Injection veins as evidence of coseismic pore-pressure spikes from the Muddy Mountain thrust, southern Nevada, USA
Bibliographic record
Abstract
Abstract High pore pressure in faults is invoked as a weakening mechanism essential for fault slip, earthquake triggering, heat transport, and fluid and chemical cycling. Eighty years ago, the long-standing paradox surrounding the mechanical behavior of low-angle thrusts in tectonics and fault mechanics was resolved by invoking the effects of high pore pressure on reducing sliding resistance. However, observational structural criteria for past pore-pressure anomalies in natural fault rocks can be controversial because there is no agreement on how to interpret the rock record. The Muddy Mountain thrust in southern Nevada, USA, is part of the regional middle to Late Cretaceous Sevier orogenic front and preserves evidence of paleoseismic slip. The thrust juxtaposed an imbricated Paleozoic carbonate succession above Jurassic and Cretaceous sandstone, molasse, and conglomerate. Multiple crosscutting relations between principal slip surfaces and fault-rock injections record repeated coseismic pressurization events. Abundant ≤10-m-high injections containing centimeter-scale clasts of footwall and fault-core rock provide conclusive evidence of transient high pore pressure in the Muddy Mountain thrust during seismic slip. The injections have grain structures consistent with rapid emplacement by turbulent flow that transitions to laminar flow along the injections. These structures preserve evidence of transient fluid pressure gradients associated with fault zone pressurization. Coseismic pressurization allowed the Muddy Mountain thrust to slip at a low dip-angle in large earthquakes.
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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 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 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".