M4.9 Earthquake 128 km WSW of Nikolski, Alaska — May 4, 2021
2021-05-04 16:47:43 UTC (2021-05-04) · approx. 5:47 AM UTC-11 local
On May 4, 2021 at 16:47 UTC, a magnitude 4.9 shallow crustal earthquake struck 128 km WSW of Nikolski, Alaska, at a depth of 53.5 km and coordinates 52.4081°, -170.5441°.
Physical scale: An earthquake of magnitude 4.9 releases seismic energy equivalent to roughly 338 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 1.4 km — a useful intuition for the size of the slip patch on the fault.
The epicenter is located in Alaska, a region characterized by Pacific Plate subduction beneath the North American Plate, producing frequent megathrust and crustal earthquakes along the Aleutian arc. The nearest mapped fault system is the Aleutian megathrust. View all earthquakes in Alaska.
Learn more: Magnitude scale · Aftershock sequences
Earthquake Details
-170.5441°E
Technical Information
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Common Questions
How strong was the magnitude 4.9 earthquake near Nikolski, Alaska?
The magnitude 4.9 earthquake that struck 128 km WSW of Nikolski, Alaska on May 4, 2021 at 16:47 UTC had a depth of 53.5 km. For context, this was a light earthquake commonly felt near the epicenter.
Where did the earthquake occur?
The earthquake epicenter was located at 52.4081°, -170.5441°, which is 128 km WSW of Nikolski, Alaska. View all earthquakes in Alaska.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 4.9 earthquakes can continue for several days and gradually diminish over time.
Has Alaska had earthquakes this big before?
The largest recorded earthquake in Alaska was the M9.2 Great Alaska earthquake of March 27, 1964. Today's magnitude 4.9 event is significantly smaller than that historical record.
Authoritative source: USGS event page (event ID: us7000e01a). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, May 4, 2021). M4.9 Earthquake 128 km WSW of Nikolski, Alaska — May 4, 2021. Retrieved December 22, 2025 from https://www.earthquaketracker.org/earthquakes/event/us7000e01a/