Global adjoint tomography: first-generation model

Journal Article · Sun Oct 02 00:00:00 EDT 2016 · Geophysical Journal International

DOI:https://doi.org/10.1093/gji/ggw356· OSTI ID:1337854

Bozdağ, Ebru ^[1]; Peter, Daniel ^[2]; Lefebvre, Matthieu ^[3]; Komatitsch, Dimitri ^[4]; Tromp, Jeroen ^[5]; Hill, Judith ^[6]; Podhorszki, Norbert ^[6]; Pugmire, David ^[6]

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1. Univ. of Nice Sophia Antipolis, Valbonne (France). Lab. Géoazur
2. King Abdullah Univ. of Science and Technology (KAUST), Thuwal (Saudi Arabia). Extreme Computing Research Center
3. Princeton Univ., Princeton, NJ (United States). Dept. of Geosciences
4. Aix-Marseille Univ., Marseille (France). LMA, CNSRS UPR
5. Princeton Univ., Princeton, NJ (United States). Dept. of Geosciences and Program in Applied and Computational Mathematics
6. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States).

We present the first-generation global tomographic model constructed based on adjoint tomography, an iterative full-waveform inversion technique. Synthetic seismograms were calculated using GPU-accelerated spectral-element simulations of global seismic wave propagation, accommodating effects due to 3-D anelastic crust & mantle structure, topography & bathymetry, the ocean load, ellipticity, rotation, and self-gravitation. Fréchet derivatives were calculated in 3-D anelastic models based on an adjoint-state method. The simulations were performed on the Cray XK7 named ‘Titan’, a computer with 18 688 GPU accelerators housed at Oak Ridge National Laboratory. The transversely isotropic global model is the result of 15 tomographic iterations, which systematically reduced differences between observed and simulated three-component seismograms. Our starting model combined 3-D mantle model S362ANI with 3-D crustal model Crust2.0. We simultaneously inverted for structure in the crust and mantle, thereby eliminating the need for widely used ‘crustal corrections’. We used data from 253 earthquakes in the magnitude range 5.8 ≤ M_w ≤ 7.0. We started inversions by combining ~30 s body-wave data with ~60 s surface-wave data. The shortest period of the surface waves was gradually decreased, and in the last three iterations we combined ~17 s body waves with ~45 s surface waves. We started using 180 min long seismograms after the 12th iteration and assimilated minor- and major-arc body and surface waves. The 15th iteration model features enhancements of well-known slabs, an enhanced image of the Samoa/Tahiti plume, as well as various other plumes and hotspots, such as Caroline, Galapagos, Yellowstone and Erebus. Furthermore, we see clear improvements in slab resolution along the Hellenic and Japan Arcs, as well as subduction along the East of Scotia Plate, which does not exist in the starting model. Point-spread function tests demonstrate that we are approaching the resolution of continental-scale studies in some areas, for example, underneath Yellowstone. Here, this is a consequence of our multiscale smoothing strategy in which we define our smoothing operator as a function of the approximate Hessian kernel, thereby smoothing gradients less wherever we have good ray coverage, such as underneath North America.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF)
• Sponsoring Organization: DOE Office of Science (SC)
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 1337854
• Journal Information: Geophysical Journal International, Vol. 207, Issue 3; ISSN 0956-540X
• Publisher: Oxford University Press
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
body waves
surface waves and free oscillations
seismic anisotropy
seismic tomography
computational seismology
wave propagation
waveform inversion