84 km S of Nikolski, 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 22 km (14 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 5.8 on 2016-03-27 — about 22,000 times the energy of this one.

Before 2016, the USGS record lists 172 earthquakes of M5 or more within 50 km; the five largest:

1. 6.9 77 km SSW of Nikolski, Alaska · 35 km WNW of this epicentre Jan 23, 1935
2. 6.9 80 km SW of Nikolski, Alaska · 43 km WNW of this epicentre Mar 9, 1957
3. 6.9 Fox Islands, Aleutian Islands, Alaska · 38 km WNW of this epicentre Jul 27, 2015
4. 6.8 46 km SSW of Nikolski, Alaska · 48 km NNW of this epicentre Jul 22, 1933
5. 6.8 79 km SW of Nikolski, Alaska · 44 km WNW of this epicentre Jan 28, 1967

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 52.1873, -168.9804. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.6 98 km SSW of Nikolski, Alaska 09:52 UTC
2. 2.3 107 km SSW of Nikolski, Alaska 09:34 UTC
3. 3.1 104 km SSW of Nikolski, Alaska 09:20 UTC
4. 2.2 99 km SSW of Nikolski, Alaska 09:18 UTC
5. 2.7 105 km SSW of Nikolski, Alaska 09:13 UTC
6. 2.4 104 km SSW of Nikolski, Alaska 09:10 UTC
7. 2.5 104 km SSW of Nikolski, Alaska 08:53 UTC
8. 2.4 104 km SSW of Nikolski, Alaska 08:32 UTC
9. 2.5 112 km SSW of Nikolski, Alaska 08:12 UTC
10. 2.7 98 km SSW of Nikolski, Alaska 08:10 UTC
11. 2.7 103 km SSW of Nikolski, Alaska 08:06 UTC
12. 2.9 100 km SSW of Nikolski, Alaska 08:02 UTC
13. 3.2 110 km SSW of Nikolski, Alaska 08:01 UTC
14. 2.9 103 km SSW of Nikolski, Alaska 07:59 UTC
15. 2.7 109 km SSW of Nikolski, Alaska 07:58 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 10:03 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.