Evidence of Localized Failure Along Altered Basaltic Blocks in Tectonic Mélange at the Updip Limit of the Seismogenic Zone: Implications for the Shallow Slow Earthquake Source
Bibliographic record
Abstract
Abstract Field studies have led to several interpretations on the mechanics behind slow earthquake phenomena downdip of the seismogenic zone. To date, field studies have not examined the shallow subduction interface which may also host slow earthquake phenomena. We examine a subduction mélange exhumed from conditions representing the source of shallow slow earthquake phenomena. The mélange consists of a shale matrix containing rigid blocks, including basalt which is altered along the margins. Cataclasite‐bearing faults attest to localized faulting along the altered margins of basaltic blocks, concurrent with distributed shear in the shale matrix. These cataclasite‐bearing faults link individual blocks. Microstructures show mutually crosscutting tensile and shear veins, consistent with failure having occurred at, or near, lithostatic pore fluid pressures. We model the stress concentrations around the altered margins of basaltic blocks during distributed shear and show that frictional failure of the altered basalt is predicted to occur at lower imposed strain rates than frictional failure of the shale, favoring fault development along block margins. Calculations of critical nucleation lengths for the blocks show they would fail dynamically at hydrostatic pore fluid pressures, producing microearthquakes. At near‐lithostatic pore fluid pressures, block lengths are below the critical nucleation length for dynamic failure and may produce slow earthquake phenomena. Mixing of velocity‐weakening blocks into a viscously flowing, velocity‐strengthening matrix may serve as a common mechanism for slow earthquake phenomena updip and downdip of the seismogenic zone.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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".