The 1700 Event: People often confuse fault lines, but the massive magnitude 9.0 earthquake that struck the Pacific coast on January 26, 1700, happened on the 1700 Cascadia earthquake subduction zone, not the San Andreas Fault Scientists learned about the 1700 Cascadia quake using 1700 Cascadia Subduction Zone Earthquake written records of an "orphan tsunami" in Japan, ghost forests of dead trees along the Pacific Northwest coast, and native oral traditions.The San Andreas Fault is located in California, not the Pacific Northwest, but the region's actual major threat is the Cascadia Subduction Zone, which is roughly 326 years overdue for a major rupture San Andreas Fault: This is primarily a California fault line running roughly 750 miles from the Salton Sea in the south up to Cape Mendocino in northern California. The northern section last ruptured significantly in 1906, making it about 120 years past that specific event, though recurrence intervals vary Cascadia Subduction Zone (CSZ): This 600-mile fault lies off the coast of the Pacific Northwest (from Northern California up to British Columbia). It produces magnitude 9.0+ megathrust earthquakes How "Overdue" is Cascadia?Last Rupture: January 26, 1700.Recurrence Interval: Geological records show full-margin earthquakes happen roughly every 200 to 500 years.Current Status: Having gone ~326 years without a full rupture, the region sits squarely inside its window for the next major event. Scientists estimate roughly a 10% to 14% chance of a full-margin megathrust quake in the next 50 years, and a ~37% chance for a smaller (magnitude 7.1+) cluster or upper-plate event.