QuakeIndex

Earthquake · reviewed by a seismologist

M 3.2ml

Earthquake near Helena, MT

No earthquake was likely felt in Helena in the 24 hours to 9:53 am MST (16:53 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 3.2 earthquake was recorded 44 km (27 mi) west-northwest of Helena, MT, at 12:53 am MDT on 23 July 2017 (06:53 UTC), 13 km deep. 5 people have reported feeling it to USGS.

USGS: 18 km WNW of Marysville, Montana

12:53 am MDT, Jul 23, 2017 · · 13 km deep · released about 1,900 lb of TNT

Every earthquake near Helena Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Powell County 31 kmLewis and Clark County 37 kmGranite County 82 kmJefferson County 83 kmDeer Lodge County 92 kmBroadwater County 95 kmSilver Bow County 101 kmCascade County 106 kmMissoula County 107 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
12:53 am MDT on 23 July 2017 ()
Where
44 km (27 mi) west-northwest of Helena, MT · earthquakes near Helena
Montana today
every earthquake in Montana in the last 24 hours
Magnitude
M 3.2 (ml)
Depth
13 km below the surface
Felt
5 reports · strongest reported intensity III
Nearest
Powell County, 31 km W
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1607 days ago

This was a small earthquake. Shaking like this is often felt indoors nearby and very rarely causes damage.

At this magnitude and depth, people at rest would likely notice it out to about 44 km (27 mi) from the epicentre. In Helena, 44 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: Lincoln 21 km, intensity II · Helena 44 km, intensity II. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 1,900 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.2 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 180,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 7,900× the energy of this one
  3. Magna, Utah 2020 M 5.7 5,600× the energy of this one
  4. This earthquake M 3.2 about 1,900 lb of TNT
  5. Around the size people start to feel M 3.0 this one released 2× more

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 7,900 times the energy of this one.

Before 2016, the USGS record lists 2 earthquakes of M5 or more within 50 km:

  1. 5.9 2 km ENE of Helena, Montana · 46 km ESE of this epicentre
  2. 5.0 2 km ENE of Helena, Montana · 46 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 46.8026, -112.5267. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Powell County, MT 31 km (19 mi) W earthquakes near Powell County
Lewis and Clark County, MT 37 km (23 mi) NNE earthquakes near Lewis and Clark County
Granite County, MT 82 km (51 mi) WSW earthquakes near Granite County
Jefferson County, MT 83 km (52 mi) SSE earthquakes near Jefferson County
Deer Lodge County, MT 92 km (57 mi) SSW earthquakes near Deer Lodge County
Broadwater County, MT 95 km (59 mi) ESE earthquakes near Broadwater County

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

Aftershocks so far

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

  1. 2.3 3 km SW of Lincoln, Montana
  2. 1.9 14 km SE of Lincoln, Montana
  3. 2.3 3 km W of Lincoln, Montana
  4. 2.4 15 km SE of Lincoln, Montana
  5. 3.0 12 km SSE of Lincoln, Montana
  6. 2.6 Western Montana
  7. 1.9 12 km ESE of Lincoln, Montana
  8. 2.3 15 km SSE of Lincoln, Montana
  9. 1.5 13 km SE of Lincoln, Montana
  10. 2.5 12 km SE of Lincoln, Montana
  11. 1.6 12 km ESE of Lincoln, Montana
  12. 2.1 15 km SE of Lincoln, Montana
  13. 2.1 13 km ESE of Lincoln, Montana
  14. 2.7 17 km WNW of Marysville, Montana
  15. 1.8 15 km ESE of Lincoln, 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.