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Volume 53 Supplement 4

Special Issue: Great Subduction Zone Earthquakes

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Tomographic image of low P velocity anomalies above slab in northern Cascadia subduction zone

Earth, Planets and Space volume 53, pages 285–293 (2001)Cite this article

Abstract

At the Cascadia margin the Juan de Fuca plate is subducting beneath the North America plate, causing active seismicity within both plates. Earthquakes occur down to a maximum depth of 80 km within the descending oceanic plate and to about 30 km in the overriding continental plate. We use a method of seismic tomography to invert 28,230 P wave arrival times from 2666 local earthquakes that occurred in and around Vancouver Island from 1970 to 1990. The tomography model uses about 30 km horizontal and 12–19 km vertical grid spacing and assumes that the seismic velocity perturbations vary continuously between grid points. Velocity structures can be obtained to a depth of 65 km. The obtained tomographic image shows an extensive low velocity zone above the subducted slab at about 45 km depth and patches of low velocities at shallower depths just seaward of the volcanic front. The deeper extensive low velocity zone may indicate the presence of partially hydrated mantle, most likely serpentinite, as a result of slab dehydration associated with the transformation of metabasalt to eclogite. One of the shallow low velocity patches coincides with an abrupt increase in surface heat flow and may reflect the presence of partial melts or water in the crust.

References

  • Auld, D. R., S. E. Dosso, D. W. Oldenburg, and L. K. Law, Monitoring temporal change in conductivity in the central Vancouver Island region, an area with past large earthquakes, Can. J. Earth Sci., 29, 601–608, 1992.

    Article  Google Scholar 

  • Benz, H. M., G. Zandt, and D. H. Oppenheimer, Lithospheric structure of northern California from teleseismic images of the upper mantle, J. Geophys. Res., 97, 4791–4807, 1992.

    Article  Google Scholar 

  • Bostock, M. G. and J. C. VanDecar, Upper mantle structure of the northern Cascadia subduction zone, Can. J. Earth Sci., 32, 1–12, 1995.

    Article  Google Scholar 

  • Cassidy, J. F. and R. M. Ellis, Shear wave constraints on a deep crustal reflective zone beneath Vancouver Island, J. Geophys. Res., 96, 19,843–19,851, 1991.

    Article  Google Scholar 

  • Cassidy, J. F. and R. M. Ellis, S-wave velocity structure of the northern Cascadia subduction zone, J. Geophys. Res., 98, 4407–4421, 1993.

    Article  Google Scholar 

  • Christensen, N., Elasticity of ultrabasic rocks, J. Geophys. Res., 71, 5921–5931, 1966.

    Article  Google Scholar 

  • Clowes, R. M., C. A. Zelt, J. R. Amor, and R. M. Ellis, Lithospheric structure in the souther Canadian Cordillera from a network of seismic refraction lines, Can. J. Earth Sci., 32, 1485–1513, 1996.

    Article  Google Scholar 

  • Clowes, R. M., D. J. Baird, and S. A. Dehler, Crustal structure of the Cascadia subduction zone, southwestern British Columbia from potential field and seismic studies, Can. J. Earth Sci., 34, 317–335, 1997.

    Article  Google Scholar 

  • Cook, F. A., A. G. Green, P. S. Simony, R. A. Price, R. Parrish, B. Milkereit, P. L. Gordy, R. L. Brown, K. C. Coflin, and C. Patenaude, Lithoprobe seismic reflection structure of the southern Canadian Cordillera: Initial results, Tectonics, 7, 157–180, 1988.

    Article  Google Scholar 

  • Crosson, R. S. and T. J. Owens, Slab geometry of the Cascadia subduction zone beneath Washington from earthquake hypocenters and teleseismic converted waves, Geophys. Res. Lett., 14, 824–827, 1987.

    Article  Google Scholar 

  • Davis, E. E. and R. D. Hyndman, Accretion and recent deformation of sediments along the northern Cascadia subduction zone, Geol. Soc Am. Bull., 101, 1465–1480, 1989.

    Article  Google Scholar 

  • Flück, P., R. D. Hyndman, and K. Wang, Three-dimensional dislocation model for great earthquakes of the Cascadia subduction zone, J. Geophys. Res., 102, 20,539–20,550, 1997.

    Article  Google Scholar 

  • Harris, R. A., H. M. Iyer, and P. B. Dawson, Imaging the Juan de Fuca plate beneath southern Oregon using teleseismic P wave residuals, J. Geophys. Res., 96, 19,879–19,889, 1991.

    Article  Google Scholar 

  • Hasegawa, A., D. Zhao, S. Hori, A. Yamamoto, and S. Horiuchi, Deep structure of the northeastern Japan arc and its relationship to seismic and volcanic activity, Nature, 352, 683–689, 1991.

