M3.9 earthquake 159 km SSW of Adak, Alaska

A magnitude 3.9 earthquake struck 159 km SSW of Adak, Alaska on Wed, Dec 9, 2020, 10:29 AM HAST (20:29 UTC), 10 km (6 mi) below the surface.

A larger quake followed: M5.0 124 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.

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	mb, body-wave	USGS National Earthquake Information Center	Preferred · Reviewed · ±0.101 · 28 stations
3.4	ML, local (Richter)	Alaska Earthquake Center	Preliminary

No one has reported feeling this quake to the USGS.

Reviewed by a seismologist.

Within 100 km, magnitude 1.5 and up: 62 in the 60 days after this one and 18 in the 30 days before it.

The first 60 of 62.

From the USGS Earthquake Hazards Program and its partner networks, event us7000cpkw (also filed as ak020ft8yb1h). Read Fri, Oct 2, 2026, 1:24 AM UTC.