QuakeIndex

Earthquake · reviewed by a seismologist

M 2.4ml

181 km S of Atka, Alaska

Yes. A magnitude 2.4 earthquake was recorded 181 km S of Atka, Alaska at 18:26 UTC on 2021-12-20, 20 km deep.

· 20 km deep · released about 120 lb 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 2.4 (ml)
Depth
20 km below the surface
Felt
no reports yet
Nearest mapped fault
Alaska-Aleutian subduction zone, 16 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 1751 days ago

This was a minor earthquake. Quakes this small are rarely felt and do not cause damage.

At this magnitude and depth, people at rest would likely notice it out to about 6 km (4 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 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.4 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 130,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 89,000× the energy of this one
  3. Around the size people start to feel M 3.0 7.9× the energy of this one
  4. This earthquake M 2.4 about 120 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 4.5 on 2017-01-10 — about 1,400 times the energy of this one.

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

  1. 6.6 208 km S of Atka, Alaska · 31 km SSW of this epicentre
  2. 5.6 185 km S of Atka, Alaska · 33 km W of this epicentre
  3. 5.4 198 km SSE of Atka, Alaska · 39 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 50.5630, -174.0993. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.3 161 km S of Atka, Alaska
  2. 3.4 207 km S of Atka, Alaska
  3. 3.8 197 km S of Atka, Alaska
  4. 2.1 148 km S of Atka, Alaska
  5. 2.2 142 km S of Atka, Alaska
  6. 3.7 190 km S of Atka, Alaska
  7. 2.1 175 km S of Atka, Alaska
  8. 2.4 165 km S of Atka, Alaska
  9. 2.3 168 km S of Atka, Alaska
  10. 3.1 153 km S of Atka, Alaska
  11. 3.0 172 km S of Atka, Alaska
  12. 3.2 163 km SSE of Atka, Alaska
  13. 2.3 Andreanof Islands, Aleutian Islands, Alaska
  14. 3.1 162 km S of Atka, Alaska
  15. 4.6 164 km S of Atka, 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.