150 km SW 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 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 192 earthquakes of M5 or more within 50 km; the five largest:

1. 7.2 162 km WSW of Adak, Alaska · 49 km NW of this epicentre Mar 16, 1957
2. 7.0 114 km WSW of Adak, Alaska · 45 km NNE of this epicentre Jul 5, 1929
3. 7.0 148 km WSW of Adak, Alaska · 31 km NNW of this epicentre Mar 11, 1957
4. 6.9 151 km WSW of Adak, Alaska · 37 km NNW of this epicentre May 15, 1993
5. 6.8 111 km SW of Adak, Alaska · 39 km ENE 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 51.0898, -178.4009. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 1.9 102 km WSW of Adak, Alaska 04:07 UTC
2. 4.5 143 km WSW of Adak, Alaska 11:47 UTC
3. 2.0 129 km SW of Adak, Alaska 18:32 UTC
4. 1.6 125 km WSW of Adak, Alaska 10:15 UTC
5. 2.2 126 km WSW of Adak, Alaska 08:08 UTC
6. 2.6 150 km WSW of Adak, Alaska 15:40 UTC
7. 2.5 143 km WSW of Adak, Alaska 14:40 UTC
8. 2.7 130 km WSW of Adak, Alaska 09:40 UTC
9. 2.6 134 km SW of Adak, Alaska 23:13 UTC
10. 2.9 154 km WSW of Adak, Alaska 15:58 UTC
11. 1.5 136 km WSW of Adak, Alaska 06:00 UTC
12. 1.9 178 km WSW of Adak, Alaska 01:13 UTC
13. 1.7 121 km WSW of Adak, Alaska 15:33 UTC
14. 1.5 125 km WSW of Adak, Alaska 12:06 UTC
15. 1.7 123 km WSW of Adak, Alaska 16:40 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 07:49 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.