A Decade of Data-Driven Analysis (2016-2026) | 17 Earthquakes M6.4+ | 2026-04-05
USGS Earthquake Database
Open-Meteo Weather API
Claude Opus 4.6 Analysis
Taiwan Study Methodology Analog
Disclaimer: As with the Taiwan study, this is an exploratory data analysis. Sample size is limited (only 17 M6.4+ events), and conclusions are for reference only.
*2026 data through April 5. The 2025 spike is primarily from the Dec 8 Aomori earthquake and its aftershock sequence.
| Date | Mag | Depth | Location | Notes |
|---|---|---|---|---|
| 2025-12-08 | 7.6 | 41 km | Off Aomori | Decade's largest, tsunami warning issued |
| 2024-01-01 | 7.5 | 10 km | Noto Peninsula | New Year's Day earthquake, severe damage |
| 2022-03-16 | 7.3 | 41 km | Off Fukushima | 3/11 aftershock zone |
| 2021-02-13 | 7.1 | 44 km | Off Fukushima | 3/11 aftershock zone |
| 2024-08-08 | 7.1 | 24 km | Hyuga-nada | Nankai Trough advisory |
| 2016-04-15 | 7.0 | 10 km | Kumamoto | Kumamoto earthquake |
| 2021-03-20 | 7.0 | 43 km | Off Miyagi | — |
| 2021-05-01 | 6.9 | 43 km | Off Miyagi-Onagawa | — |
| 2016-11-21 | 6.9 | 9 km | Fukushima-Namie | — |
| 2025-01-13 | 6.8 | 39 km | Miyazaki | — |
| 2025-11-09 | 6.8 | 18 km | Off Iwate | — |
| 2016-01-14 | 6.7 | 46 km | Hokkaido-Shizunai | — |
| 2025-12-12 | 6.7 | 19 km | Off Iwate-Kuji | Aomori aftershock |
| 2018-09-05 | 6.6 | 35 km | Hokkaido-Iburi | Island-wide blackout |
| 2025-12-08 | 6.6 | 19 km | Off Aomori | Aftershock |
| 2026-03-26 | 6.5 | 10 km | Off Iwate | — |
| 2019-06-18 | 6.4 | 12 km | Yamagata-Tsuruoka | — |
Below is the weather summary for the 15 days (day -15 to day -1) preceding each M6.4+ earthquake:
| Quake Date | Mag | Location | Avg Temp °C | Total Rain mm | Rainy Days | Heavy Rain | Avg Press hPa | Press Range hPa | Avg Humid % |
|---|---|---|---|---|---|---|---|---|---|
| 2016-01-14 | 6.7 | Hokkaido | -5.3 | 6.1 | 2 | 0 | 1012.6 | 14.4 | 76.3 |
| 2016-04-15 | 7.0 | Kumamoto | 14.8 | 102.2 | 7 | 1 | 1012.2 | 10.8 | 84.5 |
| 2016-11-21 | 6.9 | Fukushima | 8.3 | 29.5 | 3 | 0 | 1013.7 | 17.9 | 76.3 |
| 2018-09-05 | 6.6 | Hokkaido | 20.0 | 97.7 | 7 | 2 | 1008.3 | 11.5 | 83.3 |
| 2019-06-18 | 6.4 | Yamagata | 17.9 | 73.5 | 7 | 1 | 1001.6 | 24.2 | 79.7 |
| 2021-02-13 | 7.1 | Off Fukushima | 1.1 | 34.8 | 4 | 0 | 1008.7 | 26.8 | 65.9 |
| 2021-03-20 | 7.0 | Off Miyagi | 5.4 | 80.6 | 5 | 1 | 1013.0 | 24.4 | 67.8 |
| 2021-05-01 | 6.9 | Off Miyagi | 10.9 | 81.9 | 5 | 1 | 1008.8 | 30.4 | 67.0 |
| 2022-03-16 | 7.3 | Off Fukushima | 4.3 | 18.8 | 2 | 0 | 1007.3 | 19.5 | 70.4 |
| 2024-01-01 | 7.5 | Noto | 4.2 | 130.4 | 9 | 3 | 1020.5 | 21.0 | 74.7 |
| 2024-08-08 | 7.1 | Hyuga-nada | 29.3 | 14.8 | 4 | 0 | 1007.1 | 11.2 | 77.3 |
| 2025-01-13 | 6.8 | Miyazaki | 5.4 | 22.3 | 3 | 0 | 1020.1 | 12.1 | 62.3 |
| 2025-11-09 | 6.8 | Off Iwate | 11.1 | 94.3 | 9 | 1 | 1012.8 | 30.8 | 77.5 |
| 2025-12-08 | 7.6 | Off Aomori | 6.5 | 14.0 | 3 | 0 | 1008.9 | 17.6 | 78.1 |
| 2025-12-08 | 6.6 | Aomori (aftershock) | 6.5 | 14.0 | 3 | 0 | 1008.9 | 17.6 | 78.1 |
| 2025-12-12 | 6.7 | Off Kuji | 5.5 | 17.7 | 3 | 0 | 1009.2 | 16.7 | 76.0 |
| 2026-03-26 | 6.5 | Off Iwate | 5.2 | 5.9 | 0 | 0 | 1013.1 | 15.9 | 66.2 |
The control group consists of 18 randomly selected "no major earthquake" dates (evenly distributed across 2016-2025 seasons), using the same 15-day weather window.
