172 km ENE of Atka, Alaska

This was a moderate earthquake. Shaking at this size can damage poorly built structures close to the epicentre.

At this magnitude and depth, people at rest would likely notice it out to about 276 km (171 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 3.8 kilotons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 6.6 would have released about 32 times as much.

1. Northridge, California 1994 M 6.7 45× the energy of this one
2. Mineral, Virginia 2011 M 5.8 2× the energy of this one
3. Magna, Utah 2020 M 5.7 1.4× the energy of this one
4. This earthquake M 5.6 about 3.8 kilotons of TNT
5. Around the size people start to feel M 3.0 this one released 7,900× more

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

Tied for the largest within 50 km (31 mi) since 2016, with M 5.6 on 2023-10-12.

Before 2016, the USGS record lists 20 earthquakes of M5 or more within 50 km; the five largest:

1. 6.9 170 km E of Atka, Alaska · 39 km S of this epicentre Sep 2, 2011
2. 6.2 173 km WSW of Nikolski, Alaska · 25 km ENE of this epicentre Jan 14, 1968
3. 6.1 188 km E of Atka, Alaska · 36 km SSE of this epicentre Jan 4, 1968
4. 6.0 177 km WSW of Nikolski, Alaska · 43 km SE of this epicentre Aug 19, 1925
5. 6.0 164 km WSW of Nikolski, Alaska · 46 km ESE of this epicentre Mar 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 52.5259, -171.7222. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 3.1 145 km ENE of Atka, Alaska 15:01 UTC
2. 3.2 166 km WSW of Nikolski, Alaska 23:07 UTC
3. 3.8 166 km W of Nikolski, Alaska 14:46 UTC
4. 4.1 173 km W of Nikolski, Alaska 14:39 UTC
5. 3.5 163 km W of Nikolski, Alaska 14:34 UTC
6. 3.2 178 km E of Atka, Alaska 20:00 UTC
7. 2.9 178 km E of Atka, Alaska 09:03 UTC
8. 2.9 171 km ENE of Atka, Alaska 05:54 UTC
9. 2.9 175 km E of Atka, Alaska 04:31 UTC
10. 3.1 173 km E of Atka, Alaska 04:13 UTC
11. 2.5 176 km E of Atka, Alaska 07:30 UTC
12. 2.9 176 km E of Atka, Alaska 05:40 UTC
13. 2.7 172 km E of Atka, Alaska 10:59 UTC
14. 2.8 181 km E of Atka, Alaska 15:40 UTC
15. 3.4 169 km E of Atka, Alaska 15:37 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 23:15 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.