Unimak Island region, Alaska

This was a light earthquake. It is usually felt clearly nearby and can rattle windows and dishes, but damage is uncommon.

At this magnitude and depth, people at rest would likely notice it out to about 138 km (86 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 85 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 5.5 would have released about 32 times as much.

1. Northridge, California 1994 M 6.7 2,000× the energy of this one
2. Mineral, Virginia 2011 M 5.8 89× the energy of this one
3. Magna, Utah 2020 M 5.7 63× the energy of this one
4. This earthquake M 4.5 about 85 tons of TNT
5. Around the size people start to feel M 3.0 this one released 180× 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 130 times the energy of this one.

Before 2016, the USGS record lists 54 earthquakes of M5 or more within 50 km; the five largest:

1. 8.6 The 1946 Unimak Island, Alaska Earthquake · 31 km ESE of this epicentre Apr 1, 1946
2. 6.6 146 km ESE of Akutan, Alaska · 33 km W of this epicentre Apr 1, 1946
3. 6.2 136 km S of False Pass, Alaska · 33 km WNW of this epicentre Apr 2, 1946
4. 6.2 172 km SSE of False Pass, Alaska · 38 km SE of this epicentre Apr 2, 1946
5. 6.2 184 km SE of Akutan, Alaska · 43 km SSW of this epicentre Apr 6, 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 53.5683, -163.2822. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 1.8 123 km S of False Pass, Alaska 06:52 UTC
2. 2.3 Unimak Island region, Alaska 22:08 UTC
3. 1.9 98 km S of False Pass, Alaska 23:57 UTC
4. 2.1 112 km S of False Pass, Alaska 06:49 UTC
5. 2.1 156 km ESE of Akutan, Alaska 13:53 UTC
6. 2.0 171 km S of False Pass, Alaska 20:31 UTC
7. 2.5 159 km ESE of Akutan, Alaska 12:55 UTC
8. 1.8 106 km S of False Pass, Alaska 16:16 UTC
9. 1.8 120 km S of False Pass, Alaska 18:02 UTC
10. 1.9 99 km S of False Pass, Alaska 15:03 UTC
11. 3.8 117 km S of False Pass, Alaska 03:23 UTC
12. 1.9 105 km S of False Pass, Alaska 03:41 UTC
13. 1.9 97 km S of False Pass, Alaska 04:28 UTC
14. 2.2 132 km S of False Pass, Alaska 01:16 UTC
15. 1.9 158 km ESE of Akutan, Alaska 23:27 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 23:09 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.