225 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 19 km (12 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 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.5 would have released about 32 times as much.

1. Mineral, Virginia 2011 M 5.8 89,000× the energy of this one
2. Magna, Utah 2020 M 5.7 63,000× the energy of this one
3. Around the size people start to feel M 3.0 5.6× the energy of this one
4. This earthquake M 2.5 about 170 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 5.6 on 2021-09-16 — about 45,000 times the energy of this one.

Before 2016, the USGS record lists 3 earthquakes of M5 or more within 50 km:

1. 6.2 189 km SE of Chignik, Alaska · 37 km NW of this epicentre Mar 18, 1945
2. 5.6 205 km SE of Chignik, Alaska · 20 km NNW of this epicentre Feb 7, 1996
3. 5.0 213 km SE of Perryville, Alaska · 42 km WSW of this epicentre Jan 7, 2007

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 54.7494, -156.0934. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 3.1 243 km SE of Chignik, Alaska 06:03 UTC
2. 3.0 195 km SE of Chignik, Alaska 05:59 UTC
3. 3.3 190 km SE of Chignik, Alaska 04:59 UTC
4. 2.8 190 km SE of Chignik, Alaska 04:29 UTC
5. 3.2 187 km SE of Chignik, Alaska 17:30 UTC
6. 2.8 226 km SE of Chignik, Alaska 03:58 UTC
7. 3.7 197 km SE of Chignik, Alaska 00:35 UTC
8. 3.7 212 km SE of Chignik, Alaska 15:48 UTC
9. 3.0 256 km SE of Chignik, Alaska 02:33 UTC
10. 3.9 202 km SE of Chignik, Alaska 12:22 UTC
11. 3.4 215 km SE of Chignik, Alaska 20:20 UTC
12. 3.1 201 km SE of Chignik, Alaska 17:39 UTC
13. 2.8 205 km SE of Chignik, Alaska 05:24 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 12:56 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.