164 km ESE of Chignik, 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 136 km (85 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 4.8 on 2021-07-29 — about 2.8 times the energy of this one.

Before 2016, the USGS record lists 10 earthquakes of M5 or more within 50 km; the five largest:

1. 6.9 143 km ESE of Chignik, Alaska · 21 km WNW of this epicentre Feb 13, 1951
2. 6.9 171 km SW of Akhiok, Alaska · 8 km E of this epicentre Feb 6, 1964
3. 6.6 128 km SE of Chignik, Alaska · 48 km WSW of this epicentre Jul 28, 1934
4. 6.2 148 km SSW of Akhiok, Alaska · 49 km E of this epicentre Nov 10, 1944
5. 6.1 118 km ESE of Chignik, Alaska · 46 km WNW of this epicentre Mar 16, 1940

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 55.7155, -155.9787. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.8 184 km SE of Chignik, Alaska 01:24 UTC
2. 3.3 186 km SSW of Akhiok, Alaska 11:06 UTC
3. 3.3 186 km SSW of Akhiok, Alaska 11:04 UTC
4. 2.1 139 km ESE of Chignik, Alaska 07:30 UTC
5. 2.9 168 km SE of Chignik, Alaska 00:14 UTC
6. 2.5 170 km ESE of Chignik, Alaska 19:29 UTC
7. 2.5 156 km ESE of Chignik, Alaska 05:10 UTC
8. 2.9 162 km ESE of Chignik, Alaska 14:19 UTC
9. 2.9 168 km SE of Chignik, Alaska 07:15 UTC
10. 2.8 173 km ESE of Chignik, Alaska 06:40 UTC
11. 2.6 145 km ESE of Chignik, Alaska 01:26 UTC
12. 2.8 163 km SE of Chignik, Alaska 19:32 UTC
13. 2.6 170 km SE of Chignik, Alaska 18:26 UTC
14. 2.3 158 km ESE of Chignik, Alaska 14:52 UTC
15. 1.9 130 km ESE of Chignik, Alaska 10:24 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 03:54 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.