QuakeIndex

Earthquake · reviewed by a seismologist

M 4.5mb

161 km S of Adak, Alaska

Yes. A magnitude 4.5 earthquake was recorded 161 km S of Adak, Alaska at 13:27 UTC on 2021-09-15, 10 km deep.

· 10 km deep · released about 85 tons 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 4.5 (mb)
Depth
10 km below the surface
Felt
no reports yet
Measured shaking
intensity I (ShakeMap)
Nearest mapped fault
Alaska-Aleutian subduction zone, 6 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 1817 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 139 km (86 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 85 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 5.5 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 2,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 89× the energy of this one
  3. Magna, Utah 2020 M 5.7 63× the energy of this one
  4. This earthquake M 4.5 about 85 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 180× 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 4.7 on 2016-11-29 — about 2 times the energy of this one.

Before 2016, the USGS record lists 11 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.4 146 km S of Adak, Alaska · 42 km WNW of this epicentre
  2. 6.3 159 km SSE of Adak, Alaska · 46 km ENE of this epicentre
  3. 5.8 176 km S of Adak, Alaska · 45 km WSW of this epicentre
  4. 5.8 164 km S of Adak, Alaska · 33 km W of this epicentre
  5. 5.7 Andreanof Islands, Aleutian Islands, Alaska · 31 km S 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 50.4424, -176.2725. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.2 158 km S of Adak, Alaska
  2. 1.8 167 km S of Adak, Alaska
  3. 2.9 181 km S of Adak, Alaska
  4. 3.8 175 km S of Adak, Alaska
  5. 2.5 168 km S of Adak, Alaska
  6. 2.5 172 km SSE of Adak, Alaska
  7. 2.6 184 km S of Adak, Alaska
  8. 3.9 191 km S of Adak, Alaska
  9. 2.5 181 km S of Adak, Alaska
  10. 2.6 175 km S of Adak, Alaska
  11. 2.5 200 km S of Adak, Alaska
  12. 2.8 171 km S of Adak, Alaska
  13. 2.6 139 km S of Adak, Alaska
  14. 1.9 146 km SSE of Adak, Alaska
  15. 2.6 175 km S 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.