Three‐dimensional structure from feathered two‐dimensional marine seismic reflection data: The eastern Nankai Trough
Bibliographic record
Abstract
For a typical two‐dimensional (2‐D) marine multichannel seismic reflection survey, cross currents cause receiver cable side drift, and data collection becomes a limited swath 3‐D survey. Processing of swath marine survey data using standard 2‐D imaging procedures can create spurious discontinuities and wipeouts in the images of reflection events. These anomalies are commonly attributed to geology and tectonics during interpretation. We show how discontinuous reflections and wipeouts are created wherever subsurface structures have significant cross‐profile dip. We also show that more accurate imaging can be achieved by cross‐dip processing, which takes into account the 3‐D character of the data and of the geology. The final products are a much improved stack, determinations of structural dips at right angles to the survey line, and an improved velocity model. We apply this cross‐dip processing to data from the eastern Nankai Trough, SW Japan. Improved imaging combined with the new cross‐dip information allows us to constrain better the 3‐D character of the deformation in the accretionary prism and oceanic crust. In particular, the extracted structural cross‐dip values provide evidence that supports two hypotheses related to the underthrusting of a large oceanic ridge (Paleo‐Zenisu ridge) underneath the accretionary wedge: (1) Parts of the accretionary wedge basins have been uplifted and deformed due to the subduction of a volcano on the ridge. (2) The early phase of oceanic lithosphere shortening, which produced the underthrusted Paleo‐Zenisu ridge, was related to N‐S compression oblique to the general plate motion in this region.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.002 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".