139 km WSW 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 130 km (81 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 since 2016 was M 6.2 on 2017-05-08 — about 350 times the energy of this one.

Before 2016, the USGS record lists 230 earthquakes of M5 or more within 50 km; the five largest:

1. 7.2 162 km WSW of Adak, Alaska · 27 km W of this epicentre Mar 16, 1957
2. 7.0 114 km WSW of Adak, Alaska · 25 km ENE of this epicentre Jul 5, 1929
3. 7.0 148 km WSW of Adak, Alaska · 9 km WSW of this epicentre Mar 11, 1957
4. 6.9 151 km WSW of Adak, Alaska · 13 km W of this epicentre May 15, 1993
5. 6.8 111 km SW of Adak, Alaska · 41 km ESE of this epicentre Jan 4, 1912

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 51.3823, -178.4870. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.0 127 km WSW of Adak, Alaska 18:08 UTC
2. 3.3 120 km WSW of Adak, Alaska 17:47 UTC
3. 1.9 127 km W of Adak, Alaska 11:27 UTC
4. 1.8 133 km W of Adak, Alaska 01:19 UTC
5. 1.8 130 km W of Adak, Alaska 20:07 UTC
6. 1.9 124 km W of Adak, Alaska 19:41 UTC
7. 2.1 129 km W of Adak, Alaska 17:45 UTC
8. 2.0 125 km WSW of Adak, Alaska 15:19 UTC
9. 1.6 126 km W of Adak, Alaska 11:31 UTC
10. 1.9 118 km SW of Adak, Alaska 10:42 UTC
11. 2.1 108 km WSW of Adak, Alaska 09:11 UTC
12. 2.0 130 km W of Adak, Alaska 05:00 UTC
13. 1.7 129 km W of Adak, Alaska 05:00 UTC
14. 1.6 125 km W of Adak, Alaska 04:15 UTC
15. 2.1 140 km WSW of Adak, Alaska 22:54 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 13:24 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.