Cascadia and San Andreas Faults May Trigger Linked Major West Coast Earthquakes

Recent research reveals that the Cascadia subduction zone and California's San Andreas fault may be seismically linked, with earthquakes on one fault potentially triggering rapid subsequent quakes on the other, compounding risks for major West Coast cities. Studies analyzing sediment cores and turbidite layers indicate that such paired seismic events could occur within minutes to hours, creating complex emergency scenarios involving multiple urban centers simultaneously. Meanwhile, geologists are increasingly concerned about "supershear" earthquakes, a rare but powerful phenomenon where rupture speeds surpass seismic shear waves, generating destructive shock fronts analogous to sonic booms. These supershear events could deliver a "double strike" of intense ground motion, significantly amplifying damage and challenging existing infrastructure and preparedness plans in California. Experts warn that the frequency of supershear ruptures has been underestimated and, combined with the possibility of synchronized fault activity, heighten the urgency for improved seismic hazard planning across the West Coast. The convergence of these findings underscores a need for enhanced awareness and mitigation strategies to address the compounded earthquake threats in this densely populated and tectonically active region.