Earthquake near Three Forks, 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 10 km (6 mi) from the epicentre. In Three Forks, 7 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: Three Forks 7 km, intensity II. Estimated for each town centre; each link is that town's own record.

USGS catalogues this as quarry blast, not an earthquake.

How big was it?

This earthquake released about 6.2 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.5 would have released about 32 times as much.

1. Mineral, Virginia 2011 M 5.8 2,500,000× the energy of this one
2. Magna, Utah 2020 M 5.7 1,700,000× the energy of this one
3. Around the size people start to feel M 3.0 150× the energy of this one
4. This earthquake M 1.5 about 6.2 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 4.2 on 2019-08-16 — about 9,800 times the energy of this one.

Before 2016, the USGS record lists 6 earthquakes of M5 or more within 50 km; the five largest:

1. 6.6 The 1925 Clarkston Valley, Montana Earthquake · 17 km N of this epicentre Jun 28, 1925
2. 6.4 Clarkston Valley, Montana (Aftershock) · 17 km N of this epicentre Jun 28, 1925
3. 5.5 Clarkston Valley, Montana (Aftershock) · 17 km N of this epicentre Jun 28, 1925
4. 5.5 Clarkston Valley, Montana (Aftershock) · 17 km N of this epicentre Jun 28, 1925
5. 5.5 Clarkston Valley, Montana (Aftershock) · 17 km N of this epicentre Jul 10, 1925

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 45.9267, -111.4707. Map © OpenStreetMap contributors.

Nearby places

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

Aftershocks so far

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

1. 1.6 7 km WSW of Townsend, Montana 18:04 UTC
2. 1.6 8 km WSW of Townsend, Montana 18:12 UTC
3. 1.6 Western Montana 18:05 UTC
4. 1.6 6 km NNW of Logan, Montana 17:08 UTC
5. 1.6 Western Montana 15:16 UTC
6. 1.7 5 km W of Ponderosa Pines, Montana 10:34 UTC
7. 2.3 3 km WSW of Ponderosa Pines, Montana 02:40 UTC
8. 2.1 3 km SW of Ponderosa Pines, Montana 22:57 UTC
9. 2.0 11 km WSW of Radersburg, Montana 21:41 UTC
10. 2.4 3 km WSW of Ponderosa Pines, Montana 17:49 UTC
11. 2.0 7 km NE of Manhattan, Montana 12:52 UTC
12. 1.7 19 km NNE of Ennis, Montana 05:33 UTC
13. 3.3 17 km NNE of Ennis, Montana 09:29 UTC
14. 2.9 20 km SSE of Harrison, Montana 15:28 UTC
15. 1.5 2 km NW of Manhattan, Montana 20:49 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 21:23 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.