Ambient seismic noise tomography of Canada and adjacent regions: Part I. Crustal structures
Bibliographic record
Abstract
Abstract This paper presents the first continental‐scale study of the crust and upper mantle shear velocity (Vs) structure of Canada and adjacent regions using ambient noise tomography. Continuous waveform data recorded between 2003 and 2009 with 788 broadband seismograph stations in Canada and adjacent regions were used in the analysis. The higher primary frequency band of the ambient noise provides better resolution of crustal structures than previous tomographic models based on earthquake waveforms. Prominent low velocity anomalies are observed at shallow depths (<20 km) beneath the Gulf of St. Lawrence in east Canada, the sedimentary basins of west Canada, and the Cordillera. In contrast, the Canadian Shield exhibits high crustal velocities. We characterize the crust‐mantle transition in terms of not only its depth and velocity but also its sharpness, defined by its thickness and the amount of velocity increase. Considerable variations in the physical properties of the crust‐mantle transition are observed across Canada. Positive correlations between the crustal thickness, Moho velocity, and the thickness of the transition are evident throughout most of the craton except near Hudson Bay where the uppermost mantle Vs is relatively low. Prominent vertical Vs gradients are observed in the midcrust beneath the Cordillera and beneath most of the Canadian Shield. The midcrust velocity contrast beneath the Cordillera may correspond to a detachment zone associated with high temperatures immediately beneath, whereas the large midcrust velocity gradient beneath the Canadian Shield probably represents an ancient rheological boundary between the upper and lower crust.
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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 | 0.002 | 0.004 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".