Alaska earthquakes

M3.9 earthquake 86 km S of McCarthy, Alaska

A magnitude 3.9 earthquake struck 86 km S of McCarthy, Alaska on Sat, Aug 8, 2020, 9:19 PM AKDT (05:19 UTC), 8 km (5 mi) below the surface.

A larger quake followed: M4.3 85 km S of McCarthy, Alaska. This one was a foreshock.

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Map

Where this earthquake was located, with the others nearby. Select one for its page.

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The earthquake

Magnitude: 3.9 (ML, local (Richter)), minor
Magnitude from: Alaska Earthquake Center
Local time: Sat, Aug 8, 2020, 9:19 PM AKDT
UTC: 2020-08-09 05:19:44 UTC
Depth: 7.8 km (4.8 mi), shallow
Epicenter: 60.660° N, 143.025° W
Region: Alaska
Felt reports: 3
Strongest shaking: V, moderate shaking
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
3.9	ML, local (Richter)	Alaska Earthquake Center	Preferred · Preliminary
3.9	Mwr, regional moment	USGS National Earthquake Information Center	Reviewed · ±0.034 · 82 stations
4.1	ML, local (Richter)	NOAA National Tsunami Warning Center	Reviewed · 41 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.

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: 1378.0% of gravity
Peak ground velocity: 3.8 cm/s
Map: Automatic

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

Did you feel it?

3 people reported to the USGS what they felt; the strongest reported shaking was III, weak shaking.

Fault motion and ground failure

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

Faulting: Strike-slip
Moment magnitude: 3.9 Mwr
Nodal plane 1: Strike 81°, dip 73°, rake 154°
Nodal plane 2: Strike 179°, dip 66°, rake 19°

How well it is located

Reviewed by a seismologist.

Stations used: 208

Nearest places

Distance and direction from each place to the epicenter, with its forecast.

Nearby

Within 100 km, magnitude 1.5 and up: 29 in the 60 days after this one and 7 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 ak020a78edo3 (also filed as at00qes6sz, us6000bbbm). Read Thu, Oct 1, 2026, 6:47 AM UTC.