169 km SW of Akhiok, 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 21 km (13 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 680 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.9 would have released about 32 times as much.

1. Mineral, Virginia 2011 M 5.8 22,000× the energy of this one
2. Magna, Utah 2020 M 5.7 16,000× the energy of this one
3. Around the size people start to feel M 3.0 1.4× the energy of this one
4. This earthquake M 2.9 about 680 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 4.8 on 2021-07-29 — about 710 times the energy of this one.

Before 2016, the USGS record lists 8 earthquakes of M5 or more within 50 km; the five largest:

1. 6.9 143 km ESE of Chignik, Alaska · 30 km WNW of this epicentre Feb 13, 1951
2. 6.9 171 km SW of Akhiok, Alaska · 2 km WSW of this epicentre Feb 6, 1964
3. 6.2 148 km SSW of Akhiok, Alaska · 39 km E of this epicentre Nov 10, 1944
4. 5.9 169 km ESE of Chignik, Alaska · 16 km SW of this epicentre Feb 6, 1964
5. 5.8 188 km SSW of Akhiok, Alaska · 26 km S of this epicentre Jan 5, 2007

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 55.7251, -155.8219. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.8 155 km SE of Chignik, Alaska 16:58 UTC
2. 2.7 south of Alaska 20:47 UTC
3. 2.5 190 km SSW of Akhiok, Alaska 17:58 UTC
4. 2.8 186 km SSW of Akhiok, Alaska 13:19 UTC
5. 2.8 184 km SE of Chignik, Alaska 01:24 UTC
6. 3.3 186 km SSW of Akhiok, Alaska 11:06 UTC
7. 3.3 186 km SSW of Akhiok, Alaska 11:04 UTC
8. 2.9 168 km SE of Chignik, Alaska 00:14 UTC
9. 2.5 170 km ESE of Chignik, Alaska 19:29 UTC
10. 2.5 156 km ESE of Chignik, Alaska 05:10 UTC
11. 2.9 162 km ESE of Chignik, Alaska 14:19 UTC
12. 2.9 168 km SE of Chignik, Alaska 07:15 UTC
13. 2.8 173 km ESE of Chignik, Alaska 06:40 UTC
14. 2.6 145 km ESE of Chignik, Alaska 01:26 UTC
15. 2.8 163 km SE of Chignik, Alaska 19:32 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 15:19 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.