    Article  Google Scholar 

  • Hussong, D. M. and S. Uyeda, Tectonic processes and the history of the Mariana arc: A synthesis from results of DSDP Leg 60, Init. Rep. Deep Sea Drilling Proj., 60, 909–929, 1982.

    Google Scholar 

  • Hyndman, R. D., Dipping seismic reflectors, electrically conductive zones, and trapped water in the crust over a subduction plate, J. Geophys. Res., 93, 13,391–13,405, 1988.

    Article  Google Scholar 

  • Hyndman, R. D., The Lithoprobe corridor across the Vancouver Island continental margin: The structural and tectonic consequences of subduction, Can. J. Earth Sci., 32, 1777–1802, 1995.

    Article  Google Scholar 

  • Hyndman, R. D. and T. J. Lewis, Review: The thermal regime along the southern Canadian Cordillera Lithoprobe corridor, Can. J. Earth Sci., 32, 1611–1617, 1995.

    Article  Google Scholar 

  • Hyndman, R. D., C. J. Yorath, R. M. Clowes, and E. E. Davis, The northern Cascadia subduction zone at Vancouver Island: Seismic structure and tectonic history, Can. J. Earth Sci., 27, 313–329, 1990.

    Article  Google Scholar 

  • Kisslinger, E. and J. C. Lahr, Tomographic image of the Pacific slab under southern Alaska, Eclogae Geol. Helv., 84, 297–315, 1991.

    Google Scholar 

  • Kurtz, R. D., J. M. Delaurier, and J. C. Gupta, A magnetotelluric sounding across Vancouver Island detects the subducting Juan de Fuca plate, Nature, 321, 596–599, 1986.

    Article  Google Scholar 

  • Kurtz, R. D., J. M. Delaurier, and J. C. Gupta, The electrical conductivity distribution beneath Vancouver Island: A region of active plate subduction, J. Geophys. Res., 95, 10,929–10,946, 1990.

    Article  Google Scholar 

  • Lees, J. M. and R. S. Crosson, Tomographic inversion for three-dimensional velocity structure at Mount St. Helens using earthquake data, J. Geophys. Res., 94, 5716–5728, 1989.

    Article  Google Scholar 

  • Lees, J. M. and R. S. Crosson, Tomographic imaging of local earthquake delay times for three-dimensional velocity variation in western Washington, J. Geophys. Res., 95, 4763–4776, 1990.

    Article  Google Scholar 

  • Lewis, T. J., W. H. Bentkowski, E. E. Davis, R. D. Hyndman, J. G. Souther, and J. A. Wright, Subduction of the Juan de Fuca plate: Thermal consequences, J. Geophys. Res., 93, 15,207–15,225, 1988.

    Article  Google Scholar 

  • Lewis, T. J., W. H. Bentkowski, and R. D. Hyndman, Crustal temperatures near the Lithoprobe Southern Canadian Cordillera Transect, Can. J. Earth Sci., 29, 1197–1214, 1992.

    Article  Google Scholar 

  • Michaelson, C. A. and C.S. Weaver, Upper mantle structure from teleseismic P arrivals in Washington and northern Oregon, J. Geophys. Res., 91, 2077–2094, 1986.

    Article  Google Scholar 

  • Moran, S. C., J. M. Lees, and S. D. Malone, P wave crustal velocity structure in the greater Mount Rainier area from local earthquake tomography, J. Geophys. Res., 104, 10,775–10,786, 1999.

    Article  Google Scholar 

  • Peacock, S. M., Thermal and petrological structure of subduction zones, in Subduction: Top to Bottom, edited by G. Bebout, D. W. Scholl, S.H. Kirby, and J. P. Platt, pp. 119–133, American Geophysical Union, Washington, D. C., 1996.

    Google Scholar 

  • Peacock, S. M. and K. Wang, Seismic consequences of warm versus cool subduction metamorphism: Examples from Southwest and Northeast Japan, Science, 286, 937–939, 1999.

    Article  Google Scholar 

  • Rasmussen, J. and E. Humphreys, Tomographic image of the Juan de Fuca plate beneath Washington and western Oregon using teleseismic P-wave travel times, Geophys. Res. Lett., 15, 1417–1420, 1988.

    Article  Google Scholar 

  • Riddihough, R. P., Gravity and structure of an active margin—British Columbia and Washington, Can. J. Earth Sci., 16, 350–363, 1979.

    Article  Google Scholar 

  • Rogers, G. C., Seismotectonics of British Columbia, PhD thesis, University of British Columbia, Vancouver, British Columbia, 247 pp., 1983.

    Google Scholar 

  • Rogers, G. C. and H. S. Hasegawa, a second look at the British Columbia earthquake of 23 June, 1946, Bull. Seism. Soc. Am., 68, 653–676, 1978.

    Google Scholar 

  • Rogers, G. C., C. Spindler, and R. D. Hyndman, Seismicity along the Vancouver Island Lithoprobe Corridor, in Proceedings of the Project Lithoprobe: Southern Canadian Cordillera Transect Workshop, pp. 166–169, University of Calgary, Calgary, Alberta, 1990.

