147 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 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 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 5.9 on 2021-07-29 — about 22,000 times the energy of this one.

Before 2016, the USGS record lists 19 earthquakes of M5 or more within 50 km; the five largest:

1. 7.0 164 km SE of Chignik, Alaska · 50 km ENE of this epicentre Sep 4, 1989
2. 6.9 105 km ESE of Perryville, Alaska · 44 km NW of this epicentre Nov 17, 1938
3. 6.7 121 km SE of Chignik, Alaska · 31 km N of this epicentre Feb 13, 1979
4. 6.2 143 km SE of Perryville, Alaska · 47 km SW of this epicentre Mar 25, 1927
5. 6.2 189 km SE of Chignik, Alaska · 47 km ESE of this epicentre Mar 18, 1945

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 55.1704, -157.1706. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.3 167 km SE of Chignik, Alaska 01:01 UTC
2. 2.3 147 km SE of Perryville, Alaska 19:36 UTC
3. 3.0 167 km SE of Perryville, Alaska 19:29 UTC
4. 3.7 139 km SE of Perryville, Alaska 15:40 UTC
5. 3.8 149 km SSE of Chignik, Alaska 15:28 UTC
6. 3.1 137 km SE of Perryville, Alaska 12:58 UTC
7. 2.6 134 km SE of Perryville, Alaska 11:03 UTC
8. 2.8 Alaska Peninsula 08:34 UTC
9. 2.7 128 km SE of Chignik, Alaska 07:14 UTC
10. 2.8 128 km SSE of Chignik, Alaska 07:12 UTC
11. 2.5 159 km SE of Chignik, Alaska 07:04 UTC
12. 2.3 133 km SE of Chignik, Alaska 06:40 UTC
13. 2.3 149 km SE of Chignik, Alaska 06:08 UTC
14. 3.2 131 km SSE of Chignik, Alaska 05:02 UTC
15. 3.7 100 km SSE of Chignik, Alaska 04:47 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 13:54 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.