M4.9 Earthquake 81 km S of Atka, Alaska — October 11, 2021
2021-10-11 18:25:48 UTC (2021-10-11) · approx. 6:25 AM UTC-12 local
On October 11, 2021 at 18:25 UTC, a magnitude 4.9 shallow crustal earthquake struck 81 km S of Atka, Alaska, at a depth of 35.0 km and coordinates 51.4793°, -174.4301°.
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
ShakeMap — predicted shaking intensity
Modeled ground-motion intensity contoured on the Modified Mercalli scale (MMI). Computed by the USGS from the moment-tensor solution and regional ground-motion prediction equations.
Source: U.S. Geological Survey ShakeMap. View interactive ShakeMap on USGS
Earthquake Details
-174.4301°E
Technical Information
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Common Questions
How strong was the magnitude 4.9 earthquake near Atka, Alaska?
The magnitude 4.9 earthquake that struck 81 km S of Atka, Alaska on October 11, 2021 at 18:25 UTC had a depth of 35.0 km. For context, this was a light earthquake commonly felt near the epicenter.
Where did the earthquake occur?
The earthquake epicenter was located at 51.4793°, -174.4301°, which is 81 km S of Atka, 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: us6000ftru). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, October 11, 2021). M4.9 Earthquake 81 km S of Atka, Alaska — October 11, 2021. Retrieved December 22, 2025 from https://www.earthquaketracker.org/earthquakes/event/us6000ftru/