QuakeIndex

Earthquake · reviewed by a seismologist

M 1.7ml

Earthquake near Helena, MT

USGS: 4 km SE of Avon, Montana

7:50 am MDT, Mar 13, 2017 · · 15 km deep · released about 10 lb of TNT

Every earthquake near Helena Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Powell County 41 kmLewis and Clark County 62 kmJefferson County 63 kmGranite County 70 kmDeer Lodge County 70 kmSilver Bow County 76 kmBroadwater County 86 kmMissoula County 114 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
7:50 am MDT on 13 March 2017 ()
Where
40 km (25 mi) W of Helena, MT · earthquakes near Helena
Magnitude
M 1.7 (ml)
Depth
15 km below the surface
Felt
no reports yet
Nearest
Powell County, 41 km NW
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 3491 days ago

A magnitude 1.7 earthquake was recorded 40 km (25 mi) W of Helena, MT, at 7:50 am MDT on 13 March 2017 (13:50 UTC). This was a minor earthquake. Quakes this small are rarely felt and do not cause damage.

Earthquakes near other towns within 30 km: Deer Lodge.

How big was it?

This earthquake released about 10 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.7 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 1,500,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 1,100,000× the energy of this one
  3. Around the size people start to feel M 3.0 95× the energy of this one
  4. This earthquake M 1.7 about 10 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 9,400 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 · 43 km E of this epicentre
  2. 5.0 2 km ENE of Helena, Montana · 43 km E 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 46.5743, -112.5563. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Powell County, MT 41 km (26 mi) NW earthquakes near Powell County
Lewis and Clark County, MT 62 km (39 mi) NNE earthquakes near Lewis and Clark County
Jefferson County, MT 63 km (39 mi) SE earthquakes near Jefferson County
Granite County, MT 70 km (43 mi) WSW earthquakes near Granite County
Deer Lodge County, MT 70 km (43 mi) SW earthquakes near Deer Lodge County
Silver Bow County, MT 76 km (47 mi) S earthquakes near Silver Bow 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. 2.0 14 km SE of Lincoln, Montana
  2. 3.0 13 km ESE of Lincoln, Montana
  3. 2.3 13 km ESE of Lincoln, Montana
  4. 2.3 15 km SE of Lincoln, Montana
  5. 2.4 15 km SE of Lincoln, Montana
  6. 2.6 14 km SE of Lincoln, Montana
  7. 2.5 14 km SE of Lincoln, Montana
  8. 2.5 13 km SSE of Lincoln, Montana
  9. 2.9 12 km SE of Lincoln, Montana
  10. 3.0 13 km SE of Lincoln, Montana
  11. 2.4 11 km S of Lincoln, Montana
  12. 2.9 16 km SE of Lincoln, Montana
  13. 1.9 7 km SE of Lincoln, Montana
  14. 2.7 Western Montana
  15. 3.5 7 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.