136 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 37 km (23 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 1,900 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.2 would have released about 32 times as much.

1. Northridge, California 1994 M 6.7 180,000× the energy of this one
2. Mineral, Virginia 2011 M 5.8 7,900× the energy of this one
3. Magna, Utah 2020 M 5.7 5,600× the energy of this one
4. This earthquake M 3.2 about 1,900 lb of TNT
5. Around the size people start to feel M 3.0 this one released 2× more

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 6.5 on 2018-08-15 — about 89,000 times the energy of this one.

Before 2016, the USGS record lists 164 earthquakes of M5 or more within 50 km; the five largest:

1. 7.0 114 km WSW of Adak, Alaska · 43 km N of this epicentre Jul 5, 1929
2. 7.0 148 km WSW of Adak, Alaska · 45 km NW of this epicentre Mar 11, 1957
3. 6.8 111 km SW of Adak, Alaska · 26 km NNE of this epicentre Jan 4, 1912
4. 6.6 117 km SW of Adak, Alaska · 24 km NNE of this epicentre Sep 30, 1992
5. 6.5 144 km SW of Adak, Alaska · 12 km W of this epicentre Apr 16, 1927

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 51.0695, -178.1122. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 1.9 110 km SW of Adak, Alaska 21:22 UTC
2. 2.3 138 km SW of Adak, Alaska 07:40 UTC
3. 3.0 134 km SW of Adak, Alaska 10:09 UTC
4. 2.3 86 km SW of Adak, Alaska 22:43 UTC
5. 2.4 159 km SW of Adak, Alaska 20:15 UTC
6. 2.0 139 km WSW of Adak, Alaska 00:47 UTC
7. 2.0 140 km SW of Adak, Alaska 14:43 UTC
8. 4.0 149 km SW of Adak, Alaska 14:49 UTC
9. 1.8 127 km SW of Adak, Alaska 08:53 UTC
10. 1.6 111 km WSW of Adak, Alaska 21:58 UTC
11. 2.0 131 km WSW of Adak, Alaska 13:37 UTC
12. 2.4 149 km WSW of Adak, Alaska 09:56 UTC
13. 2.0 101 km SW of Adak, Alaska 01:45 UTC
14. 1.6 135 km WSW of Adak, Alaska 22:01 UTC
15. 2.8 152 km SW of Adak, Alaska 17:45 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 07:33 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.