QuakeIndex

Earthquake · reviewed by a seismologist

M 2.5ml

Earthquake near Unalaska, AK

No earthquake was likely felt in Unalaska in the 24 hours to 5:45 pm AKST (02:45 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 2.5 earthquake was recorded 42 km (26 mi) east-southeast of Unalaska, AK, at 2:00 am AKDT on 31 October 2018 (10:00 UTC), 70 km deep.

USGS: 41 km ESE of Unalaska, Alaska

2:00 am AKDT, Oct 31, 2018 · · 70 km deep · released about 170 lb 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
2:00 am AKDT on 31 October 2018 ()
Where
42 km (26 mi) east-southeast of Unalaska, AK · earthquakes near Unalaska
Magnitude
M 2.5 (ml)
Depth
70 km below the surface
Felt
no reports yet
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1185 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 it was probably too small to be felt, even directly above it. In Unalaska, 42 km away, the estimate is intensity I (not felt). 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 170 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.5 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 89,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 63,000× the energy of this one
  3. Around the size people start to feel M 3.0 5.6× the energy of this one
  4. This earthquake M 2.5 about 170 lb of TNT

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 4.8 on 2016-09-18 — about 2,800 times the energy of this one.

Before 2016, the USGS record lists 31 earthquakes of M5 or more within 50 km; the five largest:

  1. 7.1 39 km S of Akutan, Alaska · 16 km ENE of this epicentre
  2. 6.2 57 km SE of Unalaska, Alaska · 19 km SSE of this epicentre
  3. 6.2 36 km ESE of Unalaska, Alaska · 6 km WNW of this epicentre
  4. 6.2 53 km S of Akutan, Alaska · 23 km E of this epicentre
  5. 6.0 57 km SSE of Akutan, Alaska · 38 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 53.6984, -165.9740. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 1.7 37 km SSE of Unalaska, Alaska
  2. 2.4 78 km SSE of Akutan, Alaska
  3. 2.0 Fox Islands, Aleutian Islands, Alaska
  4. 1.8 12 km ENE of Dutch Harbor, Alaska
  5. 2.3 26 km S of Unalaska, Alaska
  6. 2.5 23 km SE of Akutan, Alaska
  7. 1.8 60 km SSE of Unalaska, Alaska
  8. 1.6 45 km SE of Unalaska, Alaska
  9. 3.6 40 km S of Akutan, Alaska
  10. 2.1 77 km SE of Unalaska, Alaska
  11. 1.8 30 km ESE of Unalaska, Alaska
  12. 2.1 53 km ESE of Unalaska, Alaska
  13. 2.1 34 km SSE of Unalaska, Alaska
  14. 1.8 47 km SSE of Akutan, Alaska
  15. 1.7 23 km SSW of Akutan, 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.