-consistent locations. While the catalog depths are widely distributed, the relocated hypocenters fall within a 2-km depth range, which implies that LFEs in the Tokai region occur on the plate interface, similar to LFEs in western Shikoku.


  1. Gibbons, S. J. and F. Ringdal, The detection of low magnitude seismic events using array-based waveform correlation, Geophys. J. Int., 165, 149–166, 2006.

  2. Hirose, H. and K. Obara, Repeating short- and long-term slow slip events with deep tremor activity around the Bungo channel region, southwest Japan, Earth Planets Space, 57, 961–972, 2005.

  3. Hirose, H. and K. Obara, Short-term slow slip and correlated tremor episodes in the Tokai region, central Japan, Geophys. Res. Lett., 33, L17311, doi:10.1029/2006GL026579, 2006.

  4. Ide, S., G. C. Beroza, D. R. Shelly, and T. Uchide, A scaling law for slow earthquakes, Nature, 447, 76–79, 2007a.

  5. Ide, S., D. R. Shelly, and G. C. Beroza, The mechanism of deep low frequency earthquakes: Further evidence that deep non-volcanic tremor is generated by shear slip on the plate interface, Geophys. Res. Lett., 34, L03308, doi:10.1029/2006GL028890, 2007b.

  6. Iidaka, T., T. Iwasaki, T. Takeda, T. Moriya, I. Kumakawa, E. Kurashimo, T. Kawamura, F. Yamazaki, K. Koike, and G. Aoki, Configuration of subducting Philippine Sea plate and crustal structure in the central Japan region, Geophys. Res. Lett., 30, doi:10.1029/2002GL016517, 2003.

  7. 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.

  8. Kao, H., S.-J. Shan, H. Dragert, G. Rogers, J. F. Cassidy, and K. Ramachandran, A wide depth distribution of seismic tremors along the northern Cascadia margin, Nature, 436, 841–844, 2005.

  9. Katsumata, A. and N. Kamaya, Low-frequency continuous tremor around the Moho discontinuity away from volcanoes in the southwest Japan, Geophys. Res. Lett., 30, doi:10.1029/2002GL015981, 2003.

  10. Miyazaki, S., P. Segall, J. J. McGuire, T. Kato, and Y. Hatanaka, Spatial and temporal evolution of stress and slip rate during the 2000 Tokai slow earthquake, J. Geophys. Res., 111, B03409, doi:10. 1029/2004JB003426, 2006.

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

  12. Schwartz, S. Y. and J. M. Rokosky, Slow slip events and seismic tremor at circum-Pacific subduction zones, Rev. Geophys., 45, RG3004, doi:10. 1029/2006RG000208, 2007.

  13. Shelly, D. R., G. C. Beroza, S. Ide, and S. Nakamula, Low-frequency earthquakes in Shikoku, Japan and their relationship to episodic tremor and slip, Nature, 442, 188–191, 2006.

  14. Shelly, D. R., G. C. Beroza, and S. Ide, Non-volcanic tremor and lowfrequency earthquake swarms, Nature, 446, 305–307, 2007a.

  15. Shelly, D. R., G. C. Beroza, and S. Ide, Complex evolution of transient slip derived from precise tremor locations in western Shikoku, Japan, Geochem. Geophys. Geosyst., 8, Q10014, doi:10.1029/2007GC001640, 2007b.

  16. Waldhauser, F. and W. L. Ellsworth, A double-difference earthquake location algorithm: Method and application to the northern Hayward fault, California, Bull. Seismol. Soc. Am., 90, 1353–1368, 2000.

  17. Zhang, H. and C. H. Thurber, Double-difference tomography: The method and its application to the Hayward fault, California, Bull. Seismol. Soc. Am., 93, 1875–1889, 2003.

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Correspondence to Kazuaki Ohta.

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Key words

  • Low-frequency earthquakes
  • precise hypocenter determination
  • cross-correlation coefficient
  • Nankai subduction zone
  • Tokai region