QuakeIndex

Earthquake · reviewed by a seismologist

M 2.3ml

Earthquake near Helena, MT

No earthquake was likely felt in Helena in the 24 hours to 3:01 pm MST (22:01 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 2.3 earthquake was recorded 49 km (30 mi) north of Helena, MT, at 8:39 pm MDT on 7 October 2020 (02:39 UTC), 2.8 km deep.

USGS: 13 km WSW of Craig, Montana

8:39 pm MDT, Oct 7, 2020 · · 2.8 km deep · released about 79 lb of TNT

Every earthquake near Helena Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Lewis and Clark County 22 kmPowell County 64 kmCascade County 67 kmTeton County 89 kmBroadwater County 91 kmJefferson County 100 kmMeagher County 104 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
8:39 pm MDT on 7 October 2020 ()
Where
49 km (30 mi) north of Helena, MT · earthquakes near Helena
Montana today
every earthquake in Montana in the last 24 hours
Magnitude
M 2.3 (ml)
Depth
2.8 km below the surface
Felt
no reports yet
Nearest
Lewis and Clark County, 22 km WNW
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 2225 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 19 km (12 mi) from the epicentre. In Helena, 49 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.

How big was it?

This earthquake released about 79 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.3 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 190,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 130,000× the energy of this one
  3. Around the size people start to feel M 3.0 12× the energy of this one
  4. This earthquake M 2.3 about 79 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 190,000 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 · 48 km SSE of this epicentre
  2. 5.0 2 km ENE of Helena, Montana · 48 km SSE 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 47.0248, -112.1247. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Lewis and Clark County, MT 22 km (14 mi) WNW earthquakes near Lewis and Clark County
Powell County, MT 64 km (40 mi) WSW earthquakes near Powell County
Cascade County, MT 67 km (42 mi) ENE earthquakes near Cascade County
Teton County, MT 89 km (55 mi) N earthquakes near Teton County
Broadwater County, MT 91 km (56 mi) SSE earthquakes near Broadwater County
Jefferson County, MT 100 km (62 mi) S earthquakes near Jefferson 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. 2.8 7 km SSE of Lincoln, Montana
  2. 3.2 6 km SSE of Lincoln, Montana
  3. 1.8 13 km ESE of Lincoln, Montana
  4. 2.2 13 km ESE of Lincoln, Montana
  5. 1.5 15 km ESE of Lincoln, Montana
  6. 1.7 14 km ESE of Lincoln, Montana
  7. 1.5 14 km ESE of Lincoln, Montana
  8. 1.5 12 km E of Lincoln, Montana
  9. 1.5 14 km ESE of Lincoln, Montana
  10. 1.7 15 km SE of Lincoln, Montana
  11. 2.2 6 km W of Helena Valley West Central, Montana
  12. 1.7 12 km ESE of Lincoln, Montana
  13. 2.4 8 km NNE of Helena Valley Northwest, Montana
  14. 1.5 15 km SE of Lincoln, Montana
  15. 2.0 14 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.