Have you heard of the San Andreas Fault? The subduction zone referred to is approximately where the North American tectonic plate is sliding under one of the Pacific plates in simple terms. The actual fault lines get quite complicated in the Pacific Northwest and California. If "The Big One" hits, it's going to be messy, and big ones have hit before! We're considered overdue for it, but geological time scale is nothing like human time scale.
John C Daley wrote:So what is the Cascadia subduction zone please?