M4.0 Earthquake 60 km W of Happy Valley, Alaska — December 31, 2025
2025-12-31 20:36:19 UTC (2025-12-31) · approx. 10:36 AM UTC-10 local
On December 31, 2025 at 20:36 UTC, a magnitude 4.0 intermediate depth earthquake struck 60 km W of Happy Valley, Alaska, at a depth of 117.3 km and coordinates 60.0390°, -152.7960°. The earthquake was reported felt by 3 peopleacross nearby locations, with a maximum shaking intensity of Modified Mercalli Intensity (MMI) 2.3 (weak).
Physical scale: An earthquake of magnitude 4.0 releases seismic energy equivalent to roughly 15 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 347 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
Did You Feel It? — community-reported shaking
Aggregated felt-report intensity from 3 citizen responses to the USGS Did You Feel It? system. Each colored zone represents the average MMI from reports in that area.
Source: U.S. Geological Survey Did You Feel It?. View on USGS · submit your own report
Earthquake Details
-152.7960°E
Technical Information
Nearby Earthquakes (Last 7 Days)
Common Questions
How strong was the magnitude 4.0 earthquake near Happy Valley, Alaska?
The magnitude 4.0 earthquake that struck 60 km W of Happy Valley, Alaska on December 31, 2025 at 20:36 UTC had a depth of 117.3 km. It was felt by 3 people with maximum shaking intensity of MMI 2.3 (weak). 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 4.0 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 4.0 earthquakes are often felt but rarely cause damage.
Authoritative source: USGS event page (event ID: ak2025ztthsw). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2025, December 31, 2025). M4.0 Earthquake 60 km W of Happy Valley, Alaska — December 31, 2025. Retrieved May 16, 2026 from https://www.earthquaketracker.org/earthquakes/event/ak2025ztthsw/