south of 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 25 km (16 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 4.5 on 2021-07-29 — about 500 times the energy of this one.

Before 2016, the USGS record lists 10 earthquakes of M5 or more within 50 km; the five largest:

1. 7.0 113 km ESE of Chignik, Alaska · 37 km WNW of this epicentre May 4, 1923
2. 7.0 164 km SE of Chignik, Alaska · 42 km SSW of this epicentre Sep 4, 1989
3. 6.9 143 km ESE of Chignik, Alaska · 13 km N of this epicentre Feb 13, 1951
4. 6.9 171 km SW of Akhiok, Alaska · 26 km E of this epicentre Feb 6, 1964
5. 6.6 128 km SE of Chignik, Alaska · 31 km WSW of this epicentre Jul 28, 1934

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 55.6823, -156.2479. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.4 182 km ESE of Chignik, Alaska 07:48 UTC
2. 2.5 151 km SW of Akhiok, Alaska 15:50 UTC
3. 2.9 137 km ESE of Chignik, Alaska 01:54 UTC
4. 2.3 119 km ESE of Chignik, Alaska 14:04 UTC
5. 1.9 167 km SW of Akhiok, Alaska 15:47 UTC
6. 4.8 137 km ESE of Chignik, Alaska 14:12 UTC
7. 3.1 south of Alaska 15:34 UTC
8. 2.7 168 km ESE of Chignik, Alaska 04:08 UTC
9. 2.0 157 km SW of Akhiok, Alaska 16:58 UTC
10. 2.3 167 km SW of Akhiok, Alaska 00:58 UTC
11. 2.9 167 km SW of Akhiok, Alaska 11:50 UTC
12. 2.2 161 km SW of Akhiok, Alaska 02:14 UTC
13. 3.0 190 km SE of Chignik, Alaska 19:35 UTC
14. 1.9 165 km SE of Chignik, Alaska 13:56 UTC
15. 2.6 177 km SSW of Akhiok, Alaska 17:37 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 00:39 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.