QuakeIndex

Earthquake · reviewed by a seismologist

M 3.1ml

16 km ESE of Old Harbor, Alaska

Yes. A magnitude 3.1 earthquake was recorded 16 km ESE of Old Harbor, Alaska, at 1:41 am AKDT on 21 October 2023 (09:41 UTC), 41 km deep. 1 person has reported feeling it to USGS.

· 41 km deep · released about 1,300 lb of TNT

Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Kodiak Island Borough 81 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 3.1 (ml)
Depth
41 km below the surface
Felt
1 report · strongest reported intensity II
Nearest
Kodiak Island Borough, 81 km NW
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1053 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 6 km (4 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 1,300 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.1 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 250,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 11,000× the energy of this one
  3. Magna, Utah 2020 M 5.7 7,900× the energy of this one
  4. This earthquake M 3.1 about 1,300 lb of TNT
  5. Around the size people start to feel M 3.0 this one released 1.4× 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 5.4 on 2023-02-21 — about 2,800 times the energy of this one.

Before 2016, the USGS record lists 11 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.9 47 km S of Old Harbor, Alaska · 43 km SSW of this epicentre
  2. 6.2 19 km SW of Old Harbor, Alaska · 30 km WSW of this epicentre
  3. 6.2 53 km ESE of Old Harbor, Alaska · 37 km ESE of this epicentre
  4. 6.1 36 km ESE of Akhiok, Alaska · 47 km SW of this epicentre
  5. 5.9 25 km E of Old Harbor, Alaska · 11 km ENE 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 57.1388, -153.0635. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Kodiak Island Borough, AK 81 km (50 mi) NW earthquakes near Kodiak Island Borough

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

Aftershocks so far

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

  1. 2.6 29 km NNE of Old Harbor, Alaska
  2. 3.0 24 km SW of Chiniak, Alaska
  3. 1.8 21 km NW of Old Harbor, Alaska
  4. 2.1 26 km SSW of Old Harbor, Alaska
  5. 1.6 20 km SW of Womens Bay, Alaska
  6. 1.9 38 km SSE of Old Harbor, Alaska
  7. 1.6 35 km N of Old Harbor, Alaska
  8. 2.0 24 km SW of Womens Bay, Alaska
  9. 2.0 47 km SSE of Old Harbor, Alaska
  10. 2.9 45 km SSE of Old Harbor, Alaska
  11. 1.9 45 km SSE of Old Harbor, Alaska
  12. 3.5 40 km SSE of Old Harbor, Alaska
  13. 1.9 41 km SSE of Old Harbor, Alaska
  14. 2.1 42 km SSE of Old Harbor, Alaska
  15. 2.0 34 km SSE of Old Harbor, 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.