204 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 it was probably too small to be felt, even directly above it. 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 5.7 on 2018-02-08 — about 5,600 times the energy of this one.

Before 2016, the USGS record lists 15 earthquakes of M5 or more within 50 km; the five largest:

1. 6.6 174 km W of Adak, Alaska · 43 km SE of this epicentre Apr 16, 2008
2. 6.4 187 km W of Adak, Alaska · 39 km SSE of this epicentre Apr 15, 2008
3. 6.2 230 km W of Adak, Alaska · 33 km SW of this epicentre Apr 29, 2007
4. 5.8 224 km W of Adak, Alaska · 46 km SSW of this epicentre Jul 5, 1966
5. 5.8 184 km W of Adak, Alaska · 40 km SSE of this epicentre Mar 2, 2008

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 52.1765, -179.5757. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.0 211 km W of Adak, Alaska 08:24 UTC
2. 2.8 192 km W of Adak, Alaska 12:14 UTC
3. 2.7 173 km W of Adak, Alaska 14:16 UTC
4. 2.6 167 km W of Adak, Alaska 17:09 UTC
5. 1.7 204 km W of Adak, Alaska 02:57 UTC
6. 1.9 219 km W of Adak, Alaska 17:06 UTC
7. 3.6 205 km W of Adak, Alaska 11:28 UTC
8. 2.1 173 km W of Adak, Alaska 12:00 UTC
9. 2.8 226 km W of Adak, Alaska 18:43 UTC
10. 2.9 207 km W of Adak, Alaska 18:35 UTC
11. 2.7 230 km W of Adak, Alaska 06:05 UTC
12. 1.9 180 km W of Adak, Alaska 19:26 UTC
13. 2.9 216 km W of Adak, Alaska 08:30 UTC
14. 2.1 171 km W of Adak, Alaska 11:09 UTC
15. 2.8 220 km W of Adak, Alaska 20:36 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 07:18 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.