QuakeIndex

Earthquake · reviewed by a seismologist

M 3.0ml

138 km SE of Chignik, Alaska

Yes. A magnitude 3.0 earthquake was recorded 138 km SE of Chignik, Alaska at 19:13 UTC on 2021-07-29, 25 km deep.

· 25 km deep · released about 950 lb 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 3.0 (ml)
Depth
25 km below the surface
Felt
no reports yet
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1867 days ago

This was a small earthquake. Shaking like this is often felt indoors nearby and very rarely causes damage.

At this magnitude and depth, people at rest would likely notice it out to about 27 km (17 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 950 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.0 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 350,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 16,000× the energy of this one
  3. Magna, Utah 2020 M 5.7 11,000× the energy of this one
  4. This earthquake M 3.0 about 950 lb of TNT

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 since 2016 was M 5.9 on 2021-07-29 — about 22,000 times the energy of this one.

Before 2016, the USGS record lists 15 earthquakes of M5 or more within 50 km; the five largest:

  1. 7.0 164 km SE of Chignik, Alaska · 37 km E of this epicentre
  2. 6.9 105 km ESE of Perryville, Alaska · 46 km WNW of this epicentre
  3. 6.7 121 km SE of Chignik, Alaska · 17 km NNW of this epicentre
  4. 6.6 128 km SE of Chignik, Alaska · 38 km NNE of this epicentre
  5. 6.0 168 km SE of Chignik, Alaska · 35 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 55.3214, -157.0149. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.6 146 km SE of Perryville, Alaska
  2. 2.2 133 km SE of Chignik, Alaska
  3. 2.8 152 km SSE of Chignik, Alaska
  4. 2.7 141 km SE of Chignik, Alaska
  5. 2.9 145 km SE of Perryville, Alaska
  6. 2.4 144 km SE of Perryville, Alaska
  7. 2.4 169 km SE of Chignik, Alaska
  8. 2.4 139 km SE of Perryville, Alaska
  9. 4.0 132 km SE of Perryville, Alaska
  10. 3.7 146 km SE of Perryville, Alaska
  11. 3.2 144 km SE of Perryville, Alaska
  12. 2.3 164 km SSE of Chignik, Alaska
  13. 2.0 143 km SE of Perryville, Alaska
  14. 2.5 147 km SE of Chignik, Alaska
  15. 2.5 south of 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.