High coseismic differential stress preserved in the lattice of seismically shocked garnets
Bibliographic record
Abstract
The seismogenic environments build up the highest differential stresses on Earth. Differential stress of as much as hundreds of MPa to few GPa is accumulated during the interseismic loading stage and it is abruptly released in a sequence of fast, high-stress events (earthquake rupture tip propagation, frictional fault slip, thermomechanical interactions) determining large-magnitude, local stress changes on and near the fault plane. A major challenge to obtain a quantification of these stresses is represented by their heterogeneity in space and time. However, they can be exceptionally recorded in exhumed fault rocks bearing pseudotachylytes (quenched coseismic frictional melts).Here, for the first time, we provide a measure of the residual elastic stress preserved in the lattice of seismically shocked garnets crosscut by a pseudotachylyte fault vein by means of HR-EBSD (high-angular resolution electron backscattered diffraction). The thin (3 mm-thick) pristine pseudotachylyte was produced during a single seismic event at mid-crustal conditions (ca. 500 MPa, 500 °C) within felsic gneisses in the hanging wall of the Woodroffe Thrust (Musgrave Ranges, central Australia). Centimetric garnets of the host rock are intensely fractured and extremely comminuted close to the pseudotachylyte. A local enrichment in Mn is associated with healing of the cracks close to the pseudotachylyte and with the growth of epitaxial garnet in the cataclastic portions. HR-EBSD maps (ca. 30 x 50 µm2) were acquired in the garnet at increasing distance from the pseudotachylyte and in a cataclastic domain in contact with it. Residual stresses reach up to 5 – 6 GPa in contact with the pseudotachylyte and decrease to a few hundred MPa in less than a millimeter from it. Similar high stresses are recorded also in the clasts of a cataclasite flanking the pseudotachylyte, while newly grown high-Mn garnet surrounding the clasts records lower stresses. High stress domains in the mapped areas, a few micrometers in size, are bounded by straight bands of stress sign inversion that become less regular and more closely spaced towards the pseudotachylyte. Geometrically necessary dislocations (GND) are more abundant close to the pseudotachylyte and are linked with the high-stress domains.Microstructures, stress gradients and magnitudes all suggest that the extreme residual stresses recorded in proximity of the pseudotachylyte belong to the stage of propagation of the earthquake rupture, in agreement with theoretical predictions of the stress fields at the tip of a propagating fracture. The partial preservation of the stress in the strained lattice of the garnet is made possible by the quasi-instantaneous healing of the cracks that produced a load-bearing framework to maintain the elastic strains and by the presence of high GND densities produced during the high-stress – high-strain rate rupture propagation event.
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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 | 0.000 |
| 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".