Early Postseismic Deformation of the 29 July 2021 Mw8.2 Chignik Earthquake Provides New Constraints on the Downdip Coseismic Slip
Bibliographic record
Abstract
On 29 July 2021, an Mw 8.2 megathrust earthquake struck the Alaska Peninsula. Quantifying the coseismic slip and the afterslip that followed this earthquake provides us the opportunity to clarify the megathrust slip budget and the earthquake hazard potential there. However, the estimated coseismic slip distribution inversion result is strongly affected by assumptions made in the inversion. The spatial pattern of stress-driven afterslip is mainly controlled by the coseismic slip distribution, so that it can provide new information about the coseismic slip distribution and is useful to assess the assumptions made in the coseismic inversion. The orientation and relative magnitudes of postseismic displacements at sites on the Alaska Peninsula require that the afterslip be concentrated ~130km from the trench. As a result, coseismic slip models including slip at that distance or less to shore, predict postseismic deformation that systematically misfits the observations. A narrower coseismic rupture plane with an abrupt downward termination of slip provides a much better fit to the observed postseismic signal than models where the slip tapers gently with depth. We considered multiple different viscoelastic relaxation models and find that these conclusions about the coseismic model are required regardless of the viscoelastic relaxation models used. The contribution of viscoelastic relaxation to the observed signal is not negligible, and the early postseismic observations are best reproduced with a model that features a 50 km thick elastic lithosphere for the overriding plate, and an elastic cold nose to the mantle wedge.
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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) | 0.001 | 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) | 0.002 | 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".