170 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 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 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 4.7 on 2017-08-25 — about 710 times the energy of this one.

Before 2016, the USGS record lists 19 earthquakes of M5 or more within 50 km; the five largest:

1. 6.5 144 km SW of Adak, Alaska · 50 km NNW of this epicentre Apr 16, 1927
2. 6.2 161 km SW of Adak, Alaska · 35 km NNW of this epicentre Dec 9, 1918
3. 6.0 207 km SW of Adak, Alaska · 41 km WSW of this epicentre Feb 7, 1926
4. 6.0 161 km SSW of Adak, Alaska · 42 km ESE of this epicentre Jan 11, 1934
5. 5.8 150 km SW of Adak, Alaska · 20 km NE of this epicentre Jul 7, 1929

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 50.6513, -178.1170. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 1.5 143 km SW of Adak, Alaska 10:09 UTC
2. 2.1 172 km SW of Adak, Alaska 12:47 UTC
3. 2.5 217 km SW of Adak, Alaska 21:07 UTC
4. 3.2 201 km SW of Adak, Alaska 22:29 UTC
5. 1.9 182 km SSW of Adak, Alaska 16:06 UTC
6. 3.3 127 km SSW of Adak, Alaska 02:54 UTC
7. 2.1 190 km SSW of Adak, Alaska 07:23 UTC
8. 1.9 180 km SW of Adak, Alaska 17:43 UTC
9. 2.3 136 km SW of Adak, Alaska 17:56 UTC
10. 2.5 154 km SW of Adak, Alaska 06:04 UTC
11. 2.6 133 km SW of Adak, Alaska 21:48 UTC
12. 2.9 129 km SSW of Adak, Alaska 17:59 UTC
13. 2.6 142 km SSW of Adak, Alaska 07:22 UTC
14. 2.2 147 km SW of Adak, Alaska 01:30 UTC
15. 2.9 145 km SSW of Adak, Alaska 13:08 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 08:35 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.