117 km SE 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 it was probably too small to be felt, even directly above it. 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 6.9 on 2021-10-11 — about 2,000,000 times the energy of this one.

Before 2016, the USGS record lists 11 earthquakes of M5 or more within 50 km; the five largest:

1. 6.8 117 km SSE of Ugashik, Alaska · 15 km SW of this epicentre May 29, 2015
2. 6.4 104 km SSE of Ugashik, Alaska · 31 km W of this epicentre May 20, 1979
3. 5.4 115 km SSE of Ugashik, Alaska · 9 km WSW of this epicentre Jun 9, 1971
4. 5.4 113 km SSE of Ugashik, Alaska · 18 km WSW of this epicentre Jan 27, 2004
5. 5.3 117 km SSE of Ugashik, Alaska · 20 km WSW of this epicentre Dec 28, 1985

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 56.6750, -156.2240. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.2 107 km E of Chignik, Alaska 04:02 UTC
2. 2.2 104 km SE of Ugashik, Alaska 20:49 UTC
3. 2.0 82 km ESE of Ugashik, Alaska 01:45 UTC
4. 2.6 129 km E of Chignik, Alaska 14:54 UTC
5. 3.2 130 km E of Chignik, Alaska 10:04 UTC
6. 2.5 103 km SE of Ugashik, Alaska 05:29 UTC
7. 2.6 118 km E of Chignik, Alaska 09:52 UTC
8. 2.1 116 km ENE of Chignik, Alaska 09:43 UTC
9. 2.9 124 km SSE of Ugashik, Alaska 15:42 UTC
10. 3.3 129 km E of Chignik, Alaska 20:31 UTC
11. 1.6 97 km ESE of Ugashik, Alaska 04:36 UTC
12. 1.8 90 km SSE of Ugashik, Alaska 13:17 UTC
13. 1.7 101 km W of Akhiok, Alaska 18:19 UTC
14. 1.7 95 km SE of Ugashik, Alaska 05:14 UTC
15. 2.8 128 km E of Chignik, Alaska 17:06 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 15:22 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.