The 15-day pressure range (max-min) averaged 19.0 hPa before earthquakes vs. 15.7 hPa for controls. This is the most consistent finding shared by both countries.
Several major earthquakes showed extreme pressure ranges:
Japan's winter-spring seasons experience alternating continental cold air masses and low-pressure systems, making pressure variations inherently intense. But these values far exceed same-season controls. The Taiwan study also observed elevated pressure ranges (10.7 vs 9.3 hPa), showing consistent patterns between both countries.
Average 15-day pre-earthquake rainfall was 49.3mm, 30% lower than the control group's 70.7mm. This is completely opposite to Taiwan's result (+54%).
However, the Jan 1, 2024 Noto M7.5 had 130.4mm of pre-quake rainfall (highest), and the Apr 2016 Kumamoto M7.0 had 102.2mm — not all major earthquakes occurred during dry periods.
Japan's major earthquakes skew toward winter, and Japan's winters (except Japan Sea side snow regions) have lower precipitation than summer-autumn. This difference likely reflects seasonal effects primarily.
Of 17 M6.4+ earthquakes, 8 occurred in winter (Dec-Feb) (47%), 4 in spring (Mar-May) (24%), totaling 71% in winter-spring.
Taiwan's M6.0+ also showed 78% in winter-spring. Both countries exhibit a strong winter-spring preference.
The 6.5°C average temperature difference is largely explained by this seasonal preference.
Japan's pre-earthquake average pressure range was 19.0 hPa vs. Taiwan's 10.7 hPa (nearly double).
This reflects Japan's mid-to-high latitude position, where winter low-pressure systems are more intense. It also explains why the pressure range "signal" is more pronounced in Japan.
Notable: 4 of the 5 earthquakes with pressure ranges exceeding 20 hPa occurred in the Tohoku region (Fukushima-Miyagi-Iwate area), which is the 3/11 earthquake aftershock zone. These earthquakes may be fundamentally tectonic-force driven, with pressure merely coinciding seasonally.
The Jan 1, 2024 Noto Peninsula M7.5 earthquake was preceded by 130.4mm of rainfall (including snowmelt) in 15 days, with 3 days of heavy rain (>20mm).
The Noto Peninsula is on the Japan Sea side, receiving heavy snowfall in winter. A 2024 MIT study used northern Japan as an example to demonstrate that heavy snowfall can increase underground fracture fluid pressure and induce earthquake swarms.
The Noto earthquake is the most compelling potential real-world case for that theory in a destructive earthquake.
| Indicator | Taiwan M6.0+ (18 events) | Japan M6.4+ (17 events) | Consistency |
|---|---|---|---|
| Winter-Spring % | 78% | 71% | Consistent ✓ |
| Pressure Range Diff | +15% | +21% | Consistent ✓ |
| Lower Temperature | -4.3°C | -6.5°C | Consistent ✓ (seasonal effect) |
| Rainfall Diff | +54% | -30% | Contradictory ✗ |
| Humidity Diff | +3.8% | -4.5% | Contradictory ✗ |
| Calm weather for largest? | Yes (M7.4 Hualien) | No (M7.6 Aomori, range 17.6) | Inconsistent |
Consistent patterns across both countries:
Contradictory patterns across both countries:
Rainfall and humidity show opposite directions in both countries, confirming they are not earthquake precursors but byproducts of seasonal effects.
However, pressure range is elevated in both Taiwan (+15%) and Japan (+21%).
Does this reflect atmospheric pressure changes exerting additional minor triggering force on faults already near critical state? This warrants further study.
Data sources: USGS Earthquake Catalog API | Open-Meteo Historical Weather API | Japan Meteorological Agency | MIT 2024 Snow-Earthquake Study