Alaska earthquakes

M4.0 earthquake 86 km E of Nikolski, Alaska

A magnitude 4.0 earthquake struck 86 km E of Nikolski, Alaska on Tue, Aug 17, 2021, 9:10 AM AKDT (17:10 UTC), 35 km (22 mi) below the surface.

A larger quake followed: M4.6 70 km E of Nikolski, Alaska. This one was a foreshock.

Unalaska 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 (mb), light
Local time: Tue, Aug 17, 2021, 9:10 AM AKDT
UTC: 2021-08-17 17:10:50 UTC
Depth: 35.0 km (21.7 mi), shallow
Epicenter: 52.843° N, 167.580° W
Region: Alaska
Strongest shaking: II, 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: II, weak shaking
Peak ground acceleration: 0.3% of gravity
Peak ground velocity: -2.1 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 5.0 km horizontally, 2.0 km in depth
Magnitude uncertainty: ±0.07
Depth from: Operator assigned
Station coverage gap: 123°
Stations used: 93

Nearest places

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

Unalaska, AlaskaPopulation 4,491. Forecast134 kmSSW

Nearby

Within 100 km, magnitude 1.5 and up: 69 in the 60 days after this one and 41 in the 30 days before it.

After

The first 60 of 69.

Before

Earthquakes today Alaska earthquakes Live radar here

Sources

From the USGS Earthquake Hazards Program and its partner networks, event us6000f7kd (also filed as ak021aj093h6). Read Wed, Sep 23, 2026, 6:10 PM UTC.