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.

  • Letter
  • Published:

Sedimentary underplating at the Cascadia mantle-wedge corner revealed by seismic imaging

Nature Geoscience volume 4, pages 545–548 (2011)Cite this article

Subjects

Abstract

Earth’s largest earthquakes occur in subduction zones, along the boundary between the subducting and overriding plates1. Non-volcanic tremor generated by slow slip between the plates is thought to originate on, or near, this boundary2,3. Earthquakes also occur in the down-going plate as fluids are released4, and zones of anomalously low seismic velocities observed beneath several subduction zones are interpreted to be the subducting oceanic crust5,6,7,8,9,10. Yet, the exact location of the plate boundary remains uncertain5. Here we interpret a three-dimensional seismic tomography model from the northern Cascadia subduction zone in the northwest USA. We find that the low-velocity zone varies considerably along the Cascadia margin. In places, we observe the low-velocity zone to crop out at the surface and separate from the descending plate at depths of 35–40 km. We argue that the low-velocity zone here cannot represent oceanic crust as previously suggested, and instead the zone mostly represents sediments that have been subducted and underplated beneath the North American continent. We also find that tremor signals correlate with the position of the low-velocity zone, implying that slow slip and tremor may be facilitated by trapped fluids and high pore fluid pressures in subducted sedimentary rocks at, or close to the plate boundary. Our results also imply that the plate boundary beneath Cascadia is much deeper than previously thought.

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

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

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

Figure 1: Simplified geological map of the northern Cascadia subduction zone.
Figure 2: Seismic sections across Washington State.
Figure 3: North–south and horizontal sections through the 3D P-wave tomographic velocity model.
Figure 4: Composite migrated seismic reflection profile across the Strait of Juan de Fuca.

Similar content being viewed by others

References

  1. Pacheco, J. F., Sykes, L. R. & Scholz, C. H. Nature of seismic coupling along simple plate boundaries of the subduction type. J. Geophys. Res. 108, 14133–14159 (1993).

    Article  Google Scholar 

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

    Article  Google Scholar 

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

    Google Scholar 

  4. Hacker, B. R., Peacock, S. M., Abers, G. A. & Holloway, S. D. Subduction factory 2. Are intermediate-depth earthquakes linked to metamorphic dehydration reactions? J. Geophys. Res. 108, 2030 (2003).

    Google Scholar 

  5. Nicholson, T., Bostock, M. G. & Cassidy, J. F. New constraints on subduction zone structure in northern Cascadia. Geophys. J. Int. 161, 849–859 (2005).

    Article  Google Scholar 

  6. Kato, A. et al. Variations of fluid pressure within the subducting oceanic crust and slow earthquakes. Geophys. Res. Lett. 37, L14310 (2010).

    Google Scholar 

  7. Suckale, J. et al. High-resolution seismic imaging of the western Hellenic subduction zone using teleseismic scattered waves. Geophys. J. Int. 178, 775–791 (2009).

    Article  Google Scholar 

  8. Yuan, X. et al. Subduction and collision processes in the central Andes constrained by converted seismic phases. Nature 408, 958–961 (2000).

    Article  Google Scholar 

  9. Rondenay, S., Abers, G. A. & van Keken, P. E. Seismic imaging of subduction metamorphism. Geology 36, 275–278 (2008).

    Article  Google Scholar 

  10. Rondenay, S., Bostock, M. G. & Shragge, J. Multiparameter two-dimensional inversion of scattered teleseismic body waves, 3, Application to the Cascadia 1993 data set. J. Geophys. Res. 106, 30795–30808 (2001).

    Article  Google Scholar 

  11. Abers, G. A. et al. Imaging the source region of Cascadia tremor and intermediate-depth earthquakes. Geology 37, 1119–1122 (2009).

    Article  Google Scholar 

  12. Miller, K. C. et al. Crustal structure along the west flank of the Cascades, Western Washington. J. Geophys. Res. 102, 17857–17873 (1997).

    Article  Google Scholar 

  13. Parsons, T. et al. A new view into the Cascadia subduction zone and volcanic arc: Implications for earthquake hazards along the Washington margin. Geology 26, 199–202 (1998).

    Article  Google Scholar 

  14. Brocher, T. M. et al. Wide-angle seismic recordings from the 1998 Seismic Hazards Investigation in Puget Sound (SHIPS), western Washington and British Columbia. US Geol. Surv. Open File Report 99–314, 1–129 (US Geological Survey, 1999).

