Alaska Peninsula

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 33 km (21 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 in our catalogue was M 8.2 on 2021-07-29 — about 63,000,000 times the energy of this one.

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 55.2108, -157.3799. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.3 Alaska Peninsula 09:15 UTC
2. 3.2 158 km SE of Chignik, Alaska 08:39 UTC
3. 3.5 156 km SSE of Chignik, Alaska 07:57 UTC
4. 4.1 131 km SE of Chignik, Alaska 07:49 UTC
5. 2.3 138 km SE of Perryville, Alaska 07:11 UTC
6. 2.3 132 km SE of Perryville, Alaska 06:41 UTC
7. 2.4 151 km SE of Perryville, Alaska 06:30 UTC
8. 2.5 147 km SE of Perryville, Alaska 06:26 UTC
9. 2.4 147 km SE of Chignik, Alaska 06:18 UTC
10. 2.4 120 km SE of Perryville, Alaska 06:09 UTC
11. 2.5 135 km SE of Perryville, Alaska 06:09 UTC
12. 3.8 158 km SSE of Chignik, Alaska 05:40 UTC
13. 2.2 113 km SE of Perryville, Alaska 05:29 UTC
14. 2.3 134 km SE of Perryville, Alaska 05:15 UTC
15. 2.4 139 km SE of Perryville, Alaska 05:13 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 08:32 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.