M6.9 Earthquake 30 km SSE of Onagawa Ch?, Japan — May 1, 2021
2021-05-01 01:27:27 UTC (2021-05-01) · approx. 10:27 AM UTC+9 local
Felt by 274 people across surrounding communities. Maximum shaking intensity MMI 6.4 (very strong).
On May 1, 2021 at 01:27 UTC, a magnitude 6.9 shallow crustal earthquake struck 30 km SSE of Onagawa Ch?, Japan, at a depth of 43.0 km and coordinates 38.1997°, 141.5973°. The earthquake was reported felt by 274 peopleacross surrounding communities, with a maximum shaking intensity of Modified Mercalli Intensity (MMI) 6.4 (very strong). The USGS PAGER system issued a green alert level for this event, indicating no significant casualties or damage expected. The nearest populated place is Yamoto (population 32,028).
Physical scale: An earthquake of magnitude 6.9 releases seismic energy equivalent to roughly 338 kilotons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 35 km — a useful intuition for the size of the slip patch on the fault.
The epicenter is located in Japan, a region characterized by the intersection of four tectonic plates — Pacific, Philippine Sea, Eurasian, and North American — creating multiple subduction zones. The nearest mapped fault system is the Japan Trench. View all earthquakes in Japan.
Learn more: Magnitude scale · Aftershock sequences
Nearest Populated Places
What the Shaking Felt Like
At MMI 6.4 (very strong), people in the most strongly affected areas would have experienced: Strong shaking felt by everyone. Heavy furniture may move. Books fall from shelves. Plaster and chimneys may crack. Damage is generally slight in well-built structures.
ShakeMap — predicted shaking intensity
Modeled ground-motion intensity contoured on the Modified Mercalli scale (MMI). Computed by the USGS from the moment-tensor solution and regional ground-motion prediction equations.
Source: U.S. Geological Survey ShakeMap. View interactive ShakeMap on USGS
Did You Feel It? — community-reported shaking
Aggregated felt-report intensity from 274 citizen responses to the USGS Did You Feel It? system. Each colored zone represents the average MMI from reports in that area.
Source: U.S. Geological Survey Did You Feel It?. View on USGS · submit your own report
Population exposure (USGS PAGER)
Estimated population that experienced each level of shaking. Based on the USGS PAGER rapid impact assessment, which combines ShakeMap output with global population grids.
| Shaking intensity (MMI) | Description | Population exposed |
|---|---|---|
| MMI 3 | weak | 32,786,696 |
| MMI 4 | light | 12,530,272 |
| MMI 5 | moderate | 1,302,544 |
| MMI 6 | strong | 1,473,974 |
Earthquake Details
141.5973°E
Technical Information
Nearby Earthquakes (Last 7 Days)
Common Questions
How strong was the magnitude 6.9 earthquake near Onagawa Ch?, Japan?
The magnitude 6.9 earthquake that struck 30 km SSE of Onagawa Ch?, Japan on May 1, 2021 at 01:27 UTC had a depth of 43.0 km. It was felt by 274 people with maximum shaking intensity of MMI 6.4 (very strong). For context, this was a strong earthquake capable of causing significant damage.
Where did the earthquake occur?
The earthquake epicenter was located at 38.1997°, 141.5973°, which is 30 km SSE of Onagawa Ch?, Japan. The nearest populated place is Yamoto (population 32,028). View all earthquakes in Japan.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 6.9 earthquakes can continue for weeks to months and gradually diminish over time.
Has Japan had earthquakes this big before?
The largest recorded earthquake in Japan was the M9.1 Tohoku earthquake of March 11, 2011. Today's magnitude 6.9 event is significantly smaller than that historical record.
Actions
Location
Authoritative source: USGS event page (event ID: us7000dz5t). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, May 1, 2021). M6.9 Earthquake 30 km SSE of Onagawa Ch?, Japan — May 1, 2021. Retrieved December 22, 2025 from https://www.earthquaketracker.org/earthquakes/event/us7000dz5t/