QuakeIndex

Earthquake · reviewed by a seismologist

M 5.5mww

122 km SW of Adak, Alaska

· 30 km deep · released about 2.7 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 5.5 (mww)
Depth
30 km below the surface
Felt
4 reports · strongest reported intensity IV
Measured shaking
intensity V (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 7 days ago

This was a moderate earthquake. Shaking at this size can damage poorly built structures close to the epicentre. 4 people have reported feeling it to USGS.

How big was it?

This earthquake released about 2.7 kilotons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 6.5 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 63× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 2.8× the energy of this one
  3. Magna, Utah 2020 M 5.7 2× the energy of this one
  4. This earthquake M 5.5 about 2.7 kilotons of TNT
  5. Around the size people start to feel M 3.0 this one released 5,600× 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.

Where

Epicentre 51.1987, -178.0221. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.2 129 km WSW of Adak, Alaska
  2. 4.5 142 km WSW of Adak, Alaska
  3. 2.6 76 km WSW of Adak, Alaska
  4. 2.9 90 km WSW of Adak, Alaska
  5. 2.3 113 km WSW of Adak, Alaska
  6. 2.5 122 km SW of Adak, Alaska
  7. 2.5 131 km WSW of Adak, Alaska
  8. 2.6 84 km SW of Adak, Alaska
  9. 2.4 128 km WSW of Adak, Alaska
  10. 2.9 135 km SW of Adak, Alaska
  11. 2.4 143 km WSW of Adak, Alaska
  12. 2.1 88 km WSW of Adak, Alaska
  13. 2.4 122 km WSW of Adak, Alaska
  14. 2.2 92 km SW of Adak, Alaska
  15. 2.2 99 km WSW 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.

For this area

The largest earthquake within 50 km in our catalogue was M 6.5 on 2018-08-15 — it released about 32 times the energy of this one.

From the QuakeIndex catalogue, built from the USGS FDSN event service.

On USGS

QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.