QuakeIndex

Earthquake · reviewed by a seismologist

M 3.8mb

Earthquake near Unalaska, AK

No earthquake was likely felt in Unalaska in the 24 hours to 5:22 pm AKST (02:22 UTC). The last one was M 4.4, 117 km (72 mi) ESE, at 3:00 pm AKST on 11 November 2026, estimated intensity II (weak) in town. Every earthquake near Unalaska

This page: a magnitude 3.8 earthquake was recorded 29 km (18 mi) southeast of Unalaska, AK, at 10:19 pm AKST on 20 November 2020 (07:19 UTC), 74 km deep.

USGS: 29 km SE of Unalaska, Alaska

10:19 pm AKST, Nov 20, 2020 · · 74 km deep · released about 7.6 tons of TNT

Every earthquake near Unalaska Felt it? Tell USGS Check my area
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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
10:19 pm AKST on 20 November 2020 ()
Where
29 km (18 mi) southeast of Unalaska, AK · earthquakes near Unalaska
Magnitude
M 3.8 (mb)
Depth
74 km below the surface
Felt
no reports yet
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 2109 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 37 km (23 mi) from the epicentre. In Unalaska, 29 km away, the estimate is intensity II (weak). 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.

Likely felt in: Unalaska 29 km, intensity II. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 7.6 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.8 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 22,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 1,000× the energy of this one
  3. Magna, Utah 2020 M 5.7 710× the energy of this one
  4. This earthquake M 3.8 about 7.6 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 16× 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 2019-09-14 — about 250 times the energy of this one.

Before 2016, the USGS record lists 23 earthquakes of M5 or more within 50 km; the five largest:

  1. 7.1 39 km S of Akutan, Alaska · 35 km ENE of this epicentre
  2. 6.2 57 km SE of Unalaska, Alaska · 29 km ESE of this epicentre
  3. 6.2 36 km ESE of Unalaska, Alaska · 15 km ENE of this epicentre
  4. 6.2 53 km S of Akutan, Alaska · 42 km E of this epicentre
  5. 6.1 56 km SSW of Unalaska, Alaska · 45 km SW 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 53.6612, -166.2679. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.8 34 km SSE of Unalaska, Alaska
  2. 2.9 38 km SSE of Unalaska, Alaska
  3. 1.7 27 km S of Unalaska, Alaska
  4. 2.2 66 km SE of Unalaska, Alaska
  5. 2.0 70 km SE of Unalaska, Alaska
  6. 3.0 77 km SE of Unalaska, Alaska
  7. 1.8 25 km SSW of Unalaska, Alaska
  8. 1.5 61 km ESE of Unalaska, Alaska
  9. 1.8 69 km SE of Unalaska, Alaska
  10. 2.6 36 km SE of Unalaska, Alaska
  11. 3.1 48 km S of Unalaska, Alaska
  12. 1.9 56 km SE of Unalaska, Alaska
  13. 2.7 50 km S of Akutan, Alaska
  14. 1.7 10 km WNW of Dutch Harbor, Alaska
  15. 2.0 72 km SE of Unalaska, 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.