QuakeIndex

Earthquake · reviewed by a seismologist

M 2.7ml

3 km ENE of Helena, Montana

· 5.0 km deep · released about 340 lb of TNT

Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Broadwater County 49 kmJefferson County 54 kmLewis and Clark County 65 kmPowell County 76 kmMeagher County 82 kmCascade County 93 kmSilver Bow County 94 kmDeer Lodge County 105 kmGranite County 112 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 2.7 (ml)
Depth
5.0 km below the surface
Felt
267 reports · strongest reported intensity III
Nearest
Broadwater County, 49 km SE
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 499 days ago

This was a small earthquake. Shaking like this is often felt indoors nearby and very rarely causes damage. 267 people have reported feeling it to USGS.

How big was it?

This earthquake released about 340 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.7 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 45,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 32,000× the energy of this one
  3. Around the size people start to feel M 3.0 2.8× the energy of this one
  4. This earthquake M 2.7 about 340 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 46.6040, -111.9945. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection
Broadwater County, MT 49 km (30 mi) NW of here earthquakes near Broadwater County
Jefferson County, MT 54 km (33 mi) N of here earthquakes near Jefferson County
Lewis and Clark County, MT 65 km (40 mi) SSE of here earthquakes near Lewis and Clark County
Powell County, MT 76 km (47 mi) ESE of here earthquakes near Powell County
Meagher County, MT 82 km (51 mi) W of here earthquakes near Meagher County
Cascade County, MT 93 km (58 mi) SSW of here earthquakes near Cascade County

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

Aftershocks so far

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

  1. 1.5 9 km WSW of Townsend, Montana
  2. 1.5 1 km SSE of South Hills, Montana
  3. 1.7 0 km NNW of South Hills, Montana
  4. 1.7 8 km S of Marysville, Montana
  5. 2.0 32 km ENE of Helena Valley Northeast, Montana
  6. 2.0 20 km NNE of Helena Valley Northeast, Montana
  7. 1.5 31 km ENE of Helena Valley Northeast, Montana
  8. 1.9 1 km SSE of South Hills, Montana
  9. 2.4 2 km ESE of Clancy, Montana
  10. 1.9 9 km W of Townsend, 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. 1.7 8 km WSW of Townsend, Montana
  15. 1.9 8 km WSW 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.

For this area

The largest earthquake within 50 km in our catalogue was M 4.3 on 2016-01-30 — it released about 280 times the energy of this one.

From the QuakeIndex catalogue, built from the USGS FDSN event service.

On USGS

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