QuakeIndex

Earthquake · reviewed by a seismologist

M 4.2ml

143 km SE of Chignik, Alaska

· 40 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
40 km below the surface
Felt
no reports yet
Measured shaking
intensity II (ShakeMap)
USGS impact alert
green
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1820 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 55.4197, -156.7173. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.9 155 km SE of Chignik, Alaska
  2. 3.3 149 km SE of Chignik, Alaska
  3. 2.3 143 km SE of Chignik, Alaska
  4. 3.6 161 km SSE of Chignik, Alaska
  5. 2.4 147 km SSE of Chignik, Alaska
  6. 3.0 140 km SE of Chignik, Alaska
  7. 2.7 141 km SSE of Chignik, Alaska
  8. 3.9 137 km SE of Chignik, Alaska
  9. 3.0 153 km SE of Chignik, Alaska
  10. 2.4 118 km SE of Chignik, Alaska
  11. 2.9 139 km SE of Chignik, Alaska
  12. 2.5 137 km SE of Chignik, Alaska
  13. 2.6 151 km SE of Chignik, Alaska
  14. 2.8 137 km SSE of Chignik, Alaska
  15. 2.7 167 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.

For this area

The largest earthquake within 50 km in our catalogue was M 5.9 on 2021-07-29 — it released about 350 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.