M4.0 Earthquake 186 km SSE of Unalaska, Alaska — February 23, 2021
2021-02-23 22:33:40 UTC (2021-02-23) · approx. 11:33 AM UTC-11 local
On February 23, 2021 at 22:33 UTC, a magnitude 4.0 shallow crustal earthquake struck 186 km SSE of Unalaska, Alaska, at a depth of 10.0 km and coordinates 52.2569°, -165.8236°.
Physical scale: An earthquake of magnitude 4.0 releases seismic energy equivalent to roughly 15 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 347 m — a useful intuition for the size of the slip patch on the fault.
Earthquake Details
-165.8236°E
Technical Information
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Common Questions
How strong was the magnitude 4.0 earthquake near Unalaska, Alaska?
The magnitude 4.0 earthquake that struck 186 km SSE of Unalaska, Alaska on February 23, 2021 at 22:33 UTC had a depth of 10.0 km. For context, this was a light earthquake commonly felt near the epicenter.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 4.0 earthquakes can continue for several days and gradually diminish over time.
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Understanding This Data
Magnitude 4.0 earthquakes are often felt but rarely cause damage.
Authoritative source: USGS event page (event ID: us6000dkih). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, February 23, 2021). M4.0 Earthquake 186 km SSE of Unalaska, Alaska — February 23, 2021. Retrieved May 4, 2021 from https://www.earthquaketracker.org/earthquakes/event/us6000dkih/