128 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 157 km (98 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 170 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 5.7 would have released about 32 times as much.

1. Northridge, California 1994 M 6.7 1,000× the energy of this one
2. Mineral, Virginia 2011 M 5.8 45× the energy of this one
3. Magna, Utah 2020 M 5.7 32× the energy of this one
4. This earthquake M 4.7 about 170 tons of TNT
5. Around the size people start to feel M 3.0 this one released 350× 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 8.2 on 2021-07-29 — about 180,000 times the energy of this one.

Before 2016, the USGS record lists 16 earthquakes of M5 or more within 50 km; the five largest:

1. 8.2 1938 Semidi Islands, Alaska Earthquake · 49 km WSW of this epicentre Nov 10, 1938
2. 6.9 105 km ESE of Perryville, Alaska · 23 km NW of this epicentre Nov 17, 1938
3. 6.7 121 km SE of Chignik, Alaska · 26 km NE of this epicentre Feb 13, 1979
4. 6.2 143 km SE of Perryville, Alaska · 47 km SSW of this epicentre Mar 25, 1927
5. 6.0 98 km ESE of Perryville, Alaska · 30 km WNW of this epicentre Jan 2, 1985

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 55.2815, -157.4372. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 3.0 138 km SE of Chignik, Alaska 19:13 UTC
2. 2.6 128 km SE of Perryville, Alaska 18:17 UTC
3. 3.1 155 km SSE of Chignik, Alaska 17:51 UTC
4. 2.4 136 km SE of Chignik, Alaska 17:19 UTC
5. 3.2 113 km ESE of Perryville, Alaska 16:59 UTC
6. 2.5 125 km SE of Chignik, Alaska 16:34 UTC
7. 2.6 157 km SSE of Chignik, Alaska 16:17 UTC
8. 5.3 155 km SE of Chignik, Alaska 16:09 UTC
9. 2.7 139 km SE of Perryville, Alaska 15:27 UTC
10. 2.5 144 km SSE of Chignik, Alaska 15:19 UTC
11. 2.6 133 km SE of Chignik, Alaska 15:12 UTC
12. 2.7 143 km SE of Chignik, Alaska 15:02 UTC
13. 3.1 148 km SE of Perryville, Alaska 14:52 UTC
14. 3.0 Alaska Peninsula 14:48 UTC
15. 2.8 149 km SE of Perryville, Alaska 14:45 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 19:23 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.