Alaska earthquakes

M3.8 earthquake 142 km WSW of Adak, Alaska

A magnitude 3.8 earthquake struck 142 km WSW of Adak, Alaska on Fri, Apr 20, 2018, 4:07 PM HADT (01:07 UTC), 25 km (16 mi) below the surface.

A larger quake followed: M4.2 81 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: 3.8 (mb, body-wave), minor
Magnitude from: USGS National Earthquake Information Center
Local time: Fri, Apr 20, 2018, 4:07 PM HADT
UTC: 2018-04-21 01:07:53 UTC
Depth: 25.2 km (15.7 mi), shallow
Epicenter: 51.194° N, 178.378° W
Region: Alaska
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
3.8	mb, body-wave	USGS National Earthquake Information Center	Preferred · Reviewed · ±0.146 · 12 stations
3.4	ML, local (Richter)	Alaska Earthquake Center	Preliminary

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 3.7 km horizontally, 11.3 km in depth
Magnitude uncertainty: ±0.15
Depth from: From location
Station coverage gap: 209°, poorly surrounded by stations
Stations used: 37

Nearby

Within 100 km, magnitude 1.5 and up: 101 in the 60 days after this one and 50 in the 30 days before it.

After

The first 60 of 101.

Before

Earthquakes today Alaska earthquakes Live radar here

Sources

From the USGS Earthquake Hazards Program and its partner networks, event us1000dseg (also filed as ak01853lakmd, ak19247320). Read Fri, Oct 2, 2026, 1:48 AM UTC.