QuakeIndex

Fault · Montana

Red Rock fault

41 kmlong (25 mi), as mapped
0.2–1 mm/yrhow fast it slips
< 15,000 yearssince it last broke the surface
11quakes of M2.5+ within 10 km since 2016

In plain English

The two sides move 0.2 to 1 mm a year — 2 to 10 cm every century.

Its most recent surface rupture is younger than 15,000 years.

The largest earthquake recorded near it was M 4.2 in 2023 (3 km S of Lima, Montana) — about 63 times the energy of an M3.0, the size people start to feel. It released about 30 tons of TNT.

USGS maps it as 3 sections: Sheep Creeks section, Timber Butte section, northern section.

This week vs. its last ten years

0/100

quiet

0 quakes of M1.5+ within 5 km of the trace in the last 7 days — busier than 0% of weeks since 2016. A normal week: 0–0.

Computed from the USGS catalogue · a description of the past, not a forecast · method

Lemhi faultLost River faultBeaverhead faultCentennial fault
The Red Rock fault as mapped at the surface (glowing), with the other mapped faults nearby, 11 of the M2.5+ earthquakes within 10 km of it since 2016 (dots), . Traces: USGS Quaternary Fault and Fold Database. Historic epicentres are estimates.

Every year since 2016

Earthquakes of M2.5+ with an epicentre within 10 km of the mapped trace. Near is not the same as on: some will have slipped on neighbouring faults.

The big ones recorded near it

  1. M 4.2 3 km S of Lima, Montana
    July 14, 2023 · epicentre 1 km from the trace

Before 1973 from the USGS ComCat historical catalogue (within 25 km; epicentres of old earthquakes are estimates). Since 2016, M4+ within 10 km.

Most recent near it

  1. M 2.6 9 km SE of Lima, Montana
    2025-04-20 · 10 km from the trace
  2. M 2.6 6 km E of Lima, Montana
    2023-11-16 · 9 km from the trace
  3. M 3.5 0 km WSW of Lima, Montana
    2023-08-20 · 3 km from the trace
  4. M 2.5 2 km S of Lima, Montana
    2023-07-15 · 2 km from the trace
  5. M 4.2 3 km S of Lima, Montana
    2023-07-14 · 1 km from the trace
  6. M 2.6 0 km S of Lima, Montana
    2023-07-12 · 3 km from the trace

Neighbouring faults

Fault trace, slip rate and age: USGS Quaternary Fault and Fold Database (public domain), simplified for the web. Earthquakes: USGS ComCat. QuakeIndex does not forecast earthquakes; a fault's history describes the past. For early warning use ShakeAlert.