159 km SE 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 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 5.9 on 2021-07-29 — about 32,000 times the energy of this one.

Before 2016, the USGS record lists 16 earthquakes of M5 or more within 50 km; the five largest:

1. 7.0 164 km SE of Chignik, Alaska · 21 km ENE of this epicentre Sep 4, 1989
2. 6.7 121 km SE of Chignik, Alaska · 38 km NW of this epicentre Feb 13, 1979
3. 6.6 128 km SE of Chignik, Alaska · 45 km N of this epicentre Jul 28, 1934
4. 6.2 189 km SE of Chignik, Alaska · 32 km SSE of this epicentre Mar 18, 1945
5. 6.0 168 km SE of Chignik, Alaska · 16 km E of this epicentre Nov 16, 1938

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 55.2241, -156.7216. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.4 131 km SE of Chignik, Alaska 16:05 UTC
2. 3.5 148 km SE of Chignik, Alaska 23:23 UTC
3. 3.0 179 km SE of Perryville, Alaska 22:53 UTC
4. 3.1 194 km SE of Perryville, Alaska 03:40 UTC
5. 4.8 184 km SE of Perryville, Alaska 15:16 UTC
6. 2.1 142 km SE of Chignik, Alaska 00:04 UTC
7. 2.9 186 km SE of Perryville, Alaska 04:23 UTC
8. 3.0 195 km SE of Chignik, Alaska 05:59 UTC
9. 3.3 190 km SE of Chignik, Alaska 04:59 UTC
10. 2.8 190 km SE of Chignik, Alaska 04:29 UTC
11. 3.2 187 km SE of Chignik, Alaska 17:30 UTC
12. 2.4 134 km SE of Chignik, Alaska 16:16 UTC
13. 2.5 180 km SE of Perryville, Alaska 06:55 UTC
14. 3.1 180 km SE of Perryville, Alaska 17:06 UTC
15. 3.7 197 km SE of Chignik, Alaska 00:35 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 23:20 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.