M5.7 Earthquake 99 km ESE of Chignik, Alaska — July 29, 2021
2021-07-29 06:23:02 UTC (2021-07-29) · approx. 8:23 PM UTC-10 local
On July 29, 2021 at 06:23 UTC, a magnitude 5.7 shallow crustal earthquake struck 99 km ESE of Chignik, Alaska, at a depth of 35.0 km and coordinates 55.8758°, -156.9924°.
Physical scale: An earthquake of magnitude 5.7 releases seismic energy equivalent to roughly 5 kilotons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 5.2 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
-156.9924°E
Technical Information
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Common Questions
How strong was the magnitude 5.7 earthquake near Chignik, Alaska?
The magnitude 5.7 earthquake that struck 99 km ESE of Chignik, Alaska on July 29, 2021 at 06:23 UTC had a depth of 35.0 km. For context, this was a moderate earthquake that could be widely felt.
Where did the earthquake occur?
The earthquake epicenter was located at 55.8758°, -156.9924°, which is 99 km ESE of Chignik, Alaska. View all earthquakes in Alaska.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 5.7 earthquakes can continue for days to weeks 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 5.7 event is significantly smaller than that historical record.
Authoritative source: USGS event page (event ID: us6000f2gj). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, July 29, 2021). M5.7 Earthquake 99 km ESE of Chignik, Alaska — July 29, 2021. Retrieved December 22, 2025 from https://www.earthquaketracker.org/earthquakes/event/us6000f2gj/