QuakeIndex

Earthquake · reviewed by a seismologist

M 1.6ml

Earthquake near Helena, MT

No earthquake was likely felt in Helena in the 24 hours to 2:21 pm MST (21:21 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 45 km (28 mi) northwest of Helena, MT, at 9:03 pm MST on 17 November 2018 (04:03 UTC), 5.5 km deep.

USGS: 19 km NNW of Marysville, Montana

9:03 pm MST, Nov 17, 2018 · · 5.5 km deep · released about 8.1 lb of TNT

Every earthquake near Helena Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Lewis and Clark County 26 kmPowell County 38 kmJefferson County 90 kmGranite County 94 kmCascade County 95 kmBroadwater County 95 kmTeton County 103 kmDeer Lodge County 104 kmMissoula County 111 km
Distance rings around the epicentre, with the nearest towns at their true direction and later quakes as coloured dots. Not a shaking map — see the USGS ShakeMap for that.
When
9:03 pm MST on 17 November 2018 ()
Where
45 km (28 mi) northwest of Helena, MT · earthquakes near Helena
Montana today
every earthquake in Montana in the last 24 hours
Magnitude
M 1.6 (ml)
Depth
5.5 km below the surface
Felt
no reports yet
Nearest
Lewis and Clark County, 26 km N
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 2915 days ago

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 10 km (6 mi) from the epicentre. In Helena, 45 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 8.1 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.

  1. Mineral, Virginia 2011 M 5.8 1,900,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 1,300,000× the energy of this one
  3. Around the size people start to feel M 3.0 120× the energy of this one
  4. This earthquake M 1.6 about 8.1 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 1,900,000 times the energy of this one.

Before 2016, the USGS record lists 2 earthquakes of M5 or more within 50 km:

  1. 5.9 2 km ENE of Helena, Montana · 47 km SE of this epicentre
  2. 5.0 2 km ENE of Helena, Montana · 47 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 46.8948, -112.4370. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Lewis and Clark County, MT 26 km (16 mi) N earthquakes near Lewis and Clark County
Powell County, MT 38 km (24 mi) W earthquakes near Powell County
Jefferson County, MT 90 km (56 mi) SSE earthquakes near Jefferson County
Granite County, MT 94 km (58 mi) SW earthquakes near Granite County
Cascade County, MT 95 km (59 mi) ENE earthquakes near Cascade County
Broadwater County, MT 95 km (59 mi) SE 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. 1.9 15 km SE of Lincoln, Montana
  2. 1.6 18 km SSW of Lincoln, Montana
  3. 1.9 14 km SE of Lincoln, Montana
  4. 1.7 11 km ESE of Lincoln, Montana
  5. 1.8 11 km ESE of Lincoln, Montana
  6. 1.6 6 km SSE of Lincoln, Montana
  7. 2.4 11 km ESE of Lincoln, Montana
  8. 1.8 18 km SSW of Lincoln, Montana
  9. 2.1 19 km SSW of Lincoln, Montana
  10. 2.1 31 km SSW of Augusta, Montana
  11. 1.7 7 km SSE of Lincoln, Montana
  12. 2.1 15 km SE of Lincoln, Montana
  13. 1.5 15 km SE of Lincoln, Montana
  14. 1.6 12 km WNW of Marysville, Montana
  15. 1.6 13 km SE 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

QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.