QuakeIndex

Earthquake · reviewed by a seismologist

M 4.6mb

Unimak Island region, Alaska

Yes. A magnitude 4.6 earthquake was recorded in the Unimak Island region, Alaska at 04:07 UTC on 2023-01-21, 29 km deep.

· 29 km deep · released about 120 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 4.6 (mb)
Depth
29 km below the surface
Felt
no reports yet
Measured shaking
intensity I (ShakeMap)
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1323 days ago

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 146 km (91 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 120 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 5.6 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 1,400× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 63× the energy of this one
  3. Magna, Utah 2020 M 5.7 45× the energy of this one
  4. This earthquake M 4.6 about 120 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 250× 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 5.9 on 2016-10-27 — about 89 times the energy of this one.

Before 2016, the USGS record lists 57 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.6 146 km ESE of Akutan, Alaska · 12 km WNW of this epicentre
  2. 6.2 Unimak Island region, Alaska · 39 km NNW of this epicentre
  3. 6.2 136 km SE of Akutan, Alaska · 29 km W of this epicentre
  4. 6.2 136 km S of False Pass, Alaska · 20 km NNW of this epicentre
  5. 6.2 184 km SE of Akutan, Alaska · 34 km SSE 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 53.4900, -163.6280. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.2 102 km S of False Pass, Alaska
  2. 2.2 112 km ESE of Akutan, Alaska
  3. 2.4 163 km S of False Pass, Alaska
  4. 2.1 124 km ESE of Akutan, Alaska
  5. 2.7 154 km S of False Pass, Alaska
  6. 2.8 109 km S of False Pass, Alaska
  7. 2.0 111 km SSW of False Pass, Alaska
  8. 2.0 112 km S of False Pass, Alaska
  9. 2.6 151 km S of False Pass, Alaska
  10. 2.9 106 km S of False Pass, Alaska
  11. 2.5 108 km S of False Pass, Alaska
  12. 2.8 Unimak Island region, Alaska
  13. 3.4 Unimak Island region, Alaska
  14. 2.0 126 km ESE of Akutan, Alaska
  15. 2.9 112 km S of False Pass, 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.