168 km E of Atka, 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 104 km (65 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 4.5 on 2016-08-14 — about 4 times the energy of this one.

Before 2016, the USGS record lists 27 earthquakes of M5 or more within 50 km; the five largest:

1. 7.3 Fox Islands, Aleutian Islands, Alaska · 45 km S of this epicentre Jun 24, 2011
2. 6.9 170 km E of Atka, Alaska · 32 km S of this epicentre Sep 2, 2011
3. 6.2 173 km WSW of Nikolski, Alaska · 31 km ENE of this epicentre Jan 14, 1968
4. 6.1 188 km E of Atka, Alaska · 32 km SE of this epicentre Jan 4, 1968
5. 6.0 177 km WSW of Nikolski, Alaska · 41 km ESE of this epicentre Aug 19, 1925

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 52.4559, -171.7695. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 3.6 135 km E of Atka, Alaska 15:31 UTC
2. 2.9 151 km ENE of Atka, Alaska 23:29 UTC
3. 2.5 174 km E of Atka, Alaska 06:13 UTC
4. 3.3 171 km WSW of Nikolski, Alaska 09:53 UTC
5. 2.4 152 km E of Atka, Alaska 06:49 UTC
6. 3.2 187 km E of Atka, Alaska 06:08 UTC
7. 3.2 185 km E of Atka, Alaska 10:35 UTC
8. 3.0 140 km E of Atka, Alaska 05:28 UTC
9. 3.2 163 km E of Atka, Alaska 23:39 UTC
10. 2.9 149 km E of Atka, Alaska 01:15 UTC
11. 2.4 180 km WSW of Nikolski, Alaska 23:09 UTC
12. 4.2 137 km E of Atka, Alaska 23:37 UTC
13. 3.6 138 km E of Atka, Alaska 21:47 UTC
14. 3.1 132 km E of Atka, Alaska 11:05 UTC
15. 3.0 134 km ENE of Atka, Alaska 00:23 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 06:08 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.