QuakeIndex

Earthquake · reviewed by a seismologist

M 2.9ml

178 km SE of Atka, Alaska

Yes. A magnitude 2.9 earthquake was recorded 178 km SE of Atka, Alaska at 18:04 UTC on 2021-08-21, 10 km deep.

· 10 km deep · released about 680 lb of TNT

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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 2.9 (ml)
Depth
10 km below the surface
Felt
no reports yet
Nearest mapped fault
Alaska-Aleutian subduction zone, 14 km from its surface trace — near is not the same as on
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1838 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 30 km (19 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 680 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.9 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 22,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 16,000× the energy of this one
  3. Around the size people start to feel M 3.0 1.4× the energy of this one
  4. This earthquake M 2.9 about 680 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 4.2 on 2019-03-17 — about 89 times the energy of this one.

Before 2016, the USGS record lists 6 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.9 182 km SSE of Atka, Alaska · 35 km SW of this epicentre
  2. 5.8 161 km SSE of Atka, Alaska · 50 km WSW of this epicentre
  3. 5.8 150 km SSE of Atka, Alaska · 46 km W of this epicentre
  4. 5.3 144 km SE of Atka, Alaska · 38 km WNW of this epicentre
  5. 5.1 185 km SE of Atka, Alaska · 21 km SSW 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 51.0349, -172.4323. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.7 145 km SE of Atka, Alaska
  2. 3.8 184 km SSE of Atka, Alaska
  3. 3.1 199 km SSE of Atka, Alaska
  4. 3.0 201 km SSE of Atka, Alaska
  5. 3.2 147 km SE of Atka, Alaska
  6. 2.1 163 km SSE of Atka, Alaska
  7. 2.2 158 km SSE of Atka, Alaska
  8. 2.6 202 km SE of Atka, Alaska
  9. 2.4 189 km SE of Atka, Alaska
  10. 2.9 168 km SE of Atka, Alaska
  11. 3.9 139 km SE of Atka, Alaska
  12. 3.2 195 km SSE of Atka, Alaska
  13. 2.7 186 km SE of Atka, Alaska
  14. 2.7 142 km SE of Atka, Alaska
  15. 2.9 214 km SE of Atka, 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.