Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

A wide depth distribution of seismic tremors along the northern Cascadia margin

Nature volume 436, pages 841–844 (2005)Cite this article

Abstract

The Cascadia subduction zone is thought to be capable of generating major earthquakes with moment magnitude as large as Mw = 9 at an interval of several hundred years1,2,3. The seismogenic portion of the plate interface is mostly offshore and is currently locked, as inferred from geodetic data4,5,6. However, episodic surface displacements—in the direction opposite to the long-term deformation motions caused by relative plate convergence across a locked interface—are observed about every 14 months with an unusual tremor-like seismic signature7,8,9. Here we show that these tremors are distributed over a depth range exceeding 40 km within a limited horizontal band. Many occurred within or close to the strong seismic reflectors above the plate interface where local earthquakes are absent, suggesting that the seismogenic process for tremors is fluid-related. The observed depth range implies that tremors could be associated with the variation of stress field induced by a transient slip along the deeper portion of the Cascadia interface or, alternatively, that episodic slip is more diffuse than originally suggested.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Rent or buy this article

Get just this article for as long as you need it

$39.95

Learn more

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Maps showing the distribution of seismograph stations (a) and the gradual migration path of seismic tremors (b).
Figure 2: Map and profiles showing two seismic tremors occurring at different locations and depths.
Figure 3: Two cross-sections showing the spatial distribution of seismic tremors with respect to background seismicity, regional tomography, and strong reflectors identified from seismic reflection surveys.
Figure 4: A comparison of frequency spectra between local earthquakes and ETS tremors in northern Cascadia.

References

  1. Atwater, B. F. Evidence for great Holocene earthquakes along the outer coast of Washington state. Science 236, 942–944 (1987)

    Article  ADS  CAS  Google Scholar 

  2. Atwater, B. F. & Hemphill-Haley, E. Recurrence intervals for great earthquakes of the past 3500 years at northeastern Willapa Bay, Washington. US Geol. Surv. Prof. Pap. 1576, 1–108 (1997)

    Google Scholar 

  3. Satake, K., Wang, K. & Atwater, B. F. Fault slip and seismic moment of the 1700 Cascadia earthquake inferred from Japanese tsunami descriptions. J. Geophys. Res. 108, doi:10.1029/2003JB002521 (2003)

  4. Savage, J. C. & Lisowski, M. Strain measurements and the potential for a great subduction earthquake off the coast of Washington. Science 252, 101–103 (1991)

    Article  ADS  CAS  Google Scholar 

  5. Dragert, H. & Hyndman, R. D. Continuous GPS monitoring of elastic strain in the northern Cascadia subduction zone. Geophys. Res. Lett. 22, 755–758 (1995)

    Article  ADS  Google Scholar 

  6. Wang, K., Wells, R., Mazzotti, S., Hyndman, R. D. & Sagiya, T. A revised dislocation model of interseismic deformation of the Cascadia subduction zone. J. Geophys. Res. 108, 2026, doi:10.1029/2001JB001227 (2003)

    ADS  Google Scholar 

  7. Dragert, H., Wang, K. & James, T. S. A silent slip event on the deeper Cascadia subduction interface. Science 292, 1525–1528 (2001)

    Article  ADS  CAS  Google Scholar 

  8. Miller, M. M., Melbourne, T., Johnson, D. J. & Sumner, W. Q. Periodic slow earthquakes from the Cascadia subduction zone. Science 295, 2423 (2002)

    Article  CAS  Google Scholar 

  9. Rogers, G. & Dragert, H. Episodic tremor and slip on the Cascadia subduction zone: The chatter of silent slip. Science 300, 1942–1943 (2003)

    Article  ADS  CAS  Google Scholar 

  10. Kao, H. & Shan, S.-J. The source-scanning algorithm: mapping the distribution of seismic sources in time and space. Geophys. J. Int. 157, 589–594 (2004)

    Article  ADS  Google Scholar 

  11. Ramachandran, K., Dosso, S. E., Spence, G. D., Hyndman, R. D. & Brocher, T. M. Forearc structure beneath southwestern British Columbia: A three-dimensional tomographic velocity model. J. Geophys. Res. 110, B02303, doi: 10.1029/2004JB003258 (2005)

    Article  ADS  Google Scholar 

  12. Calvert, A. J. Seismic reflection imaging of two megathrust shear zones in the northern Cascadia subduction zone. Nature 428, 163–167 (2004)

    Article  ADS  CAS  Google Scholar 

  13. Nedimovic, M. R., Hyndman, R. D., Ramachandran, K. & Spence, G. D. Reflection signature of seismic and aseismic slip on the northern Cascadia subduction interface. Nature 424, 416–420 (2003)

    Article  ADS  CAS  Google Scholar 

  14. Calvert, A. J. & Clowes, R. M. Deep, high-amplitude reflections from a major shear zone above the subducting Juan de Fuca plate. Geology 18, 1091–1094 (1990)

    Article  ADS  Google Scholar 

  15. Hyndman, R. D. Dipping seismic reflectors, electrically conductive zones, and trapped water in the crust over a subducting plate. J. Geophys. Res. 93, 13391–13405 (1988)

