The geological record reveals that great earthquakes with moment magnitude 8 or higher occur in the Cascadia subduction zone about every 500 years on average, often accompanied by tsunamis. There is evidence of at least 13 events at intervals from about 300 to 900 years with an average of 570–590 years.[16]
One expert asserts that buildings in Seattle are inadequate even to withstand an event of the size of the magnitude 7.9 1906 San Francisco earthquake, let alone a more powerful one.[17]
Kenneth Murphy, who directs FEMA's Region X, the division responsible for Oregon, Washington, Idaho, and Alaska, stated, "Our operating assumption is that everything west of Interstate 5 will be toast."[18]