125 km E 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 4 km (2 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 480 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.8 would have released about 32 times as much.

1. Mineral, Virginia 2011 M 5.8 32,000× the energy of this one
2. Magna, Utah 2020 M 5.7 22,000× the energy of this one
3. Around the size people start to feel M 3.0 2× the energy of this one
4. This earthquake M 2.8 about 480 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 1,400,000 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. 6.8 117 km SSE of Ugashik, Alaska · 20 km N of this epicentre May 29, 2015
2. 6.4 104 km SSE of Ugashik, Alaska · 33 km NW of this epicentre May 20, 1979
3. 6.3 112 km E of Chignik, Alaska · 29 km SSW of this epicentre Feb 25, 1953
4. 6.1 132 km E of Chignik, Alaska · 25 km SSE of this epicentre Sep 13, 1911
5. 5.4 115 km SSE of Ugashik, Alaska · 25 km N of this epicentre Jun 9, 1971

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 56.4184, -156.3812. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.6 Alaska Peninsula 09:16 UTC
2. 2.0 108 km SSE of Ugashik, Alaska 14:07 UTC
3. 2.0 97 km ENE of Chignik, Alaska 05:21 UTC
4. 2.3 111 km SSE of Ugashik, Alaska 12:04 UTC
5. 2.0 102 km SSE of Ugashik, Alaska 16:43 UTC
6. 2.1 Alaska Peninsula 17:56 UTC
7. 2.7 114 km E of Chignik, Alaska 11:17 UTC
8. 1.7 95 km SSE of Ugashik, Alaska 18:06 UTC
9. 3.0 112 km E of Chignik, Alaska 03:29 UTC
10. 3.2 113 km ESE of Chignik, Alaska 05:27 UTC
11. 3.1 116 km E of Chignik, Alaska 07:48 UTC
12. 1.9 Alaska Peninsula 18:46 UTC
13. 2.2 111 km E of Chignik, Alaska 03:14 UTC
14. 2.5 119 km E of Chignik, Alaska 05:24 UTC
15. 2.7 116 km E of Chignik, Alaska 09:07 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 23:47 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.