QuakeIndex

Earthquake · reviewed by a seismologist

M 4.2ml

197 km ESE of Chignik, Alaska

· 37 km deep · released about 30 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 4.2 (ml)
Depth
37 km below the surface
Felt
no reports yet
Measured shaking
intensity III (ShakeMap)
USGS impact alert
green
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1809 days ago

This was a light earthquake. It is usually felt clearly nearby and can rattle windows and dishes, but damage is uncommon.

How big was it?

This earthquake released about 30 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 5.2 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 5,600× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 250× the energy of this one
  3. Magna, Utah 2020 M 5.7 180× the energy of this one
  4. This earthquake M 4.2 about 30 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 63× 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.

Where

Epicentre 55.3849, -155.6996. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.9 185 km SSW of Akhiok, Alaska
  2. 1.8 157 km SSW of Akhiok, Alaska
  3. 3.0 169 km ESE of Chignik, Alaska
  4. 1.6 south of Alaska
  5. 2.8 190 km SSW of Akhiok, Alaska
  6. 2.4 170 km SE of Chignik, Alaska
  7. 2.6 158 km SSW of Akhiok, Alaska
  8. 2.6 166 km ESE of Chignik, Alaska
  9. 2.4 162 km SW of Akhiok, Alaska
  10. 2.0 154 km ESE of Chignik, Alaska
  11. 2.6 182 km SE of Chignik, Alaska
  12. 2.4 194 km SE of Chignik, Alaska
  13. 2.3 183 km ESE of Chignik, Alaska
  14. 2.2 155 km ESE of Chignik, Alaska
  15. 2.3 170 km SSW of Akhiok, 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.

For this area

The largest earthquake within 50 km in our catalogue was M 4.8 on 2021-07-29 — it released about 7.9 times the energy of this one.

From the QuakeIndex catalogue, built from the USGS FDSN event service.

On USGS

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