Alaska earthquakes

M6.3 earthquake 97 km SW of Adak, Alaska

A magnitude 6.3 earthquake struck 97 km SW of Adak, Alaska on Wed, Aug 22, 2018, 6:35 PM HADT (03:35 UTC), 20 km (12 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: 6.3 (Mww, W-phase moment), strong
Magnitude from: USGS National Earthquake Information Center
Local time: Wed, Aug 22, 2018, 6:35 PM HADT
UTC: 2018-08-23 03:35:12 UTC
Depth: 20.0 km (12.4 mi), shallow
Epicenter: 51.350° N, 177.760° W
Region: Alaska
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
6.3	Mww, W-phase moment	USGS National Earthquake Information Center	Preferred · Reviewed · ±0.045 · 47 stations
6.32	Mw, moment	ISC-GEM global catalog	Final · ±0.1
6.3	Mw, moment	Alaska Earthquake Center	Preliminary
6.1	Mi	NOAA National Tsunami Warning Center	Reviewed · 12 stations
6.2	Mwb, body-wave moment	USGS National Earthquake Information Center	Moment tensor · Reviewed

What happened

The USGS’s account of the effects of this earthquake.

Felt on Adak.

From the USGS event page for us1000gfvg. U.S. Geological Survey text and figures are in the public domain.

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: 1091.0% of gravity
Peak ground velocity: 6.4 cm/s
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.

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%

Fault motion and ground failure

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

Faulting: Oblique reverse
Moment magnitude: 6.3 Mww
Nodal plane 1: Strike 270°, dip 29°, rake 121°
Nodal plane 2: Strike 56°, dip 65°, rake 74°

How well it is located

Reviewed by a seismologist.

Location uncertainty: About 4.7 km horizontally, 1.8 km in depth
Magnitude uncertainty: ±0.04
Depth from: Operator assigned
Station coverage gap: 34°
Stations used: 425

Nearby

Within 100 km, magnitude 3.3 and up: 15 in the 60 days after this one and 20 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 us1000gfvg (also filed as ak20156243, ak018aspadoe, at00pdw9ys, iscgem612634106). Read Fri, Oct 2, 2026, 1:52 AM UTC.