QuakeIndex

Earthquake · reviewed by a seismologist

M 4.1mb

177 km SSE of Unalaska, Alaska

Yes. A magnitude 4.1 earthquake was recorded 177 km SSE of Unalaska, Alaska at 00:50 UTC on 2018-12-23, 10 km deep.

· 10 km deep · released about 21 tons of TNT

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10 km30 km60 km120 km N
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
10 km below the surface
Felt
no reports yet
Nearest mapped fault
Alaska-Aleutian subduction zone, 4 km from its surface trace — near is not the same as on
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 2578 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 104 km (65 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 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 4.3 on 2018-02-24 — about 2 times the energy of this one.

Before 2016, the USGS record lists 3 earthquakes of M5 or more within 50 km:

  1. 5.5 198 km SSE of Unalaska, Alaska · 32 km SSW of this epicentre
  2. 5.4 219 km SSE of Unalaska, Alaska · 44 km SSE of this epicentre
  3. 5.1 162 km SSE of Akutan, Alaska · 39 km NE 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 52.5573, -165.0476. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 2.2 207 km SSE of Unalaska, Alaska
  2. 2.8 211 km SSE of Unalaska, Alaska
  3. 2.6 195 km SE of Unalaska, Alaska
  4. 4.0 141 km SSE of Unalaska, Alaska
  5. 1.9 168 km SE of Unalaska, Alaska
  6. 2.4 197 km SSE of Unalaska, Alaska
  7. 2.2 217 km SSE of Unalaska, Alaska
  8. 2.7 177 km SSE of Akutan, Alaska
  9. 2.9 189 km SSE of Unalaska, Alaska
  10. 2.9 173 km SSE of Unalaska, Alaska
  11. 2.2 164 km SSE of Unalaska, Alaska
  12. 2.7 202 km SSE of Unalaska, Alaska
  13. 2.8 193 km SSE of Akutan, Alaska
  14. 2.7 129 km SSE of Unalaska, Alaska
  15. 2.7 172 km SSE 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.