M3.9 earthquake 156 km WSW of Adak, Alaska

A magnitude 3.9 earthquake struck 156 km WSW of Adak, Alaska on Sun, Apr 20, 2025, 2:28 PM HADT (23:28 UTC), 35 km (22 mi) below the surface.

A larger quake followed: M4.3 174 km WSW 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 · ±0.071 · 53 stations
4.0	ML, local (Richter)	Alaska Earthquake Center	Preliminary

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.

Within 100 km, magnitude 1.5 and up: at least 199 in the 60 days after this one and 128 in the 30 days before it.

The first 60 of at least 199.

From the USGS Earthquake Hazards Program and its partner networks, event us6000q7g7 (also filed as ak02552az80c). Read Fri, Oct 2, 2026, 4:27 AM UTC.