    Article  ADS  Google Scholar 

  16. Clowes, R. M. et al. LITHOPROBE-southern Vancouver island: Cenozoic subduction complex imaged by deep seismic reflections. Can. J. Earth Sci. 24, 31–51 (1987)

    Article  ADS  Google Scholar 

  17. Cassidy, J. F. & Ellis, R. M. S wave velocity structure of the northern Cascadia subduction zone. J. Geophys. Res. 98, 4407–4421 (1993)

    Article  ADS  Google Scholar 

  18. Peacock, S. M. Fluid processes in subduction zones. Science 248, 329–337 (1990)

    Article  ADS  CAS  Google Scholar 

  19. Wang, K. & Hyndman, R. D. Challenges in defining seismogenic zone using geodetic and structural observations. Eos (AGU Fall Meeting Suppl.) 85, abstr. S43D–05 (2004).

  20. Adam, J., Klaeschen, D., Kukowski, N. & Flueh, E. Upward delamination of Cascadia Basin sediment infill with landward frontal accretion thrusting caused by rapid glacial age material flux. Tectonics 23, TC3009, doi:10.1029/2002TC001475 (2004)

    Article  ADS  Google Scholar 

  21. von Huene, R., Ranero, C. R. & Vannucchi, P. Generic model of subduction erosion. Geology 32, 913–916 (2004)

    Article  ADS  Google Scholar 

  22. Hyndman, R. D., Mazzotti, S., Weichert, D. & Rogers, G. C. Frequency of large crustal earthquakes in Puget Sound-Southern Georgia Strait predicted from geodetic and geological deformation rates. J. Geophys. Res. 108, 2033, doi:10.1029/2001JB001710 (2003)

    Article  ADS  Google Scholar 

  23. Szeliga, W., Melbourne, T. I., Miller, M. M. & Santillan, V. M. Southern Cascadia episodic slow earthquakes. Geophy. Res. Lett. 31, L16602, doi:10.1029/2004GL020824 (2004)

    Article  ADS  Google Scholar 

  24. Broan, K. M., DeShon, H., Tryon, M., Dorman, L. & Schwartz, S. Transient fluid pulsing and noise in the Costa Rican subduction zone: Nearly silent slip events? Eos (AGU Fall Meet. Suppl.) 84, abstr. T41E–06 (2003).

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

    Article  ADS  CAS  Google Scholar 

  26. Katsumata, A. & Kamara, N. Low-frequency continuous tremor around the Moho discontinuity away from volcanoes in the southwest Japan. Geophys. Res. Lett. 30, 1020, doi:10.1029/2002GL015981 (2003)

    Article  ADS  Google Scholar 

  27. Linde, A. T. & Silver, P. G. Elevation changes and the great 1960 Chilean earthquake: Support for aseismic slip. Geophys. Res. Lett. 16, 1305–1308 (1989)

    Article  ADS  Google Scholar 

  28. Thatcher, W. Seismic triggering and earthquake prediction. Nature 299, 12–13 (1982)

    Article  ADS  Google Scholar 

  29. Shimazaki, K. & Nakata, T. Time predictable recurrence model for large earthquakes. Geophys. Res. Lett. 7, 279–282 (1980)

    Article  ADS  Google Scholar 

  30. Mazzotti, S. & Adams, J. Variability of near-term probability for the next great earthquake on the Cascadia subduction zone. Bull. Seismol. Soc. Am. 94, 1954–1959 (2004)

    Article  Google Scholar 

Download references

Acknowledgements

We thank I. Al-Khoubbi, T. Christie, T. Claydon and R. Hall for their efforts in deploying and maintaining the seismic network; A. Bird, T. Mulder and W. Bentkowski for their assistance in seismic data processing; R. Baldwin for his software support; A. Calvert, R. Hyndman and K. Wang for stimulating discussion; and the POLARIS consortium for providing data from the BC POLARIS array. Most SSA computation is done on the Mercury cluster of the University of Victoria. This work is supported in part by a USGS NEHRP research grant.

Author information

Authors and Affiliations

  1. Geological Survey of Canada, Pacific Geoscience Centre, 9860 West Saanich Road, Sidney, British Columbia, V8L 1B9, Canada

    Honn Kao, Shao-Ju Shan, Herb Dragert, Garry Rogers, John F. Cassidy & Kumar Ramachandran

Authors
  1. Honn Kao
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Shao-Ju Shan
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Herb Dragert
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Garry Rogers
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. John F. Cassidy
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Kumar Ramachandran
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Honn Kao.

Ethics declarations

Competing interests

Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.

Supplementary information

Supplementary Notes.

This file contains Supplementary Methods, Supplementary Table S1 (a list of tremor parameters) and Supplementary Figures S1–S4. (DOC 2633 kb)

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Kao, H., Shan, SJ., Dragert, H. et al. A wide depth distribution of seismic tremors along the northern Cascadia margin. Nature 436, 841–844 (2005). https://doi.org/10.1038/nature03903

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nature03903

This article is cited by

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing