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NW Pacific slab rheology, the seismicity cutoff, and the olivine to spinel phase change
Earth, Planets and Space volume 50, pages977–985(1998)
Along the Kamchatka-Kuril-Japan-Izu-Bonin-Mariana subduction zones, the old age of the subducting Pacific Plate and the rapid subduction rate together suggest that earthquakes should occur to the bottom of the transition zone. However, the seismicity cutoff varies in depth between 350 km and 650 km. Along these subduction zones, the largest deep-focus earthquakes invariably occur near the depth of the local seismicity cutoff regardless of its depth. The events near the seismicity cutoffs also have systematically different focal mechanisms than shallower events. Furthermore, data from S660P arrivals, residual sphere analysis, and tomographic studies all show that the slab dip consistently steepens to a near-vertical orientation at the seismicity cutoff. This change in slab dip indicates a strength loss in the slab. We hypothesize the following causal connection among all these observations: The cold temperatures in the slab kinetically hinder the olivine to spinel phase change and allow the olivine to persist metastably to depths well below its equilibrium pressure. When the phase transition occurs, it nucleates very fine-grained spinel which acts as a lubricant, allowing the initiation of earthquake faulting at high confining pressures which further nucleates additional fine-grained spinel. The cold anomaly of the slab severely inhibits the growth of the nucleated spinel crystals. The presence of the fine-grained spinel crystals reduces the strength of the coldest part of the slab by several orders of magnitude, allowing high slab deformation rates. Additionally, the phase change, by increasing the density, provides a negative buoyancy force. Combined, these processes reduce the slab membrane strength and allow the slab to descend at a steeper dip.
Bina, C. R., Patterns of deep seismicity reflect buoyancy stresses due to phase transitions, Geophys. Res. Lett., 24, 3301–3304, 1997.
Brudzinski, M. R., W. P. Chen, R. L. Nowack, and B. S. Huang, Variations of p wave speeds in the mantle transition zone beneath the northern Philippine Sea, J. Geophys. Res., 102, 11,815–11,828, 1997.
Burbach, G. V. and C. Frohlich, Intermediate and deep seismicity and lateral structure of subducted lithosphere in the Circum-Pacific region, Rev. Geophys., 24, 833–874, 1986.
Castle, J. C. and K. C. Creager, Topography of the 660-km discontinuity beneath Izu-Bonin: Implications for tectonic history and slab deformation, J. Geophys. Res., 103, 12,511–12,528, 1998.
Chiao, L.-Y., Membrane deformation rate and geometry of subducting slabs, Ph.D. Thesis, Univ. of Washington, Seattle, 1991.
Christensen, U. R., The influence of trench migration on the slab penetration into the lower mantle, Earth Planet. Sci. Lett., 140, 27–39, 1996.
Creager, K. C., Geometry, velocity structure, and penetration depths of descending slabs in the Western Pacific, Ph.D. Thesis, Univ. of California, San Diego, 1984.
Creager, K. C. and T. M. Boyd, The geometry of Aleutian subduction: Three-dimensional kinematic flow model, J. Geophys. Res., 96, 2293–2307, 1991.
Creager, K. C. and L.-Y. Chiao, Inplane deformation-rates of circum-Pacific subducting slabs (abstract), in SUBCON An Interdisciplinary Conference on the Subduction Process, vol. 1, pp. 199, Catalina Island, California, 1994.
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.
Creager, K. C., L. Y. Chiao, J. P. Winchester, and R. Engdahl, Membrane strain rates in the subducting plate beneath south America, Geophys. Res. Lett., 22, 2321–2324, 1995.
Däßler, R., D. A. Yuen, S. I. Karato, and M. R. Riedel, Two-dimensional thermo-kinetic model for the olivine-spinel phase transition in subducting slabs, Phys. Earth Planet. Inter., 94, 217–239, 1996.
Dunbar, P. K., P. A. Lockridge, and L. S. Whiteside, Significant earthquakes worldwide, NOAA earthquake catalog, 1992.
Dziewonski, A. M., T. A. Chou, and J. H. Woodhouse, Determination of earthquake source parameters from waveform data for studies of global and regional seismicity, J. Geophys. Res., 86, 2825–2852, 1981.
Engdahl, E. R., R. D. van der Hilst, and R. P. Buland, Global teleseismic earthquake relocation with improved travel times and procedures for depth determination, Bull. Seismol. Soc. Am., 88, 722–743, 1998.
Fukao, Y., M. Obayashi, H. Inoue, and M. Nenbai, Subducting slabs stagnant in the mantle transition zone, J. Geophys. Res., 97, 4809, 1992.
Green, H. and H. Houston, The mechanism of deep earthquakes, Annu. Rev. Earth Planet. Sci., 23, 169–213, 1995.
Green, H. W., T. E. Young, D. Walker, and C. H. Scholz, Anticrack-associated faulting at very high pressure in natural olivine, Nature, 348, 720–722, 1990.
Helffrich, G. R. and J. Brodholt, Relationship of deep seismicity to the thermal structure of subducted lithosphere, Nature, 353, 252–255, 1991.
