QuakeIndex

Earthquake · reviewed by a seismologist

M 2.4ml

south of Alaska

Yes. A magnitude 2.4 earthquake was recorded south of Alaska at 04:20 UTC on 2021-08-20, 25 km deep.

· 25 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
25 km below the surface
Felt
no reports yet
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1899 days ago

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

At this magnitude and depth it was probably too small to be felt, even directly above it. 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 5.5 on 2021-07-30 — about 45,000 times the energy of this one.

Before 2016, the USGS record lists 11 earthquakes of M5 or more within 50 km; the five largest:

  1. 7.0 164 km SE of Chignik, Alaska · 16 km NNE of this epicentre
  2. 6.2 189 km SE of Chignik, Alaska · 26 km S of this epicentre
  3. 6.0 168 km SE of Chignik, Alaska · 7 km NNE of this epicentre
  4. 5.6 171 km SE of Chignik, Alaska · 7 km SW of this epicentre
  5. 5.6 205 km SE of Chignik, Alaska · 35 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 55.1844, -156.4996. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.5 212 km SE of Chignik, Alaska
  2. 2.6 187 km SE of Chignik, Alaska
  3. 3.0 190 km SE of Chignik, Alaska
  4. 3.5 129 km SE of Chignik, Alaska
  5. 2.7 167 km SE of Chignik, Alaska
  6. 3.3 180 km SSE of Chignik, Alaska
  7. 3.9 184 km SE of Perryville, Alaska
  8. 3.7 199 km SE of Chignik, Alaska
  9. 2.6 127 km SE of Chignik, Alaska
  10. 3.2 159 km SE of Chignik, Alaska
  11. 2.5 198 km SE of Perryville, Alaska
  12. 2.3 159 km SSE of Chignik, Alaska
  13. 3.1 127 km SE of Chignik, Alaska
  14. 3.0 132 km SE of Chignik, Alaska
  15. 2.9 156 km SE of Chignik, 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.