Alaska earthquakes

M5.5 earthquake 122 km SW of Adak, Alaska

A magnitude 5.5 earthquake struck 122 km SW of Adak, Alaska on Sun, Sep 21, 2025, 12:30 AM HADT (09:30 UTC), 30 km (19 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: 5.5 (Mww, W-phase moment), moderate
Magnitude from: USGS National Earthquake Information Center
Local time: Sun, Sep 21, 2025, 12:30 AM HADT
UTC: 2025-09-21 09:30:27 UTC
Depth: 30.0 km (18.6 mi), shallow
Epicenter: 51.199° N, 178.022° W
Region: Alaska
Felt reports: 4
Strongest shaking: V, moderate shaking
PAGER alert: Green
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
5.5	Mww, W-phase moment	USGS National Earthquake Information Center	Preferred · Reviewed · ±0.046 · 46 stations
5.6	ML, local (Richter)	Alaska Earthquake Center	Preliminary
5.5	ML, local (Richter)	NOAA National Tsunami Warning Center	Reviewed · 22 stations
5.4	Mwb, body-wave moment	USGS National Earthquake Information Center	Moment tensor · Reviewed
5.5	Mww, W-phase moment	USGS, automatic first solution	First automatic solution · Confirmed

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.

Shaking

The USGS ShakeMap: shaking estimated from seismic stations and the quake’s size, on the Modified Mercalli intensity scale.

Strongest estimated: V, moderate shaking
Peak ground acceleration: 8.6% of gravity
Peak ground velocity: 4.8 cm/s
Map: Automatic

USGS ShakeMap: estimated shaking intensity around the epicenter — Estimated shaking intensity. Map: USGS ShakeMap.

Did you feel it?

4 people reported to the USGS what they felt; the strongest reported shaking was IV, light shaking.

Estimated impact

The USGS PAGER system estimates deaths and economic losses from the shaking and the population and buildings exposed to it.

Alert level: Green: little or no damage or loss of life expected

Deaths: estimated chance of each range
Range	Chance
Under 1	69%
1 to 10	29%
10 to 100	2%
100 to 1,000	Under 1%
1,000 to 10,000	Under 1%
10,000 to 100,000	Under 1%
100,000 to 10,000,000	Under 1%

Economic losses: estimated chance of each range
Range, million USD	Chance
Under 1	65%
1 to 10	30%
10 to 100	4%
100 to 1,000	Under 1%
1,000 to 10,000	Under 1%
10,000 to 100,000	Under 1%
100,000 to 10,000,000	Under 1%

Aftershock forecast

The chance of at least one aftershock this large or larger, from the USGS operational aftershock forecast, issued Mon, Sep 21, 2026, 9:30 AM UTC. The USGS updates it as the sequence unfolds.

Within	M3+	M4+	M5+	M6+	M7+
1 day	Under 1%	Under 1%	Under 1%	Under 1%	Under 1%
1 week	4%	Under 1%	Under 1%	Under 1%	Under 1%
1 month	16%	2%	Under 1%	Under 1%	Under 1%
1 year	74%	14%	2%	Under 1%	Under 1%

In the coming week the USGS expects about 0 aftershocks of magnitude 3 or more, and most likely between 0 and 1.

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: 5.5 Mww
Nodal plane 1: Strike 77°, dip 75°, rake 67°
Nodal plane 2: Strike 316°, dip 27°, rake 146°
Landslide alert: Green
Liquefaction alert: Green

How well it is located

Reviewed by a seismologist.

Location uncertainty: About 3.9 km horizontally, 1.8 km in depth
Magnitude uncertainty: ±0.05
Depth from: From modeling of broad-band P waveforms
Station coverage gap: 42°
Stations used: 155

Nearby

Within 100 km, magnitude 2.5 and up: 20 in the 60 days after this one and 15 in the 30 days before it.

After

Before

Earthquakes today Alaska earthquakes Live radar here

Sources

From the USGS Earthquake Hazards Program and its partner networks, event us7000qxp1 (also filed as at00t2xmeu, usauto7000qxp1, ak025c4rf0bd). Read Fri, Oct 2, 2026, 9:24 AM UTC.