Complex postseismic vertical motion following megathrust earthquakes explained by simple mechanisms
Bibliographic record
Abstract
Postseismic deformation following large megathrust earthquakes is widely observed with geodetic measurements and coastal geological investigations and contains important information on subduction zone rheology and megathrust slip behaviour. Short-term (a few years) horizontal deformation exhibits a consistent pattern common to almost all large megathrust earthquakes. For example, the coastal area moves consistently in the seaward direction, but the trench area moves in the landward direction. The horizontal deformation is readily explained by the effects of viscoelastic relaxation (VER) of earthquake-induced stress and afterslip. However, the vertical deformation exhibits greater complexity. For example, the sense of coastal deformation varies not only between different earthquakes but also along strike for the same earthquake. In this work, by separately modelling the VER and afterslip processes of synthetic and real subduction earthquakes, we show that the vertical motion can be explained in a simple manner in the same conceptual framework as for the horizontal motion, although the vertical motion is more sensitive to details of the rheological structure and afterslip. VER results in a long-wavelength, tri-segment deformation pattern consisting of near-trench uplift, midway subsidence, and near-arc uplift. The near-trench uplift and midway subsidence follow coseismic uplift and subsidence, respectively, and are both controlled by the viscosity of the sub-slab oceanic mantle. The near-arc uplift results from viscoelastic relaxation in the presence of a cold and elastic forearc mantle wedge corner (the cold nose) and is controlled by the viscosity of the hot part of the mantle wedge beneath the arc and back arc (Luo & Wang, 2021). In contrast to VER, each afterslip patch results in a local bi-modal pattern of uplift and subsidence dominated by elastic deformation, with variable wavelengths depending on the location and size of the afterslip. The complexity in postseismic vertical motion arises mainly from the heterogeneity and site-specific nature of afterslip (Luo & Wang, 2022). If observations are made near the rupture area, the observed vertical postseismic motion can be very complex, because the effects of heterogeneous afterslip around or within the rupture zone can obscure or conceal the pattern of near-trench uplift and midway subsidence due to VER. Farther away from the rupture area, the observed postseismic deformation mainly reflects the contribution of VER, and near-arc uplift appears to be ubiquitous. Separating the common VER process and the site-specific afterslip effect helps to constrain mantle rheology and illuminate fault slip behaviour. Our work also has strong implications for deciphering paleoseismic estimates of coastal motion associated with ancient earthquakes to understand coseismic vs. postseismic contribution.References:Luo, H., & Wang, K. (2021). Postseismic geodetic signature of cold forearc mantle in subduction zones. Nature Geoscience, 14(2), 104-109. https://doi.org/10.1038/s41561-020-00679-9Luo, H., & Wang, K. (2022). Finding simplicity in the complexity of postseismic coastal uplift and subsidence following great subduction earthquakes. Journal of Geophysical Research: Solid Earth, 127(10), e2022JB024471. https://doi.org/10.1029/2022JB02447
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 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".