Global and regional waveform tomography with massive datasets: new insights into the structure and evolution of the continents
Bibliographic record
Abstract
Waveform inversion was introduced in global seismic imaging in the early days of seismic tomography, in the beginning of the 1980s. Thanks to the continual improvements in the data sampling and methodology since then, waveform tomography has been getting more and more effective in extracting structural information from seismic records and producing detailed 3D models of the Earth’s crust and upper mantle. Today, tomography’s original problems relating to the large-scale Earth structure have been solved: the structure at the scale of thousands of kilometres is remarkably consistent across recent global models. Resolution of the imaging is now at hundreds of kilometres, the scale of tectonic units and major tectonic and magmatic processes. This has opened a new chapter for waveform tomography. It now fuels discoveries on the structure of individual cratons, evolution of cratons in general, origins of intraplate volcanism, plume-lithosphere interactions and other processes. In continents, high-resolution tomography can now map the deep boundaries of different tectonic blocks with useful accuracy. A global comparison with geological data shows that, as a rule, Archean crust is underlain by thick (180-250 km), cratonic mantle lithosphere. This mantle lithosphere is likely to be of the Archean age as well, as often evidenced by mantle xenoliths. Where Archean crust is unexposed (covered by sediments), its presence can be inferred from the presence of the cratonic mantle lithosphere, imaged by tomography. A growing number of previously unknown cratons in different continents are now being discovered by waveform tomography. The lateral extent of other cratons, hypothesized previously, can now be established. The lithosphere of most known cratons has been remarkably stable since its Archean formation, thanks to its compositional buoyancy and mechanical strength. In some instances, however, cratonic lithosphere is known to have been eroded. This is inferred from the existence of the thick lithosphere in the past, as evidenced by diamondiferous kimberlites, and its absence at present, as evidenced by seismic imaging. Waveform tomography of continents now reveals more and more occurrences of this process and offers new insights into its mechanisms. References Celli, N.L., S. Lebedev, A.J. Schaeffer, C. Gaina. African cratonic lithosphere carved by mantle plumes. Nature Communications, 11, 92, doi:10.1038/s41467-019-13871-2, 2020. Schaeffer, A. J., S. Lebedev. Global heterogeneity of the lithosphere and underlying mantle: A seismological appraisal based on multimode surface-wave dispersion analysis, shear-velocity tomography, and tectonic regionalization. In: "The Earth's Heterogeneous Mantle," A. Khan and F. Deschamps (eds.), pp. 3–46, Springer Geophysics, doi:10.1007/978-3-319-15627-9_1, 2015. Steinberger, B., E. Bredow, S. Lebedev, A. Schaeffer, T. H. Torsvik. Widespread volcanism in the Greenland-North Atlantic region explained by the Iceland plume. Nature Geoscience, 12, 61–68, doi:10.1038/s41561-018-0251-0, 2019.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.006 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.003 | 0.005 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.002 | 0.003 |
| Open science | 0.001 | 0.002 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".