Inoue, H., Y. Fukao, K. Tanabe, and Y. Ogata, Whole mantle P-wave travel time tomography, Phys. Earth Planet. Inter., 59, 294–328, 1990.
Ito, E. and E. Takahashi, Postspinel transformations in the system Mg2 SiO4 — Fe2 SiO4 and some geophysical implications, J. Geophys. Res., 94, 10,637–10,646, 1989.
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.
Karato, S. I., M. R. Riedel, and D. A. Yuen, How strong are the subducted slabs?, Earth Planet. Sci. Lett., 1998 (submitted).
Katsura, T. and E. Ito, The system Mg2 SiO4 -Fe2 SiO4 at high pressures and temperatures: Precise determination of stabilities of olivine, modified spinel, and spinel, J. Geophys. Res., 94, 15,663–15,670, 1989.
Kincaid, C. and P. Olson, An experimental study of subduction and slab migration, J. Geophys. Res., 92, 13,832–13,840, 1987.
Kirby, S. H., W. B. Durnam, and L. A. Stern, Mantle phase changes and deep-earthquake faulting in subducting lithosphere, Science, 252, 216–225, 1991.
Kirby, S. H., S. Stein, E. A. Okal, and D. C. Rubie, Metastable mantle phase transformations and deep earthquakes in subducting oceanic lithosphere, Rev. Geophys., 34, 261–306, 1996.
Lundgren, P. R. and D. Giardini, Seismicity, shear failure and models of deformation in deep subduction zones, Phys. Earth Planet. Inter., 74, 63–74, 1992.
McGuire, J. J., D. A. Wiens, and P. J. Shore, The March 8, 1994 (Mw 7.6), deep Tonga earthquake: Rupture outside the seismically active slab, J. Geophys. Res., 102, 15,163–15,182, 1997.
Ohtaki, T. and S. Kaneshima, Continuous high velocity aseismic zone beneath the izubonin arc, Geophys. Res. Lett., 21, 1–4, 1994.
Okino, K., M. Ando, S. Kaneshima, and K. Hirahara, The horizontally lying slab, Geophys. Res. Lett., 16, 1059–1062, 1989.
Riedel, M. R. and S. I. Karato, Grainsize evolution in subducted oceanic lithosphere associated with the olivinespinel transformation and its effects on rheology, Earth Planet. Sci. Lett., 148, 27–43, 1997.
Rubie, D. C., The olivine spinel transformation and the rheology of subducting lithosphere, Nature, 308, 505–508, 1984.
Seno, T., S. Stein, and A. E. Gripp, A model for the motion of the Philippine Sea Plate consistent with NUVEL-1 and geological data, J. Geophys. Res., 98, 17,941–17,948, 1993.
Silver, P. G. and T. H. Jordan, Total-moment spectra of fourteen large earthquakes, J. Geophys. Res., 88, 3273–3293, 1983.
Sung, C. M. and R. G. Burns, Kinetics of high-pressure phase transformations: implications to the evolution of the olivine — spinel transition in the downgoing lithosphere and its consequences on the dynamics of the mantle, Tectonophysics, 21, 1–32, 1976.
Tajima, F. and S. Grand, Variation of transition zone high velocity anomalies and depression of 660 km discontinuity associated with subduction zones from the southern Kuriles to Izu-Bonin and Ryukyu, J. Geophys. Res., 103, 15015–15038, 1998.
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.
van der Hilst, R. D., R. Engdahl, W. Spakman, and G. Nolet, Tomographic imaging of subducted lithosphere below northwest Pacific island arcs, Nature, 353, 37–42, 1991.
van der Hilst, R. D., S. Widiyantoro, K. C. Creager, and T. J. McSweeney, Deep subduction and aspherical variations in P-wavespeed at the base of Earth’s mantle, in Observational and theoretical constraints on the Core Mantle Boundary Region, edited by M. Gurnis, M. E. Wysession, E. Knittle, and B. A. Buffett, vol. 28, pp. 5–20, American Geophysical Union, Washington, D.C., 1998.
Vassiliou, M. S., B. H. Hager, and A. Raefsky, The distribution of earthquakes with depth and stress in subducting slabs, J. Geodyn., 1, 11–28, 1984.
Widiyantoro, S., Studies of seismic tomography on regional and global scale, Ph.D. Thesis, Aust. Nat. Univ., Canberra, A.C.T., 1997.
Yamaoka, K. and Y. Fukao, Spherical shell tectonics: Effects of sphericity and inextensibility on the geometry of the descending lithosphere, Rev. Geophys., 24, 27–53, 1986.
Zhong, S. and M. Gurnis, Dynamic interaction between tectonic plates, subducting slabs, and the mantle, Earth Interact., 1, 1997.
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Castle, J.C., Creager, K.C. NW Pacific slab rheology, the seismicity cutoff, and the olivine to spinel phase change. Earth Planet Sp 50, 977–985 (1998). https://doi.org/10.1186/BF03352192
- Subduction Zone
- Lower Mantle
- Core Mantle Boundary