Alaska earthquakes

M4.0 earthquake 81 km ENE of Chignik, Alaska

A magnitude 4.0 earthquake struck 81 km ENE of Chignik, Alaska on Wed, Aug 18, 2021, 6:22 PM AKDT (02:22 UTC), 11 km (7 mi) below the surface.

A larger quake followed: M4.8 137 km ESE of Chignik, Alaska. This one was a foreshock.

Naknek forecast More in Alaska

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: Wed, Aug 18, 2021, 6:22 PM AKDT
UTC: 2021-08-19 02:22:28 UTC
Depth: 11.4 km (7.1 mi), shallow
Epicenter: 56.637° N, 157.239° W
Region: Alaska
Strongest shaking: III, weak shaking
PAGER alert: Green
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: 1.9% of gravity
Peak ground velocity: -0.6 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%

How well it is located

Reviewed by a seismologist.

Stations used: 164

Nearest places

Distance and direction from each place to the epicenter, with its forecast.

Naknek, AlaskaPopulation 544. Forecast233 kmS

Nearby

Within 100 km, magnitude 1.5 and up: 171 in the 60 days after this one and 28 in the 30 days before it.

After

The first 60 of 171.

Before

Earthquakes today Alaska earthquakes Live radar here

Sources

From the USGS Earthquake Hazards Program and its partner networks, event ak021am2gth7 (also filed as us6000f865). Read Tue, Sep 22, 2026, 8:39 PM UTC.