M4.5 Earthquake Ōfunato, Japan

On August 21, 2025 at 23:06 UTC, a magnitude 4.5 shallow crustal earthquake struck 45 km SE of Ōfunato, Japan, at a depth of 52.5 km and coordinates 38.7987°, 142.1097°. This earthquake was detected by 60 seismic stations with good location accuracy and was assigned a USGS significance rating of 312, placing it among routine seismic activity.

Physical scale: An earthquake of magnitude 4.5 releases seismic energy equivalent to roughly 85 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 767 m — a useful intuition for the size of the slip patch on the fault.

This earthquake is part of an ongoing aftershock sequence following the magnitude 5.1 mainshock that occurred 19 days ago 60 km SE of Ōfunato, Japan. Since the mainshock, the USGS has recorded 0 aftershocks in this area. Aftershock activity is expected to continue for days to weeks as stresses on surrounding faults redistribute.

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

Common Questions

How strong was the magnitude 4.5 earthquake near Ōfunato, Japan?

The magnitude 4.5 earthquake that struck 45 km SE of Ōfunato, Japan on August 21, 2025 at 23:06 UTC had a depth of 52.5 km. For context, this was a light earthquake commonly felt near the epicenter.

Where did the earthquake occur?

The earthquake epicenter was located at 38.7987°, 142.1097°, which is 45 km SE of Ōfunato, Japan. View all earthquakes in Japan.

Were there aftershocks?

Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 4.5 earthquakes can continue for several days and gradually diminish over time.

Is this the same earthquake as the M5.1 one earlier?

No. This magnitude 4.5 earthquake is an aftershock of the larger magnitude 5.1 mainshock that occurred earlier 60 km SE of Ōfunato, Japan. Aftershocks are smaller earthquakes triggered by stress changes from the mainshock.

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 4.5 event is significantly smaller than that historical record.

M4.5 Earthquake 45 km SE of Ōfunato, Japan — August 21, 2025

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