100 km SSE 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 31 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 7.8 on 2020-07-22 — about 16,000,000 times the energy of this one.

Before 2016, the USGS record lists 11 earthquakes of M5 or more within 50 km; the five largest:

1. 8.2 1938 Semidi Islands, Alaska Earthquake · 13 km ENE of this epicentre Nov 10, 1938
2. 6.6 104 km SSE of Perryville, Alaska · 22 km SW of this epicentre Nov 11, 1938
3. 6.2 143 km SE of Perryville, Alaska · 47 km ESE of this epicentre Mar 25, 1927
4. 6.2 64 km SSE of Perryville, Alaska · 37 km NW of this epicentre Jul 28, 1927
5. 6.2 74 km SE of Perryville, Alaska · 28 km N of this epicentre Aug 6, 1927

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 55.1296, -158.3608. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.9 98 km SSE of Perryville, Alaska 21:53 UTC
2. 2.6 110 km SSE of Perryville, Alaska 18:31 UTC
3. 2.7 102 km SSE of Perryville, Alaska 17:32 UTC
4. 2.2 93 km SSE of Perryville, Alaska 17:09 UTC
5. 2.4 98 km SSE of Perryville, Alaska 16:48 UTC
6. 2.4 97 km SSE of Perryville, Alaska 15:50 UTC
7. 2.6 137 km SSE of Perryville, Alaska 15:33 UTC
8. 4.1 125 km SSE of Perryville, Alaska 14:58 UTC
9. 2.2 south of Alaska 14:15 UTC
10. 2.5 126 km SSE of Perryville, Alaska 13:30 UTC
11. 2.2 99 km SSE of Perryville, Alaska 11:23 UTC
12. 1.9 102 km SSE of Perryville, Alaska 08:56 UTC
13. 2.4 105 km SSE of Perryville, Alaska 08:02 UTC
14. 2.7 128 km SSE of Perryville, Alaska 07:22 UTC
15. 3.8 99 km SSE of Perryville, Alaska 05:42 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 18:54 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.