QuakeIndex

Earthquake · reviewed by a seismologist

M 4.3mb

154 km ESE of Akutan, Alaska

Yes. A magnitude 4.3 earthquake was recorded 154 km ESE of Akutan, Alaska at 22:31 UTC on 2018-04-21, 17 km deep. 1 person has reported feeling it to USGS.

· 17 km deep · released about 43 tons 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 4.3 (mb)
Depth
17 km below the surface
Felt
1 report · strongest reported intensity I
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1187 days ago

This was a light earthquake. It is usually felt clearly nearby and can rattle windows and dishes, but damage is uncommon.

At this magnitude and depth, people at rest would likely notice it out to about 120 km (75 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 43 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 5.3 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 4,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 180× the energy of this one
  3. Magna, Utah 2020 M 5.7 130× the energy of this one
  4. This earthquake M 4.3 about 43 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 89× more

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 2016-10-27 — about 250 times the energy of this one.

Before 2016, the USGS record lists 57 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.6 146 km ESE of Akutan, Alaska · 10 km NNW of this epicentre
  2. 6.2 Unimak Island region, Alaska · 38 km NNW of this epicentre
  3. 6.2 136 km SE of Akutan, Alaska · 23 km W of this epicentre
  4. 6.2 136 km S of False Pass, Alaska · 21 km N of this epicentre
  5. 6.2 184 km SE of Akutan, Alaska · 34 km SSE 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 53.4638, -163.7174. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 3.6 166 km S of False Pass, Alaska
  2. 2.9 166 km S of False Pass, Alaska
  3. 3.0 165 km S of False Pass, Alaska
  4. 2.8 162 km ESE of Akutan, Alaska
  5. 3.2 163 km S of False Pass, Alaska
  6. 2.7 164 km SE of Akutan, Alaska
  7. 3.5 165 km S of False Pass, Alaska
  8. 3.9 157 km ESE of Akutan, Alaska
  9. 3.4 164 km ESE of Akutan, Alaska
  10. 2.9 163 km ESE of Akutan, Alaska
  11. 2.9 155 km ESE of Akutan, Alaska
  12. 4.3 152 km ESE of Akutan, Alaska
  13. 2.4 Unimak Island region, Alaska
  14. 3.9 163 km ESE of Akutan, Alaska
  15. 2.7 160 km ESE of Akutan, 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.