A new analysis suggests that massive earthquakes on northern sections of the Cascadia Subduction Zone, affecting areas of the Pacific Northwest that are more heavily populated, are somewhat more frequent than has been believed in the past.The chance of one occurring within the next 50 years is also slightly higher than previously estimated.The findings, published this week in the journal Marine Geology, are based on data that is far more detailed and comprehensive than anything prior to this. It used measurements from 195 core samples containing submarine landslide deposits caused by subduction zone earthquakes, instead of only about a dozen such samples in past research.