202 km S 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 35 km (22 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 950 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.0 would have released about 32 times as much.

1. Northridge, California 1994 M 6.7 350,000× the energy of this one
2. Mineral, Virginia 2011 M 5.8 16,000× the energy of this one
3. Magna, Utah 2020 M 5.7 11,000× the energy of this one
4. This earthquake M 3.0 about 950 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 5.4 on 2019-09-09 — about 4,000 times the energy of this one.

Before 2016, the USGS record lists 12 earthquakes of M5 or more within 50 km; the five largest:

1. 6.5 184 km SSW of Adak, Alaska · 45 km NW of this epicentre Aug 15, 2007
2. 6.2 204 km S of Adak, Alaska · 20 km ESE of this epicentre Dec 9, 1918
3. 6.1 198 km S of Adak, Alaska · 11 km ENE of this epicentre May 22, 1957
4. 6.1 189 km S of Adak, Alaska · 13 km N of this epicentre Jul 3, 1960
5. 6.0 194 km SSW of Adak, Alaska · 31 km WNW of this epicentre Nov 11, 1993

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 50.0770, -177.0527. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 3.1 222 km S of Adak, Alaska 20:58 UTC
2. 2.6 200 km S of Adak, Alaska 09:24 UTC
3. 3.2 176 km S of Adak, Alaska 16:45 UTC
4. 3.5 215 km SSW of Adak, Alaska 15:48 UTC
5. 2.7 156 km S of Adak, Alaska 02:26 UTC
6. 2.9 191 km S of Adak, Alaska 19:37 UTC
7. 2.6 171 km S of Adak, Alaska 10:08 UTC
8. 2.7 220 km SSW of Adak, Alaska 14:46 UTC
9. 2.7 172 km SSW of Adak, Alaska 08:43 UTC
10. 2.4 185 km S of Adak, Alaska 08:24 UTC
11. 2.5 182 km S of Adak, Alaska 01:43 UTC
12. 2.7 165 km SSW of Adak, Alaska 17:08 UTC
13. 1.9 167 km S of Adak, Alaska 17:40 UTC
14. 2.0 166 km S of Adak, Alaska 09:56 UTC
15. 2.7 184 km SSW of Adak, Alaska 23:02 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 21:35 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.