Earthquake · reviewed by a seismologist
M 1.7ml
Earthquake near Boulder, MT
No earthquake was likely felt in Boulder in the 24 hours to 8:31 pm MST (03:31 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 1.7 earthquake was recorded 20 km (12 mi) south-southwest of Boulder, MT, at 7:15 am MDT on 29 October 2021 (13:15 UTC), 8.7 km deep.
USGS: 20 km SSW of Boulder, Montana
- When
- 7:15 am MDT on 29 October 2021 ()
- Where
- 20 km (12 mi) south-southwest of Boulder, MT · earthquakes near Boulder
- Montana today
- every earthquake in Montana in the last 24 hours
- Magnitude
- M 1.7 (ml)
- Depth
- 8.7 km below the surface
- Felt
- no reports yet
- Nearest
- Jefferson County, 13 km ENE
- Status
- Reviewed by a seismologist
USGS · last changed by USGS · we first saw it 1840 days ago
Earthquake alerts for Boulder, MT
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Alerts are on for .
Not a warning. An alert comes after USGS publishes a quake, usually minutes after the shaking. For early warning use ShakeAlert, through your phone's Wireless Emergency Alerts or the MyShake app.
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 9 km (6 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.
Earthquakes near other towns within 30 km: Whitehall, Butte.
How big was it?
This earthquake released about 11 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.7 would have released about 32 times as much.
- Mineral, Virginia 2011 M 5.8 1,300,000× the energy of this one
- Magna, Utah 2020 M 5.7 930,000× the energy of this one
- Around the size people start to feel M 3.0 83× the energy of this one
- This earthquake M 1.7 about 11 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 2,900 times the energy of this one.
Before 2016, the USGS record lists one earthquake of M5 or more within 50 km:
- 5.4 Near Butte, Montana · 24 km WSW 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 46.0648, -112.2002. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Jefferson County, MT | 13 km (8 mi) | ENE | earthquakes near Jefferson County |
| Silver Bow County, MT | 40 km (25 mi) | WSW | earthquakes near Silver Bow County |
| Broadwater County, MT | 62 km (38 mi) | ENE | earthquakes near Broadwater County |
| Deer Lodge County, MT | 73 km (45 mi) | W | earthquakes near Deer Lodge County |
| Madison County, MT | 85 km (53 mi) | SSE | earthquakes near Madison County |
| Gallatin County, MT | 101 km (63 mi) | SE | earthquakes near Gallatin 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.
- 1.8 4 km E of Butte, Montana
- 1.6 5 km ENE of Butte, Montana
- 1.6 5 km E of Butte, Montana
- 1.7 4 km E of Butte, Montana
- 1.7 5 km ENE of Butte, Montana
- 1.6 5 km E of Butte, Montana
- 1.9 6 km E of Butte, Montana
- 1.6 5 km E of Butte, Montana
- 1.7 6 km E of Butte, Montana
- 2.2 20 km W of Pony, Montana
- 1.7 6 km E of Butte, Montana
- 1.8 5 km E of Butte, Montana
- 1.8 5 km E of Butte, Montana
- 1.8 6 km E of Butte, Montana
- 1.9 6 km E 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
- The official USGS event page — the source of record for every value above
- Did you feel it? Report it to USGS — reports go to USGS, not to us
- ShakeMap for this event, when USGS has produced one
QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.