Alaska earthquakes

M4.0 earthquake 204 km W of Adak, Alaska

A magnitude 4.0 earthquake struck 204 km W of Adak, Alaska on Mon, Aug 9, 2021, 4:39 AM HADT (13:39 UTC), 169 km (105 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: 4.0 (mb), light
Local time: Mon, Aug 9, 2021, 4:39 AM HADT
UTC: 2021-08-09 13:39:59 UTC
Depth: 168.6 km (104.8 mi), intermediate-depth
Epicenter: 52.038° N, 179.601° 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: 0.1% of gravity
Peak ground velocity: -4.1 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 11.5 km horizontally, 7.2 km in depth
Magnitude uncertainty: ±0.06
Depth from: From location
Station coverage gap: 92°
Stations used: 83

Nearby

Within 100 km, magnitude 1.5 and up: 103 in the 60 days after this one and 38 in the 30 days before it.

After

The first 60 of 103.

Before

Earthquakes today Alaska earthquakes Live radar here

Sources

From the USGS Earthquake Hazards Program and its partner networks, event us6000f3l4 (also filed as ak021a5pqtj9). Read Thu, Sep 24, 2026, 11:12 AM UTC.