Can Lateral Viscosity Contrasts Explain Asymmetric Interseismic Deformation around Strike-Slip Faults?
Bibliographic record
Abstract
Abstract Geodetic studies have shown that deformation rates around several major strike-slip faults are asymmetric. This asymmetry is often explained in terms of a crustal-scale contrast in elastic properties across the fault. Motivated by the fact that elasticity variations for different rock types under similar ambient conditions are gen-erally modest, whereas effective viscosity may vary over orders of magnitude, we have developed earthquake-cycle models to evaluate whether contrasts in viscosity struc-ture and effective plate thickness can explain observed asymmetric surface deforma-tion. We find that an increased plate-thickness contrast results in a more asymmetric surface-velocity profile. Furthermore, for the same plate-thickness contrast, asymme-try of the surface deformation is most pronounced in models with a low-viscosity substrate. Initially, velocities relative to a point on the fault are higher on the side with the thin plate; however, late in the interseismic interval this reverses, and these velocities are higher on the side with the thick plate. Models with a contrast in the substrate viscosity on either side of the fault and a uniform plate thickness show behavior similar to that of the variable-thickness plate models. In both suites of asym-metric models, the surface velocity at the fault varies through the earthquake cycle. This is necessary to reconcile symmetric coseismic deformation, asymmetric interseis-mic deformation, and the requirement of zero strain in the blocks on either side of the fault over an earthquake cycle. Given the modest asymmetry in surface deformation for models capable of producing localized interseismic deformation around the fault (i.e., models with high substrate viscosities), we conclude that lateral contrasts in viscosity or effective plate thickness cannot produce dramatic asymmetries in Global Positioning System surface-velocity profiles across major strike-slip faults.
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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 | 0.001 | 0.003 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.002 | 0.002 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".