233 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 5.0 on 2016-10-01 — about 1,000 times the energy of this one.

Before 2016, the USGS record lists 5 earthquakes of M5 or more within 50 km:

1. 6.0 195 km S of False Pass, Alaska · 43 km NNW of this epicentre Aug 14, 1924
2. 5.9 228 km S of False Pass, Alaska · 14 km WNW of this epicentre Oct 13, 1972
3. 5.6 203 km SSE of False Pass, Alaska · 42 km NNE of this epicentre Jun 20, 1969
4. 5.3 223 km S of False Pass, Alaska · 10 km NNW of this epicentre Mar 12, 2015
5. 5.0 240 km SSE of False Pass, Alaska · 46 km E of this epicentre Mar 15, 1982

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 52.7799, -162.8725. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.9 245 km S of False Pass, Alaska 03:38 UTC
2. 2.7 233 km SSE of False Pass, Alaska 10:44 UTC
3. 2.7 194 km S of False Pass, Alaska 07:44 UTC
4. 2.8 229 km SSE of False Pass, Alaska 05:14 UTC
5. 3.3 269 km S of False Pass, Alaska 20:08 UTC
6. 2.9 215 km S of False Pass, Alaska 10:45 UTC
7. 3.4 262 km SE of Akutan, Alaska 00:18 UTC
8. 3.2 229 km SE of Akutan, Alaska 08:19 UTC
9. 3.2 245 km S of False Pass, Alaska 22:40 UTC
10. 3.3 244 km SE of Akutan, Alaska 17:15 UTC
11. 3.1 248 km S of False Pass, Alaska 15:29 UTC
12. 3.1 272 km S of False Pass, Alaska 05:40 UTC
13. 2.6 214 km S of False Pass, Alaska 14:35 UTC
14. 2.6 218 km S of False Pass, Alaska 10:06 UTC
15. 3.1 221 km S of False Pass, Alaska 18:21 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 04:02 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.