QuakeIndex

Earthquake · reviewed by a seismologist

M 6.1mb

101 km ESE of Sand Point, Alaska

Yes. A magnitude 6.1 earthquake was recorded 101 km ESE of Sand Point, Alaska, at 10:16 pm AKDT on 21 July 2020 (06:16 UTC), 17 km deep. 5 people have reported feeling it to USGS.

· 17 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 (mb)
Depth
17 km below the surface
Felt
5 reports · strongest reported intensity V
Measured shaking
intensity VI (ShakeMap)
USGS impact alert
green
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 326 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 7.8 on 2020-07-22 — about 350 times the energy of this one.

Before 2016, the USGS record lists 12 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.6 72 km SE of Sand Point, Alaska · 36 km W of this epicentre
  2. 6.6 104 km SSE of Perryville, Alaska · 26 km ENE of this epicentre
  3. 6.6 85 km SE of Sand Point, Alaska · 43 km WSW of this epicentre
  4. 6.5 94 km ESE of Sand Point, Alaska · 10 km WSW of this epicentre
  5. 6.3 68 km SE of Sand Point, Alaska · 38 km W 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 54.9690, -159.0413. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.2 120 km ESE of Sand Point, Alaska
  2. 1.8 62 km ESE of Sand Point, Alaska
  3. 2.1 92 km SSE of Perryville, Alaska
  4. 5.5 73 km S of Ivanof Bay, Alaska
  5. 1.6 63 km ESE of Sand Point, Alaska
  6. 2.0 63 km S of Perryville, Alaska
  7. 4.0 94 km SSE of Perryville, Alaska
  8. 1.9 64 km ESE of Sand Point, Alaska
  9. 2.2 64 km ESE of Sand Point, Alaska
  10. 1.8 66 km ESE of Sand Point, Alaska
  11. 2.2 80 km ESE of Sand Point, Alaska
  12. 2.0 74 km S of Perryville, Alaska
  13. 2.5 138 km SSE of Perryville, Alaska
  14. 2.0 77 km S of Perryville, Alaska
  15. 1.6 75 km ESE of Sand Point, 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.