Earthquake · reviewed by a seismologist
M 3.9ml
107 km SSE of Adak, Alaska
Yes. A magnitude 3.9 earthquake was recorded 107 km SSE of Adak, Alaska at 03:33 UTC on 2026-10-17, 11 km deep. No felt reports to USGS yet.
- When
- Magnitude
- M 3.9 (ml)
- Depth
- 11 km below the surface
- Felt
- no reports yet
- Measured shaking
- intensity II (ShakeMap)
- Status
- Reviewed by a seismologist
USGS · last changed by USGS · we first saw it 2 hours 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 89 km (55 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 11 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.9 would have released about 32 times as much.
- Northridge, California 1994 M 6.7 16,000× the energy of this one
- Mineral, Virginia 2011 M 5.8 710× the energy of this one
- Magna, Utah 2020 M 5.7 500× the energy of this one
- This earthquake M 3.9 about 11 tons of TNT
- Around the size people start to feel M 3.0 this one released 22× 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 6.2 on 2025-03-21 — about 2,800 times the energy of this one.
Before 2016, the USGS record lists 68 earthquakes of M5 or more within 50 km; the five largest:
- 7.1 75 km S of Adak, Alaska · 48 km NW of this epicentre
- 7.0 101 km S of Adak, Alaska · 13 km WNW of this epicentre
- 6.7 76 km SSE of Adak, Alaska · 33 km N of this epicentre
- 6.2 59 km S of Adak, Alaska · 49 km NNW of this epicentre
- 6.1 106 km SE of Adak, Alaska · 43 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 50.9517, -176.1727. Map © OpenStreetMap contributors.
Aftershocks so far
No further earthquakes have been recorded within 50 km since this one.
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
- The official USGS event page — the source of record for every value above
- Did you feel it? Report it to USGS — reports go to USGS, not to us
- ShakeMap for this event, when USGS has produced one
QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.