M4.3 Earthquake 127 km SSW of Nikolski, Alaska — February 22, 2021
2021-02-22 20:03:21 UTC (2021-02-22) · approx. 9:03 AM UTC-11 local
On February 22, 2021 at 20:03 UTC, a magnitude 4.3 shallow crustal earthquake struck 127 km SSW of Nikolski, Alaska, at a depth of 35.0 km and coordinates 51.9871°, -169.9157°.
Physical scale: An earthquake of magnitude 4.3 releases seismic energy equivalent to roughly 43 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 558 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 5.4 mainshock that occurred 27 days ago 105 km SSW of Nikolski, Alaska. Since the mainshock, the USGS has recorded 173 aftershocks in this area. Aftershock activity is expected to continue for days to weeks as stresses on surrounding faults redistribute.
Earthquake Details
-169.9157°E
Technical Information
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Common Questions
How strong was the magnitude 4.3 earthquake near Nikolski, Alaska?
The magnitude 4.3 earthquake that struck 127 km SSW of Nikolski, Alaska on February 22, 2021 at 20:03 UTC had a depth of 35.0 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 4.3 earthquakes can continue for several days and gradually diminish over time.
Is this the same earthquake as the M5.4 one earlier?
No. This magnitude 4.3 earthquake is an aftershock of the larger magnitude 5.4 mainshock that occurred earlier 105 km SSW of Nikolski, Alaska. Aftershocks are smaller earthquakes triggered by stress changes from the mainshock.
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Understanding This Data
Magnitude 4.3 earthquakes are often felt but rarely cause damage.
Authoritative source: USGS event page (event ID: us6000dk7g). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, February 22, 2021). M4.3 Earthquake 127 km SSW of Nikolski, Alaska — February 22, 2021. Retrieved May 4, 2021 from https://www.earthquaketracker.org/earthquakes/event/us6000dk7g/