144 km SSE of Chignik, 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 46 km (29 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 2021-07-29 — about 11,000 times the energy of this one.

Before 2016, the USGS record lists 18 earthquakes of M5 or more within 50 km; the five largest:

1. 6.9 105 km ESE of Perryville, Alaska · 40 km NW of this epicentre Nov 17, 1938
2. 6.7 121 km SE of Chignik, Alaska · 33 km NNE of this epicentre Feb 13, 1979
3. 6.2 143 km SE of Perryville, Alaska · 43 km SW of this epicentre Mar 25, 1927
4. 6.0 98 km ESE of Perryville, Alaska · 46 km NW of this epicentre Jan 2, 1985
5. 5.6 171 km SE of Chignik, Alaska · 43 km E of this epicentre Jun 22, 1970

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 55.1658, -157.2653. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.6 161 km SE of Chignik, Alaska 21:45 UTC
2. 2.2 141 km SE of Perryville, Alaska 20:22 UTC
3. 3.4 135 km SE of Perryville, Alaska 17:28 UTC
4. 2.1 98 km SSE of Chignik, Alaska 08:05 UTC
5. 2.7 157 km SE of Chignik, Alaska 06:46 UTC
6. 3.0 144 km SE of Perryville, Alaska 06:02 UTC
7. 2.2 150 km SE of Perryville, Alaska 05:15 UTC
8. 2.4 126 km SE of Chignik, Alaska 05:09 UTC
9. 2.2 121 km SE of Perryville, Alaska 00:16 UTC
10. 3.3 156 km SSE of Chignik, Alaska 22:00 UTC
11. 2.4 134 km SSE of Chignik, Alaska 17:58 UTC
12. 4.0 135 km SSE of Chignik, Alaska 09:54 UTC
13. 2.8 139 km SE of Chignik, Alaska 03:22 UTC
14. 2.2 121 km SE of Perryville, Alaska 21:24 UTC
15. 2.5 128 km SSE of Chignik, Alaska 18:21 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 06:15 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.