Skip to main content

Advertisement

You are viewing the new article page. Let us know what you think. Return to old version

Article | Open | Published:

Evaluation of slab images in the northwestern Pacific

Abstract

Recent P wave travel-time tomographic studies using data from the International Seismological Centre (ISC) catalog determine a large-scale subhorizontal high velocity anomaly in the northwestern Pacific subduction zones and it has been interpreted as imaging stagnant slab in the upper mantle transition zone (400 to 700 km). The limited resolution of the travel time tomographic studies in this depth range, however, makes it difficult to evaluate accurately the vertical and lateral extent of a stagnant slab. A broadband waveform modeling of triplicated regional seismic waves which are very sensitive to the transition zone structure is useful to evaluate the velocity structure along the propagation paths and therefore to constrain the spatial distribution of anomalies. This study thus compares tomographic images from the model of Obayashi et al. (1997) with results of the regional waveform modeling by Tajima and Grand (1998). The ISC tomographic model shows the largest lateral extent of high velocity anomaly in the layer of 478 to 551 km depths although part of this spread is likely due to the deteriorated resolution in that depth range. The waveform modeling suggests that the strong high velocity anomaly associated with a stagnant slab exists below 525 km with its maximum intensity in the top 50 km and decreases with increasing depth to vanish at 660 km. These results along with a recent global SH velocity model SAW12D of Li and Romanowicz (1996) which has the strongest high velocity anomaly in a depth range 500–550 km may be integrated into an image of a stagnant slab. The anomalous velocity structure associated with a stagnant slab has its maximum intensity not immediately above the 660 km discontinuity but in a depth range 100 km above it. This feature appears to be consistent with a thermo-chemical model of down-going slab in which a larger velocity contrast with the surrounding mantle is expected at a shallower depth of the transition zone. The ISC tomographic model and waveform modeling consistently show that the deflected slabs are not laterally continuous but are separated into a few subregions. Beneath the northeastern China where the resolution is good, the slab related anomaly above the 660 km discontinuity is accompanied by its downward extension into the lower mantle.

References

  1. Bina, C. R., Phase transition buoyancy contributions to stresses in subducting lithosphere, Geophys. Res. Lett., 23, 3563–3566, 1996.

  2. Brudzinski, M. R., W.-P. Chen, R. L. Nowack, and B.-S. Huang, Variations of P-Wavespeeds in the mantle transition zone beneath the northern Philippine sea with implications on mantle, dynamics, J. Geophys. Res., 102, 11,815–11,827, 1997.

  3. Bullen, K. E., An Introduction to the Theory of Seismology, 3rd edition, Cambridge Univ. Press, 1963.

  4. Castle, J. C. and K. Creager, Seismic evidence against a mantle chemical discontinuity near 660 km discontinuity beneath Izu-Bonin, Geophys. Res. Lett., 24, 241–244, 1997.

  5. Collier, J. D. and G. R. Helffrich, Topography of the “410” and “660” discontinuities in the Izu-Bonin subduction zone, Geophys. Res. Lett., 24, 1535–1538, 1997.

  6. Creager, K. C. and T. H. Jordan, Slab penetration into the lower mantle, J. Geophys. Res., 89, 3031–3049, 1984.

  7. Creager, K. C. and T. H. Jordan, Slab penetration into the lower mantle beneath the Mariana and other island arcs of the northwest Pacific, J. Geophys. Res., 91, 3573–3589, 1986.

  8. Fukao, Y., Upper mantle P structure on the ocean side of the Japan-Kurile arc, Geophys. J. R. Astron. Soc., 50, 621–642, 1977.

  9. Fukao, Y., M. Obayashi, H. Inoue, and M. Nenbai, Subducting slabs stagnant in the mantle transition zone, J. Geophys. Res., 97, 4809–4822, 1992.

  10. Grand, S. P., Mantle shear structure beneath the Americas and surrounding oceans, J. Geophys. Res., 99, 11591–11621, 1994.

  11. Herrin, E., W. Tucher, J. Taggart, D. W. Gordon, and J. L. Lobdell, Estimation of surface focus P travel times, Bull. Seismol. Soc. Am., 58, 1273–1291, 1968.

  12. Inoue, H., Y. Fukao, K. Tanabe, and Y. Ogata, Whole mantle P-wave travel time tomography, Phys. Earth Planet. Inter., 59, 294–328, 1990.

