QuakeIndex

Earthquake · reviewed by a seismologist

M 1.7ml

Earthquake near Helena, MT

No earthquake was likely felt in Helena in the 24 hours to 5:34 pm MST (00:34 UTC). The last one was M 1.6, 7 km (4 mi) SE, at 11:34 am MDT on 14 October 2026, estimated intensity II (weak) in town. Every earthquake near Helena

This page: a magnitude 1.7 earthquake was recorded 6 km (4 mi) east-southeast of Helena, MT, at 3:54 pm MST on 31 December 2016 (22:54 UTC), 3.0 km deep.

USGS: 2 km ENE of South Hills, Montana

3:54 pm MST, Dec 31, 2016 · · 3.0 km deep · released about 9.6 lb of TNT

Every earthquake near Helena Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Broadwater County 44 kmJefferson County 50 kmLewis and Clark County 69 kmMeagher County 80 kmPowell County 80 kmSilver Bow County 92 kmCascade County 95 kmDeer Lodge County 105 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
3:54 pm MST on 31 December 2016 ()
Where
6 km (4 mi) east-southeast of Helena, MT · earthquakes near Helena
Montana today
every earthquake in Montana in the last 24 hours
Magnitude
M 1.7 (ml)
Depth
3.0 km below the surface
Felt
no reports yet
Nearest
Broadwater County, 44 km SE
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 3602 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 12 km (7 mi) from the epicentre. In Helena, 6 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.

Likely felt in: Helena 6 km, intensity II. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 9.6 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 1,600,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 1,100,000× the energy of this one
  3. Around the size people start to feel M 3.0 99× the energy of this one
  4. This earthquake M 1.7 about 9.6 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 E of this epicentre
  2. 5.9 2 km ENE of Helena, Montana · 5 km NW of this epicentre
  3. 5.9 The 1935 Helena, Montana Earthquakes (Largest Aftershock) · 9 km ESE of this epicentre
  4. 5.0 2 km ENE of Helena, Montana · 5 km NW 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 46.5683, -111.9627. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Broadwater County, MT 44 km (28 mi) SE earthquakes near Broadwater County
Jefferson County, MT 50 km (31 mi) S earthquakes near Jefferson County
Lewis and Clark County, MT 69 km (43 mi) NNW earthquakes near Lewis and Clark County
Meagher County, MT 80 km (49 mi) E earthquakes near Meagher County
Powell County, MT 80 km (50 mi) WNW earthquakes near Powell County
Silver Bow County, MT 92 km (57 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

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

  1. 2.6 7 km N of Marysville, Montana
  2. 1.7 7 km W of Helena West Side, Montana
  3. 1.7 2 km NE of The Silos, Montana
  4. 1.6 6 km W of Townsend, Montana
  5. 1.9 14 km NNW of Marysville, Montana
  6. 1.6 30 km ENE of Helena Valley Northeast, Montana
  7. 2.1 28 km ENE of Helena Valley Northeast, Montana
  8. 1.8 16 km NW of Marysville, Montana
  9. 2.6 15 km WNW of Marysville, Montana
  10. 1.8 8 km N of Elliston, Montana
  11. 1.9 14 km NW of Marysville, Montana
  12. 2.5 13 km WNW of Marysville, Montana
  13. 3.4 14 km NW of Marysville, Montana
  14. 1.6 6 km W of Townsend, Montana
  15. 1.5 1 km ESE of South Hills, 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.