QuakeIndex

Earthquake · reviewed by a seismologist

M 4.0mb

135 km ESE of Nikolski, Alaska

Yes. A magnitude 4.0 earthquake was recorded 135 km ESE of Nikolski, Alaska, at 10:04 am AKDT on 23 September 2019 (18:04 UTC), 10 km deep.

· 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
no reports yet
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 2531 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 2017-05-24 — about 710 times the energy of this one.

Before 2016, the USGS record lists 47 earthquakes of M5 or more within 50 km; the five largest:

  1. 7.0 Fox Islands, Aleutian Islands, Alaska · 40 km WSW of this epicentre
  2. 6.5 127 km E of Nikolski, Alaska · 20 km N of this epicentre
  3. 6.4 118 km E of Nikolski, Alaska · 24 km NNW of this epicentre
  4. 6.4 123 km ESE of Nikolski, Alaska · 12 km WNW of this epicentre
  5. 6.3 110 km SE of Nikolski, Alaska · 45 km WSW 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 52.5749, -166.9491. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.1 137 km S of Unalaska, Alaska
  2. 1.7 99 km ESE of Nikolski, Alaska
  3. 3.1 99 km E of Nikolski, Alaska
  4. 2.5 144 km ESE of Nikolski, Alaska
  5. 1.9 122 km SSW of Unalaska, Alaska
  6. 1.8 124 km S of Unalaska, Alaska
  7. 2.0 100 km S of Unalaska, Alaska
  8. 1.6 108 km E of Nikolski, Alaska
  9. 3.1 Fox Islands, Aleutian Islands, Alaska
  10. 1.9 114 km SSW of Unalaska, Alaska
  11. 2.6 140 km S of Unalaska, Alaska
  12. 3.0 136 km ESE of Nikolski, Alaska
  13. 2.7 141 km S of Unalaska, Alaska
  14. 2.2 134 km ESE of Nikolski, Alaska
  15. 2.4 130 km S of Unalaska, 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.