QuakeIndex

Earthquake · reviewed by a seismologist

M 3.8ml

Earthquake near Tok, AK

USGS: 23 km SSW of Tanacross, Alaska

9:09 am AKDT, Apr 4, 2021 · · 2.9 km deep · released about 7.6 tons of TNT

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10 km30 km60 km120 km N Southeast Fairbanks Census Area 77 km
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
9:09 am AKDT on 4 April 2021 ()
Where
31 km (20 mi) WSW of Tok, AK · earthquakes near Tok
Magnitude
M 3.8 (ml)
Depth
2.9 km below the surface
Felt
3 reports · strongest reported intensity II
Measured shaking
intensity IV (ShakeMap)
Nearest
Southeast Fairbanks Census Area, 77 km N
Nearest mapped fault
Cathedral Rapids faults (Northern Foothills fold and thrust belt), 15 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 1516 days ago

A magnitude 3.8 earthquake was recorded 31 km (20 mi) WSW of Tok, AK, at 9:09 am AKDT on 4 April 2021 (17:09 UTC). 3 people have reported feeling it to USGS. This was a small earthquake. Shaking like this is often felt indoors nearby and very rarely causes damage.

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 4.2 on 2020-10-26 — about 4 times the energy of this one.

Before 2016, the USGS record lists 4 earthquakes of M5 or more within 50 km:

  1. 5.9 44 km WNW of Mentasta Lake, Alaska · 50 km W of this epicentre
  2. 5.1 3 km ENE of Mentasta Lake, Alaska · 30 km SSW of this epicentre
  3. 5.1 17 km ESE of Mentasta Lake, Alaska · 37 km S of this epicentre
  4. 5.0 16 km WNW of Mentasta Lake, Alaska · 35 km SW 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 63.1898, -143.5232. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Southeast Fairbanks Census Area, AK 77 km (48 mi) N earthquakes near Southeast Fairbanks Census Area

Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.

Aftershocks so far

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

  1. 1.1 19 km SE of Dot Lake Village, Alaska
  2. 3.0 13 km ENE of Slana, Alaska
  3. 2.3 13 km SE of Mentasta Lake, Alaska
  4. 3.1 13 km N of Mentasta Lake, Alaska
  5. 1.5 14 km SE of Mentasta Lake, Alaska
  6. 2.0 29 km SW of Tetlin, Alaska
  7. 2.1 29 km SW of Tetlin, Alaska
  8. 1.8 24 km SE of Mentasta Lake, Alaska
  9. 1.7 26 km SSW of Tanacross, Alaska
  10. 2.2 22 km SW of Tanacross, Alaska
  11. 1.6 25 km SSW of Tanacross, Alaska
  12. 2.2 24 km SW of Tanacross, Alaska
  13. 1.8 7 km SE of Mentasta Lake, Alaska
  14. 1.6 5 km ESE of Mentasta Lake, Alaska
  15. 1.7 23 km SE of Mentasta Lake, 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.