206 km SSE of Atka, 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 38 km (24 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 4.5 on 2017-01-10 — about 89 times the energy of this one.

Before 2016, the USGS record lists 10 earthquakes of M5 or more within 50 km; the five largest:

1. 6.2 234 km SSE of Atka, Alaska · 32 km SE of this epicentre Mar 20, 1958
2. 6.0 234 km SSE of Atka, Alaska · 38 km SSW of this epicentre Nov 9, 1929
3. 5.8 174 km SSE of Atka, Alaska · 41 km NNE of this epicentre Apr 1, 1957
4. 5.8 165 km SSE of Atka, Alaska · 47 km N of this epicentre Apr 2, 1957
5. 5.6 198 km SSE of Atka, Alaska · 9 km NNW of this epicentre Mar 7, 2015

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 50.4390, -173.2323. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.6 205 km SSE of Atka, Alaska 03:34 UTC
2. 2.9 173 km SSE of Atka, Alaska 18:37 UTC
3. 2.7 Andreanof Islands, Aleutian Islands, Alaska 09:08 UTC
4. 3.0 202 km SSE of Atka, Alaska 00:16 UTC
5. 2.9 186 km SSE of Atka, Alaska 11:37 UTC
6. 2.2 168 km SSE of Atka, Alaska 22:28 UTC
7. 2.9 199 km SSE of Atka, Alaska 01:35 UTC
8. 3.0 159 km SSE of Atka, Alaska 20:29 UTC
9. 1.9 162 km SSE of Atka, Alaska 14:51 UTC
10. 3.1 186 km SSE of Atka, Alaska 21:57 UTC
11. 2.7 Andreanof Islands, Aleutian Islands, Alaska 02:58 UTC
12. 2.9 184 km SSE of Atka, Alaska 19:19 UTC
13. 2.8 182 km SSE of Atka, Alaska 00:06 UTC
14. 2.1 217 km SSE of Atka, Alaska 07:52 UTC
15. 2.2 229 km SSE of Atka, Alaska 18:49 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 10:09 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.