QuakeIndex

Earthquake · reviewed by a seismologist

M 4.2mb

225 km SSE of False Pass, Alaska

Yes. A magnitude 4.2 earthquake was recorded 225 km SSE of False Pass, Alaska at 02:58 UTC on 2025-09-19, 10 km deep. 1 person has reported feeling it to USGS.

· 10 km deep · released about 30 tons 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
Magnitude
M 4.2 (mb)
Depth
10 km below the surface
Felt
1 report
Measured shaking
intensity I (ShakeMap)
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 342 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 112 km (70 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 30 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 5.2 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 5,600× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 250× the energy of this one
  3. Magna, Utah 2020 M 5.7 180× the energy of this one
  4. This earthquake M 4.2 about 30 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 63× 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 2019-10-26 — about 2 times the energy of this one.

Before 2016, the USGS record lists 7 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.3 226 km SSE of False Pass, Alaska · 10 km WSW of this epicentre
  2. 6.3 210 km S of King Cove, Alaska · 18 km NNE of this epicentre
  3. 6.2 194 km SSE of King Cove, Alaska · 47 km NE of this epicentre
  4. 5.7 187 km SSE of False Pass, Alaska · 41 km NW of this epicentre
  5. 5.6 203 km SSE of False Pass, Alaska · 43 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 53.0370, -161.8862. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 3.9 203 km SSE of King Cove, Alaska
  2. 3.2 240 km SSE of False Pass, Alaska
  3. 3.5 210 km SSE of False Pass, Alaska
  4. 2.8 193 km SSE of King Cove, Alaska
  5. 2.7 219 km S of King Cove, Alaska
  6. 2.8 233 km SSE of King Cove, Alaska
  7. 3.5 206 km SSE of King Cove, Alaska
  8. 2.9 204 km SSE of False Pass, Alaska
  9. 3.5 225 km SSE of False Pass, Alaska
  10. 3.2 227 km SSE of False Pass, Alaska
  11. 2.7 217 km SSE of False Pass, Alaska
  12. 3.1 236 km SSE of False Pass, Alaska
  13. 2.6 219 km S of King Cove, Alaska
  14. 2.8 212 km S of King Cove, Alaska
  15. 3.0 219 km SSE of King Cove, 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.