194 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 7 km (4 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 54 earthquakes of M5 or more within 50 km; the five largest:

1. 7.3 Fox Islands, Aleutian Islands, Alaska · 39 km NW of this epicentre Jun 24, 2011
2. 7.1 Fox Islands, Aleutian Islands, Alaska · 49 km SE of this epicentre Dec 31, 1901
3. 6.9 170 km E of Atka, Alaska · 45 km NNW of this epicentre Sep 2, 2011
4. 6.1 185 km ESE of Atka, Alaska · 10 km NW of this epicentre Dec 6, 1930
5. 6.1 207 km ESE of Atka, Alaska · 18 km SSE of this epicentre Mar 13, 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 51.8013, -171.4451. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.6 171 km SW of Nikolski, Alaska 11:16 UTC
2. 2.2 173 km ESE of Atka, Alaska 12:17 UTC
3. 2.1 176 km ESE of Atka, Alaska 06:28 UTC
4. 3.3 184 km SW of Nikolski, Alaska 23:25 UTC
5. 3.0 201 km ESE of Atka, Alaska 23:16 UTC
6. 2.2 179 km E of Atka, Alaska 07:35 UTC
7. 3.6 185 km SW of Nikolski, Alaska 17:47 UTC
8. 3.2 194 km WSW of Nikolski, Alaska 20:01 UTC
9. 2.7 195 km WSW of Nikolski, Alaska 03:44 UTC
10. 2.5 174 km E of Atka, Alaska 06:13 UTC
11. 3.4 206 km ESE of Atka, Alaska 17:14 UTC
12. 2.8 191 km ESE of Atka, Alaska 01:21 UTC
13. 2.9 193 km E of Atka, Alaska 10:39 UTC
14. 3.2 213 km ESE of Atka, Alaska 19:14 UTC
15. 3.2 187 km E of Atka, Alaska 06:08 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 09:31 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.