Earthquake near Helena Valley Southeast, MT

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 13 km (8 mi) from the epicentre. In Helena Valley Southeast, 6 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.

Likely felt in: Helena 7 km, intensity II. Estimated for each town centre; each link is that town's own record.

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.

1. Mineral, Virginia 2011 M 5.8 1,000,000× the energy of this one
2. Magna, Utah 2020 M 5.7 710,000× the energy of this one
3. Around the size people start to feel M 3.0 63× the energy of this one
4. 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

The largest earthquake within 50 km since 2016 was M 4.3 on 2016-01-30 — about 6,200 times the energy of this one.

Before 2016, the USGS record lists 4 earthquakes of M5 or more within 50 km:

1. 6.1 The 1935 Helena, Montana Earthquakes (Mainshock) · 26 km ESE of this epicentre Oct 19, 1935
2. 5.9 2 km ENE of Helena, Montana · 5 km SSW of this epicentre Oct 12, 1935
3. 5.9 The 1935 Helena, Montana Earthquakes (Largest Aftershock) · 16 km SE of this epicentre Oct 31, 1935
4. 5.0 2 km ENE of Helena, Montana · 5 km SSW of this epicentre Nov 28, 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 46.6473, -111.9830. Map © OpenStreetMap contributors.

Nearby places

Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.

Aftershocks so far

54 earthquakes have been recorded within 50 km since this one.

1. 1.5 14 km ESE of Lincoln, Montana 09:54 UTC
2. 1.7 13 km ESE of Lincoln, Montana 08:33 UTC
3. 1.6 8 km W of Townsend, Montana 22:05 UTC
4. 1.5 6 km SSW of The Silos, Montana 19:22 UTC
5. 1.5 7 km SSW of The Silos, Montana 22:09 UTC
6. 1.9 7 km SSW of The Silos, Montana 19:48 UTC
7. 1.6 14 km SE of Lincoln, Montana 12:27 UTC
8. 1.7 6 km WSW of Townsend, Montana 22:44 UTC
9. 2.2 30 km ENE of Helena Valley Northeast, Montana 14:27 UTC
10. 2.3 30 km ENE of Helena Valley Northeast, Montana 09:35 UTC
11. 1.7 10 km NW of Marysville, Montana 05:37 UTC
12. 2.2 13 km ESE of Lincoln, Montana 12:52 UTC
13. 2.1 16 km E of Lincoln, Montana 09:09 UTC
14. 1.9 15 km SE of Lincoln, Montana 05:14 UTC
15. 2.0 22 km SSE of Craig, Montana 03:06 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 23:59 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.