Alaska earthquakes

M4.0 earthquake 131 km WSW of Adak, Alaska

A magnitude 4.0 earthquake struck 131 km WSW of Adak, Alaska on Sun, Aug 22, 2021, 2:46 AM HADT (11:46 UTC), 35 km (22 mi) below the surface.

A larger quake followed: M5.5 185 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: 4.0 (ml), light
Local time: Sun, Aug 22, 2021, 2:46 AM HADT
UTC: 2021-08-22 11:46:09 UTC
Depth: 35.0 km (21.7 mi), shallow
Epicenter: 51.315° N, 178.302° W
Region: Alaska
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: 0.6% of gravity
Peak ground velocity: -1.4 cm/s
Map: Automatic

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

Did you feel it?

No one has reported feeling this quake to the USGS.

How well it is located

Reviewed by a seismologist.

Location uncertainty: About 3.5 km horizontally, 2.0 km in depth
Magnitude uncertainty: ±0.10
Depth from: Operator assigned
Station coverage gap: 203°, poorly surrounded by stations
Stations used: 45

Nearby

Within 100 km, magnitude 1.5 and up: 160 in the 60 days after this one and 39 in the 30 days before it.

After

The first 60 of 160.

Before

Earthquakes today Alaska earthquakes Live radar here

Sources

From the USGS Earthquake Hazards Program and its partner networks, event us6000f9v6 (also filed as ak021ar6kvh7). Read Thu, Sep 24, 2026, 8:38 AM UTC.