QuakeIndex

Earthquake · reviewed by a seismologist

M 2.8ml

111 km E of Chignik, Alaska

Yes. A magnitude 2.8 earthquake was recorded 111 km E of Chignik, Alaska at 01:34 UTC on 2021-10-18, 30 km deep. 1 person has reported feeling it to USGS.

· 30 km deep · released about 480 lb of TNT

Felt it? Tell USGS Check my area
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 2.8 (ml)
Depth
30 km below the surface
Felt
1 report · strongest reported intensity II
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1783 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 it was probably too small to be felt, even directly above it. 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 480 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.8 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 32,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 22,000× the energy of this one
  3. Around the size people start to feel M 3.0 2× the energy of this one
  4. This earthquake M 2.8 about 480 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 6.9 on 2021-10-11 — about 1,400,000 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. 7.0 113 km ESE of Chignik, Alaska · 50 km SSW of this epicentre
  2. 6.8 117 km SSE of Ugashik, Alaska · 37 km NNE of this epicentre
  3. 6.4 77 km ESE of Chignik, Alaska · 40 km WSW of this epicentre
  4. 6.4 104 km SSE of Ugashik, Alaska · 42 km N of this epicentre
  5. 6.3 112 km E of Chignik, Alaska · 10 km S 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 56.2794, -156.6079. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.4 122 km E of Chignik, Alaska
  2. 1.8 112 km E of Chignik, Alaska
  3. 2.2 103 km E of Chignik, Alaska
  4. 1.9 109 km E of Chignik, Alaska
  5. 2.5 80 km E of Chignik, Alaska
  6. 2.6 120 km E of Chignik, Alaska
  7. 2.2 Alaska Peninsula
  8. 2.3 113 km E of Chignik, Alaska
  9. 2.2 112 km E of Chignik, Alaska
  10. 1.9 116 km E of Chignik, Alaska
  11. 1.7 136 km E of Chignik, Alaska
  12. 1.8 118 km E of Chignik, Alaska
  13. 2.3 116 km E of Chignik, Alaska
  14. 3.1 112 km E of Chignik, Alaska
  15. 2.5 117 km E 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.