Cascadia Quake Could Trigger San Andreas Fault

A Cascadia subduction zone earthquake might trigger a rupture on the San Andreas fault, escalating a single major earthquake into a multi-state and international emergency, according to marine geologist Chris Goldfinger of Oregon State University. This dual earthquake scenario presents a broader emergency than previously considered, potentially affecting San Francisco, Portland, Seattle, and Vancouver within a compressed timeframe.

The findings stem from a study examining ancient sediment layers, known as turbidites, from both fault systems. Similarities in timing and structure were identified, with carbon dating revealing a layering pattern consistent with the theory of synchronized earthquakes. While instances of simultaneous quakes are rare, the most recent known pair occurred in 1700, just minutes to hours apart. This research traces back to a 1999 discovery where a sediment core from the San Andreas zone provided crucial early evidence.

The implications for emergency response are significant. An earthquake on either fault alone would strain national resources; a combined rupture would create an unprecedented crisis across multiple major West Coast cities simultaneously. This expands the perceived threat beyond a singular major event, highlighting the need for a broader emergency response strategy for the region.