  13. Kamiya, S., T. Miyatake, and K. Hirahara, How deep can we see the high velocity anomalies beneath the Japan islands?, Geophys. Res. Lett., 15, 828–831, 1988.

  14. Kamiya, S., T. Miyatake, and K. Hirahara, Three-dimensional P-wave velocity structure beneath the Japanese islands, Bull. Earthquake Res. Inst. Univ. Tokyo, 64, 457–485, 1989.

  15. Kawakatsu, H. and F. Niu, Seismic evidence for a 920-km discontinuity in the mantle, Nature, 371, 301–305, 1994.

  16. Kennett, B. L. N. and E. R. Engdahl, Traveltimes for global earthquake location and phase identification, Geophys. J. Int., 105, 429–465, 1991.

  17. Li, X. and B. Romanowicz, Global mantle shear velocity model developed using nonlinear asymptotic coupling theory, J. Geophys. Res., 101, 22245–22272, 1996.

  18. Obayashi, M., T. Sakurai, and Y. Fukao, Comparison of recent tomographic models, Abstract of International Symposium on New Images of the Earth’s Interior through Long-term Oceanfloor Observations, 29, 1997.

  19. Ohtaki, T. and S. Kaneshima, Continuous high velocity aseismic zone beneath the Izu-Bonin arc, Geophys. Res. Lett., 21, 1–4, 1994.

  20. Okal, E. A. and S. H. Kirby, Deep earthquakes beneath the Fiji basin, SW Pacific: Earth’s most intense deep seismicity in stagnant slabs, Phys. Earth Planet. Inter., 1998 (in press).

  21. Ringwood, A. E. and T. Irifune, Nature of the 650 km seismic discontinuity: Implications for mantle dynamics and differentiation, Nature, 331, 131–136, 1988.

  22. Sakurai, T., M. Obayashi, and Y. Fukao, Tomographic image of slab and mantle plume, Program and Abstracts, Seism. Soc. Japan, 1, 189, 1995.

  23. Su, W. J., R. L. Woodward, and A. M. Dziewonski, Degree 12 models of shear velocity heterogeneity in the mantle, J. Geophys. Res., 99, 36945–36980, 1994.

  24. Tajima, F. and S. P. Grand, Evidence of high velocity anomalies in the transition zone associated with southern Kurile subduction zone, Geophys. Res. Lett., 22, 3139–3142, 1995.

  25. Tajima, F. and S. P. Grand, Variation of transition zone high velocity anomalies and depression of the 660 km discontinuity associated with subduction zones from the southern Kuriles to Izu-Bonin, J. Geophys. Res., 103, B7, 15015–15036, 1998.

  26. van der Hilst, R. D. and T. Seno, Effects of relative plate motion on the deep structure and penetration depth of slabs below the Izu-Bonin and Mariana island arcs, Earth Planet. Sci. Lett., 120, 395–407, 1993.

  27. van der Hilst, R. D., R. Engdahl, W. Spakman, and G. Nolet, Tomographic imaging of subducted lithosphere below northwest Pacific islands arcs, Nature, 353, 37–43, 1991.

  28. van der Hilst, R. D., S. Widiyantro, and E. R. Engdahl, Evidence for deep mantle circulation from global tomography, Nature, 386, 578–589, 1997.

  29. Wicks, C. W. and M. A. Richards, A detailed map of the 660-kilometer discontinuity beneath the Izu-Bonin subduction zone, Science, 261, 1424–1426, 1993.

  30. Widiyantoro, S. and R. van der Hilst, Structure and evolution of lithospheric slab beneath the Sunda arc, Indonesia, Science, 271, 1566–1570, 1996.

  31. Zhou, H. and R. W. Clayton, P and S travel time inversions for subducting slab under the island arcs of the Northwest Pacific, J. Geophys. Res., 95, 6829–6851, 1990.

  32. Zhou, H., D. L. Anderson, and R. W. Clayton, Modeling of residual spheres for subduction zone earthquakes, 1, Apparent slab penetration signatures in the NW Pacific caused by deep diffuse mantle anomalies, J. Geophys. Res., 95, 6799–6827, 1990.

Download references

Author information

Correspondence to Fumiko Tajima.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Keywords

  • Subduction Zone
  • Depth Range
  • Lower Mantle
  • International Seismological Centre
  • Mantle Transition Zone