M3.8 earthquake 42 km E of Port Alsworth, Alaska

A magnitude 3.8 earthquake struck 42 km E of Port Alsworth, Alaska on Thu, Aug 5, 2021, 7:36 PM AKDT (03:36 UTC), 184 km (115 mi) below the surface.

A larger quake followed: M3.9 42 km ENE of Pedro Bay, Alaska. This one was a foreshock.

Map

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

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	ML, local (Richter)	Alaska Earthquake Center	Preferred · Preliminary
4.2	mb, body-wave	USGS National Earthquake Information Center	Reviewed · ±0.074 · 51 stations

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

No one has reported feeling this quake to the USGS.

Reviewed by a seismologist.

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

Within 100 km, magnitude 1.5 and up: at least 199 in the 60 days after this one and 194 in the 30 days before it.

The first 60 of at least 199.

From the USGS Earthquake Hazards Program and its partner networks, event ak021a0l5p35 (also filed as us6000f2mp). Read Fri, Oct 2, 2026, 1:12 PM UTC.