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The nature of the fore arc mantle and implications for seismic anisotropy

The nature of the fore arc mantle and implications for seismic anisotropy. Peter van Keken University of Michigan With: Erik Kneller, Shun Karato, Ikuo Katayama, Maureen Long, Geoff Abers, Ellen Syracuse Sponsored by the National Science Foundation. Fore arc mantle: high Q low T

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The nature of the fore arc mantle and implications for seismic anisotropy

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  1. The nature of the fore arc mantle and implications for seismic anisotropy Peter van Keken University of Michigan With: Erik Kneller, Shun Karato, Ikuo Katayama, Maureen Long, Geoff Abers, Ellen Syracuse Sponsored by the National Science Foundation

  2. Fore arc mantle: high Q low T hydrated trench-parallel S-wave splitting Shear wave splitting: B-type fabric partly explains patterns for Honshu, Ryukyu 3D flow likely for Marianas, Central Andes Not clear: Cascadia, Costa Rica - Nicaragua Van Keken, EPSL, 2003

  3. Fore arc mantle: high Q low T hydrated trench-parallel S-wave splitting Shear wave splitting: B-type fabric partly explains patterns for Honshu, Ryukyu 3D flow likely for Marianas, Central Andes Not clear: Cascadia, Costa Rica - Nicaragua Van Keken, EPSL, 2003

  4. Cascadia (Hyndman & Peacock EPSL 2003) Honshu (Yamano et al., 1997, cited in Yoshimoto, BSSA, 2006)

  5. Cascadia (Hyndman & Peacock EPSL 2003) Honshu (Yamano et al., 1997, cited in Yoshimoto, BSSA, 2006)

  6. Cascadia S perturbation (%) Bostock et al., Nature, 2002

  7. Cascadia S perturbation (%) Bostock et al., Nature, 2002

  8. From Hyndman & Peacock EPSL 2003

  9. Northern Honshu (39.2N) (Zhang et al., Geology, 2004)

  10. Stachnik et al., 2004 Nakajima, GLR, 2003

  11. Nicaragua Rychert et al., in prep. 1.70 Syracuse et al., in prep. Marianas: Pozgay, Wiens et al. (this meeting)

  12. teleseismic Long and van der Hilst, PEPI, 2005

  13. Hypotheses for formation of trench parallel anisotropy Melt related anisotropy

  14. Kneller et al., EPSL, 2005

  15. Test seismic expression of B-type cold corner for Ryukyu Kneller, Long, van Keken, in revision, EPSL

  16. Kneller, Long, van Keken, in revision, EPSL

  17. teleseismic Local Kneller, Long, van Keken, in revision, EPSL

  18. teleseismic Local Kneller, Long, van Keken, in revision, EPSL

  19. B-type works well for local S Teleseismic amplitudes too low in models Kneller, Long, van Keken, in revision, EPSL

  20. Andes Marianas SKS arc Anderson, 2004 & in press Pozgay et al.,GJI 2007. trench back arc local

  21. Hypotheses • 3D Flow Mechanisms • Buoyancy driven flow: crustal foundering, melt/water weakening and small scale convection (Behn et al., Science, 2007) • Slab edge effects (Buttles and Olsen, 1998; Kincaid and Griffiths, 2003) • 3D slab rollback and complex return flow (Anderson et al., 2004) • 3D Slab geometry (Hall et al., 2000): variable slab dip, curved trenches or slabs

  22. Variable Slab Dip: Transition to flat slab subduction (Andes) 500 km Trench 13º Full Coupling at 80 km 300 km 30º Slab Contours (50 km) Kneller and van Keken, Nature, in press

  23. Rheology and Finite Element Mesh 10-15 km resolution 2-3 km resolution Kneller and van Keken, Nature, in press

  24. Trench-parallel velocity: ux(cm/yr) Inflow channel with trench-parallel velocity component Magnitude is strongly dependent on rheology Kneller and van Keken, Nature, in press Particle stream lines

  25. Trench-parallel orientation of maximum stretch SKS, Anderson et al., 2004 800 km 17º z = -50 km 10º 500 km ~ 500 km 30º 30º z = -75 km 10º z = -100 km ~ 500 km 30º Kneller and van Keken, Nature, in press Local S, Anderson et al., in press

  26. Kneller and van Keken, Nature, in press Contours from Syracuse & Abers, G3, 2006. Splitting from Pozgay et al., GJI, 2007

  27. Curved Trench (Marianas) 900 km 1500 km 400 km 60º 300 km Trench Slab Contours (50 km) Kneller and van Keken,Nature, in press

  28. Maximum stretch directions 400 km 500 km Splitting: Pozgay et al., GJI, 2007 Contours: Syracuse and Abers, 2006

  29. Fore arc mantle: high Q low T hydrated trench-parallel S-wave splitting Shear wave splitting: B-type fabric partly explains patterns for Honshu, Ryukyu 3D flow likely for Marianas, Central Andes Not clear: Cascadia, Costa Rica - Nicaragua Van Keken, EPSL, 2003

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