174 km ESE 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 25 km (16 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 since 2016 was M 4.8 on 2021-07-29 — about 250 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. 7.0 164 km SE of Chignik, Alaska · 36 km SW of this epicentre Sep 4, 1989
2. 6.9 143 km ESE of Chignik, Alaska · 37 km NNW of this epicentre Feb 13, 1951
3. 6.9 171 km SW of Akhiok, Alaska · 24 km NNE of this epicentre Feb 6, 1964
4. 6.6 128 km SE of Chignik, Alaska · 49 km WNW of this epicentre Jul 28, 1934
5. 6.1 210 km SE of Chignik, Alaska · 42 km SSE of this epicentre Nov 15, 1955

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 55.5163, -155.9731. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 3.6 148 km SW of Akhiok, Alaska 07:48 UTC
2. 3.1 185 km SSW of Akhiok, Alaska 05:18 UTC
3. 2.3 155 km ESE of Chignik, Alaska 01:05 UTC
4. 2.4 186 km SE of Chignik, Alaska 23:44 UTC
5. 2.3 186 km SSW of Akhiok, Alaska 23:24 UTC
6. 2.1 170 km SSW of Akhiok, Alaska 03:01 UTC
7. 2.6 175 km SW of Akhiok, Alaska 21:24 UTC
8. 2.6 168 km ESE of Chignik, Alaska 08:02 UTC
9. 2.3 170 km ESE of Chignik, Alaska 05:41 UTC
10. 3.2 165 km ESE of Chignik, Alaska 10:19 UTC
11. 2.4 154 km SW of Akhiok, Alaska 20:04 UTC
12. 3.2 190 km SE of Chignik, Alaska 23:20 UTC
13. 2.4 147 km ESE of Chignik, Alaska 22:08 UTC
14. 2.5 154 km SE of Chignik, Alaska 09:00 UTC
15. 2.7 159 km SSW of Akhiok, Alaska 00:56 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 16:22 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.