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 8 km (5 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 1,900 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.2 would have released about 32 times as much.

1. Northridge, California 1994 M 6.7 180,000× the energy of this one
2. Mineral, Virginia 2011 M 5.8 7,900× the energy of this one
3. Magna, Utah 2020 M 5.7 5,600× the energy of this one
4. This earthquake M 3.2 about 1,900 lb of TNT
5. Around the size people start to feel M 3.0 this one released 2× 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 in our catalogue was M 6.9 on 2021-10-11 — about 350,000 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 56.3167, -156.5242. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 4.4 114 km E of Chignik, Alaska 18:46 UTC
2. 1.9 111 km E of Chignik, Alaska 14:17 UTC
3. 2.6 115 km E of Chignik, Alaska 08:02 UTC
4. 1.9 95 km E of Chignik, Alaska 01:10 UTC
5. 2.1 114 km E of Chignik, Alaska 21:28 UTC
6. 2.0 Alaska Peninsula 02:37 UTC
7. 2.4 108 km SSE of Ugashik, Alaska 22:18 UTC
8. 1.7 118 km SSE of Ugashik, Alaska 05:28 UTC
9. 2.4 110 km ENE of Chignik, Alaska 19:44 UTC
10. 2.1 91 km ESE of Chignik, Alaska 16:55 UTC
11. 2.4 111 km E of Chignik, Alaska 02:47 UTC
12. 2.0 115 km E of Chignik, Alaska 11:04 UTC
13. 2.5 115 km E of Chignik, Alaska 01:40 UTC
14. 2.4 116 km E of Chignik, Alaska 00:56 UTC
15. 1.8 112 km SSE of Ugashik, Alaska 08:51 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 04:56 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.