QuakeIndex

Earthquake · reviewed by a seismologist

M 2.8ml

Earthquake near Boulder, MT

No earthquake was likely felt in Boulder in the 24 hours to 2:52 pm MST (21:52 UTC). The last one was M 3.0, 33 km (21 mi) SSW, at 9:32 pm MDT on 26 April 2026, estimated intensity II (weak) in town; 42 felt reports to USGS. Every earthquake near Boulder

This page: a magnitude 2.8 earthquake was recorded 4 km (2 mi) northeast of Boulder, MT, at 7:00 pm MDT on 17 April 2020 (01:00 UTC), 5.0 km deep. 9 people have reported feeling it to USGS.

USGS: 3 km NE of Boulder, Montana

7:00 pm MDT, Apr 17, 2020 · · 5.0 km deep · released about 480 lb of TNT

Every earthquake near Boulder Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Jefferson County 15 kmBroadwater County 46 kmSilver Bow County 60 kmDeer Lodge County 84 kmPowell County 92 kmMeagher County 96 kmLewis and Clark County 99 kmGranite County 104 kmMadison 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
7:00 pm MDT on 17 April 2020 ()
Where
4 km (2 mi) northeast of Boulder, MT · earthquakes near Boulder
Montana today
every earthquake in Montana in the last 24 hours
Magnitude
M 2.8 (ml)
Depth
5.0 km below the surface
Felt
9 reports · strongest reported intensity IV
Nearest
Jefferson County, 15 km S
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 2316 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 27 km (17 mi) from the epicentre. In Boulder, 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: Boulder 4 km, intensity III. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 480 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.8 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 32,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 22,000× the energy of this one
  3. Around the size people start to feel M 3.0 2× the energy of this one
  4. This earthquake M 2.8 about 480 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

No earthquake of M4 or more has been recorded within 50 km since our catalogue begins in 2016.

Before 2016, the USGS record lists 10 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.6 The 1925 Clarkston Valley, Montana Earthquake · 48 km ESE of this epicentre
  2. 6.4 Clarkston Valley, Montana (Aftershock) · 48 km ESE of this epicentre
  3. 6.1 The 1935 Helena, Montana Earthquakes (Mainshock) · 50 km NE of this epicentre
  4. 5.9 2 km ENE of Helena, Montana · 39 km N of this epicentre
  5. 5.9 The 1935 Helena, Montana Earthquakes (Largest Aftershock) · 36 km NNE 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 46.2575, -112.0823. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Jefferson County, MT 15 km (9 mi) S earthquakes near Jefferson County
Broadwater County, MT 46 km (28 mi) E earthquakes near Broadwater County
Silver Bow County, MT 60 km (37 mi) SW earthquakes near Silver Bow County
Deer Lodge County, MT 84 km (52 mi) WSW earthquakes near Deer Lodge County
Powell County, MT 92 km (57 mi) NW earthquakes near Powell County
Meagher County, MT 96 km (60 mi) ENE earthquakes near Meagher County

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

Aftershocks so far

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

  1. 1.7 4 km ENE of Butte, Montana
  2. 1.9 5 km ENE of Butte, Montana
  3. 1.6 4 km E of Butte, Montana
  4. 1.8 5 km E of Butte, Montana
  5. 1.8 5 km ENE of Butte, Montana
  6. 2.1 5 km ENE of Butte, Montana
  7. 1.7 5 km ENE of Butte, Montana
  8. 1.6 5 km E of Butte, Montana
  9. 1.6 4 km E of Butte, Montana
  10. 1.5 5 km E of Butte, Montana
  11. 2.0 11 km SSW of Radersburg, Montana
  12. 1.6 5 km ENE of Butte, Montana
  13. 1.5 5 km E of Butte, Montana
  14. 2.0 5 km ENE of Butte, Montana
  15. 1.9 5 km ENE of Butte, 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.