QuakeIndex

Earthquake · reviewed by a seismologist

M 3.4ml

76 km SE of Chignik, Alaska

Yes. A magnitude 3.4 earthquake was recorded 76 km SE of Chignik, Alaska at 16:21 UTC on 2018-07-22, 41 km deep. 2 people have reported feeling it to USGS.

· 41 km deep · released about 1.9 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 3.4 (ml)
Depth
41 km below the surface
Felt
2 reports · strongest reported intensity IV
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1186 days ago

This was a small earthquake. Shaking like this is often felt indoors nearby and very rarely causes damage.

At this magnitude and depth, people at rest would likely notice it out to about 41 km (25 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 1.9 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.4 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 89,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 4,000× the energy of this one
  3. Magna, Utah 2020 M 5.7 2,800× the energy of this one
  4. This earthquake M 3.4 about 1.9 tons of TNT
  5. Around the size people start to feel M 3.0 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 4.0 on 2016-01-01 — about 7.9 times the energy of this one.

Before 2016, the USGS record lists 8 earthquakes of M5 or more within 50 km; the five largest:

  1. 7.0 113 km ESE of Chignik, Alaska · 41 km E of this epicentre
  2. 6.7 121 km SE of Chignik, Alaska · 50 km SSE of this epicentre
  3. 6.4 77 km ESE of Chignik, Alaska · 32 km NNE of this epicentre
  4. 5.5 51 km SSE of Chignik, Alaska · 49 km W of this epicentre
  5. 5.1 123 km SE of Chignik, Alaska · 49 km SSE 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 55.8736, -157.4262. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.2 34 km ESE of Chignik, Alaska
  2. 2.0 31 km ESE of Chignik, Alaska
  3. 1.7 36 km ESE of Chignik, Alaska
  4. 2.7 73 km SE of Chignik, Alaska
  5. 2.2 81 km ESE of Chignik, Alaska
  6. 2.4 61 km ESE of Chignik, Alaska
  7. 2.1 37 km ESE of Chignik, Alaska
  8. 2.9 49 km E of Chignik, Alaska
  9. 1.9 123 km SE of Chignik, Alaska
  10. 2.3 72 km ESE of Chignik, Alaska
  11. 2.6 70 km SSE of Chignik, Alaska
  12. 2.0 62 km ESE of Chignik, Alaska
  13. 3.7 100 km SE of Chignik, Alaska
  14. 2.6 99 km ESE of Chignik, Alaska
  15. 2.4 57 km ESE of Chignik, 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.