QuakeIndex

Earthquake · reviewed by a seismologist

M 7.8mww

2020 Perryville, Alaska Earthquake

· 28 km deep · released about 7.6 megatons 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 7.8 (mww)
Depth
28 km below the surface
Felt
195 reports · strongest reported intensity IX
Measured shaking
intensity VII (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 280 days ago

This was a major earthquake. Serious damage is likely near the epicentre. Follow official information from USGS and local authorities. 195 people have reported feeling it to USGS.

How big was it?

This earthquake released about 7.6 megatons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 8.8 would have released about 32 times as much.

  1. Great Alaska earthquake 1964 M 9.2 130× the energy of this one
  2. Tōhoku, Japan 2011 M 9.1 89× the energy of this one
  3. San Francisco 1906 M 7.9 1.4× the energy of this one
  4. This earthquake M 7.8 about 7.6 megatons of TNT
  5. Ridgecrest, California 2019 M 7.1 this one released 11× more
  6. Loma Prieta, California 1989 M 6.9 this one released 22× 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 55.0715, -158.5960. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 4.0 94 km SSE of Perryville, Alaska
  2. 2.1 100 km SSE of Perryville, Alaska
  3. 2.9 131 km SSE of Perryville, Alaska
  4. 2.3 112 km SSE of Perryville, Alaska
  5. 2.0 74 km S of Perryville, Alaska
  6. 2.5 138 km SSE of Perryville, Alaska
  7. 2.2 119 km SSE of Perryville, Alaska
  8. 3.2 89 km SSE of Perryville, Alaska
  9. 4.1 84 km S of Perryville, Alaska
  10. 2.5 127 km SSE of Perryville, Alaska
  11. 2.2 123 km SSE of Perryville, Alaska
  12. 3.9 140 km SSE of Perryville, Alaska
  13. 4.5 120 km SSE of Perryville, Alaska
  14. 2.6 96 km S of Perryville, Alaska
  15. 3.8 126 km SSE of Perryville, 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 5.7 on 2016-05-31.

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

On USGS

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