QuakeIndex

Earthquake · reviewed by a seismologist

M 2.9ml

28 km ENE of Helena Valley Northeast, Montana

· 20 km deep · released about 680 lb of TNT

Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Broadwater County 49 kmMeagher County 55 kmCascade County 64 kmLewis and Clark County 72 kmJefferson County 80 kmJudith Basin County 102 kmPowell County 102 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
Magnitude
M 2.9 (ml)
Depth
20 km below the surface
Felt
10 reports · strongest reported intensity II
Nearest
Broadwater County, 49 km S
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 558 days ago

This was a small earthquake. Shaking like this is often felt indoors nearby and very rarely causes damage. 10 people have reported feeling it to USGS.

How big was it?

This earthquake released about 680 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.9 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 22,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 16,000× the energy of this one
  3. Around the size people start to feel M 3.0 1.4× the energy of this one
  4. This earthquake M 2.9 about 680 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.

Where

Epicentre 46.7621, -111.5907. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection
Broadwater County, MT 49 km (30 mi) N of here earthquakes near Broadwater County
Meagher County, MT 55 km (34 mi) WNW of here earthquakes near Meagher County
Cascade County, MT 64 km (40 mi) SSW of here earthquakes near Cascade County
Lewis and Clark County, MT 72 km (45 mi) ESE of here earthquakes near Lewis and Clark County
Jefferson County, MT 80 km (49 mi) NNE of here earthquakes near Jefferson County
Judith Basin County, MT 102 km (63 mi) WSW of here earthquakes near Judith Basin County

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

Aftershocks so far

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

  1. 1.5 16 km NE of Helena Valley Northwest, Montana
  2. 1.6 14 km SSE of Craig, Montana
  3. 2.4 21 km SSE of Craig, Montana
  4. 1.5 1 km SSE of South Hills, Montana
  5. 1.7 0 km NNW of South Hills, Montana
  6. 2.0 32 km ENE of Helena Valley Northeast, Montana
  7. 2.0 20 km NNE of Helena Valley Northeast, Montana
  8. 1.5 31 km ENE of Helena Valley Northeast, Montana
  9. 1.9 1 km SSE of South Hills, Montana
  10. 2.4 2 km ESE of Clancy, Montana
  11. 1.6 3 km NNW of Townsend, Montana
  12. 1.6 6 km W of Townsend, Montana
  13. 1.7 7 km W of Townsend, Montana
  14. 1.6 7 km W of Townsend, Montana
  15. 1.6 8 km W of Townsend, 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.