QuakeIndex

Earthquake · reviewed by a seismologist

M 3.9mb

Andreanof Islands, Aleutian Islands, Alaska

Yes. A magnitude 3.9 earthquake was recorded in the Andreanof Islands, Aleutian Islands, Alaska at 13:58 UTC on 2023-12-28, 35 km deep.

· 35 km deep · released about 11 tons of TNT

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Distance rings around the epicentre, with the nearest towns at their true direction and later quakes as coloured dots. Not a shaking map — see the USGS ShakeMap for that.
When
Magnitude
M 3.9 (mb)
Depth
35 km below the surface
Felt
no reports yet
Nearest mapped fault
Alaska-Aleutian subduction zone, 23 km from its surface trace — near is not the same as on
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 987 days ago

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 83 km (52 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 4.7 on 2022-04-12 — about 16 times the energy of this one.

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

  1. 6.7 254 km SW of Adak, Alaska · 46 km NE of this epicentre
  2. 6.0 295 km SW of Adak, Alaska · 23 km SE of this epicentre
  3. 5.6 289 km SW of Adak, Alaska · 26 km ESE of this epicentre
  4. 5.5 292 km SW of Adak, Alaska · 28 km ESE of this epicentre

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 50.1961, -179.9962. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.6 south of the Aleutian Islands
  2. 2.7 283 km SW of Adak, Alaska
  3. 3.5 276 km SW of Adak, Alaska
  4. 3.6 Andreanof Islands, Aleutian Islands, Alaska
  5. 3.1 290 km SW of Adak, Alaska
  6. 2.9 289 km SW of Adak, Alaska
  7. 3.0 Andreanof Islands, Aleutian Islands, Alaska
  8. 3.0 295 km SW of Adak, Alaska
  9. 2.2 292 km SW of Adak, Alaska
  10. 3.0 Andreanof Islands, Aleutian Islands, Alaska
  11. 3.1 284 km SW of Adak, Alaska
  12. 2.9 285 km SW of Adak, Alaska
  13. 2.0 263 km SW of Adak, Alaska
  14. 2.8 286 km SW of Adak, Alaska
  15. 4.0 299 km SW of Adak, Alaska

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of . QuakeIndex does not forecast aftershocks. When USGS issues an operational aftershock forecast it appears on the USGS event page.

On USGS

QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.