Earthquake · reviewed by a seismologist
M 1.9ml
Earthquake near Big Sky, MT
No earthquake was likely felt in Big Sky in the 24 hours to 9:08 am MST (16:08 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 1.9 earthquake was recorded 37 km (23 mi) west-northwest of Big Sky, MT, at 3:42 pm MDT on 28 July 2021 (21:42 UTC), 1.2 km deep.
USGS: 12 km NNW of Ennis, Montana
- When
- 3:42 pm MDT on 28 July 2021 ()
- Where
- 37 km (23 mi) west-northwest of Big Sky, MT · earthquakes near Big Sky
- Montana today
- every earthquake in Montana in the last 24 hours
- Magnitude
- M 1.9 (ml)
- Depth
- 1.2 km below the surface
- Felt
- no reports yet
- Nearest
- Madison County, 18 km SW
- Nearest mapped fault
- Madison fault, 12 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 1932 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 15 km (9 mi) from the epicentre. In Big Sky, 37 km away, the estimate is intensity II (weak). 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 24 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.9 would have released about 32 times as much.
- Mineral, Virginia 2011 M 5.8 640,000× the energy of this one
- Magna, Utah 2020 M 5.7 450,000× the energy of this one
- Around the size people start to feel M 3.0 40× the energy of this one
- This earthquake M 1.9 about 24 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 1,400 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 45.4595, -111.7760. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Madison County, MT | 18 km (11 mi) | SW | earthquakes near Madison County |
| Gallatin County, MT | 48 km (30 mi) | E | earthquakes near Gallatin County |
| Jefferson County, MT | 77 km (48 mi) | NNW | earthquakes near Jefferson County |
| Silver Bow County, MT | 84 km (52 mi) | NW | earthquakes near Silver Bow County |
| Beaverhead County, MT | 95 km (59 mi) | WSW | earthquakes near Beaverhead County |
| Park County, MT | 97 km (60 mi) | E | earthquakes near Park County |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
47 earthquakes have been recorded within 50 km since this one.
- 2.4 14 km SSW of Whitehall, Montana
- 1.5 16 km S of Whitehall, Montana
- 3.3 16 km SSW of Whitehall, Montana
- 1.9 12 km WNW of Pony, Montana
- 1.5 29 km S of Ennis, Montana
- 1.6 5 km SSW of Willow Creek, Montana
- 2.1 3 km WNW of Pony, Montana
- 1.5 Western Montana
- 2.0 3 km WNW of Pony, Montana
- 1.8 18 km N of Ennis, Montana
- 2.5 3 km WNW of Pony, Montana
- 1.7 16 km N of Big Sky, Montana
- 1.6 28 km SE of Virginia City, Montana
- 1.6 14 km ESE of Harrison, Montana
- 1.7 28 km S 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.