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. Van Keken, EPSL, 2003 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

3. Van Keken, EPSL, 2003 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

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

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

8. From Hyndman & Peacock EPSL 2003

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

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

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

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

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

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

18. Local teleseismic 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. Pozgay et al.,GJI 2007. trench arc back arc Andes Anderson, 2004 & in press Marianas SKS 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) 13º 30º Full Coupling at 80 km 500 km 300 km Trench Slab Contours (50 km) Kneller and van Keken, Nature, in press

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

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

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

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

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

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

29. Van Keken, EPSL, 2003 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