Alaska earthquakes

M5.6 earthquake 209 km WSW of Adak, Alaska

A magnitude 5.6 earthquake struck 209 km WSW of Adak, Alaska on Thu, Feb 18, 2021, 11:11 PM HAST (09:11 UTC), 19 km (12 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: 5.6 (mww), moderate
Local time: Thu, Feb 18, 2021, 11:11 PM HAST
UTC: 2021-02-19 09:11:21 UTC
Depth: 19.0 km (11.8 mi), shallow
Epicenter: 50.945° N, 179.254° W
Region: Alaska
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: 11.4% 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.

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: Oblique reverse
Moment magnitude: 5.6 Mww
Nodal plane 1: Strike 285°, dip 26°, rake 132°
Nodal plane 2: Strike 60°, dip 71°, rake 72°

How well it is located

Reviewed by a seismologist.

Location uncertainty: About 5.3 km horizontally, 1.8 km in depth
Magnitude uncertainty: ±0.04
Depth from: From modeling of broad-band P waveforms
Station coverage gap: 114°
Stations used: 268

Nearby

Within 100 km, magnitude 2.6 and up: 43 in the 60 days after this one and 17 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 us6000divk (also filed as at00qorquz, ak0212auao7g, iscgem619908923). Read Fri, Sep 25, 2026, 11:38 AM UTC.