QuakeIndex

Earthquake · reviewed by a seismologist

M 5.5mww

140 km SE of Chignik, Alaska

· 43 km deep · released about 2.7 kilotons 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 5.5 (mww)
Depth
43 km below the surface
Felt
1 report · strongest reported intensity I
Measured shaking
intensity III (ShakeMap)
USGS impact alert
green
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 279 days ago

This was a moderate earthquake. Shaking at this size can damage poorly built structures close to the epicentre. 1 person has reported feeling it to USGS.

How big was it?

This earthquake released about 2.7 kilotons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 6.5 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 63× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 2.8× the energy of this one
  3. Magna, Utah 2020 M 5.7 2× the energy of this one
  4. This earthquake M 5.5 about 2.7 kilotons of TNT
  5. Around the size people start to feel M 3.0 this one released 5,600× 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 55.3344, -156.9608. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 3.4 173 km SE of Chignik, Alaska
  2. 4.0 136 km SSE of Chignik, Alaska
  3. 2.9 155 km SE of Chignik, Alaska
  4. 3.3 149 km SE of Chignik, Alaska
  5. 1.6 143 km SSE of Chignik, Alaska
  6. 2.9 126 km SSE of Chignik, Alaska
  7. 2.3 143 km SE of Chignik, Alaska
  8. 3.6 161 km SSE of Chignik, Alaska
  9. 2.4 147 km SSE of Chignik, Alaska
  10. 2.2 145 km SE of Perryville, Alaska
  11. 3.0 140 km SE of Chignik, Alaska
  12. 2.5 139 km SE of Perryville, Alaska
  13. 2.7 141 km SSE of Chignik, Alaska
  14. 3.9 137 km SE of Chignik, Alaska
  15. 3.8 139 km SE of Perryville, 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 4 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.