Castle Mountain Fault
Alaska, USA · continental transform · 740.0 km of mapped active fault in 224 traces
background as of 7 November 2026.
consistent with baseline
| Window | the last 30.0 days |
|---|---|
| Earthquakes counted | 0 at M4.5 or above |
| Expected in that window | 0.08 |
What this system normally does
From 1995 to 2025 the catalogue holds 28 earthquakes of M4.5 or larger attributable to this system: about 0.93 a year. That figure is what "elevated" on this page is measured against.
The fault itself
| Mapped length | 740.0 km |
|---|---|
| Traces | 224 |
| Tectonic setting | continental transform |
| Slip types | Reverse-Strike-Slip |
| Depth attributed to it | down to 50.0 km |
| Extent | 61.31 to 61.87 latitude, -151.10 to -147.75 longitude |
Recorded history
NOAA's hazard records hold 2 significant earthquakes and one tsunami attributed to this system since 1964.
The deadliest was the 28 March 1964 magnitude 9.2 earthquake (Alaska), which killed 139 people.
The most recent entry is the 30 November 2018 magnitude 7.1 earthquake (Alaska: Anchorage).
| Date | What | Where | Toll |
|---|---|---|---|
| 28 March 1964 | tsunami (waves to 51.8 m) | Prince William Sound, Ak | 139 dead, $400 million damage |
| 28 March 1964 | magnitude 9.2 earthquake | Alaska | 139 dead, $400 million damage |
| 30 November 2018 | magnitude 7.1 earthquake | Alaska: Anchorage | 2 homes destroyed, $150 million damage |
A dash means NOAA recorded no number, not that nobody died. Older entries are fewer because fewer were written down, not because less happened.
Recorded history: NOAA NCEI hazard databases, public domain, retrieved 2026-10-22.
Who to listen to if you live here
Ready Alaska is the agency that tells people on this system what to do. https://ready.alaska.gov/ (in English)
Other systems in Alaska, USA
Where these numbers come from
Fault geometry, length and segment counts: GEM Global Active Faults Database (GEM GAF-DB), GEM Foundation, https://github.com/GEMScienceTools/gem-global-active-faults Licence: CC-BY-SA-4.0. Figures derived from it here are offered under the same licence. Earthquake counts, magnitudes and depths: United States Geological Survey, public domain. The activity judgement is ours, computed from those two inputs, and is not a statement by either agency.