Evidence for an active transtensional Beaufort Range fault in the northern Cascadia forearc
Bibliographic record
Abstract
Geologic records of fault slip in subduction forearcs provide critical data on stress and strain in the upper plate and the seismogenic potential of hazardous faults. However, few active upper-plate faults have been identified in the northern Cascadia forearc. Here we investigate the slip history of the Beaufort Range fault (BRF) on Vancouver Island, BC, Canada, a proposed source of the 1946 M 7.3 Vancouver Island earthquake, the largest recorded in Cascadia. We use recently-collected lidar data, field mapping, and surveying of offset landforms to map the extent of previously unidentified post-glacial (<14 ka) tectonic scarps and reconstruct 3D fault slip vectors. Post-glacial landforms show increasing displacement with age, suggesting at least three Mw~6.5-7.5 earthquakes since ~14 ka, the most recent <4 ka. These displacements suggest the BRF is one of the fastest-slipping faults in the northern Cascadia forearc (0.5-2 mm/yr). Kinematic slip inversions of offset geomorphic piercing lines are consistent with right-lateral transtension along a steeply NE-dipping fault. Because BRF fault geometry and kinematics are similar to the 1946 earthquake, it is a plausible source. The kinematic similarity of millennial and decadal slip data suggests the BRF has accommodated transtension over multiple earthquake cycles.
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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 | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 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".