QuakeIndex

Earthquake · reviewed by a seismologist

M 3.5mb

Fox Islands, Aleutian Islands, Alaska

Yes. A magnitude 3.5 earthquake was recorded in the Fox Islands, Aleutian Islands, Alaska at 23:20 UTC on 2023-08-23, 49 km deep.

· 49 km deep · released about 2.7 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 3.5 (mb)
Depth
49 km below the surface
Felt
no reports yet
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1113 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 41 km (25 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 2.7 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.5 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 63,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 2,800× the energy of this one
  3. Magna, Utah 2020 M 5.7 2,000× the energy of this one
  4. This earthquake M 3.5 about 2.7 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 5.6× 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 5.8 on 2019-10-26 — about 2,800 times the energy of this one.

Before 2016, the USGS record lists 71 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.6 135 km SW of Nikolski, Alaska · 34 km SE of this epicentre
  2. 6.1 88 km SW of Nikolski, Alaska · 47 km ENE of this epicentre
  3. 6.0 128 km SW of Nikolski, Alaska · 16 km SE of this epicentre
  4. 6.0 164 km WSW of Nikolski, Alaska · 50 km WNW of this epicentre
  5. 6.0 161 km WSW of Nikolski, Alaska · 38 km W 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 52.2224, -170.4079. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 3.9 142 km WSW of Nikolski, Alaska
  2. 3.9 143 km WSW of Nikolski, Alaska
  3. 4.3 125 km WSW of Nikolski, Alaska
  4. 3.1 133 km SW of Nikolski, Alaska
  5. 3.0 150 km WSW of Nikolski, Alaska
  6. 3.0 111 km SW of Nikolski, Alaska
  7. 3.7 99 km SW of Nikolski, Alaska
  8. 2.1 114 km SW of Nikolski, Alaska
  9. 3.9 151 km SW of Nikolski, Alaska
  10. 4.2 155 km WSW of Nikolski, Alaska
  11. 2.7 96 km SW of Nikolski, Alaska
  12. 2.8 147 km WSW of Nikolski, Alaska
  13. 4.6 147 km WSW of Nikolski, Alaska
  14. 3.7 148 km WSW of Nikolski, Alaska
  15. 4.4 139 km WSW of Nikolski, 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.