140 km ESE of Atka, Alaska

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

At this magnitude and depth it was probably too small to be felt, even directly above it. 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 680 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.9 would have released about 32 times as much.

1. Mineral, Virginia 2011 M 5.8 22,000× the energy of this one
2. Magna, Utah 2020 M 5.7 16,000× the energy of this one
3. Around the size people start to feel M 3.0 1.4× the energy of this one
4. This earthquake M 2.9 about 680 lb of TNT

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 2021-06-30 — about 350 times the energy of this one.

Before 2016, the USGS record lists 23 earthquakes of M5 or more within 50 km; the five largest:

1. 7.3 Fox Islands, Aleutian Islands, Alaska · 29 km ENE of this epicentre Jun 24, 2011
2. 6.9 170 km E of Atka, Alaska · 43 km NE of this epicentre Sep 2, 2011
3. 6.5 143 km ESE of Atka, Alaska · 19 km S of this epicentre Oct 14, 1960
4. 6.3 143 km E of Atka, Alaska · 11 km NNE of this epicentre Apr 5, 1957
5. 6.1 185 km ESE of Atka, Alaska · 45 km E of this epicentre Dec 6, 1930

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

Epicentre 51.9247, -172.2017. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.9 173 km ESE of Atka, Alaska 18:23 UTC
2. 3.0 139 km E of Atka, Alaska 07:22 UTC
3. 4.0 155 km ESE of Atka, Alaska 02:15 UTC
4. 3.1 120 km ESE of Atka, Alaska 01:52 UTC
5. 3.2 173 km E of Atka, Alaska 14:28 UTC
6. 2.1 135 km ESE of Atka, Alaska 18:32 UTC
7. 3.2 110 km ESE of Atka, Alaska 19:06 UTC
8. 1.9 106 km ESE of Atka, Alaska 15:42 UTC
9. 2.4 163 km E of Atka, Alaska 09:50 UTC
10. 3.2 174 km ESE of Atka, Alaska 15:45 UTC
11. 2.3 135 km ESE of Atka, Alaska 15:23 UTC
12. 3.1 169 km ESE of Atka, Alaska 05:02 UTC
13. 3.0 132 km E of Atka, Alaska 06:18 UTC
14. 3.2 126 km ESE of Atka, Alaska 20:29 UTC
15. 2.9 163 km E of Atka, Alaska 23:32 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 09:59 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.