M4.9 Earthquake 52 km NNE of Nanao, Japan — September 16, 2021
2021-09-16 09:42:29 UTC (2021-09-16) · approx. 6:42 PM UTC+9 local
Felt by 25 people across nearby locations. Maximum shaking intensity MMI 6.1 (very strong).
On September 16, 2021 at 09:42 UTC, a magnitude 4.9 shallow crustal earthquake struck 52 km NNE of Nanao, Japan, at a depth of 10.0 km and coordinates 37.4707°, 137.2472°. The earthquake was reported felt by 25 peopleacross nearby locations, with a maximum shaking intensity of Modified Mercalli Intensity (MMI) 6.1 (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 Toyama (population 325,532).
Physical scale: An earthquake of magnitude 4.9 releases seismic energy equivalent to roughly 338 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 1.4 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
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 25 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 | 5,059,639 |
| MMI 4 | light | 1,004,451 |
| MMI 5 | moderate | 15,560 |
| MMI 6 | strong | 11,580 |
Earthquake Details
137.2472°E
Technical Information
Nearby Earthquakes (Last 7 Days)
Common Questions
How strong was the magnitude 4.9 earthquake near Nanao, Japan?
The magnitude 4.9 earthquake that struck 52 km NNE of Nanao, Japan on September 16, 2021 at 09:42 UTC had a depth of 10.0 km. It was felt by 25 people with maximum shaking intensity of MMI 6.1 (very strong). For context, this was a light earthquake commonly felt near the epicenter.
Where did the earthquake occur?
The earthquake epicenter was located at 37.4707°, 137.2472°, which is 52 km NNE of Nanao, Japan. The nearest populated place is Toyama (population 325,532). View all earthquakes in Japan.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 4.9 earthquakes can continue for several days 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 4.9 event is significantly smaller than that historical record.
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Location
Authoritative source: USGS event page (event ID: us7000fbrh). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, September 16, 2021). M4.9 Earthquake 52 km NNE of Nanao, Japan — September 16, 2021. Retrieved December 22, 2025 from https://www.earthquaketracker.org/earthquakes/event/us7000fbrh/