Intraslab earthquakes , frequently associated with stresses within the subducting plate in convergent margins , occur most frequently in northern Cascadia along the west coast of Vancouver Island and in the Puget Sound , and in southern Cascadia within the subducting Gorda Plate , near the Mendocino Triple Junction offshore of northern California . The 1949 Olympia earthquake was a damaging magnitude 6.7 intraslab earthquake that occurred at 52 km depth and caused 8 deaths . Another notable intraslab earthquake in the Puget Sound region was the magnitude 6.8 2001 Nisqually earthquake . Intraslab earthquakes in Cascadia occur in areas where the subducting plate has high curvature . Much of the seismicity that occurs off the coast of northern California is due to intraplate deformation within the Gorda Plate . Similar to the distribution of interplate earthquakes in Cascadia , intraslab earthquakes are infrequent in Oregon
2001 Nisqually earthquake
2001 Nisqually earthquake
Cascadia subduction zone