123 km SE 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 14 earthquakes of M5 or more within 50 km; the five largest:

1. 6.9 105 km ESE of Perryville, Alaska · 30 km W of this epicentre Nov 17, 1938
2. 6.7 121 km SE of Chignik, Alaska · 9 km NE of this epicentre Feb 13, 1979
3. 6.6 128 km SE of Chignik, Alaska · 42 km NE of this epicentre Jul 28, 1934
4. 6.0 98 km ESE of Perryville, Alaska · 37 km W of this epicentre Jan 2, 1985
5. 5.2 116 km SE of Perryville, Alaska · 46 km WSW of this epicentre Dec 19, 2004

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 55.3905, -157.2572. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 4.1 131 km SE of Chignik, Alaska 07:49 UTC
2. 2.4 151 km SE of Perryville, Alaska 06:30 UTC
3. 2.5 147 km SE of Perryville, Alaska 06:26 UTC
4. 2.4 147 km SE of Chignik, Alaska 06:18 UTC
5. 3.8 158 km SSE of Chignik, Alaska 05:40 UTC
6. 2.4 125 km SE of Chignik, Alaska 05:18 UTC
7. 2.4 139 km SE of Perryville, Alaska 05:13 UTC
8. 2.3 137 km SE of Perryville, Alaska 04:57 UTC
9. 2.5 157 km SSE of Chignik, Alaska 04:30 UTC
10. 2.7 146 km SE of Chignik, Alaska 04:26 UTC
11. 3.2 153 km SE of Chignik, Alaska 04:11 UTC
12. 2.6 160 km SSE of Chignik, Alaska 03:59 UTC
13. 5.5 140 km SE of Chignik, Alaska 03:52 UTC
14. 3.2 152 km SSE of Chignik, Alaska 03:36 UTC
15. 2.3 130 km SSE of Chignik, Alaska 02:23 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 08:56 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.