Alaska earthquakes

M3.9 earthquake 122 km WSW of Adak, Alaska

A magnitude 3.9 earthquake struck 122 km WSW of Adak, Alaska on Thu, Apr 21, 2016, 1:28 PM HADT (22:28 UTC), 10 km (6 mi) below the surface.

A larger quake followed: M5.1 39 km SW of Adak, Alaska. This one was a foreshock.

Map

Where this earthquake was located, with the others nearby. Select one for its page.

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The earthquake

Magnitude: 3.9 (mb, body-wave), minor
Magnitude from: USGS National Earthquake Information Center
Local time: Thu, Apr 21, 2016, 1:28 PM HADT
UTC: 2016-04-21 22:28:03 UTC
Depth: 10.0 km (6.2 mi), shallow
Epicenter: 51.634° N, 178.368° W
Region: Alaska
Strongest shaking: III, weak shaking
Tsunami flag: No
Status: Reviewed by a seismologist

Magnitude estimates

Different scales measure different things and differ by a few tenths. The USGS marks one as preferred, and it is the one this page uses.

Mag.	Scale	Computed by	Notes
3.9	mb, body-wave	USGS National Earthquake Information Center	Preferred · Reviewed · ±0.068 · 57 stations
4.2	ML, local (Richter)	Alaska Earthquake Center	Preliminary

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
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 7.7 km horizontally, 1.9 km in depth
Magnitude uncertainty: ±0.07
Depth from: Operator assigned
Station coverage gap: 141°
Stations used: 79

Nearby

Within 100 km, magnitude 1.5 and up: 181 in the 60 days after this one and 69 in the 30 days before it.

After

The first 60 of 181.

Before

Earthquakes today Alaska earthquakes Live radar here

Sources

From the USGS Earthquake Hazards Program and its partner networks, event us20005kp6 (also filed as ak13490098, ak01655lger2). Read Sun, Oct 4, 2026, 12:35 PM UTC.