210 km ESE 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 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 5.8 on 2020-08-16 — about 16,000 times the energy of this one.

Before 2016, the USGS record lists 23 earthquakes of M5 or more within 50 km; the five largest:

1. 7.1 Fox Islands, Aleutian Islands, Alaska · 27 km E of this epicentre Dec 31, 1901
2. 6.9 240 km SE of Atka, Alaska · 47 km S of this epicentre Jul 29, 1965
3. 6.1 185 km ESE of Atka, Alaska · 48 km NNW of this epicentre Dec 6, 1930
4. 6.1 207 km ESE of Atka, Alaska · 25 km NNE of this epicentre Mar 13, 1957
5. 6.0 228 km ESE of Atka, Alaska · 25 km SSE of this epicentre May 18, 1957

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 51.4354, -171.4063. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.8 216 km SW of Nikolski, Alaska 13:34 UTC
2. 4.4 178 km ESE of Atka, Alaska 04:00 UTC
3. 3.0 185 km ESE of Atka, Alaska 17:53 UTC
4. 3.0 193 km ESE of Atka, Alaska 21:42 UTC
5. 3.7 192 km ESE of Atka, Alaska 22:55 UTC
6. 3.1 177 km ESE of Atka, Alaska 22:50 UTC
7. 3.6 184 km ESE of Atka, Alaska 01:14 UTC
8. 4.3 178 km ESE of Atka, Alaska 16:35 UTC
9. 3.2 182 km ESE of Atka, Alaska 14:37 UTC
10. 3.5 192 km ESE of Atka, Alaska 07:01 UTC
11. 3.8 229 km SW of Nikolski, Alaska 05:42 UTC
12. 2.9 191 km ESE of Atka, Alaska 10:48 UTC
13. 2.5 238 km ESE of Atka, Alaska 14:49 UTC
14. 3.1 196 km SW of Nikolski, Alaska 21:22 UTC
15. 3.2 194 km ESE of Atka, Alaska 07:52 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 12:09 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.