The Role of Deformation Bands in Dictating Poromechanical Properties of Unconsolidated Sand and Sandstone
Bibliographic record
Abstract
Abstract Cataclastic shear bands in sands and sandstones are typically stronger, stiffer, and exhibit lower permeability than the surrounding matrix, and therefore act as barriers to fluid flow. Previous work has quantified the reduction in permeability associated with these features; however, little is known about the role of shear band structure in controlling the way they impact permeability and elastic properties. Here, we report on a suite of laboratory measurements designed to measure the poromechanical properties for host material and natural shear bands, over effective stresses from 1–65 MPa. In order to investigate the role of host material properties in controlling poromechanical evolution with stress, we sampled shear bands from two well‐studied sandstones representing structurally distinct end‐members: a poorly cemented marine terrace sand from the footwall of the McKinleyville thrust fault in Humboldt County, California, and a strongly‐cemented sandstone from the hanging wall of the Moab Fault in Moab, Utah. The permeability‐porosity trends are similar for all samples, with permeability decreasing systematically with increasing effective stress and decreasing porosity. The permeability of the host material is consistently >1 order of magnitude greater than the shear bands for both localities. For the unconsolidated case, shear bands are less permeable and stiffer than the host material, whereas for the consolidated case, shear bands are slightly less permeable, and wave speeds are slower than in the host. We attribute the differences between the McKinleyville and Moab examples to changes in structure of the nearby host material that accompanied formation of the shear band.
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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 | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 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".