155 km SE of Chignik, Alaska

This was a moderate earthquake. Shaking at this size can damage poorly built structures close to the epicentre.

At this magnitude and depth, people at rest would likely notice it out to about 229 km (142 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 1.3 kilotons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 6.3 would have released about 32 times as much.

1. Northridge, California 1994 M 6.7 130× the energy of this one
2. Mineral, Virginia 2011 M 5.8 5.6× the energy of this one
3. Magna, Utah 2020 M 5.7 4× the energy of this one
4. This earthquake M 5.3 about 1.3 kilotons of TNT
5. Around the size people start to feel M 3.0 this one released 2,800× 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 5.9 on 2021-07-29 — about 7.9 times the energy of this one.

Before 2016, the USGS record lists 15 earthquakes of M5 or more within 50 km; the five largest:

1. 7.0 164 km SE of Chignik, Alaska · 37 km ENE of this epicentre Sep 4, 1989
2. 6.7 121 km SE of Chignik, Alaska · 35 km NNW of this epicentre Feb 13, 1979
3. 6.2 189 km SE of Chignik, Alaska · 35 km SE of this epicentre Mar 18, 1945
4. 6.0 168 km SE of Chignik, Alaska · 31 km ENE of this epicentre Nov 16, 1938
5. 5.6 171 km SE of Chignik, Alaska · 23 km E of this epicentre Jun 22, 1970

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 55.1678, -156.9458. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 3.7 146 km SE of Perryville, Alaska 09:57 UTC
2. 3.2 144 km SE of Perryville, Alaska 09:54 UTC
3. 2.3 164 km SSE of Chignik, Alaska 09:49 UTC
4. 2.0 143 km SE of Perryville, Alaska 09:46 UTC
5. 2.5 147 km SE of Chignik, Alaska 09:42 UTC
6. 2.5 south of Alaska 09:37 UTC
7. 2.5 167 km SE of Chignik, Alaska 09:30 UTC
8. 3.0 147 km SSE of Chignik, Alaska 09:27 UTC
9. 2.3 Alaska Peninsula 09:15 UTC
10. 3.2 158 km SE of Chignik, Alaska 08:39 UTC
11. 3.5 156 km SSE of Chignik, Alaska 07:57 UTC
12. 4.1 131 km SE of Chignik, Alaska 07:49 UTC
13. 4.4 166 km SE of Chignik, Alaska 07:24 UTC
14. 2.4 151 km SE of Perryville, Alaska 06:30 UTC
15. 2.5 147 km SE of Perryville, Alaska 06:26 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 06:05 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.