167 km SSE 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 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 5.9 on 2021-07-29 — about 32,000 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. 7.0 164 km SE of Chignik, Alaska · 43 km NE of this epicentre Sep 4, 1989
2. 6.7 121 km SE of Chignik, Alaska · 48 km NNW of this epicentre Feb 13, 1979
3. 6.2 189 km SE of Chignik, Alaska · 26 km ESE of this epicentre Mar 18, 1945
4. 6.0 168 km SE of Chignik, Alaska · 36 km NE of this epicentre Nov 16, 1938
5. 5.6 171 km SE of Chignik, Alaska · 23 km ENE of this epicentre Jun 22, 1970

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 55.0486, -156.9080. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.8 198 km SE of Perryville, Alaska 21:03 UTC
2. 2.4 191 km SE of Perryville, Alaska 17:16 UTC
3. 2.4 209 km SE of Chignik, Alaska 03:04 UTC
4. 2.1 159 km SSE of Chignik, Alaska 12:57 UTC
5. 3.0 133 km SE of Chignik, Alaska 06:14 UTC
6. 2.7 138 km SE of Chignik, Alaska 05:53 UTC
7. 3.1 123 km SE of Chignik, Alaska 10:37 UTC
8. 2.6 202 km SE of Perryville, Alaska 11:20 UTC
9. 3.4 205 km SE of Perryville, Alaska 21:05 UTC
10. 3.0 206 km SE of Perryville, Alaska 19:52 UTC
11. 2.6 209 km SE of Perryville, Alaska 19:45 UTC
12. 2.9 203 km SE of Perryville, Alaska 19:01 UTC
13. 3.0 204 km SE of Perryville, Alaska 18:15 UTC
14. 3.1 202 km SE of Perryville, Alaska 18:02 UTC
15. 3.1 200 km SE of Perryville, Alaska 14:19 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 10:23 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.