128 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 5 km (3 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 340 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.7 would have released about 32 times as much.

1. Mineral, Virginia 2011 M 5.8 45,000× the energy of this one
2. Magna, Utah 2020 M 5.7 32,000× the energy of this one
3. Around the size people start to feel M 3.0 2.8× the energy of this one
4. This earthquake M 2.7 about 340 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 63,000 times the energy of this one.

Before 2016, the USGS record lists 15 earthquakes of M5 or more within 50 km; the five largest:

1. 7.0 164 km SE of Chignik, Alaska · 43 km ESE of this epicentre Sep 4, 1989
2. 6.9 105 km ESE of Perryville, Alaska · 41 km W of this epicentre Nov 17, 1938
3. 6.7 121 km SE of Chignik, Alaska · 7 km NW of this epicentre Feb 13, 1979
4. 6.6 128 km SE of Chignik, Alaska · 33 km NE of this epicentre Jul 28, 1934
5. 6.0 168 km SE of Chignik, Alaska · 43 km ESE 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 55.4074, -157.0873. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.7 143 km SE of Chignik, Alaska 09:29 UTC
2. 3.3 145 km SE of Perryville, Alaska 14:47 UTC
3. 2.4 159 km SE of Chignik, Alaska 11:48 UTC
4. 3.0 152 km SE of Chignik, Alaska 08:58 UTC
5. 2.9 129 km SE of Chignik, Alaska 06:54 UTC
6. 2.9 157 km SE of Chignik, Alaska 06:26 UTC
7. 2.9 167 km SE of Chignik, Alaska 04:34 UTC
8. 2.5 147 km SSE of Chignik, Alaska 00:17 UTC
9. 3.6 161 km SE of Chignik, Alaska 23:31 UTC
10. 3.4 171 km SE of Chignik, Alaska 21:29 UTC
11. 3.0 141 km SE of Chignik, Alaska 20:05 UTC
12. 2.3 125 km SE of Chignik, Alaska 17:41 UTC
13. 3.2 154 km SSE of Chignik, Alaska 06:43 UTC
14. 2.5 126 km SE of Chignik, Alaska 05:52 UTC
15. 2.7 169 km SE of Chignik, Alaska 02:45 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 06:28 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.