139 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 71 km (44 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 5.4 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.7 would have released about 32 times as much.

1. Northridge, California 1994 M 6.7 32,000× the energy of this one
2. Mineral, Virginia 2011 M 5.8 1,400× the energy of this one
3. Magna, Utah 2020 M 5.7 1,000× the energy of this one
4. This earthquake M 3.7 about 5.4 tons of TNT
5. Around the size people start to feel M 3.0 this one released 11× 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 5,600,000 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. 8.2 1938 Semidi Islands, Alaska Earthquake · 44 km WNW of this epicentre Nov 10, 1938
2. 6.9 105 km ESE of Perryville, Alaska · 40 km NNW of this epicentre Nov 17, 1938
3. 6.7 121 km SE of Chignik, Alaska · 48 km NNE of this epicentre Feb 13, 1979
4. 6.2 143 km SE of Perryville, Alaska · 24 km SW of this epicentre Mar 25, 1927
5. 6.0 98 km ESE of Perryville, Alaska · 45 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 55.0667, -157.5141. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.1 127 km SE of Perryville, Alaska 04:52 UTC
2. 2.0 124 km SE of Perryville, Alaska 10:39 UTC
3. 3.0 123 km SE of Perryville, Alaska 07:53 UTC
4. 2.3 128 km SE of Perryville, Alaska 06:19 UTC
5. 4.3 159 km SSE of Chignik, Alaska 18:00 UTC
6. 2.7 121 km SE of Perryville, Alaska 16:27 UTC
7. 2.5 140 km SE of Perryville, Alaska 09:51 UTC
8. 3.4 146 km SE of Perryville, Alaska 07:15 UTC
9. 2.3 146 km SE of Perryville, Alaska 04:30 UTC
10. 3.0 149 km SE of Perryville, Alaska 03:54 UTC
11. 2.3 144 km SE of Perryville, Alaska 03:47 UTC
12. 2.5 134 km SE of Perryville, Alaska 23:05 UTC
13. 3.3 145 km SE of Perryville, Alaska 14:47 UTC
14. 3.6 114 km SE of Perryville, Alaska 03:17 UTC
15. 2.5 147 km SSE of Chignik, Alaska 00:17 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 17:35 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.