175 km SE of Perryville, Alaska

This was a small earthquake. Shaking like this is often felt indoors nearby and very rarely causes damage.

At this magnitude and depth, people at rest would likely notice it out to about 30 km (19 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 950 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.0 would have released about 32 times as much.

1. Northridge, California 1994 M 6.7 350,000× the energy of this one
2. Mineral, Virginia 2011 M 5.8 16,000× the energy of this one
3. Magna, Utah 2020 M 5.7 11,000× the energy of this one
4. This earthquake M 3.0 about 950 lb of TNT

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 5.4 on 2021-07-29 — about 4,000 times the energy of this one.

Before 2016, the USGS record lists 9 earthquakes of M5 or more within 50 km; the five largest:

1. 6.2 143 km SE of Perryville, Alaska · 43 km W of this epicentre Mar 25, 1927
2. 6.2 189 km SE of Chignik, Alaska · 36 km ENE of this epicentre Mar 18, 1945
3. 5.9 182 km SE of Perryville, Alaska · 29 km SSW of this epicentre Dec 23, 1938
4. 5.6 171 km SE of Chignik, Alaska · 44 km NE of this epicentre Jun 22, 1970
5. 5.5 160 km SE of Perryville, Alaska · 17 km WNW of this epicentre Mar 10, 2012

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 54.8601, -157.0739. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.8 162 km SE of Perryville, Alaska 05:17 UTC
2. 2.8 202 km SE of Perryville, Alaska 11:15 UTC
3. 3.3 207 km SE of Perryville, Alaska 09:21 UTC
4. 3.3 158 km SE of Perryville, Alaska 04:21 UTC
5. 3.1 139 km SE of Chignik, Alaska 15:19 UTC
6. 3.3 164 km SE of Chignik, Alaska 14:23 UTC
7. 2.5 201 km SE of Perryville, Alaska 01:38 UTC
8. 2.6 153 km SSE of Chignik, Alaska 01:23 UTC
9. 2.8 140 km SE of Perryville, Alaska 22:10 UTC
10. 2.5 161 km SE of Chignik, Alaska 07:47 UTC
11. 2.3 144 km SE of Perryville, Alaska 16:31 UTC
12. 3.0 203 km SE of Perryville, Alaska 13:16 UTC
13. 2.8 137 km SSE of Chignik, Alaska 06:54 UTC
14. 3.6 207 km SE of Perryville, Alaska 22:15 UTC
15. 2.6 204 km SE of Perryville, Alaska 06:36 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 08:59 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.