    Google Scholar 

  • Spence, G. D. and N. A. Mclean, Seismic structure across the active subduction zone of western Canada, Can. J. Earth Sci, 36, 1999 (in press).

  • Spence, G. D., R. D. Hyndman, E. E. Davis, and C. J. Yorath, Seismic structure of the northern Cascadia accretionary prism: Evidence from new multichannel seismic reflection data, in Continental Lithosphere: Deep Reflections, Geodynamics 22, pp. 257–263, American Geophysical Union, Washington, D.C., 1991.

    Chapter  Google Scholar 

  • Stanley, D., A. Villasenor, and H. Benz, Subduction zone and crustal dynamics of western Washington: A tectonic model for earthquake hazards evaluation, U.S. Geological Survey Open-File Report 99–311, 1999.

  • Suyehiro, K., N. Takahashi, Y. Ariie, Y. Yokoi, R. Hino, M. Shinohara, T. Kanazawa, N, Hirata, H. Tokuyama, and A. Taira, Continental crust, crustal underplating, and low-Q upper mantle beneath and oceanic island arc, Science, 272, 390–392, 1996.

    Article  Google Scholar 

  • Taber, J. J. and S. W. Smith, Seismicity and focal mechanisms associated with the subduction of the Juan de Fuca plate beneath the Olympic Peninsula, Washington, Bull. Seism. Soc. Am., 75, 237–249, 1985.

    Google Scholar 

  • VanDecar, J. C., Upper mantle structure of the Cascadia subduction zone from non-linear teleseismictravel-time inversion, Ph.D. thesis, University of Washington, Seattle, Washington, 1991.

    Google Scholar 

  • Verdonck, D. and G. Zandt, Three-dimensional crustal structure of the Mendocino triple junction region from local earthquake travel times, J. Geophys. Res., 99, 23,843–23,858, 1994.

    Article  Google Scholar 

  • Wahlstrom, R. and G. C. Rogers, Relocation of earthquakes west of Vancouver Island, British Columbia, 1965–1983, Can. J. Earth Sci., 29, 953–961, 1992.

    Article  Google Scholar 

  • Wang, K., T. Mulder, G. C. Rogers, and R. D. Hyndman, Case for very low coupling stress on the Cascadia subduction fault, J. Geophys. Res., 100, 12,907–12,918, 1995.

    Article  Google Scholar 

  • Zelt, B. C., R. M. Ellis, and R. M. Clowes, Crustal velocity structure in the eastern Insular and southernmost Coast Belts, Can. J. Earth Sci., 30, 1014–1027, 1993.

    Article  Google Scholar 

  • Zelt, B. C., R. M. Ellis, and R. M. Clowes, Inversion of three-dimensional wide-angle seismic data from the southwestern Canadian Cordillera, J. Geophys. Res., 101, 8503–8529, 1996.

    Article  Google Scholar 

  • Zhao, D., A. Hasegawa, and S. Horiuchi, Tomographic imaging of P and S wave velocity structure beneath northeastern Japan, J. Geophys. Res., 97, 19,909–19,928, 1992.

    Article  Google Scholar 

  • Zhao, D., A. Hasegawa, and H. Kanamori, Deep structure of Japan subduction zone as derived from local, regional, and teleseismic events, J. Geophys. Res., 99, 22,313–22,329, 1994.

    Article  Google Scholar 

  • Zhao, D., D. Christensen, and H. Pulpan, Tomographic imaging of the Alaska subduction zone, J. Geophys. Res., 100, 6487–6504, 1995.

    Article  Google Scholar 

  • Zhao, D., H. Kanamori, H. Negishi, and D. Wiens, Tomography of the source area of the 1995 Kobe earthquake: evidence for fluids at the Hypocenter?, Science, 274, 1891–1893, 1996.

    Article  Google Scholar 

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Authors and Affiliations

  1. Department of Earth Sciences, Ehime University, Matsuyama, 790-8577, Japan

    Dapeng Zhao

  2. Pacific Geoscience Centre, Geological Survey of Canada, 9860 W Saanich Rd, Sidney, B.C., Canada, V8L 4B2

    Kelin Wang & Garry C. Rogers

  3. Department of Geology, Arizona State University, Box 871404, Tempe, AZ, 85287-1404, USA

    Simon M. Peacock

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  1. Dapeng Zhao
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  2. Kelin Wang
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  3. Garry C. Rogers
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  4. Simon M. Peacock
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Correspondence to Dapeng Zhao.

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Zhao, D., Wang, K., Rogers, G.C. et al. Tomographic image of low P velocity anomalies above slab in northern Cascadia subduction zone. Earth Planet Sp 53, 285–293 (2001). https://doi.org/10.1186/BF03352385

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  • DOI: https://doi.org/10.1186/BF03352385

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