161 km S of False Pass, 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 23 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 5.9 on 2016-10-27 — about 32,000 times the energy of this one.

Before 2016, the USGS record lists 55 earthquakes of M5 or more within 50 km; the five largest:

1. 8.6 The 1946 Unimak Island, Alaska Earthquake · 47 km ENE of this epicentre Apr 1, 1946
2. 6.6 146 km ESE of Akutan, Alaska · 23 km NW of this epicentre Apr 1, 1946
3. 6.2 136 km SE of Akutan, Alaska · 36 km W of this epicentre Apr 1, 1946
4. 6.2 136 km S of False Pass, Alaska · 31 km NNW of this epicentre Apr 2, 1946
5. 6.2 172 km SSE of False Pass, Alaska · 46 km E of this epicentre Apr 2, 1946

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 53.4050, -163.5298. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.8 120 km S of False Pass, Alaska 05:58 UTC
2. 2.5 115 km S of False Pass, Alaska 08:09 UTC
3. 2.2 154 km S of False Pass, Alaska 20:45 UTC
4. 2.4 160 km S of False Pass, Alaska 14:03 UTC
5. 4.4 153 km S of False Pass, Alaska 06:42 UTC
6. 3.3 154 km S of False Pass, Alaska 06:28 UTC
7. 4.4 147 km S of False Pass, Alaska 05:21 UTC
8. 2.4 149 km S of False Pass, Alaska 04:27 UTC
9. 4.5 152 km S of False Pass, Alaska 03:42 UTC
10. 4.4 129 km S of False Pass, Alaska 22:59 UTC
11. 1.9 122 km SSW of False Pass, Alaska 11:51 UTC
12. 2.6 170 km S of False Pass, Alaska 09:19 UTC
13. 3.0 151 km S of False Pass, Alaska 00:21 UTC
14. 2.8 162 km S of False Pass, Alaska 21:16 UTC
15. 2.8 156 km S of False Pass, Alaska 12:24 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 23:09 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.