1. Seismic Waveform Tomography Jeroen Tromp

2. Classical Tomography Theoretical limitations due to use of 1D background models Data coverage Pervasive (ab)use of “Crustal corrections”

3. We need abundant high-quality data We also need to harness the data that we already have The solution to gaps in data coverage is not only more data, but also using more of the data we already have This requires sophisticated forward and inverse modeling tools, data assimilation, and computational resources A Marriage of Data and Simulation

4. Challenges in Seismic Tomography Theoretical limitations  Finite-frequency effects have become important

5. P Wave: Finite-Frequency Effects 27 s 18 s 9 s

6. Challenges in Seismic Tomography Data coverage  Uneven global distribution of earthquakes and stations  Amount of usable data is determined by the accuracy of the forward method

7. IRIS

8. Argentina, September 3, 2008, Mw=6.3, depth 571 km Bandpass between 17-60 seconds

9. Challenges in Seismic Tomography Crustal effects  Can be highly nonlinear, thus “crustal corrections” are questionable

10. Global Crustal Thickness Crust2.0 (Bassin et al. 2000)

11. “Adjoint Tomography” Forward simulations and Fréchet derivatives in 3D background models Dramatic increase in usable data, resulting in superior data coverage Iterative model updates No crustal corrections! Ultimately use entire seismograms: full waveform inversion

12. # 1 # 500 all combined FLOPS: FLoating-point OPerations per Seconds Latest trend: GPU computing My Laptop TOP500.org Supercomputing: Exponential Growth 1 billion (10 ) 9 (1 GigaFLOPS) 1 trillion (10 ) 12 (1 TeraFLOPS) 1 quadrillion (10 ) 15 (1 PetaFLOPS) 18 1 quintillion (10 ) (1 ExaFLOPS) 2018  2020 My iPhone Titan, Cray (ORNL) 20 TeraFLOPS Your 2032 Laptop GigaFLOPS Time (years) Your 2032 iPhone

13. Adjoint Tomography of Europe earthquakesstationsiterationssimulationsCPU hours measurement s 1907453017,1002.3 million123,205 Hejun Zhu

14. 200805291546A EU00 EU30 Goal: Fitting frequency-dependent phase and amplitude anomalies in targeted windows automated window selection: FLEXWIN (Maggi et al. 2009)

15. Optimization Taylor expansion: Choose misfit function, e.g., Model update: Gradient update: Optimization: Preconditioned conjugate gradient method L-BFGS quasi-Newton method

17. Wortel & Spakman (2000) Mediterranean-Calabria Paleotectonics

18. Depth 75 km Middle Hungarian line Pannonian Basin Massif Central Central graben Armorican Massif Harz Tornquist-Teisseyre Zone Bohemian massif Central Slovakian volcanic field Eifel hotspot & Rhine graben

19. Depth 625 km Eastern Alpine Tethys Western Alpine Tethys

20. Wortel & Spakman Alps slab Eifel plume Lithospheric delamination

21. 200805291546A EU00 EU30

22. Traveltime Histograms P-SV(Z)P-SV(R)SH(T) Rayleigh(Z)Rayleigh(R)Love(T)

23. ORNL Titan: 2013 #1 Supercomputer 2013 allocation: 100M core hours

24. Goal on Titan: Use all Global Earthquakes! ~6000 events since 1999 with 5.5 ≤ Mw ≤ 7.0 ~50 million measurements!

25. Conclusions Modern numerical methods and computers are used to simulate seismic wave propagation in 3D Earth models Adjoint methods are used to calculate misfit gradients in 3D Earth models We are bridging the gap between high-resolution body-wave tomography and lower resolution inversions based on long-period body waves, surface waves and free oscillations Simultaneous analysis of wavespeeds, attenuation and anisotropy will improve our understanding of temperature, composition, partial melting and water contents within the Earth’s interior