145 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 25 km (16 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 680 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.9 would have released about 32 times as much.

1. Mineral, Virginia 2011 M 5.8 22,000× the energy of this one
2. Magna, Utah 2020 M 5.7 16,000× the energy of this one
3. Around the size people start to feel M 3.0 1.4× the energy of this one
4. This earthquake M 2.9 about 680 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 5.5 on 2021-07-29 — about 7,900 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. 8.2 1938 Semidi Islands, Alaska Earthquake · 44 km NW of this epicentre Nov 10, 1938
2. 6.2 143 km SE of Perryville, Alaska · 2 km NNW of this epicentre Mar 25, 1927
3. 5.9 182 km SE of Perryville, Alaska · 37 km SE of this epicentre Dec 23, 1938
4. 5.5 160 km SE of Perryville, Alaska · 26 km E of this epicentre Mar 10, 2012
5. 5.4 139 km SSE of Perryville, Alaska · 30 km WSW of this epicentre Jan 1, 1991

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 54.8806, -157.7314. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.3 113 km SE of Perryville, Alaska 04:08 UTC
2. 2.6 143 km SE of Perryville, Alaska 23:35 UTC
3. 2.6 125 km SE of Perryville, Alaska 22:25 UTC
4. 2.8 127 km SE of Perryville, Alaska 21:56 UTC
5. 3.9 131 km SE of Perryville, Alaska 18:44 UTC
6. 3.1 133 km SE of Perryville, Alaska 18:38 UTC
7. 2.2 138 km SE of Perryville, Alaska 17:46 UTC
8. 2.5 151 km SE of Perryville, Alaska 16:56 UTC
9. 2.6 148 km SE of Perryville, Alaska 16:54 UTC
10. 2.8 134 km SE of Perryville, Alaska 15:11 UTC
11. 3.3 143 km SE of Perryville, Alaska 14:55 UTC
12. 3.2 137 km SE of Perryville, Alaska 14:20 UTC
13. 4.1 146 km SE of Perryville, Alaska 13:06 UTC
14. 3.1 116 km SE of Perryville, Alaska 13:06 UTC
15. 2.2 131 km SE of Perryville, Alaska 12:58 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 21:55 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.