Andreanof Islands, Aleutian Islands, 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 99 km (62 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 21 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 5.1 would have released about 32 times as much.

1. Northridge, California 1994 M 6.7 7,900× the energy of this one
2. Mineral, Virginia 2011 M 5.8 350× the energy of this one
3. Magna, Utah 2020 M 5.7 250× the energy of this one
4. This earthquake M 4.1 about 21 tons of TNT
5. Around the size people start to feel M 3.0 this one released 45× 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 since 2016 was M 6.5 on 2018-08-15 — about 4,000 times the energy of this one.

Before 2016, the USGS record lists 212 earthquakes of M5 or more within 50 km; the five largest:

1. 7.9 77 km WSW of Adak, Alaska · 47 km E of this epicentre Jun 10, 1996
2. 7.3 88 km WSW of Adak, Alaska · 39 km E of this epicentre Jul 7, 1929
3. 7.2 162 km WSW of Adak, Alaska · 40 km WSW of this epicentre Mar 16, 1957
4. 7.0 114 km WSW of Adak, Alaska · 11 km ESE of this epicentre Jul 5, 1929
5. 7.0 148 km WSW of Adak, Alaska · 27 km SW of this epicentre Mar 11, 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 51.4945, -178.3041. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 1.6 99 km W of Adak, Alaska 13:52 UTC
2. 2.2 101 km W of Adak, Alaska 13:41 UTC
3. 2.1 101 km W of Adak, Alaska 13:38 UTC
4. 1.5 100 km W of Adak, Alaska 13:14 UTC
5. 1.9 87 km W of Adak, Alaska 12:36 UTC
6. 2.2 100 km W of Adak, Alaska 11:12 UTC
7. 1.5 99 km W of Adak, Alaska 10:22 UTC
8. 2.1 100 km W of Adak, Alaska 09:58 UTC
9. 2.1 100 km W of Adak, Alaska 09:58 UTC
10. 1.6 100 km W of Adak, Alaska 09:40 UTC
11. 2.0 101 km W of Adak, Alaska 08:42 UTC
12. 1.6 101 km W of Adak, Alaska 07:45 UTC
13. 1.9 100 km W of Adak, Alaska 06:19 UTC
14. 1.7 100 km W of Adak, Alaska 05:51 UTC
15. 2.2 100 km W of Adak, Alaska 05:27 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 12:25 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.