Seismicity Relocation and Fault Structure Near the Leech River Fault Zone, Southern Vancouver Island
Bibliographic record
Abstract
Abstract Relatively low rates of seismicity and fault loading have made it challenging to correlate microseismicity to mapped surface faults on the forearc of southern Vancouver Island. Here we use precise relocations of microseismicity integrated with existing geologic data to present the first identification of subsurface seismogenic structures associated with the Leech River fault zone on southern Vancouver Island. We used the HypoDD double‐difference relocation method to relocate 1,253 earthquakes reported by the Canadian National Seismograph Network catalog from 1992 to 2015. Our results reveal an ~8–10 km wide, NNE dipping zone of seismicity representing a subsurface structure along the eastern 30 km of the terrestrial Leech River fault zone and extending 20 km farther eastward offshore, where the fault bifurcates beneath the Juan de Fuca Strait. Using a clustering analysis, we identify secondary structures within the NNE dipping fault zone, many of which are subvertical and exhibit right‐lateral strike‐slip focal mechanisms. We suggest that the arrangement of these near‐vertical dextral secondary structures within a more general NE dipping fault zone, located 10–15 km beneath the Leech River fault as imaged by LITHOPROBE, may be a consequence of the reactivation of this fault system as a right‐lateral structure in crust with a preexisting NNE dipping structural fabric. Our results provide the first confirmation of active terrestrial crustal faults on Vancouver Island using a relocation method. We suggest that slowly slipping active crustal faults, especially in regions with preexisting foliations, may result in microseismicity along fracture arrays rather than along single planar structures.
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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 | 0.001 | 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".