178 km E of Atka, 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 36 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 2018-08-25 — about 22,000 times the energy of this one.

Before 2016, the USGS record lists 40 earthquakes of M5 or more within 50 km; the five largest:

1. 7.3 Fox Islands, Aleutian Islands, Alaska · 43 km SSW of this epicentre Jun 24, 2011
2. 6.9 170 km E of Atka, Alaska · 27 km SSW of this epicentre Sep 2, 2011
3. 6.2 173 km WSW of Nikolski, Alaska · 26 km NE of this epicentre Jan 14, 1968
4. 6.1 188 km E of Atka, Alaska · 20 km SSE of this epicentre Jan 4, 1968
5. 6.0 177 km WSW of Nikolski, Alaska · 29 km ESE of this epicentre Aug 19, 1925

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 52.4054, -171.6027. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 3.4 158 km E of Atka, Alaska 01:23 UTC
2. 3.1 187 km E of Atka, Alaska 08:41 UTC
3. 3.0 192 km WSW of Nikolski, Alaska 07:02 UTC
4. 3.3 193 km WSW of Nikolski, Alaska 20:16 UTC
5. 3.6 182 km WSW of Nikolski, Alaska 16:11 UTC
6. 3.5 194 km E of Atka, Alaska 02:23 UTC
7. 4.3 185 km E of Atka, Alaska 14:20 UTC
8. 3.9 186 km E of Atka, Alaska 12:05 UTC
9. 3.6 196 km WSW of Nikolski, Alaska 09:52 UTC
10. 4.7 189 km WSW of Nikolski, Alaska 09:36 UTC
11. 3.8 194 km WSW of Nikolski, Alaska 23:44 UTC
12. 2.2 155 km WSW of Nikolski, Alaska 06:38 UTC
13. 2.6 170 km WSW of Nikolski, Alaska 03:17 UTC
14. 3.3 172 km E of Atka, Alaska 03:14 UTC
15. 2.7 171 km E of Atka, Alaska 01:36 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 05:58 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.