149 km SSE of Chignik, Alaska

This was a light earthquake. It is usually felt clearly nearby and can rattle windows and dishes, but damage is uncommon.

At this magnitude and depth, people at rest would likely notice it out to about 101 km (63 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 21 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 5.1 would have released about 32 times as much.

1. Northridge, California 1994 M 6.7 7,900× the energy of this one
2. Mineral, Virginia 2011 M 5.8 350× the energy of this one
3. Magna, Utah 2020 M 5.7 250× the energy of this one
4. This earthquake M 4.1 about 21 tons of TNT
5. Around the size people start to feel M 3.0 this one released 45× 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 500 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 · 44 km NW of this epicentre Nov 17, 1938
2. 6.7 121 km SE of Chignik, Alaska · 36 km N 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. 6.2 189 km SE of Chignik, Alaska · 47 km ESE of this epicentre Mar 18, 1945
5. 6.0 168 km SE of Chignik, Alaska · 49 km ENE of this epicentre Nov 16, 1938

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 55.1352, -157.2161. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 3.0 152 km SE of Chignik, Alaska 16:28 UTC
2. 2.6 151 km SE of Chignik, Alaska 16:26 UTC
3. 2.6 157 km SSE of Chignik, Alaska 16:17 UTC
4. 5.3 155 km SE of Chignik, Alaska 16:09 UTC
5. 2.7 139 km SE of Perryville, Alaska 15:27 UTC
6. 2.5 144 km SSE of Chignik, Alaska 15:19 UTC
7. 3.6 150 km SE of Chignik, Alaska 15:13 UTC
8. 2.6 133 km SE of Chignik, Alaska 15:12 UTC
9. 2.7 143 km SE of Chignik, Alaska 15:02 UTC
10. 3.1 148 km SE of Perryville, Alaska 14:52 UTC
11. 3.0 Alaska Peninsula 14:48 UTC
12. 2.8 149 km SE of Perryville, Alaska 14:45 UTC
13. 2.8 141 km SE of Chignik, Alaska 14:42 UTC
14. 2.4 141 km SSE of Chignik, Alaska 14:17 UTC
15. 3.2 123 km SE of Chignik, Alaska 14:03 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 17:21 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.