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Conclusions… Challenge:

Conclusions… Challenge: Seismic waves are affected by variations in temperature, pressure, composition, mineralogy, structure (layering, scales and distribution of multiphase materials, texture, fabric, grain size, etc.) and water content. Conclusions… Challenge:

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Conclusions… Challenge:

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  1. Conclusions… Challenge: Seismic waves are affected by variations in temperature, pressure, composition, mineralogy, structure (layering, scales and distribution of multiphase materials, texture, fabric, grain size, etc.) and water content.

  2. Conclusions… Challenge: Seismic waves are affected by variations in temperature, pressure, composition, mineralogy, structure (layering, scales and distribution of multiphase materials, texture, fabric, grain size, etc.) and water content. 2) There are differences depending upon whether the water is in the form of hydrous melts, hydrous phases, or incorporated into the crystal structure of nominally anhydrous minerals.

  3. Solution: There are ways to distinguish between them Ex/ Increase in Water vs. Temperature S Velocity DECREASE DECREASE P Velocity decrease DECREASE Attenuation INCREASE increase

  4. Solution: There are ways to distinguish between them Ex/ Increase in Water vs. Temperature S Velocity DECREASE DECREASE P Velocity decrease DECREASE Attenuation INCREASE increase (Amounts vary GREATLY depending upon compositions and values of temperature and pressure)

  5. Solution: There are ways to distinguish between them Ex/ Increase in Water vs. Temperature S Velocity DECREASE DECREASE P Velocity decrease DECREASE Attenuation INCREASE increase (Water increase in ringwoodite of 1% would lower S velocities by about 5.4% and P velocities by about 1.5% [Jacobsen et al., 2004; Jacobsen and Smyth, 2006; Karato, 2006]; ----> Water increases P-to-S velocity ratio)

  6. Solution: There are ways to distinguish between them Ex/ Increase in Water vs. Temperature S Velocity DECREASE DECREASE P Velocity decrease DECREASE Attenuation INCREASE increase (Temperature affects on attenuation are greater at higher temperatures and lower pressures)

  7. Solution: There are ways to distinguish between them Ex/ Increase in Water vs. Temperature S Velocity DECREASE DECREASE P Velocity decrease DECREASE AttenuationINCREASE increase 410 Height elevate depress 660 Height depress elevate TZ Width increase decrease

  8. Solution: There are ways to distinguish between them Ex/ Increase in Water vs. Temperature S Velocity DECREASE DECREASE P Velocity decrease DECREASE AttenuationINCREASE increase 410 Height elevate depress 660 Height depress elevate TZ Width increase decrease (Water increase could elevate 410 by 10-30 km, depress the 660 by up to 4 km, and so increase TZ Width [Smyth and Frost, 2002; Hirschmann et al., 2005; Higo et al., 2001])

  9. Solution: There are ways to distinguish between them Ex/ Increase in Water vs. Temperature S Velocity DECREASE DECREASE P Velocity decrease DECREASE AttenuationINCREASE increase 410 Height elevate depress 660 Height depress elevate TZ Width increase decrease (Temperature increase of 400ºC could depress 410 by 30-50 km, elevate the 660 by 7-40 km, so greatly reduce TZ Width [Litasov et al., 2006])

  10. Solution: There are ways to distinguish between them Ex/ Increase in Water vs. Temperature S Velocity DECREASE DECREASE P Velocity decrease DECREASE AttenuationINCREASE increase 410 Height elevate depress 660 Height depress elevate TZ Width increase decrease 410 Thickness broaden sharpen 660 Thickness broaden sharpen

  11. Solution: There are ways to distinguish between them Ex/ Increase in Water vs. Temperature S Velocity DECREASE DECREASE P Velocity decrease DECREASE AttenuationINCREASE increase 410 Height elevate depress 660 Height depress elevate TZ Width increase decrease 410 Thickness broaden sharpen 660 Thickness broaden sharpen (Wet mantle --> broaden 410 by up to 40 km, broaden 660 by up to 8 km [Smyth and Frost, 2002; Hirschmann et al., 2005; Higo et al., 2001])

  12. Solution: There are ways to distinguish between them Ex/ Increase in Water vs. Temperature S Velocity DECREASE DECREASE P Velocity decrease DECREASE AttenuationINCREASE increase 410 Height elevate depress 660 Height depress elevate TZ Width increase decrease 410 Thickness broaden sharpen 660 Thickness broaden sharpen (Hot mantle --> sharpen 410 and 660 by by around 5 km (Helffrich and Bina, 1994)

  13. Most Seismically-Observed Mantle Water is in Subduction Zones (not surprisingly!)

  14. Petro-thermo-mechanical models can now predict what kinds of features we would expect to see seismically Gerya et al. [2006]

  15. Flow and Temperature… Gerya et al. [2006]

  16. P Velocity… Gerya et al. [2006]

  17. S Velocity… Presence of cold, wet plumes predict >20% Poisson ratio variations, as opposed to ~2% variations due to only temperatures Gerya et al. [2006]

  18. Inability of thermal models to explain seismic parameters is seen in subduction zone tomography observations: Wiens et al. [2008]

  19. Thermal Model Predictions Tonga Observations Wiens et al. [2008]

  20. Thermal Model Predictions Tonga Observations Wiens et al. [2008]

  21. Velocity Tomography away from subduction zones also show features that may be associated with water. van der Lee et al. [2008]

  22. van der Lee et al. [2008]

  23. 1 2 3 4 5 van der Lee et al. [2008]

  24. “Reciever Functions” of P-to-S converted phases find LZVs in forearc mantles interpreted as serpentinization from slab-expelled water Tibi et al. [2008]

  25. LVZ S-velocities as low as 3.6 km/s suggest serpentinization of 30-50%, corresponding to chemically bound water contents of 4-6 wt% Tibi et al. [2008]

  26. Kawakatsu and Watada [2008]

  27. Kawakatsu and Watada [2008]

  28. Percentages show S-velocity reductions relative to slab velocities; parentheses show suggested water content in wt%) Kawakatsu and Watada [2008]

  29. The presence of water can determine the magnitude and orientation of seismic anisotropy in olivine

  30. Seismic shear-wave splitting results from Nakajima and Hasegawa [2004]

  31. Geodynamic models suggest the possibility of water just above the 410 discontinuity…. Leahy and Bercovici [2007]

  32. Leahy and Bercovici [2007]

  33. Mantle reverberations show discontinuity depth and impedance Courier and Revenaugh [2007]

  34. Discontinuity depths….. Courier and Revenaugh [2007]

  35. Reflection Coefficients… Results show a LVZ above the 410 with reduced 410 impedance attributed to partial melt from volatile-induced melting. Courier and Revenaugh [2007]

  36. Seismic Arrays (in this case RISTRA) can identify layer velocities from traveltime moveouts. Gao et al. [2007]

  37. Triplication patterns reveal vertical velocity structures Gao et al. [2007]

  38. LVZ above 410 is interpreted as partial melting due to water released from the Transition Zone Water on Top of Transition Zone? Gao et al. [2007]

  39. Water causes increased Seismic Attenuation Stein and Wysession [2003]

  40. Large High-Attenuation region 700-1200 km deep (Q < 100 !!!) with only slightly negative velocities Lawrence and Wysession [2006]

  41. Depth = 1000 km A Vertical Cross-Section through Earth’s mantle at 1000 km depth shows the high-attenuation region above circum-Pacific subducted lithosphere Lawrence and Wysession [2006]

  42. Shieh et al. [1998]

  43. Lawrence and Wysession [2006]

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