124 km SSE of Ugashik, 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 32 km (20 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 6.9 on 2021-10-11 — about 1,000,000 times the energy of this one.

Before 2016, the USGS record lists 13 earthquakes of M5 or more within 50 km; the five largest:

1. 6.8 117 km SSE of Ugashik, Alaska · 8 km WNW of this epicentre May 29, 2015
2. 6.4 104 km SSE of Ugashik, Alaska · 27 km WNW of this epicentre May 20, 1979
3. 6.3 112 km E of Chignik, Alaska · 46 km SSW of this epicentre Feb 25, 1953
4. 6.1 132 km E of Chignik, Alaska · 41 km S of this epicentre Sep 13, 1911
5. 5.4 115 km SSE of Ugashik, Alaska · 9 km NNW of this epicentre Jun 9, 1971

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 56.5680, -156.3010. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.5 112 km E of Chignik, Alaska 11:46 UTC
2. 2.5 102 km ENE of Chignik, Alaska 06:30 UTC
3. 2.5 103 km ENE of Chignik, Alaska 15:23 UTC
4. 2.4 109 km W of Akhiok, Alaska 01:26 UTC
5. 2.7 119 km SE of Ugashik, Alaska 04:51 UTC
6. 2.2 96 km SSE of Ugashik, Alaska 08:14 UTC
7. 2.3 109 km SE of Ugashik, Alaska 01:53 UTC
8. 2.2 107 km E of Chignik, Alaska 04:02 UTC
9. 2.2 104 km SE of Ugashik, Alaska 20:49 UTC
10. 2.6 129 km E of Chignik, Alaska 14:54 UTC
11. 3.2 130 km E of Chignik, Alaska 10:04 UTC
12. 2.5 103 km SE of Ugashik, Alaska 05:29 UTC
13. 2.6 118 km E of Chignik, Alaska 09:52 UTC
14. 2.1 116 km ENE of Chignik, Alaska 09:43 UTC
15. 2.3 96 km E of Chignik, Alaska 13:38 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 05:25 UTC. QuakeIndex does not forecast aftershocks. When USGS issues an operational aftershock forecast it appears on the USGS event page.

Revisions

USGS refines a solution as more stations report. Every change we have seen is listed here.

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.