EarthBrowserEarthquake · Thursday, September 17, 2026
Magnitude 3.9 earthquake 169 km WSW of Nikolski, Alaska
A magnitude 3.9 (minor) earthquake struck 169 km WSW of Nikolski, Alaska on Thursday, September 17, 2026 at , at a depth of 111 km (intermediate).
- Magnitude
- 3.9Minor
- Depth
- 111km · intermediate
- Time
- Epicenter
- 52.23° N
171.07° W - Aftershocks so far
- 5within 250 km
- Largest aftershock
- 4.7M
53 days ago · USGS id aka2026slngie · last revised
The full globe opens the 3D cross-section: the hypocenter at depth, the plate boundary and subducting slab where there is one, the aftershock sequence as it grows, and the sea floor around an offshore epicenter.
What a magnitude 3.9 means
Minor earthquakes are often felt by people nearby but almost never cause damage.
A magnitude 3.9 releases about 32 times the seismic energy of a magnitude 2.9, roughly the energy of 11 tonnes of TNT. Magnitude measures the energy released at the source; how hard the ground shook at any one place depends on distance, depth and local geology, and is reported separately as intensity.
Intermediate-depth earthquakes (70 to 300 km) occur inside subducting slabs. The extra distance to the surface spreads the shaking over a wider area at lower intensity.
Nearby earthquakes and aftershocks
This event is part of a sequence: a larger magnitude 6.5 struck 62 km away on Sep 17, 14:19 UTC, so this is most likely one of its aftershocks.
Frequently asked questions
How is earthquake magnitude measured?
Modern magnitudes are moment magnitudes (Mw), computed from the seismic moment: the area of the fault that slipped, how far it slipped and the rigidity of the rock. Each whole step up the scale is about 32 times more energy, so a magnitude 7 releases roughly a thousand times the energy of a magnitude 5.
What is the difference between magnitude and intensity?
Magnitude is one number for the whole earthquake, describing the energy released at the source. Intensity describes the shaking at a particular place, on the Modified Mercalli scale from I (not felt) to X+ (extreme), and falls off with distance from the epicenter.
What is an aftershock?
An aftershock is a smaller earthquake in the same area after a larger one, as the crust around the ruptured fault adjusts to the new stresses. They are most frequent in the first hours and days and fade over weeks to months, though a large mainshock can produce aftershocks for years.
Why do the magnitude and location change?
The first solution uses the nearest stations only. As recordings arrive from more seismographs around the world, USGS revises the magnitude, depth and epicenter, sometimes several times in the first hours. This page reflects the latest revision.
Where does this earthquake data come from?
From the U.S. Geological Survey’s real-time earthquake feeds, which combine the USGS National Earthquake Information Center with regional seismic networks worldwide. EarthBrowser ingests the feed every minute.