131 km WSW 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 22 km (14 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 950 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.0 would have released about 32 times as much.

1. Northridge, California 1994 M 6.7 350,000× the energy of this one
2. Mineral, Virginia 2011 M 5.8 16,000× the energy of this one
3. Magna, Utah 2020 M 5.7 11,000× the energy of this one
4. This earthquake M 3.0 about 950 lb of TNT

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 180,000 times the energy of this one.

Before 2016, the USGS record lists 227 earthquakes of M5 or more within 50 km; the five largest:

1. 7.3 88 km WSW of Adak, Alaska · 43 km ENE of this epicentre Jul 7, 1929
2. 7.2 162 km WSW of Adak, Alaska · 41 km WNW of this epicentre Mar 16, 1957
3. 7.0 114 km WSW of Adak, Alaska · 19 km NE of this epicentre Jul 5, 1929
4. 7.0 148 km WSW of Adak, Alaska · 21 km W of this epicentre Mar 11, 1957
5. 6.9 151 km WSW of Adak, Alaska · 26 km WNW of this epicentre May 15, 1993

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 51.3154, -178.3078. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 1.6 154 km WSW of Adak, Alaska 23:27 UTC
2. 2.6 156 km WSW of Adak, Alaska 15:28 UTC
3. 1.6 157 km WSW of Adak, Alaska 05:17 UTC
4. 2.6 144 km WSW of Adak, Alaska 06:19 UTC
5. 3.0 150 km WSW of Adak, Alaska 06:19 UTC
6. 1.7 133 km WSW of Adak, Alaska 21:04 UTC
7. 1.6 127 km WSW of Adak, Alaska 20:37 UTC
8. 1.8 158 km WSW of Adak, Alaska 11:12 UTC
9. 1.7 120 km WSW of Adak, Alaska 03:11 UTC
10. 2.0 108 km WSW of Adak, Alaska 15:57 UTC
11. 1.9 128 km WSW of Adak, Alaska 04:28 UTC
12. 1.5 125 km WSW of Adak, Alaska 08:51 UTC
13. 3.1 144 km W of Adak, Alaska 21:06 UTC
14. 2.0 157 km WSW of Adak, Alaska 08:06 UTC
15. 1.6 141 km WSW of Adak, Alaska 12:15 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 13:06 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.