1. Seismic velocity gradients across the transition zone
CIDER-06 Group B
Seismic velocity gradients across the transition zone

2. Participants Fabio Cammarano (UCB) Colleen Dalton (Harvard)
Nico DeKoker (Michigan)
Federica Marone (UCB)
Antonio Piazzoni (Munich)
Barbara Romanowicz (UCB)
Yi Wang (SUNY)

3. What have we tried to do?
Compute elastic velocity profiles (Vp and Vs) in the upper mantle based on 3 different mineral physics based methods
Compare two different compositional models: pyrolite and piclogite
Compare fits to seismic data (travel times and modes)
Understand where differences are coming from and assess how fits to seismic data can be improved

4. Compositional models (Ita and Stixrude 1992)
Pyrolite (%)
MgO
SiO
FeO
Al2O
CaO 3.3
Piclogite (%)
MgO
SiO
FeO
Al2O
CaO
Duffy and Anderson, 1989
Anderson and Bass, 1984
Ringwood, 1979

5. Phase diagrams

6. Computation of elastic properties from mineral physics
1) Stixrude and Lithgow-Bertelloni (2005)
Gibbs Free Energy Minimization (a)
2) Piazzoni et al. (2006 – submitted to G-cubed)
Gibbs Free Energy Minimization (b)
3) Weidner and Wang (1998, 2000)
Use directly data from experiments –
All use the same temperature profile (1600K potential temperature)

7. Seismic velocity profiles (Vs)
Piro
Piclo
PREM
S&LB
Weidner
Piazzoni

8. Fit to global dataset of seismic P wave travel times (EHB catalog)

11. Fit to normal mode data: spheroidal modes

12. Fit to normal mode data: toroidal modes

13. Conclusions: Velocities obtained are too slow
Colder temperature?
Velocity gradient in the transition zone is better for piclogite than for pyrolite:
Effect of Ca content?
Possible effect of water: test using a homologous temperature model

14. Fit to global dataset of seismic P wave travel times (EHB catalog)

15. Test with 150K colder potential temperature
Pyro
Piclo
PREM
S&L 1600K
S&L -150K
S&L -150K

16. Conclusions (2) What helps – a combination of:
Colder temperatures
Effect of convection on adiabats
Stagnant slabs?
Increase in Ca content (oceanic crust?)
What can be improved (future):
Elastic properties at high T,P need to be better known
Understand better differences between thermodynamic models
Effect of water through and on Q
Need to include high resolution seismic constraints on velocity jumps at 400 and 660 km.

18. Attenuation profiles