The limitations of time migration and trace stretch in the presence of lateral velocity gradients
Bibliographic record
Abstract
This paper quantifies the imaging errors that result from the assumptions of time migration and a preliminary, laterally-variable "stretch" of the data, in the presence of lateral velocity gradients. The analysis is restricted to media that are approximately homogeneous in the vertical direction, with dip in the same direction as for the velocity gradient. It is shown that a time migration that explicitly recognizes the lateral variation in velocity results in underestimation of steep dips by only a few degrees, even for large gradients of 0.1 s"1. A preliminary stretch of the data, followed by time migration and stretch removal, however, results in a net overestimation of moderate dips by a few degrees and overestimation of steep dips by 15° or more. The errors increase with increasing gradient and decreasing average velocity.
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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 | 0.009 | 0.045 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.002 |
| Scholarly communication | 0.002 | 0.004 |
| Open science | 0.002 | 0.002 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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".