  15. Brocher, T. et al. Report for explosion data acquired in the 1999 Seismic Hazards Investigation in Puget Sound (SHIPS), Washington. US Geol. Surv. Open File Report 00-318, 1–85 (US Geological Survey, 2000).

  16. Preston, L. A. Simultaneous Inversion of 3D Velocity Structure, Hypocenter Locations, and Reflector Geometry in Cascadia PhD thesis, Univ. Washington 1–112 (2003).

  17. Preston, L. A., Creager, K. C., Crosson, R. S., Brocher, T. M. & Tréhu, A. M. Intraslab earthquakes: Dehydration of the Cascadia slab. Science 302, 1197–1200 (2003).

    Article  Google Scholar 

  18. Nedimović, 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  Google Scholar 

  19. Brocher, T. M. et al. Upper crustal structure in Puget Lowland, Washington: Results from the 1998 Seismic Hazards Investigation in Puget Sound. J. Geophys. Res. 106, 13541–13564 (2001).

    Article  Google Scholar 

  20. Brandon, M. T., Roden-Tice, M. K. & Garver, J. L. Late Cenozoic exhumation of the Cascadia accretionary wedge in the Olympic Mountains, northwest Washington State. Bull. Geol. Soc. Am. 110, 985–1009 (1998).

    Article  Google Scholar 

  21. Calkins, J. A. et al. Shallow structure of the Cascadia subduction zone beneath western Washington from spectral ambient noise correlation. J. Geophys. Res. 116, B07302 (2011).

  22. Van Wagoner, T. M., Crosson, R. S., Creager, K. C., Medema, G. & Preston, L. Crustal structure and relocated earthquakes in the Puget Lowland, Washington, from high resolution seismic tomography. J. Geophys. Res. 107, 2381 (2002).

    Article  Google Scholar 

  23. 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  Google Scholar 

  24. Hyndman, R. D. Dipping reflectors, electrically conductive zones and free water beneath a subduction zone. J. Geophys. Res. 93, 13391–13405 (1988).

    Article  Google Scholar 

  25. Audet, P., Bostock, M. G., Christensen, N. I. & Peacock, S. M. Seismic evidence for overpressured subducted oceanic crust and megathrust fault sealing. Nature 457, 76–78 (2009).

    Article  Google Scholar 

  26. Audet, P. et al. Slab morphology in the Cascadia fore arc and its relation to episodic tremor and slip. J. Geophys. Res. 115, B00A16 (2010).

    Article  Google Scholar 

  27. Royle, G. T., Calvert, A. J. & Kao, H. Observations of non-volcanic tremor during the northern Cascadia slow-slip event in February 2002. Geophys. Res. Lett. 33, L18313 (2006).

    Article  Google Scholar 

  28. Wech, A. G., Creager, K. C. & Melbourne, T. I. Seismic and geodetic constraints on Cascadia slow slip. J. Geophys. Res. 114, B10316 (2009).

    Article  Google Scholar 

  29. La Rocca, M. et al. Cascadia tremor located near plate interface constrained by S minus P wave times. Science 323, 620–623 (2009).

    Article  Google Scholar 

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

    Article  Google Scholar 

Download references

Acknowledgements

We thank G. Abers for providing the geometry of the CAFE teleseismic profile and H. Kao for providing some tremor locations in Canada. This project was funded by the Natural Sciences and Engineering Research Council of Canada and US Geological Survey through grant 06HQGR0029. The acquisition of the various field data was supported by the US Geological Survey, the Geological Survey of Canada, the National Science Foundation, and several US and Canadian universities. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. Department of Energy’s National Nuclear Security Administration, under contract DE-AC04-94AL85000.

Author information

Authors and Affiliations

  1. Department of Earth Sciences, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, V5A 1S6, Canada

    Andrew J. Calvert & Amir M. Farahbod

  2. Department of Geophysics and Atmospheric Sciences, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA

    Leiph A. Preston

Authors
  1. Andrew J. Calvert
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Leiph A. Preston
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Amir M. Farahbod
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

L.A.P. created the tomographic velocity model and interpreted seismicity within the model; A.M.F. computed the tremor locations; A.J.C. interpreted velocity variations within the model and wrote the paper.

Corresponding author

Correspondence to Andrew J. Calvert.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

Supplementary Information (PDF 3496 kb)

Rights and permissions

Reprints and permissions

About this article

Cite this article

Calvert, A., Preston, L. & Farahbod, A. Sedimentary underplating at the Cascadia mantle-wedge corner revealed by seismic imaging. Nature Geosci 4, 545–548 (2011). https://doi.org/10.1038/ngeo1195

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/ngeo1195

This article is cited by

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