Seven times in the past 3,500 years, the CSZ has buckled and fractured to produce an earthquake so massive that it left a mark in the geologic record. There's a one-in-10 chance that the next major Cascadia quake will occur sometime in the next 50 years. The odds of a lesser but still major event are even greater.

Is Cascadia overdue?

The estimated time between Cascadia subduction zone earthquakes is anywhere from 200 to 800 years. The last on record was Jan. 26, 1700. That means another earthquake is neither impossible nor overdue, Nissen says.

How often does the Cascadia earthquake happen?

In the Cascadia subduction zone 13 megathrust events have been identified in the last 6000 years, an average one every 500 to 600 years.