M3.9 Earthquake south of Alaska — October 20, 2025
2025-10-20 23:52:59 UTC (2025-10-20) · approx. 1:52 PM UTC-10 local
On October 20, 2025 at 23:52 UTC, a magnitude 3.9 shallow crustal earthquake struck south of Alaska, at a depth of 10.0 km and coordinates 53.5880°, -156.2966°.
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
-156.2966°E
Technical Information
Nearby Earthquakes (Last 7 Days)
Common Questions
How strong was the magnitude 3.9 earthquake south of Alaska?
The magnitude 3.9 earthquake that struck south of Alaska on October 20, 2025 at 23:52 UTC had a depth of 10.0 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.
What should I do after an earthquake?
If you were in the affected area: check yourself and others for injuries, inspect your home for damage, and be prepared for aftershocks. For detailed guidance, see our earthquake safety guide and emergency planning resources.
Actions
Understanding This Data
Magnitude 3.9 earthquakes are typically only recorded by instruments.
Authoritative source: USGS event page (event ID: us6000rid8). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2025, October 20, 2025). M3.9 Earthquake south of Alaska — October 20, 2025. Retrieved May 26, 2026 from https://www.earthquaketracker.org/earthquakes/event/us6000rid8/