south of 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 101 km (63 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 4.8 on 2021-07-29 — about 11 times the energy of this one.

Before 2016, the USGS record lists 11 earthquakes of M5 or more within 50 km; the five largest:

1. 7.0 164 km SE of Chignik, Alaska · 50 km SW of this epicentre Sep 4, 1989
2. 6.9 143 km ESE of Chignik, Alaska · 24 km WNW of this epicentre Feb 13, 1951
3. 6.9 171 km SW of Akhiok, Alaska · 8 km ENE of this epicentre Feb 6, 1964
4. 6.6 128 km SE of Chignik, Alaska · 48 km W of this epicentre Jul 28, 1934
5. 6.2 148 km SSW of Akhiok, Alaska · 48 km E of this epicentre Nov 10, 1944

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 55.6849, -155.9644. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.4 145 km E of Chignik, Alaska 16:09 UTC
2. 3.0 157 km SW of Akhiok, Alaska 17:43 UTC
3. 2.4 163 km ESE of Chignik, Alaska 15:59 UTC
4. 3.2 152 km SSW of Akhiok, Alaska 08:40 UTC
5. 2.5 165 km ESE of Chignik, Alaska 01:38 UTC
6. 2.5 155 km SW of Akhiok, Alaska 07:19 UTC
7. 2.5 156 km SE of Chignik, Alaska 02:05 UTC
8. 2.2 south of Alaska 03:46 UTC
9. 3.5 157 km SSW of Akhiok, Alaska 10:51 UTC
10. 2.3 153 km ESE of Chignik, Alaska 09:20 UTC
11. 3.1 134 km ESE of Chignik, Alaska 04:47 UTC
12. 3.4 166 km SSW of Akhiok, Alaska 19:36 UTC
13. 2.2 south of Alaska 09:41 UTC
14. 2.0 188 km SE of Chignik, Alaska 04:18 UTC
15. 2.4 154 km SSW of Akhiok, Alaska 02:11 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 02:12 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.