234 km SSE of Sand Point, 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 30 km (19 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 680 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.9 would have released about 32 times as much.

1. Mineral, Virginia 2011 M 5.8 22,000× the energy of this one
2. Magna, Utah 2020 M 5.7 16,000× the energy of this one
3. Around the size people start to feel M 3.0 1.4× the energy of this one
4. This earthquake M 2.9 about 680 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 4.2 on 2020-10-26 — about 89 times the energy of this one.

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

1. 5.7 208 km SSE of Sand Point, Alaska · 26 km NNW of this epicentre May 17, 1964
2. 5.5 233 km S of Sand Point, Alaska · 26 km W of this epicentre May 20, 1972
3. 5.0 188 km SSE of Sand Point, Alaska · 47 km NNW of this epicentre Oct 16, 2001

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 53.3004, -159.6006. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.9 south of Alaska 08:39 UTC
2. 2.6 217 km S of Sand Point, Alaska 01:49 UTC
3. 3.0 209 km SSE of Sand Point, Alaska 09:03 UTC
4. 3.0 216 km SSE of Sand Point, Alaska 21:32 UTC
5. 2.9 192 km SSE of Sand Point, Alaska 16:38 UTC
6. 3.1 213 km SSE of Sand Point, Alaska 13:28 UTC
7. 3.1 210 km S of Sand Point, Alaska 19:56 UTC
8. 2.7 south of Alaska 12:08 UTC
9. 3.2 210 km SSE of Sand Point, Alaska 06:50 UTC
10. 3.5 191 km SSE of Sand Point, Alaska 00:59 UTC
11. 3.3 202 km SSE of Sand Point, Alaska 02:12 UTC
12. 3.1 232 km SSE of Sand Point, Alaska 02:58 UTC
13. 3.3 234 km S of Sand Point, Alaska 12:24 UTC
14. 3.2 231 km S of Sand Point, Alaska 14:34 UTC
15. 2.7 229 km S of Sand Point, Alaska 05:01 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 19:51 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.