162 km S of False Pass, 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 34 km (21 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 5.9 on 2016-10-27 — about 11,000 times the energy of this one.

Before 2016, the USGS record lists 55 earthquakes of M5 or more within 50 km; the five largest:

1. 6.6 146 km ESE of Akutan, Alaska · 20 km NW of this epicentre Apr 1, 1946
2. 6.2 Unimak Island region, Alaska · 48 km NNW of this epicentre Oct 14, 1933
3. 6.2 136 km SE of Akutan, Alaska · 31 km W of this epicentre Apr 1, 1946
4. 6.2 136 km S of False Pass, Alaska · 30 km NNW of this epicentre Apr 2, 1946
5. 6.2 172 km SSE of False Pass, Alaska · 50 km E of this epicentre Apr 2, 1946

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 53.3992, -163.5961. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.3 115 km S of False Pass, Alaska 12:47 UTC
2. 2.8 152 km S of False Pass, Alaska 08:44 UTC
3. 4.3 158 km S of False Pass, Alaska 07:52 UTC
4. 2.7 144 km S of False Pass, Alaska 04:41 UTC
5. 3.1 156 km S of False Pass, Alaska 13:52 UTC
6. 2.5 120 km S of False Pass, Alaska 12:06 UTC
7. 2.6 145 km S of False Pass, Alaska 15:15 UTC
8. 2.2 163 km ESE of Akutan, Alaska 14:36 UTC
9. 2.3 152 km ESE of Akutan, Alaska 14:14 UTC
10. 3.0 125 km ESE of Akutan, Alaska 09:09 UTC
11. 2.0 153 km S of False Pass, Alaska 04:26 UTC
12. 3.0 122 km ESE of Akutan, Alaska 15:20 UTC
13. 2.6 125 km S of False Pass, Alaska 16:59 UTC
14. 3.5 121 km ESE of Akutan, Alaska 08:00 UTC
15. 2.8 121 km ESE of Akutan, Alaska 07:44 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 17:59 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.