QuakeIndex

Earthquake · reviewed by a seismologist

M 5.9ml

127 km SE of Chignik, Alaska

Yes. A magnitude 5.9 earthquake was recorded 127 km SE of Chignik, Alaska at 06:23 UTC on 2021-07-29, less than 1 km deep. 14 people have reported feeling it to USGS.

· 0.8 km deep · released about 11 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 5.9 (ml)
Depth
0.8 km below the surface
Felt
14 reports · strongest reported intensity IV
Measured shaking
intensity III (ShakeMap)
USGS impact alert
green
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 326 days ago

This was a moderate earthquake. Shaking at this size can damage poorly built structures close to the epicentre.

At this magnitude and depth, people at rest would likely notice it out to about 328 km (204 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 11 kilotons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 6.9 would have released about 32 times as much.

  1. Ridgecrest, California 2019 M 7.1 63× the energy of this one
  2. Loma Prieta, California 1989 M 6.9 32× the energy of this one
  3. Northridge, California 1994 M 6.7 16× the energy of this one
  4. This earthquake M 5.9 about 11 kilotons of TNT
  5. Mineral, Virginia 2011 M 5.8 this one released 1.4× more
  6. Magna, Utah 2020 M 5.7 this one released 2× 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 (31 mi) since our catalogue begins in 2016. The previous largest was M 4.9 on 2017-02-27.

Before 2016, the USGS record lists 18 earthquakes of M5 or more within 50 km; the five largest:

  1. 7.0 164 km SE of Chignik, Alaska · 49 km E of this epicentre
  2. 6.9 105 km ESE of Perryville, Alaska · 33 km W of this epicentre
  3. 6.7 121 km SE of Chignik, Alaska · 9 km NNE of this epicentre
  4. 6.6 128 km SE of Chignik, Alaska · 41 km NE of this epicentre
  5. 6.0 168 km SE of Chignik, Alaska · 48 km ESE of this epicentre

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 55.3726, -157.2050. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 4.2 131 km SSE of Chignik, Alaska
  2. 3.6 139 km SE of Perryville, Alaska
  3. 2.7 155 km SE of Chignik, Alaska
  4. 3.0 125 km SE of Perryville, Alaska
  5. 2.9 145 km SE of Perryville, Alaska
  6. 3.4 166 km SE of Chignik, Alaska
  7. 2.5 95 km SE of Chignik, Alaska
  8. 3.3 148 km SE of Perryville, Alaska
  9. 3.2 135 km SE of Chignik, Alaska
  10. 3.0 162 km SE of Chignik, Alaska
  11. 3.2 166 km SSE of Chignik, Alaska
  12. 3.4 140 km SE of Perryville, Alaska
  13. 4.6 148 km SE of Chignik, Alaska
  14. 3.2 145 km SE of Perryville, Alaska
  15. 3.3 113 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.

On USGS

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