‘The longest record for a subduction zone is from Cascadia, where scientists have linked buried marshes and submarine landslides with a series of about 22 megaquake quakes going back 10,000 years. The time between quakes ranges from 200 to 1,000 years, with an average of about 500 years’
Related On This Site: The last big Cascadia subduction zone earthquake likely occurred on Jan 27th, 1700, at magnitude 9.0. The article suggests an occurence anywhere from 300-350 year intervals up to 400-600 year average intervals (new research suggests the former). It’s just over 311 years and counting.
From The USGS: February 14th, 2011 Earthquake Near Mt. St. Helens-4.3……Seattle Earthquake-January 30th 2009-4.5 On The Richter Scale…From The Seattle Times: ‘Hard Lessons Learned Since The 2001 Nisqually Quake’…From OregonLive.Com: ‘Big Earthquake Coming Sooner Than We Thought, Oregon Geologist Says