QuakeIndex

Earthquake · reviewed by a seismologist

M 4.2mb

113 km ESE of Sand Point, Alaska

Yes. A magnitude 4.2 earthquake was recorded 113 km ESE of Sand Point, Alaska at 06:30 UTC on 2020-07-22, 28 km deep. 2 people have reported feeling it to USGS.

· 28 km deep · released about 30 tons of TNT

Felt it? Tell USGS Check my area
10 km30 km60 km120 km N
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 4.2 (mb)
Depth
28 km below the surface
Felt
2 reports · strongest reported intensity II
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 2232 days ago

This was a light earthquake. It is usually felt clearly nearby and can rattle windows and dishes, but damage is uncommon.

At this magnitude and depth, people at rest would likely notice it out to about 109 km (68 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 30 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 5.2 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 5,600× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 250× the energy of this one
  3. Magna, Utah 2020 M 5.7 180× the energy of this one
  4. This earthquake M 4.2 about 30 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 63× 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 250,000 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 · 45 km W of this epicentre
  2. 6.6 104 km SSE of Perryville, Alaska · 23 km NE of this epicentre
  3. 6.6 85 km SE of Sand Point, Alaska · 47 km WSW of this epicentre
  4. 6.5 94 km ESE of Sand Point, Alaska · 19 km WNW of this epicentre
  5. 6.3 68 km SE of Sand Point, Alaska · 48 km WNW 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 54.8808, -158.9014. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.7 132 km SSE of Perryville, Alaska
  2. 2.6 101 km SSE of Perryville, Alaska
  3. 2.2 96 km SSE of Perryville, Alaska
  4. 1.8 74 km ESE of Sand Point, Alaska
  5. 2.2 120 km ESE of Sand Point, Alaska
  6. 2.1 92 km SSE of Perryville, Alaska
  7. 5.5 73 km S of Ivanof Bay, Alaska
  8. 2.2 123 km SSE of Perryville, Alaska
  9. 4.0 94 km SSE of Perryville, Alaska
  10. 2.1 100 km SSE of Perryville, 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. 3.2 89 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.

On USGS

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