Study shows impact of Cascadia tsunami on Puget Sound communities Seattle's Fenix Underground storefront after the 2001 Nisqually earthquake. (FEMA, Washington State Governor's Office) Thanks to a new study from the Washington State Department of Natural Resources (DNR), we now have an idea of the potential impact of a tsunami on Puget Sound communities if there were a 9.0 magnitude earthquake along the Cascadia subduction zone. The study, prepared by geologists within the Washington Geological Survey division of DNR, was conducted to develop preparation and response plans for those in heavily populated areas that would be impacted by a Cascadia earthquake and tsunami.