QuakeIndex

Earthquake · reviewed by a seismologist

M 4.8ml

137 km ESE of Chignik, Alaska

Yes. A magnitude 4.8 earthquake was recorded 137 km ESE of Chignik, Alaska at 14:12 UTC on 2021-10-01, 45 km deep. 1 person has reported feeling it to USGS.

· 45 km deep · released about 240 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 4.8 (ml)
Depth
45 km below the surface
Felt
1 report · strongest reported intensity II
Measured shaking
intensity IV (ShakeMap)
USGS impact alert
green
Tsunami
USGS flagged this event for tsunami evaluation. Follow tsunami.gov for official messages.
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 325 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 164 km (102 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 240 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 5.8 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 710× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 32× the energy of this one
  3. Magna, Utah 2020 M 5.7 22× the energy of this one
  4. This earthquake M 4.8 about 240 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 500× 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 (31 mi) since our catalogue begins in 2016. The previous largest was M 4.5 on 2021-07-29.

Before 2016, the USGS record lists 10 earthquakes of M5 or more within 50 km; the five largest:

  1. 7.0 113 km ESE of Chignik, Alaska · 29 km WSW of this epicentre
  2. 6.9 143 km ESE of Chignik, Alaska · 11 km S of this epicentre
  3. 6.9 171 km SW of Akhiok, Alaska · 35 km SE of this epicentre
  4. 6.6 128 km SE of Chignik, Alaska · 40 km SW of this epicentre
  5. 6.3 112 km E of Chignik, Alaska · 37 km NNW 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 55.8999, -156.3121. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.9 137 km ESE of Chignik, Alaska
  2. 2.4 111 km E of Chignik, Alaska
  3. 2.7 119 km E of Chignik, Alaska
  4. 2.6 114 km E of Chignik, Alaska
  5. 2.8 115 km E of Chignik, Alaska
  6. 3.4 111 km E of Chignik, Alaska
  7. 3.3 116 km E of Chignik, Alaska
  8. 4.1 114 km E of Chignik, Alaska
  9. 3.1 115 km E of Chignik, Alaska
  10. 2.3 116 km E of Chignik, Alaska
  11. 2.6 121 km E of Chignik, Alaska
  12. 2.4 113 km E of Chignik, Alaska
  13. 2.3 136 km E of Chignik, Alaska
  14. 3.6 115 km E of Chignik, Alaska
  15. 2.2 114 km E 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.