QuakeIndex

Fault · Alaska

Castle Mountain fault

186 kmlong (116 mi), as mapped
1–5 mm/yrhow fast it slips
< 15,000 yearssince it last broke the surface
381quakes of M2.5+ within 10 km since 2016

In plain English

The two sides move 1 to 5 mm a year — 10 to 50 cm (4 to 20 inches) every century.

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

The largest earthquake recorded near it was M 6.8 in 1933 (Southern Alaska) — about 600,000 times the energy of an M3.0, the size people start to feel. It released about 280 kilotons of TNT.

USGS maps it as 3 sections: Susitna section, Talkeetna west section, east section.

This week vs. its last ten years

86/100

elevated

5 quakes of M1.5+ within 5 km of the trace in the last 7 days — busier than 86% of weeks since 2016. A normal week: 1–3.

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

Denali faultGranite Point anticline (Cook Inlet folds) M 6.8 · 1933 · Southern Alaska M 6.8 · 1936 · 4 km NE of Beluga, Alaska M 6.4 · 1964 · 23 km S of Glacier View, Alaska
The Castle Mountain fault as mapped at the surface (glowing), with the other mapped faults nearby, 381 of the M2.5+ earthquakes within 10 km of it since 2016 (dots), and the epicentres of the large historic earthquakes recorded near it (rings). 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 6.8 Southern Alaska
    April 27, 1933 · epicentre 25 km from the trace
  2. M 6.8 4 km NE of Beluga, Alaska
    October 23, 1936 · epicentre 17 km from the trace
  3. M 6.4 23 km S of Glacier View, Alaska
    April 3, 1964 · epicentre 24 km from the trace
  4. M 5.1 2 km E of Big Lake, Alaska
    November 7, 2020 · epicentre 9 km from the trace
  5. M 4.8 4 km ENE of Glacier View, Alaska
    October 6, 2022 · epicentre 9 km from the trace
  6. M 4.6 8 km NNW of Meadow Lakes, Alaska
    February 10, 2026 · epicentre 2 km from the trace
  7. M 4.5 15 km W of Big Lake, Alaska
    January 23, 2019 · epicentre 3 km from the trace
  8. M 4.5 1 km N of Big Lake, Alaska
    November 30, 2018 · epicentre 6 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 2.7 23 km SSW of Susitna, Alaska
    2026-09-28 · 8 km from the trace
  2. M 2.5 23 km SSW of Susitna, Alaska
    2026-09-28 · 7 km from the trace
  3. M 3.2 21 km SW of Susitna, Alaska
    2026-09-23 · 2 km from the trace
  4. M 2.6 3 km WNW of Big Lake, Alaska
    2026-09-21 · 6 km from the trace
  5. M 2.5 24 km SSW of Susitna, Alaska
    2026-08-29 · 8 km from the trace
  6. M 3.3 13 km ENE of Susitna, Alaska
    2026-08-23 · 4 km from the trace

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.