QuakeIndex

Earthquake · reviewed by a seismologist

M 6.9mww

125 km SE of Perryville, Alaska

Yes. A magnitude 6.9 earthquake was recorded 125 km SE of Perryville, Alaska at 11:57 UTC on 2021-08-14, 21 km deep. 10 people have reported feeling it to USGS.

· 21 km deep · released about 340 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 6.9 (mww)
Depth
21 km below the surface
Felt
10 reports · strongest reported intensity V
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 325 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 555 km (345 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 340 kilotons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 7.9 would have released about 32 times as much.

  1. Tōhoku, Japan 2011 M 9.1 2,000× the energy of this one
  2. San Francisco 1906 M 7.9 32× the energy of this one
  3. Ridgecrest, California 2019 M 7.1 2× the energy of this one
  4. This earthquake M 6.9 about 340 kilotons of TNT
  5. Northridge, California 1994 M 6.7 this one released 2× more
  6. Mineral, Virginia 2011 M 5.8 this one released 45× 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 8.2 on 2021-07-29 — about 89 times the energy of this one.

Before 2016, the USGS record lists 13 earthquakes of M5 or more within 50 km; the five largest:

  1. 8.2 1938 Semidi Islands, Alaska Earthquake · 34 km W of this epicentre
  2. 6.9 105 km ESE of Perryville, Alaska · 26 km NNW of this epicentre
  3. 6.7 121 km SE of Chignik, Alaska · 43 km NE of this epicentre
  4. 6.2 143 km SE of Perryville, Alaska · 32 km SSW of this epicentre
  5. 6.0 98 km ESE of Perryville, Alaska · 30 km NNW 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 55.1767, -157.6441. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.7 138 km SE of Perryville, Alaska
  2. 2.3 132 km SE of Perryville, Alaska
  3. 2.3 86 km ESE of Perryville, Alaska
  4. 2.1 143 km SE of Perryville, Alaska
  5. 1.9 103 km SSE of Chignik, Alaska
  6. 2.5 130 km SE of Perryville, Alaska
  7. 3.0 137 km SE of Perryville, Alaska
  8. 2.4 131 km SE of Chignik, Alaska
  9. 2.4 133 km SE of Perryville, Alaska
  10. 2.0 112 km SSE of Perryville, Alaska
  11. 2.4 156 km SSE of Chignik, Alaska
  12. 3.0 136 km SE of Perryville, Alaska
  13. 3.7 150 km SSE of Chignik, Alaska
  14. 3.4 156 km SSE of Chignik, Alaska
  15. 2.0 132 km SE 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.

On USGS

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