137 km SE 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 30 km (19 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 5.0 on 2016-06-29 — about 1,400 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. 7.0 153 km SE of Adak, Alaska · 20 km ESE of this epicentre Jan 17, 1903
2. 6.4 106 km SE of Adak, Alaska · 50 km N of this epicentre May 8, 1986
3. 6.3 159 km SSE of Adak, Alaska · 39 km SSW of this epicentre Apr 3, 1915
4. 6.1 106 km SE of Adak, Alaska · 32 km NNW of this epicentre Mar 22, 1927
5. 6.1 105 km SE of Adak, Alaska · 47 km N of this epicentre Dec 1, 1970

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 50.8918, -175.4340. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.7 148 km SE of Adak, Alaska 07:06 UTC
2. 1.6 115 km SE of Adak, Alaska 12:19 UTC
3. 3.3 176 km SE of Adak, Alaska 22:57 UTC
4. 1.9 120 km SE of Adak, Alaska 18:13 UTC
5. 2.9 125 km SSW of Atka, Alaska 17:56 UTC
6. 3.3 181 km SSE of Adak, Alaska 10:33 UTC
7. 1.6 96 km SE of Adak, Alaska 20:35 UTC
8. 1.9 91 km SSE of Adak, Alaska 19:19 UTC
9. 3.3 96 km SE of Adak, Alaska 20:45 UTC
10. 3.3 129 km SSW of Atka, Alaska 22:54 UTC
11. 2.4 174 km SE of Adak, Alaska 00:45 UTC
12. 3.1 92 km SSE of Adak, Alaska 17:54 UTC
13. 2.6 93 km SSE of Adak, Alaska 10:08 UTC
14. 3.8 129 km SSW of Atka, Alaska 05:53 UTC
15. 3.3 129 km SSW of Atka, Alaska 05:29 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 07:02 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.