M4.9 Earthquake 71 km SSW of Adak, Alaska — October 20, 2025
2025-10-20 18:45:26 UTC (2025-10-20) · approx. 6:45 AM UTC-12 local
Felt by 2 people across nearby locations.
On October 20, 2025 at 18:45 UTC, a magnitude 4.9 shallow crustal earthquake struck 71 km SSW of Adak, Alaska, at a depth of 37.3 km and coordinates 51.2964°, -177.0718°. The earthquake was reported felt by 2 peopleacross nearby locations, with a maximum shaking intensity of Modified Mercalli Intensity (MMI) 3.3 (light). This earthquake was detected by 98 seismic stations with good location accuracy and was assigned a USGS significance rating of 370, placing it among routine seismic activity.
Physical scale: An earthquake of magnitude 4.9 releases seismic energy equivalent to roughly 338 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 1.4 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
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 2 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
-177.0718°E
Technical Information
Nearby Earthquakes (Last 7 Days)
Common Questions
How strong was the magnitude 4.9 earthquake near Adak, Alaska?
The magnitude 4.9 earthquake that struck 71 km SSW of Adak, Alaska on October 20, 2025 at 18:45 UTC had a depth of 37.3 km. It was felt by 2 people with maximum shaking intensity of MMI 3.3 (light). For context, this was a light earthquake commonly felt near the epicenter.
Where did the earthquake occur?
The earthquake epicenter was located at 51.2964°, -177.0718°, which is 71 km SSW of Adak, Alaska. View all earthquakes in Alaska.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 4.9 earthquakes can continue for several days 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 4.9 event is significantly smaller than that historical record.
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.
Authoritative source: USGS event page (event ID: us6000ric9). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2025, October 20, 2025). M4.9 Earthquake 71 km SSW of Adak, Alaska — October 20, 2025. Retrieved May 26, 2026 from https://www.earthquaketracker.org/earthquakes/event/us6000ric9/