QuakeIndex

quarry blast · reviewed by a seismologist

M 1.8ml

Earthquake near Montana City, MT

USGS: 2 km NW of Montana City, Montana

12:41 pm MST, Dec 14, 2017 · · -2.0 km deep · released about 13 lb of TNT

Every earthquake near Montana City Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Broadwater County 43 kmJefferson County 48 kmLewis and Clark County 71 kmMeagher County 79 kmPowell County 81 kmSilver Bow County 91 kmCascade County 97 kmDeer Lodge County 104 kmGranite 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
12:41 pm MST on 14 December 2017 ()
Where
2 km (1 mi) NW of Montana City, MT · earthquakes near Montana City
Magnitude
M 1.8 (ml)
Depth
-2.0 km below the surface
Felt
no reports yet
Nearest
Broadwater County, 43 km SE
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 3214 days ago

A magnitude 1.8 earthquake was recorded 2 km (1 mi) NW of Montana City, MT, at 12:41 pm MST on 14 December 2017 (19:41 UTC). This was a minor earthquake. Quakes this small are rarely felt and do not cause damage.

Earthquakes near other towns within 30 km: East Helena, Helena, Helena Valley Southeast, Clancy, Helena West Side, Helena Valley West Central.

USGS catalogues this as quarry blast, not an earthquake.

How big was it?

This earthquake released about 13 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.8 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 1,100,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 810,000× the energy of this one
  3. Around the size people start to feel M 3.0 72× the energy of this one
  4. This earthquake M 1.8 about 13 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

No earthquake of M4 or more has been recorded within 50 km since our catalogue begins in 2016.

Before 2016, the USGS record lists 4 earthquakes of M5 or more within 50 km:

  1. 6.1 The 1935 Helena, Montana Earthquakes (Mainshock) · 24 km ENE of this epicentre
  2. 5.9 2 km ENE of Helena, Montana · 7 km NNW of this epicentre
  3. 5.9 The 1935 Helena, Montana Earthquakes (Largest Aftershock) · 8 km E of this epicentre
  4. 5.0 2 km ENE of Helena, Montana · 7 km NNW 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 46.5492, -111.9573. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Broadwater County, MT 43 km (27 mi) SE earthquakes near Broadwater County
Jefferson County, MT 48 km (30 mi) S earthquakes near Jefferson County
Lewis and Clark County, MT 71 km (44 mi) NNW earthquakes near Lewis and Clark County
Meagher County, MT 79 km (49 mi) E earthquakes near Meagher County
Powell County, MT 81 km (50 mi) WNW earthquakes near Powell County
Silver Bow County, MT 91 km (56 mi) SW earthquakes near Silver Bow County

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

Aftershocks so far

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

  1. 1.6 12 km WNW of Marysville, Montana
  2. 2.0 7 km SSW of Marysville, Montana
  3. 1.7 7 km SSW of Marysville, Montana
  4. 1.7 6 km W of Townsend, Montana
  5. 1.6 6 km SSW of The Silos, Montana
  6. 1.6 14 km S of Craig, Montana
  7. 1.6 19 km NNE of Marysville, Montana
  8. 1.6 5 km W of Townsend, Montana
  9. 1.7 6 km WSW of Townsend, Montana
  10. 1.5 7 km SSW of The Silos, Montana
  11. 1.6 17 km S of Craig, Montana
  12. 1.9 9 km WSW of Townsend, Montana
  13. 1.6 10 km NW of Helena Valley Northwest, Montana
  14. 1.6 7 km WSW of Townsend, Montana
  15. 1.8 11 km S of Craig, 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.