133 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 6.2 on 2017-05-08 — about 89,000 times the energy of this one.

Before 2016, the USGS record lists 25 earthquakes of M5 or more within 50 km; the five largest:

1. 6.6 174 km W of Adak, Alaska · 44 km WSW of this epicentre Apr 16, 2008
2. 6.4 118 km WSW of Adak, Alaska · 49 km SSE of this epicentre Sep 26, 2012
3. 6.3 128 km W of Adak, Alaska · 5 km SE of this epicentre May 10, 1939
4. 6.2 145 km WSW of Adak, Alaska · 42 km SSW of this epicentre Aug 1, 1927
5. 6.2 Andreanof Islands, Aleutian Islands, Alaska · 48 km SE of this epicentre Sep 19, 1948

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 52.0039, -178.5609. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.2 131 km W of Adak, Alaska 09:59 UTC
2. 2.6 128 km WSW of Adak, Alaska 00:41 UTC
3. 2.0 133 km W of Adak, Alaska 06:55 UTC
4. 2.7 141 km WSW of Adak, Alaska 23:40 UTC
5. 2.0 150 km WSW of Adak, Alaska 23:15 UTC
6. 1.5 150 km W of Adak, Alaska 16:08 UTC
7. 1.8 155 km W of Adak, Alaska 21:38 UTC
8. 1.7 155 km W of Adak, Alaska 20:34 UTC
9. 2.1 154 km W of Adak, Alaska 01:50 UTC
10. 2.0 132 km WSW of Adak, Alaska 19:26 UTC
11. 2.1 132 km WSW of Adak, Alaska 18:10 UTC
12. 2.5 159 km W of Adak, Alaska 23:00 UTC
13. 2.5 160 km W of Adak, Alaska 23:00 UTC
14. 1.9 154 km W of Adak, Alaska 13:54 UTC
15. 1.9 152 km W of Adak, Alaska 20:10 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 17:18 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.