Thermal control on the updip and downdip extents of megathrust earthquake rupture: revisiting Dr. Roy Hyndman's seminal contributions 30 years later
Bibliographic record
Abstract
How far earthquake ruptures extend updip and downdip along subduction megathrusts has important science and hazard implications. In the Hyndman hypothesis proposed in the 1990s, the updip limit was set by a change in clay mineralogy at 100–150 °C, and the downdip limit by a temperature of ∼350 °C or the serpentinized mantle wedge corner (MWC), whichever was shallower. These limits were based on reported changes in fault friction behaviour with temperature and petrology. Many recent megathrust ruptures extended much beyond these limits, but the core idea of the hypothesis is still of great scientific value. Here, I highlight advances in earthquake science over the past three decades relevant to this subject and explain how the Hyndman hypothesis should be accordingly revised. The key point is that the clayey shallow segment of the megathrust and the MWC segment that is rich in lizardite serpentinite can act as “soft barriers” to seismic slip instead of hard limits. They impede seismic slip but may still participate in the slip while undergoing rate-strengthening, or they may even facilitate the slip by exhibiting dynamic weakening at high enough slip rates. In most subduction zones, antigorite serpentinites exhibit seismic behaviour to allow rupture to occur 10–20 km deeper than the MWC while radiating high-frequency seismic energy. In very warm subduction zones, seismic rupture is limited to be shallower than the MWC by thermally activated creep, and the ∼350 °C limit approximately holds. In this situation, the thermal and petrologic conditions at the MWC harbour Episodic Tremor and Slip.
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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 | 0.002 | 0.003 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.003 |
| Scholarly communication | 0.002 | 0.003 |
| Open science | 0.001 | 0.002 |
| Research integrity | 0.001 | 0.003 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
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".