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Seismic evidence for overpressured subducted oceanic crust and megathrust fault sealing


Water and hydrous minerals play a key part in geodynamic processes at subduction zones1,2,3 by weakening the plate boundary, aiding slip and permitting subduction—and indeed plate tectonics—to occur4. The seismological signature of water within the forearc mantle wedge is evident in anomalies with low seismic shear velocity marking serpentinization5,6,7. However, seismological observations bearing on the presence of water within the subducting plate itself are less well documented. Here we use converted teleseismic waves to obtain observations of anomalously high Poisson’s ratios within the subducted oceanic crust from the Cascadia continental margin to its intersection with forearc mantle. On the basis of pressure, temperature and compositional considerations, the elevated Poisson’s ratios indicate that water is pervasively present in fluid form at pore pressures near lithostatic values. Combined with observations of a strong negative velocity contrast at the top of the oceanic crust, our results imply that the megathrust is a low-permeability boundary. The transition from a low- to high-permeability plate interface downdip into the mantle wedge is explained by hydrofracturing of the seal by volume changes across the interface caused by the onset of crustal eclogitization and mantle serpentinization. These results may have important implications for our understanding of seismogenesis, subduction zone structure and the mechanism of episodic tremor and slip.

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Figure 1: Geographical map of northern Cascadia subduction zone.
Figure 2: Radial receiver function results beneath northern Cascadia.
Figure 3: Schematic interpretation of receiver function results.


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

    ADS  CAS  Article  Google Scholar 

  2. Stern, R. J. Subduction zones. Rev. Geophys. 40 10.1029/2001RG000108 (2002)

  3. Kirby, S. H., Engdahl, E. R. & Denlinger, R. in Subduction Top to Bottom (eds Bebout, G. E., Scholl, D. W., Kirby, S. H. & Platt, J. P.) 195–214 (Am. Geophys. Un., 1996)

    Google Scholar 

  4. O’Neill, C., Jellinek, A. M. & Lenardic, A. Conditions for the onset of plate tectonics on terrestrial planets and moons. Earth Planet. Sci. Lett. 261, 20–32 (2007)

    ADS  Article  Google Scholar 

  5. Hyndman, R. D. & Peacock, S. M. Serpentinization of the forearc mantle. Earth Planet. Sci. Lett. 212, 417–432 (2003)

    ADS  CAS  Article  Google Scholar 

  6. Bostock, M. G., Hyndman, R. S., Rondenay, S. & Peacock, S. M. An inverted continental Moho and serpentinization of the forearc mantle. Nature 417, 536–539 (2002)

    ADS  CAS  Article  Google Scholar 

  7. Kawakatsu, H. & Watada, S. Seismic evidence for deep-water transportation in the mantle. Science 316, 1468–1471 (2007)

    ADS  CAS  Article  Google Scholar 

  8. Kao, H. et al. A wide depth distribution of seismic tremors along the northern Cascadia margin. Nature 436, 841–844 (2005)

    ADS  CAS  Article  Google Scholar 

  9. Shelly, D. R., Beroza, G. C. & Ide, S. Low-frequency earthquakes in Shikoku, Japan, and their relationship to episodic tremor and slip. Nature 442, 488–491 (2006)

    Article  Google Scholar 

  10. Wang, Z., Zhao, D., Mishra, O. P. & Yamada, A. Structural heterogeneity and its implications for the low frequency tremors in Southwest Japan. Earth Planet. Sci. Lett. 251, 66–78 (2006)

    ADS  CAS  Article  Google Scholar 

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

    ADS  Article  Google Scholar 

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

    ADS  CAS  Article  Google Scholar 

  13. Abers, G. A., van Keken, P. E., Kneller, E. A., Ferris, A. & Stachnik, J. C. The thermal structure of subduction zones constrained by seismic imaging: Implications for slab dehydration and wedge flow. Earth Planet. Sci. Lett. 241, 387–397 (2006)

    ADS  CAS  Article  Google Scholar 

  14. Zandt, G. & Ammon, C. J. Continental crust composition constrained by measurements of crustal Poisson’s ratio. Nature 374, 152–154 (1995)

    ADS  CAS  Article  Google Scholar 

  15. Zhu, L. & Kanamori, H. Moho depth variation in southern California from teleseismic receiver functions. J. Geophys. Res. 105, 2969–2980 (2000)

    ADS  Article  Google Scholar 

  16. Christensen, N. I. Poisson’s ratio and crustal seismology. J. Geophys. Res. 101, 3139–3156 (1996)

    ADS  CAS  Article  Google Scholar 

  17. Christensen, N. I. Serpentinites, peridotites, and seismology. Int. Geol. Rev. 46, 795–816 (2004)

    Article  Google Scholar 

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

    ADS  Article  Google Scholar 

  19. Moore, J. C. & Vrolijk, P. Fluids in accretionary prisms. Rev. Geophys. 30, 113–135 (1992)

    Article  Google Scholar 

  20. Christensen, N. I. Pore pressure and oceanic crustal seismic structure. Geophys. J. R. Astron. Soc. 79, 411–423 (1984)

    ADS  Article  Google Scholar 

  21. Kodaira, S. et al. High pore fluid pressure may cause silent slip in the Nankai Trough. Science 304, 1295–1298 (2004)

    ADS  CAS  Article  Google Scholar 

  22. Gerver, M. & Markushevitch, V. Determination of a seismic wave velocity from the travel time curve. Geophys. J. R. Astron. Soc. 11, 165–173 (1966)

    ADS  Article  Google Scholar 

  23. Wielandt, E. in Seismic Tomography (ed. Nolet, G.) 85–98 (Reidel, 1987)

    Book  Google Scholar 

  24. Fisher, A. T. Permeability within basaltic oceanic crust. Rev. Geophys. 36, 143–182 (1998)

    ADS  Article  Google Scholar 

  25. Caine, J. S., Evans, J. P. & Foster, C. B. Fault zone architecture and permeability structure. Geology 24, 1025–1028 (1996)

    ADS  Article  Google Scholar 

  26. Kato, A., Sakaguchi, A., Yoshida, S. & Mochizuki, H. Permeability measurements and precipitation sealing of basalt in an ancient exhumed fault of a subduction zone. Bull. Earthq. Res. Inst. Univ. Tokyo 78, 83–89 (2003)

    Google Scholar 

  27. Meneghini, F. & Moore, J. C. Deformation and hydrofracturing in a subduction thrust at seismogenic depths: The Rodeo Cove thrust zone, Marin Headlands, California. Geol. Soc. Am. Bull. 119, 174–183 (2007)

    ADS  Article  Google Scholar 

  28. 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 (2005)

    ADS  Article  Google Scholar 

  29. Ahrens, T. J. & Schubert, G. Gabbro–eclogite reaction rate and its geophysical significance. Rev. Geophys. 13, 383–400 (1975)

    ADS  CAS  Article  Google Scholar 

  30. Coleman, R. G. Petrologic and geophysical nature of serpentinites. Geol. Soc. Am. Bull. 82, 897–918 (1971)

    ADS  Article  Google Scholar 

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We thank E. Davis and M. Jellinek for discussions. Data used in this study come from the Canadian National Seismological Network and are distributed freely by the Geological Survey of Canada.

Author Contributions P.A. and M.G.B. designed the study, analysed the data and wrote the paper; N.I.C. and S.M.P. participated in the interpretation of results.

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Correspondence to Pascal Audet.

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Audet, P., Bostock, M., Christensen, N. et al. Seismic evidence for overpressured subducted oceanic crust and megathrust fault sealing. Nature 457, 76–78 (2009).

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