quarry blast · reviewed by a seismologist
M 1.8ml
Earthquake near Helena, MT
USGS: 0 km SE of South Hills, Montana
- When
- 12:15 pm MST on 16 November 2017 ()
- Where
- 6 km (3 mi) SE of Helena, MT · earthquakes near Helena
- Magnitude
- M 1.8 (ml)
- Depth
- -2.0 km below the surface
- Felt
- no reports yet
- Nearest
- Broadwater County, 45 km ESE
- Status
- Reviewed by a seismologist
USGS · last changed by USGS · we first saw it 3242 days ago
A magnitude 1.8 earthquake was recorded 6 km (3 mi) SE of Helena, MT, at 12:15 pm MST on 16 November 2017 (19:15 UTC). This was a minor earthquake. Quakes this small are rarely felt and do not cause damage.
Earthquakes near other towns within 30 km: Montana City, East Helena, Helena Valley Southeast, Clancy, Helena West Side, Helena Valley West Central.
USGS catalogues this as quarry blast, not an earthquake.
How big was it?
This earthquake released about 15 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 1,000,000× the energy of this one
- Magna, Utah 2020 M 5.7 710,000× the energy of this one
- Around the size people start to feel M 3.0 63× the energy of this one
- This earthquake M 1.8 about 15 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 4 earthquakes of M5 or more within 50 km:
- 6.1 The 1935 Helena, Montana Earthquakes (Mainshock) · 26 km E of this epicentre
- 5.9 2 km ENE of Helena, Montana · 5 km N of this epicentre
- 5.9 The 1935 Helena, Montana Earthquakes (Largest Aftershock) · 11 km E of this epicentre
- 5.0 2 km ENE of Helena, Montana · 5 km N 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 46.5535, -111.9907. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Broadwater County, MT | 45 km (28 mi) | ESE | earthquakes near Broadwater County |
| Jefferson County, MT | 48 km (30 mi) | S | earthquakes near Jefferson County |
| Lewis and Clark County, MT | 70 km (43 mi) | NNW | earthquakes near Lewis and Clark County |
| Powell County, MT | 79 km (49 mi) | WNW | earthquakes near Powell County |
| Meagher County, MT | 82 km (51 mi) | E | earthquakes near Meagher County |
| Silver Bow County, MT | 89 km (56 mi) | SW | earthquakes near Silver Bow County |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
7 earthquakes have been recorded within 50 km since this one.
- 1.8 16 km WNW of Marysville, Montana
- 1.8 6 km SSW of The Silos, Montana
- 2.4 6 km WSW of Elliston, Montana
- 1.8 2 km NW of Montana City, Montana
- 2.1 6 km WSW of Elliston, Montana
- 3.2 9 km SW of Elliston, Montana
- 1.5 10 km ENE of Marysville, 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.