M3.3 Earthquake 67 km SW of Nikolski, Alaska — September 13, 2021
2021-09-13 23:52:57 UTC (2021-09-13) · approx. 12:52 PM UTC-11 local
On September 13, 2021 at 23:52 UTC, a magnitude 3.3 shallow crustal earthquake struck 67 km SW of Nikolski, Alaska, at a depth of 35.0 km and coordinates 52.4729°, -169.4979°.
Physical scale: An earthquake of magnitude 3.3 releases seismic energy equivalent to roughly 1.3 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 114 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 5.0 mainshock that occurred 17 days ago 63 km SSW of Nikolski, Alaska. Since the mainshock, the USGS has recorded 25 aftershocks in this area. Aftershock activity is expected to continue for days to weeks as stresses on surrounding faults redistribute.
Earthquake Details
-169.4979°E
Technical Information
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Common Questions
How strong was the magnitude 3.3 earthquake near Nikolski, Alaska?
The magnitude 3.3 earthquake that struck 67 km SW of Nikolski, Alaska on September 13, 2021 at 23:52 UTC had a depth of 35.0 km. For context, this was a minor earthquake typically detected only by instruments.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 3.3 earthquakes can continue for several days and gradually diminish over time.
Is this the same earthquake as the M5.0 one earlier?
No. This magnitude 3.3 earthquake is an aftershock of the larger magnitude 5.0 mainshock that occurred earlier 63 km SSW of Nikolski, Alaska. Aftershocks are smaller earthquakes triggered by stress changes from the mainshock.
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Understanding This Data
Magnitude 3.3 earthquakes are typically only recorded by instruments.
Authoritative source: USGS event page (event ID: us6000fqwh). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, September 13, 2021). M3.3 Earthquake 67 km SW of Nikolski, Alaska — September 13, 2021. Retrieved November 23, 2021 from https://www.earthquaketracker.org/earthquakes/event/us6000fqwh/