Alaska earthquakes

M5.4 earthquake 123 km WSW of Adak, Alaska

A magnitude 5.4 earthquake struck 123 km WSW of Adak, Alaska on Thu, Aug 16, 2018, 7:35 PM HADT (04:35 UTC), 32 km (20 mi) below the surface.

A larger quake followed: M6.3 97 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: 5.4 (Mww, W-phase moment), moderate
Magnitude from: USGS National Earthquake Information Center
Local time: Thu, Aug 16, 2018, 7:35 PM HADT
UTC: 2018-08-17 04:35:30 UTC
Depth: 31.8 km (19.7 mi), shallow
Epicenter: 51.297° N, 178.154° W
Region: Alaska
Tsunami flag: Yes: a large quake in an oceanic region
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
5.4	Mww, W-phase moment	USGS National Earthquake Information Center	Preferred · Reviewed · ±0.045 · 47 stations
5.42	Mw, moment	ISC-GEM global catalog	Final · ±0.1
5.4	Mw, moment	Alaska Earthquake Center	Preliminary
5.5	Mi	NOAA National Tsunami Warning Center	Reviewed · 12 stations

Tsunami

The USGS flags a quake this large in an oceanic region. The flag does not mean a tsunami happened; the tsunami warning centers decide that, and their messages are below when they issued any.

Current tsunami warnings: tsunami.gov. Warnings in force in the US also appear on our alerts pages.

Did you feel it?

No one has reported feeling this quake to the USGS.

Fault motion and ground failure

How the rock slipped, from the moment tensor, and the USGS estimate of landslides and liquefaction.

Faulting: Reverse (thrust)
Moment magnitude: 5.4 Mww
Nodal plane 1: Strike 250°, dip 34°, rake 88°
Nodal plane 2: Strike 72°, dip 56°, rake 91°

How well it is located

Reviewed by a seismologist.

Location uncertainty: About 5.7 km horizontally, 3.4 km in depth
Magnitude uncertainty: ±0.04
Depth from: From location
Station coverage gap: 38°
Stations used: 328

Nearby

Within 100 km, magnitude 2.4 and up: 73 in the 60 days after this one and 48 in the 30 days before it.

After

The first 60 of 73.

Before

Earthquakes today Alaska earthquakes Live radar here

Sources

From the USGS Earthquake Hazards Program and its partner networks, event us1000gb5u (also filed as ak20107508, ak018aisnrnk, at00pdl8r5, iscgem612535855). Read Fri, Oct 2, 2026, 9:34 AM UTC.