QuakeIndex

Earthquake · reviewed by a seismologist

M 3.7ml

152 km SSE of Chignik, Alaska

Yes. A magnitude 3.7 earthquake was recorded 152 km SSE of Chignik, Alaska at 22:36 UTC on 2021-08-02, 19 km deep. 1 person has reported feeling it to USGS.

· 19 km deep · released about 5.4 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 3.7 (ml)
Depth
19 km below the surface
Felt
1 report · strongest reported intensity III
Measured shaking
intensity I (ShakeMap)
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1856 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 73 km (45 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 5.4 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.7 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 32,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 1,400× the energy of this one
  3. Magna, Utah 2020 M 5.7 1,000× the energy of this one
  4. This earthquake M 3.7 about 5.4 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 11× 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 2021-07-29 — about 2,000 times the energy of this one.

Before 2016, the USGS record lists 15 earthquakes of M5 or more within 50 km; the five largest:

  1. 7.0 164 km SE of Chignik, Alaska · 43 km ENE of this epicentre
  2. 6.7 121 km SE of Chignik, Alaska · 33 km NNW of this epicentre
  3. 6.2 189 km SE of Chignik, Alaska · 39 km SE of this epicentre
  4. 6.0 168 km SE of Chignik, Alaska · 38 km ENE of this epicentre
  5. 5.6 171 km SE of Chignik, Alaska · 29 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 55.1606, -157.0446. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 3.3 133 km SE of Perryville, Alaska
  2. 2.1 142 km SE of Perryville, Alaska
  3. 3.6 137 km SE of Perryville, Alaska
  4. 3.6 154 km SE of Perryville, Alaska
  5. 2.3 120 km SSE of Chignik, Alaska
  6. 2.3 122 km SE of Chignik, Alaska
  7. 1.9 139 km SE of Chignik, Alaska
  8. 2.2 148 km SE of Perryville, Alaska
  9. 2.6 161 km SE of Chignik, Alaska
  10. 2.2 141 km SE of Perryville, Alaska
  11. 3.4 135 km SE of Perryville, Alaska
  12. 2.7 157 km SE of Chignik, Alaska
  13. 3.0 144 km SE of Perryville, Alaska
  14. 2.2 150 km SE of Perryville, Alaska
  15. 2.4 126 km SE 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.