M3.9 Earthquake 229 km ESE of Attu Station, Alaska — April 20, 2026
2026-04-20 21:47:38 UTC (2026-04-20) · approx. 9:47 AM UTC+12 local
On April 20, 2026 at 21:47 UTC, a magnitude 3.9 shallow crustal earthquake struck 229 km ESE of Attu Station, Alaska, at a depth of 12.4 km and coordinates 52.3452°, 176.4755°.
Physical scale: An earthquake of magnitude 3.9 releases seismic energy equivalent to roughly 11 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 296 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
176.4755°E
Technical Information
Nearby Earthquakes (Last 7 Days)
Common Questions
How strong was the magnitude 3.9 earthquake near Attu Station, Alaska?
The magnitude 3.9 earthquake that struck 229 km ESE of Attu Station, Alaska on April 20, 2026 at 21:47 UTC had a depth of 12.4 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 3.9 earthquakes can continue for several days and gradually diminish over time.
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Understanding This Data
Magnitude 3.9 earthquakes are typically only recorded by instruments.
Authoritative source: USGS event page (event ID: us7000sgzv). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2026, April 20, 2026). M3.9 Earthquake 229 km ESE of Attu Station, Alaska — April 20, 2026. Retrieved October 7, 2026 from https://www.earthquaketracker.org/earthquakes/event/us7000sgzv/