Alaska earthquakes

M4.0 earthquake 25 km SSE of Adak, Alaska

A magnitude 4.0 earthquake struck 25 km SSE of Adak, Alaska on Sat, May 20, 2017, 3:23 PM HADT (00:23 UTC), 52 km (32 mi) below the surface.

A larger quake followed: M5.3 88 km WSW of Atka, 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: 4.0 (mb, body-wave), light
Magnitude from: USGS National Earthquake Information Center
Local time: Sat, May 20, 2017, 3:23 PM HADT
UTC: 2017-05-21 00:23:56 UTC
Depth: 52.0 km (32.3 mi), shallow
Epicenter: 51.657° N, 176.510° 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
4.0	mb, body-wave	USGS National Earthquake Information Center	Preferred · Reviewed · ±0.084 · 38 stations
4.0	mb, body-wave	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 8.5 km horizontally, 6.5 km in depth
Magnitude uncertainty: ±0.08
Depth from: From location
Station coverage gap: 182°, poorly surrounded by stations
Stations used: 65

Nearby

Within 100 km, magnitude 1.5 and up: 131 in the 60 days after this one and 108 in the 30 days before it.

After

The first 60 of 131.

Before

Earthquakes today Alaska earthquakes Live radar here

Sources

From the USGS Earthquake Hazards Program and its partner networks, event us10008txq (also filed as ak16086220, ak0176h6wzen). Read Fri, Oct 2, 2026, 12:25 PM UTC.