QuakeIndex

Earthquake · reviewed by a seismologist

M 3.8mb

139 km SE of Akutan, Alaska

Yes. A magnitude 3.8 earthquake was recorded 139 km SE of Akutan, Alaska, at 6:07 pm AKDT on 4 August 2018 (02:07 UTC), 10 km deep.

· 10 km deep · released about 7.6 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 3.8 (mb)
Depth
10 km below the surface
Felt
no reports yet
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1186 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 82 km (51 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 7.6 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.8 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 22,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 1,000× the energy of this one
  3. Magna, Utah 2020 M 5.7 710× the energy of this one
  4. This earthquake M 3.8 about 7.6 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 16× 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 5.5 on 2018-05-27 — about 350 times the energy of this one.

Before 2016, the USGS record lists 38 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.6 146 km ESE of Akutan, Alaska · 39 km NE of this epicentre
  2. 6.6 92 km SE of Akutan, Alaska · 49 km NW of this epicentre
  3. 6.2 136 km SE of Akutan, Alaska · 18 km NNE of this epicentre
  4. 6.2 136 km S of False Pass, Alaska · 49 km NE of this epicentre
  5. 6.2 184 km SE of Akutan, Alaska · 50 km ESE 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 53.2950, -164.1993. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.7 145 km SSE of Akutan, Alaska
  2. 3.6 100 km SE of Akutan, Alaska
  3. 2.3 126 km SE of Akutan, Alaska
  4. 2.6 139 km SE of Akutan, Alaska
  5. 3.0 134 km SE of Akutan, Alaska
  6. 3.1 136 km SE of Akutan, Alaska
  7. 2.5 142 km ESE of Akutan, Alaska
  8. 2.2 95 km SE of Akutan, Alaska
  9. 2.6 154 km ESE of Akutan, Alaska
  10. 2.3 121 km SE of Akutan, Alaska
  11. 3.1 136 km SE of Akutan, Alaska
  12. 2.3 134 km SSE of Akutan, Alaska
  13. 2.8 Unimak Island region, Alaska
  14. 2.7 107 km ESE of Akutan, Alaska
  15. 2.8 101 km SE 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.