QuakeIndex

Earthquake · reviewed by a seismologist

M 2.5md

35 km W of Chignik Lake, Alaska

Yes. A magnitude 2.5 earthquake was recorded 35 km W of Chignik Lake, Alaska, at 12:22 am AKST on 18 December 2021 (09:22 UTC), 5.6 km deep.

· 5.6 km deep · released about 160 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 2.5 (md)
Depth
5.6 km below the surface
Felt
no reports yet
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1789 days ago

This was a minor earthquake. Quakes this small are rarely felt and do not cause damage.

At this magnitude and depth, people at rest would likely notice it out to about 21 km (13 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 160 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.5 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 95,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 68,000× the energy of this one
  3. Around the size people start to feel M 3.0 6× the energy of this one
  4. This earthquake M 2.5 about 160 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 4.0 on 2020-07-22 — about 190 times the energy of this one.

Before 2016, the USGS record lists one earthquake of M5 or more within 50 km:

  1. 5.2 48 km NW of Chignik Lake, Alaska · 45 km N 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 56.2168, -159.3300. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.7 41 km W of Chignik Lake, Alaska
  2. 1.9 40 km WNW of Chignik Lake, Alaska
  3. 1.6 13 km SE of Perryville, Alaska
  4. 1.9 11 km ENE of Perryville, Alaska
  5. 2.1 7 km NNE of Perryville, Alaska
  6. 1.8 19 km SSW of Chignik Lake, Alaska
  7. 2.4 3 km SSW of Ivanof Bay, Alaska
  8. 1.6 20 km NE of Perryville, Alaska
  9. 2.0 6 km WSW of Ivanof Bay, Alaska
  10. 1.6 17 km E of Perryville, Alaska
  11. 1.5 13 km WNW of Ivanof Bay, Alaska
  12. 1.8 7 km NW of Perryville, Alaska
  13. 2.0 8 km WNW of Ivanof Bay, Alaska
  14. 2.5 18 km WSW of Chignik Lake, Alaska
  15. 2.5 7 km SSE 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.