162 km WSW of Adak, Alaska

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 9 km (6 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 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 6.1 on 2021-09-24 — about 63,000 times the energy of this one.

Before 2016, the USGS record lists 256 earthquakes of M5 or more within 50 km; the five largest:

1. 7.2 162 km WSW of Adak, Alaska · 31 km NNW of this epicentre Mar 16, 1957
2. 7.0 114 km WSW of Adak, Alaska · 49 km NE of this epicentre Jul 5, 1929
3. 7.0 148 km WSW of Adak, Alaska · 20 km NNE of this epicentre Mar 11, 1957
4. 6.9 151 km WSW of Adak, Alaska · 23 km N of this epicentre May 15, 1993
5. 6.8 177 km WSW of Adak, Alaska · 29 km NW of this epicentre Oct 7, 1989

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 51.1679, -178.6854. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.2 147 km WSW of Adak, Alaska 13:16 UTC
2. 2.1 125 km WSW of Adak, Alaska 05:07 UTC
3. 1.7 145 km WSW of Adak, Alaska 13:31 UTC
4. 2.9 159 km WSW of Adak, Alaska 12:01 UTC
5. 2.9 164 km WSW of Adak, Alaska 10:20 UTC
6. 2.2 162 km WSW of Adak, Alaska 09:13 UTC
7. 3.0 158 km WSW of Adak, Alaska 03:29 UTC
8. 2.8 161 km WSW of Adak, Alaska 00:29 UTC
9. 2.2 154 km WSW of Adak, Alaska 00:12 UTC
10. 2.6 153 km WSW of Adak, Alaska 23:53 UTC
11. 3.0 163 km WSW of Adak, Alaska 23:41 UTC
12. 3.9 156 km WSW of Adak, Alaska 23:28 UTC
13. 2.1 149 km WSW of Adak, Alaska 23:12 UTC
14. 2.6 149 km WSW of Adak, Alaska 09:54 UTC
15. 1.6 115 km WSW of Adak, Alaska 22:01 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 17:19 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.