Earthquake near Helena, MT

This was a small earthquake. Shaking like this is often felt indoors nearby and very rarely causes damage.

At this magnitude and depth, people at rest would likely notice it out to about 21 km (13 mi) from the epicentre. In Helena, 44 km away, the estimate is intensity II (weak). 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: Townsend, Boulder, Clancy.

How big was it?

This earthquake released about 170 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.5 would have released about 32 times as much.

1. Mineral, Virginia 2011 M 5.8 89,000× the energy of this one
2. Magna, Utah 2020 M 5.7 63,000× the energy of this one
3. Around the size people start to feel M 3.0 5.6× the energy of this one
4. This earthquake M 2.5 about 170 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 10 earthquakes of M5 or more within 50 km; the five largest:

1. 6.6 The 1925 Clarkston Valley, Montana Earthquake · 27 km SE of this epicentre Jun 28, 1925
2. 6.4 Clarkston Valley, Montana (Aftershock) · 27 km SE of this epicentre Jun 28, 1925
3. 6.1 The 1935 Helena, Montana Earthquakes (Mainshock) · 40 km NNE of this epicentre Oct 19, 1935
4. 5.9 2 km ENE of Helena, Montana · 43 km NNW of this epicentre Oct 12, 1935
5. 5.9 The 1935 Helena, Montana Earthquakes (Largest Aftershock) · 34 km N of this epicentre Oct 31, 1935

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 46.2404, -111.7777. Map © OpenStreetMap contributors.

Nearby places

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. 1.9 5 km NNW of Logan, Montana 17:30 UTC
2. 1.5 3 km SE of Helena Valley West Central, Montana 21:20 UTC
3. 1.6 8 km W of Townsend, Montana 22:47 UTC
4. 1.8 7 km NW of Logan, Montana 03:31 UTC
5. 1.9 9 km W of Townsend, Montana 23:37 UTC
6. 1.8 8 km W of Townsend, Montana 23:02 UTC
7. 1.6 6 km SSW of The Silos, Montana 21:33 UTC
8. 1.7 8 km W of Townsend, Montana 20:49 UTC
9. 2.2 6 km NNW of Logan, Montana 16:55 UTC
10. 1.7 7 km WSW of Townsend, Montana 21:45 UTC
11. 1.7 4 km ESE of The Silos, Montana 07:22 UTC
12. 1.9 7 km N of Manhattan, Montana 06:38 UTC
13. 1.5 6 km NE of Three Forks, Montana 18:21 UTC
14. 2.7 3 km ENE of Helena, Montana 21:38 UTC
15. 1.9 6 km SSW of The Silos, Montana 21:34 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 22:12 UTC. 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.