Global adjoint tomography - Model GLAD-M25

Abstract
Building on global adjoint tomography model GLAD-M15, we present transversely isotropic global model GLAD-M25, which is the result of 10 quasi-Newton tomographic iterations with an earthquake database consisting of 1480 events in the magnitude range 5.5 ≤ Mw ≤ 7.2, an almost sixfold increase over the first-generation model. We calculated fully 3-D synthetic seismograms with a shortest period of 17 s based on a GPU-accelerated spectral-element wave propagation solver which accommodates effects due to 3-D anelastic crust and mantle structure, topography and bathymetry, the ocean load, ellipticity, rotation and self-gravitation. We used an adjoint-state method to calculate Fréchet derivatives in 3-D anelastic Earth models facilitated by a parsimonious storage algorithm. The simulations were performed on the Cray XK7 'Titan' and the IBM Power 9 'Summit' at the Oak Ridge Leadership Computing Facility. We quantitatively evaluated GLAD-M25 by assessing misfit reductions and traveltime anomaly histograms in 12 measurement categories. We performed similar assessments for a held-out data set consisting of 360 earthquakes, with results comparable to the actual inversion. We highlight the new model for a variety of plumes and subduction zones.

Citation
Lei, W., Ruan, Y., Bozdağ, E., Peter, D., Lefebvre, M., Komatitsch, D., … Pugmire, D. (2020). Global adjoint tomography—model GLAD-M25. Geophysical Journal International, 223(1), 1–21. doi:10.1093/gji/ggaa253

Acknowledgements
We thank Jeroen Ritsema, Steve Grand and two anonymous reviewers for detailed comments and suggestions which helped to improve an earlier version of the manuscript. This research used resources of the Oak Ridge Leadership Computing Facility, which is a DOE Office of Science User Facility supported under contract DE-AC05-00OR22725. Additional computational resources were provided by the Princeton Institute for Computational Science & Engineering (PICSciE). We acknowledge IRIS (iris.edu) and ORFEUS (orfeus-eu.org) for providing the data used in this study. We thank Ryan Modrak, Ridvan Örsvuran, Frederik J. Simons and James Smith for fruitful discussions, and Caio Ciardelli for implementing the spherical harmonic model expansion. The open source spectral-element software package SPECFEM3D GLOBE and the seismicmeasurement software package FLEXWIN used for this article are freely available via the Computational Infrastructure for Geodynamics (CIG; geodynamics.org). This research was supported by NSF grant 1644826.

Publisher
Oxford University Press (OUP)

Journal
Geophysical Journal International

DOI
10.1093/gji/ggaa253

Additional Links
https://academic.oup.com/gji/article/223/1/1/5841525

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