An unconsidered source of earthquakes and tsunamis from the Kanto region of Japan
Bibliographic record
Abstract
The assessment of seismic hazards along subduction zone coastlines provides important information regarding the frequency and magnitude of earthquakes and tsunamis that can be expected in the future. Unlike many subduction zone coastlines that involve one tectonic plate subducting under another, seismic hazard assessments for the Kanto region of Japan are complicated by the presence of a nearby triple junction; where one continental (CON) and two oceanic plates (PHS, PAC) collide. The CON/PHS (Sagami Trough) and CON/PAC (Japan Trench) boundaries are recognized earthquake sources. However, historical and geological evidence of a large PHS/PAC (Izu-Bonin Trench) earthquake has been lacking and decades worth of instrumental data point to low seismicity along this boundary. Here we show that two unusually large tsunamis are evidenced by sandy deposits preserved along 50 km of coastline in the Kanto region. The oldest of them, deposited about 1,000 years ago, contains evidence consistent with tsunami deposits reported elsewhere (e.g., marine foraminifera, rip-up clasts, pebbles, erosional base) and represents a previously unknown prehistoric earthquake. In computer simulations, this earthquake deposited sand that extended too far inland to represent any known historical earthquake originating from the CON/PHS and CON/PAC boundaries alone. Rather, the greater inland inundation points to significantly greater displacement on the CON/PHS and CON/PAC boundaries, which may be unrealistic, or much smaller displacement along the previously unconsidered PHS/PAC megathrust. This plate-boundary fault adds another source for earthquakes in Tokyo and tsunamis in the Pacific Ocean.
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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 | 0.002 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 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".