202 km W 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 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 680 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.9 would have released about 32 times as much.

1. Mineral, Virginia 2011 M 5.8 22,000× the energy of this one
2. Magna, Utah 2020 M 5.7 16,000× the energy of this one
3. Around the size people start to feel M 3.0 1.4× the energy of this one
4. This earthquake M 2.9 about 680 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 5.2 on 2016-11-23 — about 2,800 times the energy of this one.

Before 2016, the USGS record lists 69 earthquakes of M5 or more within 50 km; the five largest:

1. 7.2 207 km WSW of Adak, Alaska · 39 km S of this epicentre Dec 19, 2007
2. 6.9 203 km WSW of Adak, Alaska · 40 km S of this epicentre Mar 31, 1913
3. 6.9 231 km WSW of Adak, Alaska · 50 km SSW of this epicentre May 14, 1969
4. 6.7 237 km WSW of Adak, Alaska · 48 km SW of this epicentre Oct 13, 1926
5. 6.7 205 km WSW of Adak, Alaska · 18 km S of this epicentre Oct 13, 1926

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 51.7070, -179.5586. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 1.7 227 km WSW of Adak, Alaska 12:03 UTC
2. 1.9 Andreanof Islands, Aleutian Islands, Alaska 03:29 UTC
3. 2.0 204 km WSW of Adak, Alaska 19:29 UTC
4. 2.9 211 km W of Adak, Alaska 20:37 UTC
5. 1.7 216 km WSW of Adak, Alaska 00:11 UTC
6. 2.0 198 km WSW of Adak, Alaska 00:45 UTC
7. 1.9 Andreanof Islands, Aleutian Islands, Alaska 05:09 UTC
8. 1.5 213 km W of Adak, Alaska 10:06 UTC
9. 1.7 222 km WSW of Adak, Alaska 17:13 UTC
10. 1.6 175 km W of Adak, Alaska 15:19 UTC
11. 1.6 194 km WSW of Adak, Alaska 06:59 UTC
12. 1.9 230 km WSW of Adak, Alaska 09:38 UTC
13. 1.8 200 km W of Adak, Alaska 05:12 UTC
14. 2.0 Andreanof Islands, Aleutian Islands, Alaska 15:10 UTC
15. 1.5 169 km W of Adak, Alaska 17:34 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 06:26 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.