QuakeIndex

Earthquake · reviewed by a seismologist

M 6.1mww

116 km SE of Adak, Alaska

Yes. A magnitude 6.1 earthquake was recorded 116 km SE of Adak, Alaska at 14:55 UTC on 2023-12-21, 20 km deep. 3 people have reported feeling it to USGS.

· 20 km deep · released about 21 kilotons 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 6.1 (mww)
Depth
20 km below the surface
Felt
3 reports · strongest reported intensity IV
Measured shaking
intensity IV (ShakeMap)
USGS impact alert
green
Tsunami
USGS flagged this event for tsunami evaluation. Follow tsunami.gov for official messages.
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 343 days ago

This was a strong earthquake. Damage is likely near the epicentre and it is felt over a wide area.

At this magnitude and depth, people at rest would likely notice it out to about 366 km (227 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 21 kilotons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 7.1 would have released about 32 times as much.

  1. Ridgecrest, California 2019 M 7.1 32× the energy of this one
  2. Loma Prieta, California 1989 M 6.9 16× the energy of this one
  3. Northridge, California 1994 M 6.7 7.9× the energy of this one
  4. This earthquake M 6.1 about 21 kilotons of TNT
  5. Mineral, Virginia 2011 M 5.8 this one released 2.8× more
  6. Magna, Utah 2020 M 5.7 this one released 4× 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 6.3 on 2019-11-24 — about 2 times the energy of this one.

Before 2016, the USGS record lists 109 earthquakes of M5 or more within 50 km; the five largest:

  1. 8.6 1957 Atka, Alaska Earthquake · 38 km NNW of this epicentre
  2. 7.0 153 km SE of Adak, Alaska · 42 km SSE of this epicentre
  3. 7.0 101 km SW of Atka, Alaska · 37 km N of this epicentre
  4. 6.9 100 km ESE of Adak, Alaska · 35 km N of this epicentre
  5. 6.8 99 km SW of Atka, Alaska · 37 km NNE 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 51.2097, -175.3313. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 1.8 67 km SE of Adak, Alaska
  2. 3.1 110 km SSW of Atka, Alaska
  3. 1.9 93 km SW of Atka, Alaska
  4. 3.1 91 km SW of Atka, Alaska
  5. 2.9 112 km SSW of Atka, Alaska
  6. 2.6 95 km SW of Atka, Alaska
  7. 2.0 81 km ESE of Adak, Alaska
  8. 2.6 86 km ESE of Adak, Alaska
  9. 1.8 99 km SW of Atka, Alaska
  10. 2.9 76 km SE of Adak, Alaska
  11. 3.8 129 km SSW of Atka, Alaska
  12. 3.3 129 km SSW of Atka, Alaska
  13. 4.9 124 km SSW of Atka, Alaska
  14. 3.5 113 km SE of Adak, Alaska
  15. 3.1 106 km ESE 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.