142 km SE 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 30 km (19 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 4.4 on 2016-03-25 — about 130 times the energy of this one.

Before 2016, the USGS record lists 31 earthquakes of M5 or more within 50 km; the five largest:

1. 6.9 182 km SSE of Atka, Alaska · 45 km S of this epicentre Jan 27, 1906
2. 6.5 99 km SE of Atka, Alaska · 49 km NNW of this epicentre Nov 9, 2015
3. 6.1 108 km SE of Atka, Alaska · 49 km N of this epicentre May 1, 1933
4. 6.1 109 km SE of Atka, Alaska · 45 km N of this epicentre Jul 17, 1985
5. 6.1 96 km SE of Atka, Alaska · 49 km NNW of this epicentre Sep 14, 1998

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 51.2151, -172.8737. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 3.1 160 km SSE of Atka, Alaska 09:24 UTC
2. 2.4 98 km SE of Atka, Alaska 13:43 UTC
3. 3.2 147 km SE of Atka, Alaska 00:41 UTC
4. 1.8 100 km SE of Atka, Alaska 19:18 UTC
5. 2.9 120 km SE of Atka, Alaska 16:30 UTC
6. 2.1 163 km SSE of Atka, Alaska 07:16 UTC
7. 2.2 158 km SSE of Atka, Alaska 11:51 UTC
8. 2.3 144 km SSE of Atka, Alaska 09:19 UTC
9. 3.2 151 km SSE of Atka, Alaska 10:05 UTC
10. 2.9 112 km SE of Atka, Alaska 15:01 UTC
11. 1.7 105 km SE of Atka, Alaska 19:51 UTC
12. 2.2 98 km SE of Atka, Alaska 08:18 UTC
13. 3.1 101 km SE of Atka, Alaska 02:29 UTC
14. 3.0 106 km SE of Atka, Alaska 21:13 UTC
15. 3.7 109 km SE of Atka, Alaska 15:35 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 08:15 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.