M5.9 Earthquake 5 km SW of Chiba, Japan — October 7, 2021
2021-10-07 13:41:24 UTC (2021-10-07) · approx. 10:41 PM UTC+9 local
Felt by 5,682 people across a wide area. Maximum shaking intensity MMI 5.8 (strong).
On October 7, 2021 at 13:41 UTC, a magnitude 5.9 shallow crustal earthquake struck 5 km SW of Chiba, Japan, at a depth of 62.0 km and coordinates 35.5736°, 140.0705°. The earthquake was reported felt by 5,682 peopleacross a wide area, with a maximum shaking intensity of Modified Mercalli Intensity (MMI) 5.8 (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 Soka (population 231,445).
Physical scale: An earthquake of magnitude 5.9 releases seismic energy equivalent to roughly 11 kilotons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 7.1 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 5.8 (strong), people in the most strongly affected areas would have experienced: Moderate shaking that everyone in the area would feel. Sleeping people are awakened. Dishes and windows may break. Unstable objects may be knocked over.
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 5,682 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 | 5,530,554 |
| MMI 4 | light | 27,412,164 |
| MMI 5 | moderate | 15,085,290 |
| MMI 6 | strong | 242,332 |
Earthquake Details
140.0705°E
Technical Information
Nearby Earthquakes (Last 7 Days)
Common Questions
How strong was the magnitude 5.9 earthquake near Chiba, Japan?
The magnitude 5.9 earthquake that struck 5 km SW of Chiba, Japan on October 7, 2021 at 13:41 UTC had a depth of 62.0 km. It was felt by 5,682 people with maximum shaking intensity of MMI 5.8 (strong). For context, this was a moderate earthquake that could be widely felt.
Where did the earthquake occur?
The earthquake epicenter was located at 35.5736°, 140.0705°, which is 5 km SW of Chiba, Japan. The nearest populated place is Soka (population 231,445). View all earthquakes in Japan.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 5.9 earthquakes can continue for days to weeks 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 5.9 event is significantly smaller than that historical record.
Actions
Location
Authoritative source: USGS event page (event ID: us6000fsl6). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, October 7, 2021). M5.9 Earthquake 5 km SW of Chiba, Japan — October 7, 2021. Retrieved December 22, 2025 from https://www.earthquaketracker.org/earthquakes/event/us6000fsl6/