168 km SE of Atka, 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 30 km (19 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 4.5 on 2023-08-06 — about 250 times the energy of this one.

Before 2016, the USGS record lists 4 earthquakes of M5 or more within 50 km:

1. 6.5 143 km ESE of Atka, Alaska · 49 km N of this epicentre Oct 14, 1960
2. 6.0 130 km ESE of Atka, Alaska · 49 km NNW of this epicentre Oct 1, 1960
3. 5.0 150 km SE of Atka, Alaska · 39 km WSW of this epicentre Aug 10, 2014
4. 5.0 125 km SE of Atka, Alaska · 48 km WNW of this epicentre Nov 9, 2015

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 51.3114, -172.2245. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.8 202 km SE of Atka, Alaska 04:36 UTC
2. 3.3 137 km SE of Atka, Alaska 13:27 UTC
3. 3.1 193 km SE of Atka, Alaska 04:59 UTC
4. 3.4 159 km SE of Atka, Alaska 21:58 UTC
5. 3.2 172 km SE of Atka, Alaska 18:32 UTC
6. 2.8 141 km SE of Atka, Alaska 18:05 UTC
7. 3.2 139 km SE of Atka, Alaska 16:40 UTC
8. 3.3 140 km SE of Atka, Alaska 07:57 UTC
9. 3.7 195 km SE of Atka, Alaska 04:01 UTC
10. 3.7 126 km ESE of Atka, Alaska 13:23 UTC
11. 2.7 211 km SE of Atka, Alaska 09:54 UTC
12. 4.4 178 km ESE of Atka, Alaska 04:00 UTC
13. 4.3 178 km ESE of Atka, Alaska 16:35 UTC
14. 2.7 145 km SE of Atka, Alaska 06:18 UTC
15. 3.1 173 km ESE of Atka, Alaska 12:01 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 14:28 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.