QuakeIndex

Earthquake · reviewed by a seismologist

M 8.2mww

2021 Chignik, Alaska Earthquake

Yes. A magnitude 8.2 earthquake was recorded 2021 Chignik, Alaska Earthquake at 06:15 UTC on 2021-07-29, 35 km deep. 512 people have reported feeling it to USGS.

· 35 km deep · released about 30 megatons of TNT

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10 km30 km60 km120 km N
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 8.2 (mww)
Depth
35 km below the surface
Felt
512 reports · strongest reported intensity IX
Measured shaking
intensity VII (ShakeMap)
USGS impact alert
yellow
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 211 days ago

This was a major earthquake. Serious damage is likely near the epicentre. Follow official information from USGS and local authorities.

At this magnitude and depth, people at rest would likely notice it out to about 1,025 km (637 mi) from the epicentre. 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 30 megatons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 9.2 would have released about 32 times as much.

  1. Great Alaska earthquake 1964 M 9.2 32× the energy of this one
  2. Tōhoku, Japan 2011 M 9.1 22× the energy of this one
  3. This earthquake M 8.2 about 30 megatons of TNT
  4. San Francisco 1906 M 7.9 this one released 2.8× more
  5. Ridgecrest, California 2019 M 7.1 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.

For this area

The largest earthquake within 50 km in our catalogue was M 5.1 on 2020-08-18.

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 55.3635, -157.8876. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.7 139 km SE of Perryville, Alaska
  2. 2.2 69 km SE of Perryville, Alaska
  3. 3.0 Alaska Peninsula
  4. 2.6 94 km SE of Perryville, Alaska
  5. 2.5 101 km SE of Perryville, Alaska
  6. 2.6 133 km SE of Perryville, Alaska
  7. 2.7 127 km SSE of Chignik, Alaska
  8. 2.4 136 km SE of Perryville, Alaska
  9. 2.3 107 km SSE of Chignik, Alaska
  10. 2.5 100 km SE of Perryville, Alaska
  11. 3.7 135 km SE of Perryville, Alaska
  12. 3.4 136 km SE of Perryville, Alaska
  13. 2.5 100 km SE of Perryville, Alaska
  14. 3.5 131 km SE of Perryville, Alaska
  15. 2.6 119 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.

On USGS

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