QuakeIndex

Earthquake · reviewed by a seismologist

M 6.9mww

112 km E of Chignik, Alaska

· 52 km deep · released about 340 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 6.9 (mww)
Depth
52 km below the surface
Felt
320 reports · strongest reported intensity VIII
Measured shaking
intensity VI (ShakeMap)
USGS impact alert
green
Tsunami
USGS flagged this event for tsunami evaluation. Follow tsunami.gov for official messages.
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 278 days ago

This was a strong earthquake. Damage is likely near the epicentre and it is felt over a wide area. 320 people have reported feeling it to USGS.

How big was it?

This earthquake released about 340 kilotons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 7.9 would have released about 32 times as much.

  1. Tōhoku, Japan 2011 M 9.1 2,000× the energy of this one
  2. San Francisco 1906 M 7.9 32× the energy of this one
  3. Ridgecrest, California 2019 M 7.1 2× the energy of this one
  4. This earthquake M 6.9 about 340 kilotons of TNT
  5. Northridge, California 1994 M 6.7 this one released 2× more
  6. Mineral, Virginia 2011 M 5.8 this one released 45× 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 56.2954, -156.5810. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.7 122 km E of Chignik, Alaska
  2. 2.4 117 km E of Chignik, Alaska
  3. 4.1 114 km E of Chignik, Alaska
  4. 3.1 115 km E of Chignik, Alaska
  5. 2.3 116 km E of Chignik, Alaska
  6. 2.6 121 km E of Chignik, Alaska
  7. 2.4 113 km E of Chignik, Alaska
  8. 2.3 136 km E of Chignik, Alaska
  9. 3.6 115 km E of Chignik, Alaska
  10. 2.2 114 km E of Chignik, Alaska
  11. 2.4 117 km E of Chignik, Alaska
  12. 2.2 113 km E of Chignik, Alaska
  13. 2.3 115 km E of Chignik, Alaska
  14. 2.5 113 km E of Chignik, Alaska
  15. 2.5 Alaska Peninsula

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 2021-10-01.

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

On USGS

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