216 km W of Adak, Alaska

This was a light earthquake. It is usually felt clearly nearby and can rattle windows and dishes, but damage is uncommon.

At this magnitude and depth, people at rest would likely notice it out to about 118 km (73 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 85 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 5.5 would have released about 32 times as much.

1. Northridge, California 1994 M 6.7 2,000× the energy of this one
2. Mineral, Virginia 2011 M 5.8 89× the energy of this one
3. Magna, Utah 2020 M 5.7 63× the energy of this one
4. This earthquake M 4.5 about 85 tons of TNT
5. Around the size people start to feel M 3.0 this one released 180× 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

The largest earthquake within 50 km (31 mi) since our catalogue begins in 2016. The previous largest was M 4.0 on 2016-03-18.

Before 2016, the USGS record lists 62 earthquakes of M5 or more within 50 km; the five largest:

1. 7.2 207 km WSW of Adak, Alaska · 41 km SSE of this epicentre Dec 19, 2007
2. 6.9 203 km WSW of Adak, Alaska · 43 km SSE of this epicentre Mar 31, 1913
3. 6.9 231 km WSW of Adak, Alaska · 44 km S of this epicentre May 14, 1969
4. 6.8 235 km WSW of Adak, Alaska · 48 km SSW of this epicentre May 6, 1987
5. 6.7 237 km WSW of Adak, Alaska · 40 km SSW of this epicentre Oct 13, 1926

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 51.6903, -179.7588. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 3.8 219 km W of Adak, Alaska 05:07 UTC
2. 2.8 192 km WSW of Adak, Alaska 16:16 UTC
3. 2.1 219 km WSW of Adak, Alaska 15:18 UTC
4. 2.1 194 km W of Adak, Alaska 15:23 UTC
5. 2.1 193 km W of Adak, Alaska 21:12 UTC
6. 2.1 200 km WSW of Adak, Alaska 19:31 UTC
7. 2.1 181 km W of Adak, Alaska 09:41 UTC
8. 2.4 205 km W of Adak, Alaska 16:45 UTC
9. 2.0 219 km WSW of Adak, Alaska 11:21 UTC
10. 2.4 221 km WSW of Adak, Alaska 08:09 UTC
11. 2.4 230 km W of Adak, Alaska 00:07 UTC
12. 2.1 237 km WSW of Adak, Alaska 13:09 UTC
13. 1.6 225 km W of Adak, Alaska 05:01 UTC
14. 2.7 213 km W of Adak, Alaska 01:13 UTC
15. 2.7 194 km WSW of Adak, Alaska 07:56 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 11:17 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.