207 km S 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 4.6 on 2023-04-22 — about 250 times the energy of this one.

Before 2016, the USGS record lists 4 earthquakes of M5 or more within 50 km:

1. 6.6 208 km S of Atka, Alaska · 23 km E of this epicentre Apr 30, 1913
2. 6.1 193 km SE of Adak, Alaska · 26 km NW of this epicentre Aug 19, 1992
3. 5.6 178 km SE of Adak, Alaska · 41 km NW of this epicentre Dec 26, 1971
4. 5.6 185 km S of Atka, Alaska · 22 km NNE of this epicentre May 25, 1988

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 50.3525, -174.6415. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.4 159 km S of Atka, Alaska 08:39 UTC
2. 3.0 204 km SSE of Adak, Alaska 04:07 UTC
3. 3.3 170 km S of Atka, Alaska 03:27 UTC
4. 2.8 179 km SE of Adak, Alaska 04:59 UTC
5. 3.3 201 km S of Atka, Alaska 04:23 UTC
6. 3.2 190 km SE of Adak, Alaska 07:11 UTC
7. 2.9 210 km S of Atka, Alaska 19:53 UTC
8. 2.6 236 km S of Atka, Alaska 04:55 UTC
9. 3.4 242 km S of Atka, Alaska 16:36 UTC
10. 2.5 167 km S of Atka, Alaska 12:56 UTC
11. 2.8 213 km SSE of Adak, Alaska 05:31 UTC
12. 2.6 228 km SSE of Adak, Alaska 01:12 UTC
13. 2.5 239 km S of Atka, Alaska 10:37 UTC
14. 2.5 174 km S of Atka, Alaska 06:56 UTC
15. 1.8 185 km SSE of Adak, Alaska 11:26 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 05:17 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.