174 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, 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 63 earthquakes of M5 or more within 50 km; the five largest:

1. 7.2 162 km WSW of Adak, Alaska · 40 km SSE of this epicentre Mar 16, 1957
2. 7.2 207 km WSW of Adak, Alaska · 48 km SSW of this epicentre Dec 19, 2007
3. 6.9 203 km WSW of Adak, Alaska · 46 km SSW of this epicentre Mar 31, 1913
4. 6.8 177 km WSW of Adak, Alaska · 47 km S of this epicentre Oct 7, 1989
5. 6.7 205 km WSW of Adak, Alaska · 35 km SW 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 51.7319, -179.1602. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 1.9 185 km WSW of Adak, Alaska 01:24 UTC
2. 1.9 180 km W of Adak, Alaska 19:26 UTC
3. 2.7 178 km WSW of Adak, Alaska 17:10 UTC
4. 3.1 160 km W of Adak, Alaska 23:55 UTC
5. 2.0 166 km W of Adak, Alaska 21:56 UTC
6. 1.8 167 km W of Adak, Alaska 15:56 UTC
7. 2.1 171 km W of Adak, Alaska 11:09 UTC
8. 1.6 152 km WSW of Adak, Alaska 00:05 UTC
9. 1.6 201 km WSW of Adak, Alaska 12:34 UTC
10. 1.8 157 km W of Adak, Alaska 22:16 UTC
11. 2.0 196 km WSW of Adak, Alaska 10:18 UTC
12. 1.9 140 km W of Adak, Alaska 00:56 UTC
13. 2.6 201 km W of Adak, Alaska 11:26 UTC
14. 2.7 194 km W of Adak, Alaska 21:08 UTC
15. 3.0 183 km W of Adak, Alaska 13:45 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 15:00 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.