April 2026 Offshore Washington Earthquake Swarm

Claim vs. Data

Viral claim (Stefan Burns, Apr 12 2026): "Significant earthquake swarm has begun off the Oregon-Washington coast in the Cascadia Subduction Zone. Magnitude 9 events are possible here."

What USGS data shows: The swarm is real — 23 events April 8–12 (an 18-event burst on Apr 12), max M4.2 — but it's located at ~129°W on the Juan de Fuca Ridge, approximately 400 km west of the Cascadia Subduction Zone trench (~124.5°W). These are two different fault systems.

Key Facts

Fact	Detail
Events	23 since Apr 8, 18 in an 8-hour burst on Apr 12 (07:30–16:04 UTC)
Max magnitude	M4.2 (Apr 12 15:04 UTC)
Location	~47°N 129°W, off Washington coast
Depth	18-event ridge swarm all ~10 km (USGS default for poorly constrained offshore events)
Fault system	Juan de Fuca Ridge (mid-ocean spreading center)
Distance to CSZ	~400 km east to the subduction trench

Why This Matters

• Juan de Fuca Ridge swarms are relatively routine at mid-ocean spreading centers. They reflect magmatic/hydrothermal processes.
• Cascadia Subduction Zone M9s originate from the locked plate interface near shore (~124–125°W), a completely different structure.
• The last great CSZ earthquake was January 26, 1700 (M~9.0). Average recurrence is ~240–500 years. That's real — but this swarm provides zero evidence about megathrust timing.

Visualization

Interactive map showing swarm epicenters, the Juan de Fuca Ridge, and the CSZ trench:

Data Source

USGS FDSN Event Web Service: earthquake.usgs.gov/fdsnws/event/1/