QuakeIndex

Earthquake · reviewed by a seismologist

M 1.7md

Earthquake near Big Sky, MT

No earthquake was likely felt in Big Sky in the 24 hours to 8:32 am MST (15:32 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 1.7 earthquake was recorded 46 km (29 mi) southwest of Big Sky, MT, at 10:22 pm MDT on 7 October 2017 (04:22 UTC), 9.7 km deep.

USGS: 28 km SSE of Virginia City, Montana

10:22 pm MDT, Oct 7, 2017 · · 9.7 km deep · released about 11 lb of TNT

Every earthquake near Big Sky Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Madison County 32 kmGallatin County 75 kmBeaverhead County 82 kmClark County 93 kmFremont County 96 kmPark County 113 kmSilver Bow County 114 km
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
10:22 pm MDT on 7 October 2017 ()
Where
46 km (29 mi) southwest of Big Sky, MT · earthquakes near Big Sky
Montana today
every earthquake in Montana in the last 24 hours
Magnitude
M 1.7 (md)
Depth
9.7 km below the surface
Felt
no reports yet
Nearest
Madison County, 32 km N
Nearest mapped fault
Madison fault, 20 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 3320 days ago

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 8 km (5 mi) from the epicentre. In Big Sky, 46 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 11 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.7 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 1,400,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 1,000,000× the energy of this one
  3. Around the size people start to feel M 3.0 89× the energy of this one
  4. This earthquake M 1.7 about 11 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 4.3 on 2016-06-13 — about 9,100 times the energy of this one.

Before 2016, the USGS record lists 5 earthquakes of M5 or more within 50 km:

  1. 6.1 30 km SSW of Big Sky, Montana · 23 km E of this epicentre
  2. 5.2 32 km WNW of Hebgen Lake Estates, Montana · 29 km SE of this epicentre
  3. 5.2 26 km WNW of Hebgen Lake Estates, Montana · 35 km SE of this epicentre
  4. 5.0 31 km W of Hebgen Lake Estates, Montana · 33 km SE of this epicentre
  5. 5.0 39 km W of Hebgen Lake Estates, Montana · 40 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 45.0440, -111.8527. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Madison County, MT 32 km (20 mi) N earthquakes near Madison County
Gallatin County, MT 75 km (47 mi) NE earthquakes near Gallatin County
Beaverhead County, MT 82 km (51 mi) W earthquakes near Beaverhead County
Clark County, ID 93 km (58 mi) SSW earthquakes near Clark County
Fremont County, ID 96 km (60 mi) SSE earthquakes near Fremont County
Park County, MT 113 km (70 mi) ENE earthquakes near Park County

Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.

Aftershocks so far

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

  1. 3.0 17 km WNW of Hebgen Lake Estates, Montana
  2. 2.2 42 km NE of Spencer, Idaho
  3. 1.8 42 km NE of Spencer, Idaho
  4. 2.0 43 km NE of Spencer, Idaho
  5. 2.2 42 km NE of Spencer, Idaho
  6. 1.6 43 km NE of Spencer, Idaho
  7. 2.7 40 km NNE of Spencer, Idaho
  8. 1.8 43 km NE of Spencer, Idaho
  9. 2.8 41 km NNE of Spencer, Idaho
  10. 1.6 30 km SE of Dillon, Montana
  11. 1.6 43 km S of Virginia City, Montana
  12. 2.4 41 km NE of Spencer, Idaho
  13. 2.9 43 km NE of Spencer, Idaho
  14. 1.9 39 km SSW of Big Sky, Montana
  15. 2.0 42 km WNW of Hebgen Lake Estates, 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

QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.