Alaska earthquakes

M4.2 earthquake 128 km SSE of Chignik, Alaska

A magnitude 4.2 earthquake struck 128 km SSE of Chignik, Alaska on Mon, Aug 16, 2021, 8:24 AM AKDT (16:24 UTC), 33 km (21 mi) below the surface.

A larger quake followed: M4.5 64 km SE of Perryville, Alaska. This one was a foreshock.

Sand Point 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: 4.2 (ml), light
Local time: Mon, Aug 16, 2021, 8:24 AM AKDT
UTC: 2021-08-16 16:24:04 UTC
Depth: 33.2 km (20.6 mi), shallow
Epicenter: 55.277° N, 157.433° W
Region: Alaska
Strongest shaking: I, not felt 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: I, not felt shaking
Peak ground acceleration: 0.1% of gravity
Peak ground velocity: -3.5 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: 4.3 Mwr
Nodal plane 1: Strike 279°, dip 12°, rake 141°
Nodal plane 2: Strike 48°, dip 82°, rake 80°

How well it is located

Reviewed by a seismologist.

Stations used: 104

Nearest places

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

Sand Point, AlaskaPopulation 1,064. Forecast194 kmE

Nearby

Within 100 km, magnitude 1.5 and up: 184 in the 60 days after this one and 15 in the 30 days before it.

After

The first 60 of 184.

Before

Earthquakes today Alaska earthquakes Live radar here

Sources

From the USGS Earthquake Hazards Program and its partner networks, event ak021ahc77j3 (also filed as us6000f71z). Read Wed, Sep 23, 2026, 12:03 AM UTC.