Earthquake · reviewed by a seismologist
M 1.5ml
Earthquake near Big Sky, MT
No earthquake was likely felt in Big Sky in the 24 hours to 7:09 am MST (14:09 UTC). The last one was M 3.7, 68 km (42 mi) SE, at 7:22 am MDT on 28 October 2025, estimated intensity II (weak) in town; 11 felt reports to USGS. Every earthquake near Big Sky
This page: a magnitude 1.5 earthquake was recorded 40 km (25 mi) west-northwest of Big Sky, MT, at 10:41 pm MDT on 21 August 2026 (04:41 UTC), 4.2 km deep.
USGS: 13 km NNW of Ennis, Montana
- When
- 10:41 pm MDT on 21 August 2026 ()
- Where
- 40 km (25 mi) west-northwest of Big Sky, MT · earthquakes near Big Sky
- Montana today
- every earthquake in Montana in the last 24 hours
- Magnitude
- M 1.5 (ml)
- Depth
- 4.2 km below the surface
- Felt
- no reports yet
- Nearest
- Madison County, 16 km SSW
- Nearest mapped fault
- Madison fault, 15 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 78 days ago
Earthquake alerts for Big Sky, MT
Get a notification in this browser when USGS records an earthquake near Big Sky, MT. No account or email needed.
Alerts are on for .
Not a warning. An alert comes after USGS publishes a quake, usually minutes after the shaking. For early warning use ShakeAlert, through your phone's Wireless Emergency Alerts or the MyShake app.
This was a minor earthquake. Quakes this small are rarely felt and do not cause damage.
At this magnitude and depth, people at rest would likely notice it out to about 9 km (6 mi) from the epicentre. In Big Sky, 40 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 5.4 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.5 would have released about 32 times as much.
- Mineral, Virginia 2011 M 5.8 2,800,000× the energy of this one
- Magna, Utah 2020 M 5.7 2,000,000× the energy of this one
- Around the size people start to feel M 3.0 180× the energy of this one
- This earthquake M 1.5 about 5.4 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 4.0 on 2016-09-03 — about 6,200 times the energy of this one.
Before 2016, the USGS record lists one earthquake of M5 or more within 50 km:
- 6.1 30 km SSW of Big Sky, Montana · 49 km SSE 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 45.4495, -111.8220. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Madison County, MT | 16 km (10 mi) | SSW | earthquakes near Madison County |
| Gallatin County, MT | 52 km (32 mi) | E | earthquakes near Gallatin County |
| Jefferson County, MT | 77 km (48 mi) | NNW | earthquakes near Jefferson County |
| Silver Bow County, MT | 82 km (51 mi) | NW | earthquakes near Silver Bow County |
| Beaverhead County, MT | 91 km (56 mi) | WSW | earthquakes near Beaverhead County |
| Park County, MT | 100 km (62 mi) | E | earthquakes near Park County |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
12 earthquakes have been recorded within 50 km since this one.
- 1.3 28 km S of Ennis, Montana
- 1.0 11 km WSW of Sheridan, Montana
- 1.2 28 km SSE of Virginia City, Montana
- 2.4 20 km SW of Whitehall, Montana
- 1.0 8 km SE of Big Sky, Montana
- 2.1 15 km ENE of Twin Bridges, Montana
- 1.6 15 km S of Whitehall, Montana
- 0.5 11 km NNE of Ennis, Montana
- 1.4 28 km S of Ennis, Montana
- 0.9 29 km S of Ennis, Montana
- 1.9 14 km ESE of Harrison, Montana
- 2.1 12 km NW of Ennis, Montana
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.