Slab morphology in the Cascadia fore arc and its relation to episodic tremor and slip
Bibliographic record
Abstract
Episodic tremor and slip (ETS) events in subduction zones occur in the general vicinity of the plate boundary, downdip of the locked zone. In developing an understanding of the ETS phenomenon it is important to relate the spatial occurrence of nonvolcanic tremor to the principal structural elements within the subduction complex. In Cascadia, active and passive source seismic data image a highly reflective, dipping, low‐velocity zone (LVZ) beneath the fore‐arc crust; however, its continuity along the margin is not established with certainty, and its interpretation is debated. In this work we have assembled a large teleseismic body wave data set comprising stations from northern California to northern Vancouver Island. Using stacked receiver functions we demonstrate that the LVZ is well developed along the entire margin from the coast eastward to the fore‐arc basins (Georgia Strait, Puget Sound, and Willamette Valley). Combined with observations and predictions of intraslab seismicity, seismic velocity structure, and tremor hypocenters, our results support the thesis that the LVZ represents the signature of subducted oceanic crust, consistent with thermal‐petrological modeling of subduction zone metamorphism. The location of tremor epicenters along the revised slab contours indicates their occurrence close to but seaward of the wedge corner. Based on evidence for high pore fluid pressure within the oceanic crust and a downdip transition in permeability of the plate interface, we propose a conceptual model for the generation of ETS where the occurrence and recurrence of propagating slow slip and low‐frequency tremor are explained by episodic pore fluid pressure buildup and fluid release into or across the plate boundary.
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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 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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".