M4.2 Earthquake 137 km SE of Perryville, Alaska — October 17, 2021
2021-10-17 19:27:11 UTC (2021-10-17) · approx. 8:27 AM UTC-11 local
On October 17, 2021 at 19:27 UTC, a magnitude 4.2 shallow crustal earthquake struck 137 km SE of Perryville, Alaska, at a depth of 33.9 km and coordinates 55.0517°, -157.5922°. The nearest populated place is Sand Point (population 976).
Physical scale: An earthquake of magnitude 4.2 releases seismic energy equivalent to roughly 30 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 476 m — a useful intuition for the size of the slip patch on the fault.
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
-157.5922°E
Technical Information
Nearby Earthquakes (Last 7 Days)
Common Questions
How strong was the magnitude 4.2 earthquake near Perryville, Alaska?
The magnitude 4.2 earthquake that struck 137 km SE of Perryville, Alaska on October 17, 2021 at 19:27 UTC had a depth of 33.9 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 4.2 earthquakes can continue for several days and gradually diminish over time.
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Understanding This Data
Magnitude 4.2 earthquakes are often felt but rarely cause damage.
Authoritative source: USGS event page (event ID: ak021dbxbor4). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, October 17, 2021). M4.2 Earthquake 137 km SE of Perryville, Alaska — October 17, 2021. Retrieved December 25, 2021 from https://www.earthquaketracker.org/earthquakes/event/ak021dbxbor4/