At 14:46 Japan Standard Time on 11 March 2011, an exceptionally large earthquake ruptured the plate boundary off northeastern Honshu. Strong shaking affected a broad area, and a major tsunami reached communities along the Pacific coast. The event became known as the 2011 Tōhoku earthquake and tsunami.
What happened
The rupture occurred where the Pacific Plate descends beneath the plate carrying northern Japan. The offshore setting did not prevent severe consequences: the movement of the seabed generated a tsunami that caused extensive inundation along parts of Iwate, Miyagi and Fukushima prefectures.
The source page began as coverage of a magnitude 7.3 earthquake on 9 March and its aftershocks. Two days later, the much larger 11 March event transformed the page into a minute-by-minute emergency log. Modern reviews distinguish the 9 March foreshock from the main rupture on 11 March.
Why early reports changed
Initial automated estimates varied as additional seismic stations and waveform data became available. The source recorded successive values near magnitude 7.9, 8.8 and 8.9. Such revision is normal after a very large earthquake because the full rupture can outlast the first processing window.
Early casualty and damage totals also represented only what agencies and newsrooms could confirm at that moment. Communications, access constraints and continuing hazards meant that the scale of the disaster could not be established from the first reports. Speculative economic estimates from the live log have been omitted here.
First-hours reporting timeline
The archive registered a very large offshore earthquake and noted severe shaking in Miyagi Prefecture, together with tsunami warnings for the Pacific coast.
Magnitude estimates were revised upward as more data arrived, indicating an event far larger than the first automatic solution.
Reports indicated that tsunami waves were reaching the coast. The archive repeatedly directed coastal readers to official evacuation instructions.
Flooding and severe disruption were being reported around the Sendai region, while rail and other transport services were suspended.
Emergency reports described widespread fires, building damage and coastal inundation across several prefectures.
Tsunami alerts extended around the Pacific. The live page advised readers to use the warning services relevant to their own country.
The archive emphasized that the available impact picture remained incomplete, particularly in coastal districts of Iwate and Miyagi.
Areas described in the live log
Miyagi Prefecture: The source described the strongest instrumental intensity, severe disruption in and around Sendai, Ishinomaki, Kesennuma and other coastal communities, and extensive tsunami inundation.
Iwate Prefecture: Reports included flooding around coastal settlements, fires, landslides and serious disruption in communities including Miyako, Ōfunato and Rikuzentakata.
Fukushima Prefecture: The live account recorded strong shaking, structural damage, fires and tsunami impacts along the coast. Information changed quickly and remained incomplete during the reporting window.
Ibaraki, Tochigi, Chiba and Tokyo: Reports described strong shaking, transport interruptions, scattered structural damage and fires. Effects differed considerably by location and building condition.
Aftershock sequence
Numerous strong earthquakes followed the main rupture across a long section of the offshore fault system. The table below preserves a concise selection from the source’s Japan Meteorological Agency list. Magnitudes and intensities reflect the values reported at the time.
| Origin time (JST) | Region | Reported magnitude | JMA intensity |
|---|---|---|---|
| 15:06, 11 March | Sanriku offshore | 7.0 | 5− |
| 15:15, 11 March | Ibaraki offshore | 7.4 | 6− |
| 15:26, 11 March | Sanriku offshore | 7.2 | 4 |
| 16:15, 11 March | Fukushima offshore | 6.8 | 4 |
| 16:29, 11 March | Sanriku offshore | 6.6 | 5+ |
| 17:12, 11 March | Ibaraki offshore | 6.4 | 4 |
| 17:19, 11 March | Ibaraki offshore | 6.7 | 4 |
| 17:47, 11 March | Fukushima offshore | 6.0 | 3 |
Times, labels and preliminary values are retained as archive data. Agency catalogs may revise an event after further analysis.
The 9 March foreshock
On 9 March, a magnitude 7.2 earthquake occurred east of Honshu at 02:45 UTC, followed by many moderate and strong aftershocks. Limited tsunami waves were observed, and the initial archive reported comparatively light effects. In retrospect, this event is treated as a foreshock to the much larger rupture two days later.
Reported 9 March parameters
How to read this archive
Live disaster reporting captures uncertainty as well as facts. A later reader should not combine every preliminary statement into a final event record. Magnitude may be recalculated, duplicate aftershocks may be reconciled, place names may be standardized and impact totals may change substantially as field assessments progress.
For present-day safety decisions, use national and local emergency authorities rather than this historical page. If strong or prolonged shaking is felt near a coast, follow local tsunami evacuation guidance without waiting for an archive or news article to update.
Archive categories
This event remains indexed under damaging earthquakes, dangerous earthquakes, tsunamis, aftershocks and in-depth articles.