Pacific Northwest overdue for big one, sediments show
"A new 6,500-year record of megathrust earthquakes in the Pacific Northwest pieced together from lost coastal marshes and offshore sediments is providing the clearest picture yet of the quake and tsunami dangers for along the 750-mile long Cascadia subduction zone from Northern California to British Columbia.
By bringing together the data from the ocean and coastal marshes into a geophysical model that takes into account how the crust bows upwards between quakes, the researchers have confirmed that the the northern portion ruptures violently on the average of once every 480 years. The southern portion along Oregon and California breaks every 230 years on average.
The last rupture was a Sumatra-style, simultaneous unzipping along entire length of the hazardous subduction zone in 1700."