Earthquake · reviewed by a seismologist
M 1.6ml
Earthquake near Helena, MT
No earthquake was likely felt in Helena in the 24 hours to 1:18 am MST (08:18 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 1.6 earthquake was recorded 41 km (26 mi) north-northeast of Helena, MT, at 1:21 am MDT on 9 August 2018 (07:21 UTC), 9.3 km deep.
USGS: 14 km SSE of Craig, Montana
- When
- 1:21 am MDT on 9 August 2018 ()
- Where
- 41 km (26 mi) north-northeast of Helena, MT · earthquakes near Helena
- Montana today
- every earthquake in Montana in the last 24 hours
- Magnitude
- M 1.6 (ml)
- Depth
- 9.3 km below the surface
- Felt
- no reports yet
- Nearest
- Lewis and Clark County, 42 km WNW
- Status
- Reviewed by a seismologist
USGS · last changed by USGS · we first saw it 3018 days ago
Earthquake alerts for Helena, MT
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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, 41 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: Helena Valley Northwest, Helena Valley Northeast.
How big was it?
This earthquake released about 7.8 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.6 would have released about 32 times as much.
- Mineral, Virginia 2011 M 5.8 1,900,000× the energy of this one
- Magna, Utah 2020 M 5.7 1,400,000× the energy of this one
- Around the size people start to feel M 3.0 120× the energy of this one
- This earthquake M 1.6 about 7.8 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 4.3 on 2016-01-30 — about 12,000 times the energy of this one.
Before 2016, the USGS record lists 4 earthquakes of M5 or more within 50 km:
- 6.1 The 1935 Helena, Montana Earthquakes (Mainshock) · 44 km SSE of this epicentre
- 5.9 2 km ENE of Helena, Montana · 40 km SSW of this epicentre
- 5.9 The 1935 Helena, Montana Earthquakes (Largest Aftershock) · 46 km S of this epicentre
- 5.0 2 km ENE of Helena, Montana · 40 km SSW 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 46.9510, -111.8888. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Lewis and Clark County, MT | 42 km (26 mi) | WNW | earthquakes near Lewis and Clark County |
| Cascade County, MT | 58 km (36 mi) | NE | earthquakes near Cascade County |
| Broadwater County, MT | 75 km (47 mi) | SSE | earthquakes near Broadwater County |
| Powell County, MT | 80 km (50 mi) | W | earthquakes near Powell County |
| Meagher County, MT | 84 km (52 mi) | ESE | earthquakes near Meagher County |
| Jefferson County, MT | 93 km (58 mi) | S | earthquakes near Jefferson County |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
58 earthquakes have been recorded within 50 km since this one.
- 1.8 5 km NW of Helena Valley Southeast, Montana
- 1.6 2 km E of South Hills, Montana
- 1.6 2 km E of South Hills, Montana
- 1.8 31 km ENE of Helena Valley Northeast, Montana
- 1.9 30 km ENE of Helena Valley Northeast, Montana
- 1.8 8 km SSE of Marysville, Montana
- 1.6 3 km SW of Helena Valley Northwest, Montana
- 1.6 1 km SSE of South Hills, Montana
- 1.6 1 km SSE of South Hills, Montana
- 1.7 2 km NNW of Montana City, Montana
- 2.2 6 km W of Helena Valley West Central, Montana
- 2.4 8 km NNE of Helena Valley Northwest, Montana
- 1.7 15 km NW of Marysville, Montana
- 2.3 2 km WNW of East Helena, Montana
- 1.8 23 km WSW of Craig, 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.