139 km E of Chignik, 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 51 km (32 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 3.8 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.6 would have released about 32 times as much.

1. Northridge, California 1994 M 6.7 45,000× the energy of this one
2. Mineral, Virginia 2011 M 5.8 2,000× the energy of this one
3. Magna, Utah 2020 M 5.7 1,400× the energy of this one
4. This earthquake M 3.6 about 3.8 tons of TNT
5. Around the size people start to feel M 3.0 this one released 7.9× 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 6.9 on 2021-10-11 — about 89,000 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. 7.0 113 km ESE of Chignik, Alaska · 48 km SW of this epicentre May 4, 1923
2. 6.9 143 km ESE of Chignik, Alaska · 36 km S of this epicentre Feb 13, 1951
3. 6.9 171 km SW of Akhiok, Alaska · 49 km SSE of this epicentre Feb 6, 1964
4. 6.3 112 km E of Chignik, Alaska · 27 km WNW of this epicentre Feb 25, 1953
5. 6.1 132 km E of Chignik, Alaska · 10 km NW of this epicentre Sep 13, 1911

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 56.1216, -156.1809. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 3.0 114 km E of Chignik, Alaska 13:09 UTC
2. 2.5 108 km E of Chignik, Alaska 08:08 UTC
3. 2.5 118 km E of Chignik, Alaska 20:41 UTC
4. 1.8 114 km E of Chignik, Alaska 03:13 UTC
5. 2.4 114 km E of Chignik, Alaska 20:53 UTC
6. 2.3 116 km E of Chignik, Alaska 16:08 UTC
7. 1.6 143 km E of Chignik, Alaska 00:17 UTC
8. 1.6 116 km ESE of Chignik, Alaska 19:20 UTC
9. 1.7 115 km E of Chignik, Alaska 07:36 UTC
10. 2.5 138 km WSW of Akhiok, Alaska 23:05 UTC
11. 2.2 119 km E of Chignik, Alaska 01:52 UTC
12. 3.0 127 km WSW of Akhiok, Alaska 16:00 UTC
13. 2.5 110 km E of Chignik, Alaska 00:26 UTC
14. 3.1 118 km E of Chignik, Alaska 21:39 UTC
15. 2.3 119 km E of Chignik, Alaska 04:40 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 21:48 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.