QuakeIndex

Earthquake · reviewed by a seismologist

M 1.6ml

Earthquake near Helena, MT

No earthquake was likely felt in Helena in the 24 hours to 12:27 am MST (07:27 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 1.6 earthquake was recorded 42 km (26 mi) northeast of Helena, MT, at 2:28 pm MDT on 1 September 2017 (20:28 UTC), 11 km deep.

USGS: 30 km ENE of Helena Valley Northeast, Montana

2:28 pm MDT, Sep 1, 2017 · · 11 km deep · released about 7.1 lb of TNT

Every earthquake near Helena Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Broadwater County 56 kmCascade County 57 kmMeagher County 59 kmLewis and Clark County 67 kmJefferson County 86 kmPowell County 101 kmJudith Basin County 101 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
2:28 pm MDT on 1 September 2017 ()
Where
42 km (26 mi) northeast of Helena, MT · earthquakes near Helena
Montana today
every earthquake in Montana in the last 24 hours
Magnitude
M 1.6 (ml)
Depth
11 km below the surface
Felt
no reports yet
Nearest
Broadwater County, 56 km S
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 3358 days ago

This was a minor earthquake. Quakes this small are rarely felt and do not cause damage.

At this magnitude and depth it was probably too small to be felt, even directly above it. In Helena, 42 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 7.1 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.6 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 2,100,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 1,500,000× the energy of this one
  3. Around the size people start to feel M 3.0 130× the energy of this one
  4. This earthquake M 1.6 about 7.1 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) · 27 km S of this epicentre
  2. 5.9 2 km ENE of Helena, Montana · 39 km SW of this epicentre
  3. 5.9 The 1935 Helena, Montana Earthquakes (Largest Aftershock) · 37 km SSW of this epicentre
  4. 5.0 2 km ENE of Helena, Montana · 39 km SW 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 46.8312, -111.6073. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Broadwater County, MT 56 km (35 mi) S earthquakes near Broadwater County
Cascade County, MT 57 km (36 mi) NNE earthquakes near Cascade County
Meagher County, MT 59 km (37 mi) ESE earthquakes near Meagher County
Lewis and Clark County, MT 67 km (42 mi) WNW earthquakes near Lewis and Clark County
Jefferson County, MT 86 km (53 mi) SSW earthquakes near Jefferson County
Powell County, MT 101 km (63 mi) W earthquakes near Powell County

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

Aftershocks so far

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

  1. 1.6 2 km E of South Hills, Montana
  2. 1.6 2 km E of South Hills, Montana
  3. 1.8 31 km ENE of Helena Valley Northeast, Montana
  4. 1.9 30 km ENE of Helena Valley Northeast, Montana
  5. 1.6 3 km SW of Helena Valley Northwest, Montana
  6. 1.6 1 km SSE of South Hills, Montana
  7. 1.6 1 km SSE of South Hills, Montana
  8. 2.2 36 km SSW of Stockett, Montana
  9. 1.7 2 km NNW of Montana City, Montana
  10. 1.5 21 km NE of Townsend, Montana
  11. 2.2 6 km W of Helena Valley West Central, Montana
  12. 2.4 8 km NNE of Helena Valley Northwest, Montana
  13. 2.9 11 km SW of Winston, Montana
  14. 2.3 2 km WNW of East Helena, Montana
  15. 1.6 2 km NW of Montana City, 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.