QuakeIndex

Earthquake · reviewed by a seismologist

M 4.0mb

162 km S of False Pass, Alaska

Yes. A magnitude 4.0 earthquake was recorded 162 km S of False Pass, Alaska at 02:07 UTC on 2020-09-20, 10 km deep. 1 person has reported feeling it to USGS.

· 10 km deep · released about 15 tons 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 4.0 (mb)
Depth
10 km below the surface
Felt
1 report · strongest reported intensity II
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 2176 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 96 km (60 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 15 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 5.0 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 11,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 500× the energy of this one
  3. Magna, Utah 2020 M 5.7 350× the energy of this one
  4. This earthquake M 4.0 about 15 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 32× 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 5.9 on 2016-10-27 — about 710 times the energy of this one.

Before 2016, the USGS record lists 55 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.6 146 km ESE of Akutan, Alaska · 20 km NW of this epicentre
  2. 6.2 Unimak Island region, Alaska · 49 km NNW of this epicentre
  3. 6.2 136 km SE of Akutan, Alaska · 32 km W of this epicentre
  4. 6.2 136 km S of False Pass, Alaska · 30 km NNW of this epicentre
  5. 6.2 172 km SSE of False Pass, Alaska · 49 km E 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 53.3971, -163.5888. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.8 151 km S of False Pass, Alaska
  2. 2.6 160 km S of False Pass, Alaska
  3. 2.8 118 km ESE of Akutan, Alaska
  4. 3.0 152 km S of False Pass, Alaska
  5. 3.9 149 km S of False Pass, Alaska
  6. 1.8 119 km S of False Pass, Alaska
  7. 2.3 115 km S of False Pass, Alaska
  8. 2.8 152 km S of False Pass, Alaska
  9. 4.3 158 km S of False Pass, Alaska
  10. 2.7 144 km S of False Pass, Alaska
  11. 3.1 156 km S of False Pass, Alaska
  12. 2.5 120 km S of False Pass, Alaska
  13. 2.6 145 km S of False Pass, Alaska
  14. 2.2 163 km ESE of Akutan, Alaska
  15. 2.3 152 km ESE of Akutan, 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.