Alaska earthquakes

M4.8 earthquake 128 km WSW of Adak, Alaska

A magnitude 4.8 earthquake struck 128 km WSW of Adak, Alaska on Sun, Aug 22, 2021, 2:45 AM HADT (11:45 UTC), 52 km (32 mi) below the surface.

A larger quake followed: M6.1 187 km WSW of Adak, Alaska. This one was a foreshock.

Map

Where this earthquake was located, with the others nearby. Select one for its page.

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The earthquake

Magnitude: 4.8 (mb), light
Local time: Sun, Aug 22, 2021, 2:45 AM HADT
UTC: 2021-08-22 11:45:03 UTC
Depth: 51.9 km (32.2 mi), shallow
Epicenter: 51.406° N, 178.327° W
Region: Alaska
Felt reports: 1
Strongest shaking: III, weak shaking
Tsunami flag: No
Status: Reviewed by a seismologist

Shaking

The USGS ShakeMap: shaking estimated from seismic stations and the quake’s size, on the Modified Mercalli intensity scale.

Strongest estimated: III, weak shaking
Peak ground acceleration: 2.5% of gravity
Peak ground velocity: -0.1 cm/s
Map: Automatic

USGS ShakeMap: estimated shaking intensity around the epicenter — Estimated shaking intensity. Map: USGS ShakeMap.

Did you feel it?

1 person reported to the USGS what they felt; the strongest reported shaking was II, weak shaking.

How well it is located

Reviewed by a seismologist.

Location uncertainty: About 4.9 km horizontally, 5.3 km in depth
Magnitude uncertainty: ±0.03
Depth from: From location
Station coverage gap: 125°
Stations used: 307

Nearby

Within 100 km, magnitude 1.8 and up: 102 in the 60 days after this one and 53 in the 30 days before it.

After

The first 60 of 102.

Before

Earthquakes today Alaska earthquakes Live radar here

Sources

From the USGS Earthquake Hazards Program and its partner networks, event us6000f9mn (also filed as ak021ar6kmjd). Read Fri, Sep 25, 2026, 3:32 PM UTC.