Dextral slip along the Western Nepal Fault System accommodates significant orogen-parallel shear
Bibliographic record
Abstract
Abstract New mapping in northwestern Nepal documents geomorphic landforms that are truncated and offset by active faults along the Western Nepal Fault System (WNFS), a right-slip fault system that accommodates orogen-parallel strain in the West Nepal Himalaya between Simikot and Tansen. Neotectonic field investigations in this study focus on the northwestern segment of the WNFS in the Jumla and Dolpa districts, where field observations of dextral-oblique slip on the Talphi, Kuri Santha, and Tripurakot faults indicate active deformation within the Himalayan thrust wedge. The surface trace of the Talphi fault is expressed by prominent fault scarps, deflected and offset stream channels, and shutter ridges that delineate an ~40 km long, subvertical, ~N40°W striking fault that traverses areas of high topographic relief. Our field mapping documents truncated and offset fluvial terrace risers that, when combined with Quaternary geochronology, suggest a minimum dextral-oblique slip rate of 2.7 ± 0.6 mm/yr since ca. 130 ka. The Kuri Santha fault strikes subparallel to the Talphi fault, and mapping of offset fluvial terrace treads and Quaternary geochronology suggest a minimum fault slip rate of 1.0 ± 0.2 mm/yr since ca. 43 ka. Approximately 60 km to the southeast, near Tripurakot, shutter ridges provide compelling evidence for dextral displacement along an ~N65°W striking, steeply northeast dipping fault. Several geomorphic features documented along strike of the Talphi, Kuri Santha, and Tripurakot faults are consistent with surface expressions of active structures, suggesting all three faults reach >40 km in length. The similar geometry, kinematics, and proximity of the Talphi, Kuri Santha, and Tripurakot faults is consistent with a kinematic link between the structures, which would imply these three surface-rupturing faults could produce large magnitude earthquakes, a critical contribution to seismic hazard and risk analysis in western Nepal. Our data are consistent with a kinematic linkage between the Karakoram fault and a foreland-ward propagation of orogen-parallel strain. The Talphi, Kuri Santha, and Tripurakot faults also show geometric similarities with splay faults in marine subduction zones that accommodate intra-wedge deformation and produce repeated late Quaternary surface ruptures. Our study underscores the importance of understanding intra-wedge fault splays in mega-thrust fault systems, globally.
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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 | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".