Earthquake · reviewed by a seismologist
M 1.8ml
Earthquake near Helena, MT
No earthquake was likely felt in Helena in the 24 hours to 1:07 pm MST (20:07 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 1.8 earthquake was recorded 43 km (27 mi) northwest of Helena, MT, at 2:54 am MDT on 16 August 2017 (08:54 UTC), 12 km deep.
USGS: 16 km NW of Marysville, Montana
- When
- 2:54 am MDT on 16 August 2017 ()
- Where
- 43 km (27 mi) northwest of Helena, MT · earthquakes near Helena
- Montana today
- every earthquake in Montana in the last 24 hours
- Magnitude
- M 1.8 (ml)
- Depth
- 12 km below the surface
- Felt
- no reports yet
- Nearest
- Lewis and Clark County, 32 km NNE
- Status
- Reviewed by a seismologist
USGS · last changed by USGS · we first saw it 3374 days ago
Earthquake alerts for Helena, 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 6 km (4 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 14 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.8 would have released about 32 times as much.
- Mineral, Virginia 2011 M 5.8 1,100,000× the energy of this one
- Magna, Utah 2020 M 5.7 760,000× the energy of this one
- Around the size people start to feel M 3.0 68× the energy of this one
- This earthquake M 1.8 about 14 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 1,100,000 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 SE of this epicentre
- 5.0 2 km ENE of Helena, Montana · 45 km SE 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 46.8375, -112.4788. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Lewis and Clark County, MT | 32 km (20 mi) | NNE | earthquakes near Lewis and Clark County |
| Powell County, MT | 34 km (21 mi) | W | earthquakes near Powell County |
| Jefferson County, MT | 86 km (53 mi) | SSE | earthquakes near Jefferson County |
| Granite County, MT | 88 km (54 mi) | SW | earthquakes near Granite County |
| Broadwater County, MT | 94 km (58 mi) | SE | earthquakes near Broadwater County |
| Deer Lodge County, MT | 97 km (60 mi) | SSW | earthquakes near Deer Lodge 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.
- 2.7 15 km SE of Lincoln, Montana
- 1.9 15 km SE of Lincoln, Montana
- 1.6 14 km SE of Lincoln, Montana
- 1.8 15 km ESE of Lincoln, Montana
- 1.6 14 km SE of Lincoln, Montana
- 1.8 14 km SE of Lincoln, Montana
- 1.6 15 km SE of Lincoln, Montana
- 1.5 15 km SE of Lincoln, Montana
- 2.7 17 km SE of Lincoln, Montana
- 3.5 18 km SE of Lincoln, Montana
- 2.6 10 km SE of Lincoln, Montana
- 1.7 15 km SE of Lincoln, Montana
- 2.7 18 km WNW of Marysville, Montana
- 2.1 9 km SE of Lincoln, Montana
- 1.8 Western 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.