QuakeIndex

Earthquake · reviewed by a seismologist

M 2.8ml

142 km E of Chignik, Alaska

Yes. A magnitude 2.8 earthquake was recorded 142 km E of Chignik, Alaska at 03:06 UTC on 2020-08-11, less than 1 km deep.

· 0.9 km deep · released about 480 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 2.8 (ml)
Depth
0.9 km below the surface
Felt
no reports yet
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 2213 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 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 4.5 on 2017-03-28 — about 350 times the energy of this one.

Before 2016, the USGS record lists 9 earthquakes of M5 or more within 50 km; the five largest:

  1. 7.0 113 km ESE of Chignik, Alaska · 47 km WSW of this epicentre
  2. 6.9 143 km ESE of Chignik, Alaska · 31 km SSW of this epicentre
  3. 6.9 171 km SW of Akhiok, Alaska · 43 km SSE of this epicentre
  4. 6.3 112 km E of Chignik, Alaska · 31 km WNW of this epicentre
  5. 6.1 132 km E of Chignik, Alaska · 16 km NNW 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 56.0733, -156.1485. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 3.2 152 km ESE of Chignik, Alaska
  2. 2.7 south of Alaska
  3. 2.6 125 km ESE of Chignik, Alaska
  4. 1.8 133 km SW of Akhiok, Alaska
  5. 2.5 170 km ESE of Chignik, Alaska
  6. 2.5 156 km ESE of Chignik, Alaska
  7. 2.9 162 km ESE of Chignik, Alaska
  8. 2.7 122 km E of Chignik, Alaska
  9. 2.6 145 km ESE of Chignik, Alaska
  10. 2.3 158 km ESE of Chignik, Alaska
  11. 1.9 130 km ESE of Chignik, Alaska
  12. 2.1 170 km ESE of Chignik, Alaska
  13. 4.2 130 km ESE of Chignik, Alaska
  14. 1.8 160 km ESE of Chignik, Alaska
  15. 4.5 162 km ESE 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.