The whole premise of the article and paper is that the water its self is from the plate boundary. "The seep fluid chemistry is unique for Cascadia and includes

The whole premise of the article and paper is that the water its self is from the plate boundary. "The seep fluid chemistry is unique for Cascadia and includes extreme enrichment of boron and lithium and depletion of chloride, potassium, and magnesium. We conclude that the fluids are sourced from pore water compaction and mineral dehydration reactions with minimum source temperatures of 150° to 250°C, placing the source at or near the plate boundary offshore Central Oregon."