QuakeIndex

Earthquake · reviewed by a seismologist

M 3.9mb

208 km W of Adak, Alaska

Yes. A magnitude 3.9 earthquake was recorded 208 km W of Adak, Alaska at 20:28 UTC on 2017-03-24, 65 km deep.

· 65 km deep · released about 11 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 3.9 (mb)
Depth
65 km below the surface
Felt
no reports yet
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1195 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 61 km (38 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 11 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.9 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 16,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 710× the energy of this one
  3. Magna, Utah 2020 M 5.7 500× the energy of this one
  4. This earthquake M 3.9 about 11 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 22× 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 5.2 on 2016-11-23 — about 89 times the energy of this one.

Before 2016, the USGS record lists 18 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.6 174 km W of Adak, Alaska · 40 km SE of this epicentre
  2. 6.4 187 km W of Adak, Alaska · 32 km SE of this epicentre
  3. 6.2 230 km W of Adak, Alaska · 24 km WSW of this epicentre
  4. 5.8 224 km W of Adak, Alaska · 35 km SSW of this epicentre
  5. 5.8 184 km W of Adak, Alaska · 34 km SE 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 52.0906, -179.6433. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.8 199 km W of Adak, Alaska
  2. 4.0 210 km W of Adak, Alaska
  3. 4.5 208 km W of Adak, Alaska
  4. 2.2 213 km W of Adak, Alaska
  5. 2.8 187 km W of Adak, Alaska
  6. 2.7 230 km W of Adak, Alaska
  7. 3.8 220 km W of Adak, Alaska
  8. 1.8 174 km W of Adak, Alaska
  9. 2.3 227 km W of Adak, Alaska
  10. 2.4 187 km W of Adak, Alaska
  11. 2.8 200 km W of Adak, Alaska
  12. 3.0 175 km W of Adak, Alaska
  13. 2.8 Andreanof Islands, Aleutian Islands, Alaska
  14. 2.6 221 km W of Adak, Alaska
  15. 2.5 188 km W of Adak, 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.