171 km E of Atka, 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 10 km (6 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 4.6 on 2016-01-18 — about 500 times the energy of this one.

Before 2016, the USGS record lists 52 earthquakes of M5 or more within 50 km; the five largest:

1. 7.3 Fox Islands, Aleutian Islands, Alaska · 16 km SW of this epicentre Jun 24, 2011
2. 6.9 170 km E of Atka, Alaska · 2 km NW of this epicentre Sep 2, 2011
3. 6.3 143 km E of Atka, Alaska · 35 km WSW of this epicentre Apr 5, 1957
4. 6.1 185 km ESE of Atka, Alaska · 34 km SSE of this epicentre Dec 6, 1930
5. 6.1 157 km ESE of Atka, Alaska · 38 km SSW of this epicentre Jul 13, 1959

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 52.1574, -171.6872. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 3.9 191 km ESE of Atka, Alaska 05:29 UTC
2. 3.0 140 km E of Atka, Alaska 05:28 UTC
3. 3.0 196 km SW of Nikolski, Alaska 19:02 UTC
4. 2.1 191 km SW of Nikolski, Alaska 00:35 UTC
5. 3.0 174 km E of Atka, Alaska 02:26 UTC
6. 3.2 185 km ESE of Atka, Alaska 16:47 UTC
7. 3.1 156 km ESE of Atka, Alaska 23:22 UTC
8. 3.4 181 km WSW of Nikolski, Alaska 00:02 UTC
9. 3.2 163 km E of Atka, Alaska 23:39 UTC
10. 3.8 189 km ESE of Atka, Alaska 15:01 UTC
11. 3.1 153 km E of Atka, Alaska 19:58 UTC
12. 2.9 149 km E of Atka, Alaska 01:15 UTC
13. 2.8 190 km E of Atka, Alaska 23:39 UTC
14. 2.7 178 km WSW of Nikolski, Alaska 15:32 UTC
15. 3.8 182 km ESE of Atka, Alaska 15:02 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 06:16 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.