QuakeIndex

Earthquake · reviewed by a seismologist

M 4.1mb

56 km WNW of Cold Bay, Alaska

Yes. A magnitude 4.1 earthquake was recorded 56 km WNW of Cold Bay, Alaska, at 11:48 am AKDT on 5 July 2021 (19:48 UTC), 177 km deep.

· 177 km deep · released about 21 tons of TNT

Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Aleutians East Borough 97 km
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 4.1 (mb)
Depth
177 km below the surface
Felt
no reports yet
Measured shaking
intensity II (ShakeMap)
Nearest
Aleutians East Borough, 97 km ESE
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1890 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 it was probably too small to be felt, even directly above it. 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 21 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 5.1 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 7,900× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 350× the energy of this one
  3. Magna, Utah 2020 M 5.7 250× the energy of this one
  4. This earthquake M 4.1 about 21 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 45× 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 4.4 on 2017-03-02 — about 2.8 times the energy of this one.

Before 2016, the USGS record lists one earthquake of M5 or more within 50 km:

  1. 5.5 66 km NNW of False Pass, Alaska · 21 km W 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 55.4337, -163.4891. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Aleutians East Borough, AK 97 km (60 mi) ESE earthquakes near Aleutians East Borough

Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.

Aftershocks so far

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

  1. 3.8 36 km NNE of False Pass, Alaska
  2. 2.6 30 km NW of False Pass, Alaska
  3. 3.2 35 km WNW of Cold Bay, Alaska
  4. 1.8 21 km WNW of Cold Bay, Alaska
  5. 2.7 23 km W of Cold Bay, Alaska
  6. 2.1 44 km WNW of Cold Bay, Alaska
  7. 2.0 42 km NW of Cold Bay, Alaska
  8. 2.6 19 km NNW of False Pass, Alaska
  9. 2.0 26 km NW of Cold Bay, Alaska
  10. 3.0 26 km NNW of False Pass, Alaska
  11. 4.0 77 km NNW of False Pass, Alaska
  12. 2.9 28 km W of Cold Bay, Alaska
  13. 1.9 23 km NE of False Pass, Alaska
  14. 2.1 53 km N of False Pass, Alaska
  15. 2.8 16 km W of Cold Bay, 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.