Detection of a D″ discontinuity in the south Atlantic using PKKP
Bibliographic record
Abstract
A strong arrival in the early coda of major‐arc PKKPab is observed on recordings of earthquakes in the Banda Sea region from the short‐period, small‐aperture Yellowknife array. The arrival has a move‐out close to PKKPab with an average delay of ∼12 s. We show that the phase is most likely an underside reflection from a D″ discontinuity above the PKKP reflection point at the core‐mantle boundary beneath the southern Atlantic on the edge of the African superplume. Differential travel times between PKKPab and PKdKP (the underside reflection at the D″ discontinuity) is used to constrain potential D″ velocity models. The high amplitude of PKdKP requires proximity to the b‐caustic adding further velocity control. We find that a P‐velocity model with a sharp positive velocity jump ∼280 km above the core‐mantle boundary, and a negative velocity gradient closer to the core‐mantle boundary, fits the data well.
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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 | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
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".