128 km SE of Perryville, 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 8.2 on 2021-07-29 — about 22,000 times the energy of this one.

Before 2016, the USGS record lists 13 earthquakes of M5 or more within 50 km; the five largest:

1. 8.2 1938 Semidi Islands, Alaska Earthquake · 37 km W of this epicentre Nov 10, 1938
2. 6.9 105 km ESE of Perryville, Alaska · 29 km NNW of this epicentre Nov 17, 1938
3. 6.7 121 km SE of Chignik, Alaska · 44 km NE of this epicentre Feb 13, 1979
4. 6.2 143 km SE of Perryville, Alaska · 30 km SSW of this epicentre Mar 25, 1927
5. 6.0 98 km ESE of Perryville, Alaska · 34 km NNW of this epicentre Jan 2, 1985

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 55.1526, -157.6035. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.6 133 km SE of Perryville, Alaska 13:33 UTC
2. 2.4 158 km SE of Perryville, Alaska 13:26 UTC
3. 2.6 152 km SSE of Chignik, Alaska 13:22 UTC
4. 2.9 Alaska Peninsula 13:16 UTC
5. 4.1 149 km SE of Perryville, Alaska 13:14 UTC
6. 2.4 140 km SE of Perryville, Alaska 13:13 UTC
7. 2.7 127 km SSE of Chignik, Alaska 13:03 UTC
8. 2.6 140 km SSE of Chignik, Alaska 13:01 UTC
9. 2.4 136 km SE of Perryville, Alaska 12:59 UTC
10. 2.3 107 km SSE of Chignik, Alaska 12:54 UTC
11. 2.5 100 km SE of Perryville, Alaska 12:50 UTC
12. 4.3 134 km SE of Chignik, Alaska 12:42 UTC
13. 2.7 143 km SE of Perryville, Alaska 12:36 UTC
14. 3.7 135 km SE of Perryville, Alaska 12:28 UTC
15. 3.4 136 km SE of Perryville, Alaska 12:17 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 17:14 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.