Study Finds Cascadia and San Andreas Faults May Trigger Near-Simultaneous Quakes
Researchers uncovered sediment evidence that major earthquakes on the Cascadia megathrust and the northern San Andreas fault have sometimes occurred minutes to hours apart.
By examining deep-sea sediment cores spanning roughly 3,100 years, scientists discovered unusual “doublet” turbidite sequences that point to back-to-back earthquakes on the Cascadia subduction zone and the northern segment of the San Andreas fault. Radiocarbon dating linked three such paired events within the past 1,500 years, the latest coinciding with the historic 1700 Cascadia quake. Lead author Chris Goldfinger explains that the fine material at the base of these layers likely records a Cascadia rupture, while the overlying coarse deposit reflects a subsequent San Andreas slip.
The research, involving collaborators from Oregon State University, NOAA, the University of Washington and other institutions, argues that fault interaction, though not inevitable, has occurred in the geological record. If a similar synchronization were to happen today, major urban centers such as San Francisco, Portland, Seattle and Vancouver could face simultaneous emergency demands. The study calls for updated seismic preparedness that accounts for the possibility of closely timed, large-scale earthquakes along both fault systems.
