154 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 35 km (22 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 950 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.0 would have released about 32 times as much.

1. Northridge, California 1994 M 6.7 350,000× the energy of this one
2. Mineral, Virginia 2011 M 5.8 16,000× the energy of this one
3. Magna, Utah 2020 M 5.7 11,000× the energy of this one
4. This earthquake M 3.0 about 950 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 22,000 times the energy of this one.

Before 2016, the USGS record lists 58 earthquakes of M5 or more within 50 km; the five largest:

1. 8.6 The 1946 Unimak Island, Alaska Earthquake · 48 km E of this epicentre Apr 1, 1946
2. 6.6 146 km ESE of Akutan, Alaska · 17 km WNW of this epicentre Apr 1, 1946
3. 6.2 Unimak Island region, Alaska · 44 km NW of this epicentre Oct 14, 1933
4. 6.2 136 km SE of Akutan, Alaska · 34 km W of this epicentre Apr 1, 1946
5. 6.2 136 km S of False Pass, Alaska · 24 km NW 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 53.4700, -163.5505. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.4 118 km SSW of False Pass, Alaska 07:48 UTC
2. 1.6 120 km SSW of False Pass, Alaska 08:53 UTC
3. 2.0 114 km SSW of False Pass, Alaska 04:20 UTC
4. 2.2 126 km S of False Pass, Alaska 19:02 UTC
5. 2.6 167 km S of False Pass, Alaska 06:14 UTC
6. 2.4 160 km ESE of Akutan, Alaska 03:01 UTC
7. 2.4 165 km S of False Pass, Alaska 14:17 UTC
8. 2.5 164 km S of False Pass, Alaska 13:58 UTC
9. 2.3 154 km S of False Pass, Alaska 00:25 UTC
10. 3.2 157 km S of False Pass, Alaska 23:38 UTC
11. 2.2 157 km S of False Pass, Alaska 07:58 UTC
12. 2.2 158 km ESE of Akutan, Alaska 10:03 UTC
13. 2.4 161 km ESE of Akutan, Alaska 05:59 UTC
14. 3.7 143 km ESE of Akutan, Alaska 05:21 UTC
15. 3.5 159 km S of False Pass, Alaska 05:20 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 21:20 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.