QuakeIndex

Earthquake · reviewed by a seismologist

M 2.4ml

Earthquake near Helena West Side, MT

No earthquake was likely felt in Helena West Side in the 24 hours to 1:28 pm MST (20:28 UTC). The last one was M 1.7, 10 km (6 mi) ESE, at 12:27 pm MDT on 29 July 2026, estimated intensity II (weak) in town. Every earthquake near Helena West Side

This page: a magnitude 2.4 earthquake was recorded 4 km (2 mi) northeast of Helena West Side, MT, at 5:19 am MST on 4 December 2023 (12:19 UTC), 4.2 km deep. 47 people have reported feeling it to USGS.

USGS: 3 km NE of Helena West Side, Montana

5:19 am MST, Dec 4, 2023 · · 4.2 km deep · released about 120 lb of TNT

Every earthquake near Helena West Side Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Broadwater County 55 kmJefferson County 55 kmLewis and Clark County 60 kmPowell County 70 kmMeagher County 89 kmSilver Bow County 92 kmCascade County 95 kmDeer Lodge County 100 kmGranite County 106 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
5:19 am MST on 4 December 2023 ()
Where
4 km (2 mi) northeast of Helena West Side, MT · earthquakes near Helena West Side
Montana today
every earthquake in Montana in the last 24 hours
Magnitude
M 2.4 (ml)
Depth
4.2 km below the surface
Felt
47 reports · strongest reported intensity III
Nearest
Broadwater County, 55 km SE
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 286 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 21 km (13 mi) from the epicentre. In Helena West Side, 4 km away, the estimate is intensity III (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 5 km, intensity III. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 120 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.4 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 130,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 89,000× the energy of this one
  3. Around the size people start to feel M 3.0 7.9× the energy of this one
  4. This earthquake M 2.4 about 120 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

The largest earthquake within 50 km since 2016 was M 5.8 on 2017-07-06 — about 130,000 times the energy of this one.

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

  1. 6.1 The 1935 Helena, Montana Earthquakes (Mainshock) · 33 km E of this epicentre
  2. 5.9 2 km ENE of Helena, Montana · 6 km ESE of this epicentre
  3. 5.9 The 1935 Helena, Montana Earthquakes (Largest Aftershock) · 20 km ESE of this epicentre
  4. 5.0 2 km ENE of Helena, Montana · 6 km ESE 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 46.6200, -112.0798. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Broadwater County, MT 55 km (34 mi) SE earthquakes near Broadwater County
Jefferson County, MT 55 km (34 mi) S earthquakes near Jefferson County
Lewis and Clark County, MT 60 km (38 mi) NNW earthquakes near Lewis and Clark County
Powell County, MT 70 km (43 mi) WNW earthquakes near Powell County
Meagher County, MT 89 km (55 mi) E earthquakes near Meagher County
Silver Bow County, MT 92 km (57 mi) SSW earthquakes near Silver Bow County

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

Aftershocks so far

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

  1. 1.9 8 km WSW of Townsend, Montana
  2. 1.7 13 km ESE of Lincoln, Montana
  3. 1.5 14 km ESE of Lincoln, Montana
  4. 2.2 1 km NW of East Helena, Montana
  5. 1.5 14 km ESE of Lincoln, Montana
  6. 1.7 13 km ESE of Lincoln, Montana
  7. 1.6 8 km W of Townsend, Montana
  8. 1.5 6 km SSW of The Silos, Montana
  9. 2.4 13 km SE of Lincoln, Montana
  10. 1.5 7 km SSW of The Silos, Montana
  11. 1.9 7 km SSW of The Silos, Montana
  12. 1.9 14 km SE of Lincoln, Montana
  13. 1.6 14 km SE of Lincoln, Montana
  14. 2.2 30 km ENE of Helena Valley Northeast, Montana
  15. 2.3 30 km ENE of Helena Valley Northeast, 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.