A low‐velocity zone atop the transition zone in northwestern Canada
Bibliographic record
Abstract
Seismic studies over the past decade have identified an S wave low‐velocity zone (LVZ) above the transition zone at various locations around the globe. This layer is hypothesized to be a lens of dense, hydrous, silicate melt ponding atop the 410 km discontinuity, beneath the silicate melt‐density crossover predicted to exist within the upper mantle. We have assembled a P and S receiver function data set to quantify the physical properties and geographical extent of the layer in northwestern Canada. Geographic profiles formed from 1‐D migration of receiver functions computed for the Canadian Northwest Experiment (CANOE) and Portable Observatories for Lithospheric Analysis and Research Investigating Seismicity (POLARIS) Slave arrays reveal an LVZ beneath many stations at a nominal depth of ∼340 km. To constrain layer thickness and Poisson's ratio, we performed a grid search over a suite of 1‐D velocity profiles to model the relative delay times of direct conversions and reverberations from the top of the LVZ and 410 km discontinuity, as recorded at the Yellowknife array. In addition, we performed linearized inversion of transmission coefficient amplitudes to estimate S velocity contrasts at the bounding interfaces. The LVZ is characterized by a thickness of ∼36 km with an S velocity contrast of −7.8% and Poisson's ratio of 0.42. Taken at face value, the two latter results require an increase in P velocity into the LVZ. The Poisson's ratio lies well above the IASP91 average of ∼0.29–0.3 for this depth range and favors the presence of high melt or fluid fractions.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| 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 | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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 teacher head, 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".