Earthquake · reviewed by a seismologist
M 1.5ml
Earthquake near Helena, MT
No earthquake was likely felt in Helena in the 24 hours to 1:27 pm MST (20:27 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 1.5 earthquake was recorded 43 km (26 mi) west-northwest of Helena, MT, at 8:38 pm MST on 7 December 2018 (03:38 UTC), 6.9 km deep.
USGS: 15 km NNE of Avon, Montana
- When
- 8:38 pm MST on 7 December 2018 ()
- Where
- 43 km (26 mi) west-northwest of Helena, MT · earthquakes near Helena
- Montana today
- every earthquake in Montana in the last 24 hours
- Magnitude
- M 1.5 (ml)
- Depth
- 6.9 km below the surface
- Felt
- no reports yet
- Nearest
- Powell County, 31 km WNW
- Status
- Reviewed by a seismologist
USGS · last changed by USGS · we first saw it 2895 days ago
Earthquake alerts for Helena, MT
Get a notification in this browser when USGS records an earthquake near Helena, MT. No account or email needed.
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 8 km (5 mi) from the epicentre. In Helena, 43 km away, the estimate is intensity I (not felt). 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: Lincoln.
How big was it?
This earthquake released about 5.9 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.5 would have released about 32 times as much.
- Mineral, Virginia 2011 M 5.8 2,500,000× the energy of this one
- Magna, Utah 2020 M 5.7 1,800,000× the energy of this one
- Around the size people start to feel M 3.0 160× the energy of this one
- This earthquake M 1.5 about 5.9 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 2,500,000 times the energy of this one.
Before 2016, the USGS record lists 2 earthquakes of M5 or more within 50 km:
- 5.9 2 km ENE of Helena, Montana · 45 km ESE of this epicentre
- 5.0 2 km ENE of Helena, Montana · 45 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 46.7338, -112.5548. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Powell County, MT | 31 km (19 mi) | WNW | earthquakes near Powell County |
| Lewis and Clark County, MT | 45 km (28 mi) | NNE | earthquakes near Lewis and Clark County |
| Granite County, MT | 77 km (48 mi) | WSW | earthquakes near Granite County |
| Jefferson County, MT | 78 km (48 mi) | SSE | earthquakes near Jefferson County |
| Deer Lodge County, MT | 84 km (52 mi) | SSW | earthquakes near Deer Lodge County |
| Broadwater County, MT | 92 km (57 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.
- 1.6 11 km ESE of Lincoln, Montana
- 2.0 12 km ESE of Lincoln, Montana
- 1.6 Western Montana
- 2.3 7 km SSE of Lincoln, Montana
- 1.6 18 km NW of Marysville, Montana
- 1.8 12 km ESE of Lincoln, Montana
- 2.3 Western Montana
- 1.6 7 km SSE of Lincoln, Montana
- 1.9 15 km SE of Lincoln, Montana
- 1.6 18 km SSW of Lincoln, Montana
- 1.9 14 km SE of Lincoln, Montana
- 1.7 11 km ESE of Lincoln, Montana
- 1.8 11 km ESE of Lincoln, Montana
- 1.6 6 km SSE of Lincoln, Montana
- 2.4 11 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
- 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.