177 km SSW of Adak, Alaska

Yes. A magnitude 3.9 earthquake was recorded 177 km SSW of Adak, Alaska at 22:03 UTC on 2021-09-27, 10 km deep.

2021-09-27 22:03 UTC · 10 km deep · released about 11 tons of TNT

Distance rings around the epicentre, with the nearest towns at their true direction and later quakes as coloured dots. Not a shaking map — see the USGS ShakeMap for that.

When: 2021-09-27 22:03 UTC
Magnitude: M 3.9 (mb)
Depth: 10 km below the surface
Felt: no reports yet
Nearest mapped fault: Alaska-Aleutian subduction zone, 16 km from its surface trace — near is not the same as on
Status: Reviewed by a seismologist

USGS · last changed by USGS 1806 days ago · we first saw it 1806 days ago

This was a small earthquake. Shaking like this is often felt indoors nearby and very rarely causes damage.

At this magnitude and depth, people at rest would likely notice it out to about 89 km (55 mi) from the epicentre. Estimated from magnitude, depth and distance with the intensity equation USGS Did You Feel It? uses; felt reports, where there are any, are the measurement.

How big was it?

This earthquake released about 11 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.9 would have released about 32 times as much.

Northridge, California 1994 M 6.7 16,000× the energy of this one
Mineral, Virginia 2011 M 5.8 710× the energy of this one
Magna, Utah 2020 M 5.7 500× the energy of this one
This earthquake M 3.9 about 11 tons of TNT
Around the size people start to feel M 3.0 this one released 22× more

Energy from the Gutenberg–Richter relation (log₁₀E = 1.5M + 4.8), rounded to two figures; bar length is magnitude, which is already a logarithm of energy. Magnitudes of past earthquakes from the USGS catalogue.

For this area

The largest earthquake within 50 km since 2016 was M 4.3 on 2018-03-11 — about 4 times the energy of this one.

Before 2016, the USGS record lists 11 earthquakes of M5 or more within 50 km; the five largest:

6.5 184 km SSW of Adak, Alaska · 38 km SE of this epicentre Aug 15, 2007
6.0 207 km SW of Adak, Alaska · 47 km W of this epicentre Feb 7, 1926
6.0 130 km SSW of Adak, Alaska · 49 km NE of this epicentre Mar 20, 1927
6.0 161 km SSW of Adak, Alaska · 30 km E of this epicentre Jan 11, 1934
5.8 150 km SW of Adak, Alaska · 30 km N of this epicentre Jul 7, 1929

Since 2016: the QuakeIndex catalogue (US, M1.5+), built from the USGS FDSN event service. Before 2016: USGS ComCat, M5+ from 1900. Distances are between epicentres. This is the record, not a forecast.

Where

Map loads when it scrolls into view

Aftershocks so far

51 earthquakes have been recorded within 50 km since this one.

3.6 133 km SSW of Adak, Alaska 00:43 UTC
2.5 187 km SW of Adak, Alaska 11:32 UTC
3.2 181 km SSW of Adak, Alaska 17:17 UTC
2.3 195 km SW of Adak, Alaska 01:34 UTC
2.8 220 km SSW of Adak, Alaska 03:31 UTC
2.8 170 km SW of Adak, Alaska 07:49 UTC
2.5 158 km SW of Adak, Alaska 05:41 UTC
2.8 135 km SSW of Adak, Alaska 00:38 UTC
2.2 137 km SSW of Adak, Alaska 00:33 UTC
2.6 136 km SW of Adak, Alaska 00:10 UTC
2.8 210 km SSW of Adak, Alaska 20:10 UTC
2.4 222 km SSW of Adak, Alaska 05:03 UTC
2.4 180 km SW of Adak, Alaska 03:56 UTC
2.4 163 km SW of Adak, Alaska 02:23 UTC
2.0 138 km SW of Adak, Alaska 13:19 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 08:26 UTC. QuakeIndex does not forecast aftershocks. When USGS issues an operational aftershock forecast it appears on the USGS event page.

On USGS

The official USGS event page — the source of record for every value above
Did you feel it? Report it to USGS — reports go to USGS, not to us
ShakeMap for this event, when USGS has produced one

QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.