Using Episodic Tremor and Slip to Characterize Subduction Under Vancouver Island
Bibliographic record
Abstract
The tectonic behavior of the northernmost part of the Cascadia Subduction Zone (CSZ), near the boundary between the Juan de Fuca and Explorer plates, is poorly characterized. A previous study was unable to find geodetically detectable slip accompanying tremor under northern Vancouver Island using long-term average Episodic Tremor and Slip (ETS) velocities [Bartlow, 2020]. However, the methods used previously required tremor counts in the Pacific Northwest Seismic Network catalog to surpass a specified threshold to be considered an ETS event. By studying individual ETS events in more detail, we have been able to detect slip accompanying tremor under Northern Vancouver Island, but the amplitudes of both are small compared to those detected in southern Vancouver Island and the rest of Cascadia. Modifying the methods of Bartlow [2020] to allow the tremor count threshold defining an ETS event to vary with respect to location results in long-term average ETS velocities that detect slip that was previously undetected. Additionally, methods incorporating the Akaike Information Criterion (AIC) were tested, as AIC is a mathematical criterion often used to select the best fit model out of a pool of models. Isolating slow slip motion allows us to study the overall plate motion without modeling any other sources of constant tectonic deformation. This study aims to characterize the apparent segmentation boundary seen in the tremor data between northern and southern Vancouver Island, which may imply slower subduction underneath northern Vancouver Island. This boundary is in proximity to the historical definition of the Nootka Fault Zone (NFZ), but there have been recent papers contradicting one another on the extent and angle of the NFZ [Merrill et al., 2022, Hutchinson et al., 2023]. Additionally, this area of Cascadia corresponds with known propagator wakes and variable subducting slab dip angle [Wilson, 2002, Carbotte et al., 2024]. Using information gained by studying ETS in the region, this study proposes the presence of a sliver between the Explorer and Juan de Fuca plates that is still subducting, but at a slower rate than the Juan de Fuca.
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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 | 0.002 |
| 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 | 0.000 |
| 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".