175 km SW of Adak, 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 11 km (7 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 6.1 on 2021-09-24 — about 89,000 times the energy of this one.

Before 2016, the USGS record lists 167 earthquakes of M5 or more within 50 km; the five largest:

1. 7.2 162 km WSW of Adak, Alaska · 47 km N of this epicentre Mar 16, 1957
2. 7.0 148 km WSW of Adak, Alaska · 38 km NNE of this epicentre Mar 11, 1957
3. 6.9 151 km WSW of Adak, Alaska · 41 km N of this epicentre May 15, 1993
4. 6.8 177 km WSW of Adak, Alaska · 40 km NNW of this epicentre Oct 7, 1989
5. 6.7 194 km WSW of Adak, Alaska · 48 km NW of this epicentre Sep 12, 1969

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 51.0040, -178.7380. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.2 159 km WSW of Adak, Alaska 14:50 UTC
2. 2.4 138 km WSW of Adak, Alaska 08:35 UTC
3. 2.8 148 km SW of Adak, Alaska 02:40 UTC
4. 2.8 133 km WSW of Adak, Alaska 22:34 UTC
5. 4.2 150 km SW of Adak, Alaska 10:56 UTC
6. 4.2 150 km SW of Adak, Alaska 10:56 UTC
7. 4.2 147 km WSW of Adak, Alaska 10:56 UTC
8. 2.8 148 km SW of Adak, Alaska 02:12 UTC
9. 2.7 159 km SW of Adak, Alaska 08:00 UTC
10. 2.2 140 km SW of Adak, Alaska 18:34 UTC
11. 3.0 127 km WSW of Adak, Alaska 01:43 UTC
12. 2.7 150 km SW of Adak, Alaska 23:20 UTC
13. 2.5 156 km SW of Adak, Alaska 18:19 UTC
14. 2.6 190 km WSW of Adak, Alaska 22:03 UTC
15. 2.7 190 km WSW of Adak, Alaska 02:26 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 14:42 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.