251 km SW of Adak, 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 89 km (55 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 11 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.9 would have released about 32 times as much.

1. Northridge, California 1994 M 6.7 16,000× the energy of this one
2. Mineral, Virginia 2011 M 5.8 710× the energy of this one
3. Magna, Utah 2020 M 5.7 500× the energy of this one
4. This earthquake M 3.9 about 11 tons of TNT
5. Around the size people start to feel M 3.0 this one released 22× 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 4.3 on 2017-07-01 — about 4 times the energy of this one.

Before 2016, the USGS record lists 4 earthquakes of M5 or more within 50 km:

1. 6.8 Andreanof Islands, Aleutian Islands, Alaska · 11 km ESE of this epicentre Jun 22, 1913
2. 6.0 207 km SW of Adak, Alaska · 45 km NNE of this epicentre Feb 7, 1926
3. 6.0 254 km SW of Adak, Alaska · 10 km SSE of this epicentre Jul 8, 1929
4. 6.0 257 km SW of Adak, Alaska · 7 km WSW of this epicentre Jul 3, 1957

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 50.1310, -178.9063. Map © OpenStreetMap contributors.

Aftershocks so far

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

1. 2.6 271 km SSW of Adak, Alaska 03:49 UTC
2. 2.9 234 km SW of Adak, Alaska 09:50 UTC
3. 3.9 265 km SSW of Adak, Alaska 06:13 UTC
4. 2.9 229 km SW of Adak, Alaska 05:17 UTC
5. 3.2 275 km SW of Adak, Alaska 08:59 UTC
6. 2.8 263 km SW of Adak, Alaska 19:26 UTC
7. 2.5 217 km SW of Adak, Alaska 21:07 UTC
8. 3.0 222 km SW of Adak, Alaska 09:44 UTC
9. 3.2 201 km SW of Adak, Alaska 22:29 UTC
10. 3.7 269 km SW of Adak, Alaska 04:02 UTC
11. 3.6 266 km SW of Adak, Alaska 11:45 UTC
12. 3.0 270 km SW of Adak, Alaska 09:20 UTC
13. 3.0 252 km SW of Adak, Alaska 14:12 UTC
14. 3.0 261 km SW of Adak, Alaska 01:22 UTC
15. 2.4 237 km SW of Adak, Alaska 00:41 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 16:47 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.