Fox Islands, Aleutian Islands, Alaska

Yes. A magnitude 3.9 earthquake was recorded in the Fox Islands, Aleutian Islands, Alaska at 05:16 UTC on 2016-09-18, 33 km deep.

2016-09-18 05:16 UTC · 33 km deep · released about 11 tons of TNT

Felt it? Tell USGS Check my area

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: 2016-09-18 05:16 UTC
Magnitude: M 3.9 (mb)
Depth: 33 km below the surface
Felt: no reports yet
Status: Reviewed by a seismologist

USGS · last changed by USGS 1199 days ago · we first saw it 1199 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 83 km (52 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 4.6 on 2016-01-05 — about 11 times the energy of this one.

Before 2016, the USGS record lists 110 earthquakes of M5 or more within 50 km; the five largest:

6.9 80 km SW of Nikolski, Alaska · 46 km NE of this epicentre Mar 9, 1957
6.8 79 km SW of Nikolski, Alaska · 47 km NE of this epicentre Jan 28, 1967
6.6 135 km SW of Nikolski, Alaska · 9 km SW of this epicentre Dec 23, 1906
6.2 91 km SW of Nikolski, Alaska · 35 km NE of this epicentre Feb 10, 1953
6.2 87 km SW of Nikolski, Alaska · 39 km NE of this epicentre Oct 23, 1957

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

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

2.9 149 km SW of Nikolski, Alaska 18:15 UTC
3.7 144 km SSW of Nikolski, Alaska 13:38 UTC
2.4 90 km SW of Nikolski, Alaska 18:52 UTC
3.4 95 km SW of Nikolski, Alaska 05:04 UTC
4.0 150 km SW of Nikolski, Alaska 09:24 UTC
2.5 129 km SW of Nikolski, Alaska 21:33 UTC
5.1 132 km SW of Nikolski, Alaska 21:01 UTC
2.4 88 km SW of Nikolski, Alaska 06:04 UTC
2.4 91 km SW of Nikolski, Alaska 20:13 UTC
2.0 81 km SW of Nikolski, Alaska 13:23 UTC
3.0 77 km SW of Nikolski, Alaska 04:34 UTC
3.6 134 km SW of Nikolski, Alaska 00:02 UTC
3.0 141 km SW of Nikolski, Alaska 21:42 UTC
4.5 139 km SW of Nikolski, Alaska 21:34 UTC
2.9 165 km SSW of Nikolski, Alaska 01:54 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 10:35 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.