QuakeIndex

Earthquake · reviewed by a seismologist

M 2.6ml

Earthquake near Boulder, MT

No earthquake was likely felt in Boulder in the 24 hours to 9:59 am MST (16:59 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 2.6 earthquake was recorded 20 km (12 mi) east-southeast of Boulder, MT, at 2:44 pm MDT on 17 July 2018 (20:44 UTC), 6.7 km deep.

USGS: 15 km SSE of Elkhorn, Montana

2:44 pm MDT, Jul 17, 2018 · · 6.7 km deep · released about 240 lb of TNT

Every earthquake near Boulder Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Jefferson County 12 kmBroadwater County 38 kmSilver Bow County 64 kmGallatin County 90 kmMeagher County 90 kmMadison County 91 kmDeer Lodge County 95 kmPowell County 111 kmLewis and Clark County 115 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
2:44 pm MDT on 17 July 2018 ()
Where
20 km (12 mi) east-southeast of Boulder, MT · earthquakes near Boulder
Montana today
every earthquake in Montana in the last 24 hours
Magnitude
M 2.6 (ml)
Depth
6.7 km below the surface
Felt
no reports yet
Nearest
Jefferson County, 12 km W
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 2960 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 23 km (14 mi) from the epicentre. In Boulder, 20 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: Boulder 20 km, intensity II. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 240 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.6 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 63,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 45,000× the energy of this one
  3. Around the size people start to feel M 3.0 4× the energy of this one
  4. This earthquake M 2.6 about 240 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 4.0 on 2016-09-03 — about 140 times the energy of this one.

Before 2016, the USGS record lists 7 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.6 The 1925 Clarkston Valley, Montana Earthquake · 31 km ESE of this epicentre
  2. 6.4 Clarkston Valley, Montana (Aftershock) · 31 km ESE of this epicentre
  3. 5.9 The 1935 Helena, Montana Earthquakes (Largest Aftershock) · 45 km N of this epicentre
  4. 5.5 Clarkston Valley, Montana (Aftershock) · 31 km ESE of this epicentre
  5. 5.5 Clarkston Valley, Montana (Aftershock) · 31 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 46.1395, -111.9055. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Jefferson County, MT 12 km (7 mi) W earthquakes near Jefferson County
Broadwater County, MT 38 km (24 mi) NE earthquakes near Broadwater County
Silver Bow County, MT 64 km (40 mi) WSW earthquakes near Silver Bow County
Gallatin County, MT 90 km (56 mi) SE earthquakes near Gallatin County
Meagher County, MT 90 km (56 mi) ENE earthquakes near Meagher County
Madison County, MT 91 km (56 mi) S earthquakes near Madison County

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

Aftershocks so far

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

  1. 1.7 10 km ENE of Townsend, Montana
  2. 2.2 15 km S of Whitehall, Montana
  3. 1.6 5 km W of Townsend, Montana
  4. 1.7 6 km WSW of Townsend, Montana
  5. 1.5 7 km SSW of The Silos, Montana
  6. 2.5 2 km ESE of Logan, Montana
  7. 1.9 9 km WSW of Townsend, Montana
  8. 1.6 7 km WSW of Townsend, Montana
  9. 1.8 7 km WSW of Townsend, Montana
  10. 2.0 16 km S of Whitehall, Montana
  11. 1.6 1 km SE of South Hills, Montana
  12. 1.8 3 km N of Logan, Montana
  13. 1.7 4 km WSW of Three Forks, Montana
  14. 1.7 17 km S of Whitehall, Montana
  15. 2.2 6 km W of Willow Creek, 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.