Alaska earthquakes

M5.4 earthquake 185 km WSW of Adak, Alaska

A magnitude 5.4 earthquake struck 185 km WSW of Adak, Alaska on Sun, Feb 28, 2021, 12:44 AM HAST (10:44 UTC), 22 km (14 mi) below the surface.

Map

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

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The earthquake

Magnitude: 5.4 (mww), moderate
Local time: Sun, Feb 28, 2021, 12:44 AM HAST
UTC: 2021-02-28 10:44:50 UTC
Depth: 22.0 km (13.7 mi), shallow
Epicenter: 51.068° N, 178.968° W
Region: Alaska
Felt reports: 2
Strongest shaking: V, moderate shaking
PAGER alert: Green
Tsunami flag: Yes: a large quake in an oceanic region
Status: Reviewed by a seismologist

Tsunami

The USGS flags a quake this large in an oceanic region. The flag does not mean a tsunami happened; the tsunami warning centers decide that, and their messages are below when they issued any.

Current tsunami warnings: tsunami.gov. Warnings in force in the US also appear on our alerts pages.

Shaking

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

Strongest estimated: V, moderate shaking
Peak ground acceleration: 7.2% of gravity
Peak ground velocity: 1.0 cm/s
Map: Automatic

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

Did you feel it?

2 people reported to the USGS what they felt; the strongest reported shaking was IV, light shaking.

Estimated impact

The USGS PAGER system estimates deaths and economic losses from the shaking and the population and buildings exposed to it.

Alert level: Green: little or no damage or loss of life expected

Deaths: estimated chance of each range
Range	Chance
Under 1	69%
1 to 10	29%
10 to 100	2%
100 to 1,000	Under 1%
1,000 to 10,000	Under 1%
10,000 to 100,000	Under 1%
100,000 to 10,000,000	Under 1%

Economic losses: estimated chance of each range
Range, million USD	Chance
Under 1	65%
1 to 10	30%
10 to 100	4%
100 to 1,000	Under 1%
1,000 to 10,000	Under 1%
10,000 to 100,000	Under 1%
100,000 to 10,000,000	Under 1%

Fault motion and ground failure

How the rock slipped, from the moment tensor, and the USGS estimate of landslides and liquefaction.

Faulting: Reverse (thrust)
Moment magnitude: 5.4 Mww
Nodal plane 1: Strike 262°, dip 32°, rake 102°
Nodal plane 2: Strike 69°, dip 59°, rake 83°

How well it is located

Reviewed by a seismologist.

Location uncertainty: About 3.9 km horizontally, 1.9 km in depth
Magnitude uncertainty: ±0.05
Depth from: From modeling of broad-band P waveforms
Station coverage gap: 124°
Stations used: 199

Nearby

Within 100 km, magnitude 2.4 and up: 32 in the 60 days after this one and 41 in the 30 days before it.

After

Before

Earthquakes today Alaska earthquakes Live radar here

Sources

From the USGS Earthquake Hazards Program and its partner networks, event us7000dec0 (also filed as at00qp8j6t, usauto7000dec0, ak0212pqxcxf, iscgem619876776). Read Thu, Sep 24, 2026, 12:40 PM UTC.