According to scientists at Oregon State University, the area known as the Cascadia subduction zone has experienced a cluster of four massive earthquakes during the past 1600 years.

They say if historical trends continue, this cluster could be over and the zone may already have entered a long quiet period of 500 to 1,000 years, which appears to be common following a cluster of earthquake events.

Or, the current cluster of earthquakes may have one or more events left in it -- some clusters within the past 10,000 years have had clusters of up to five events -- and within a cluster, the average time interval between earthquakes is 300 years.

Since the last major Cascadia earthquake occurred in the year 1700, the next event may well be imminent, the report says.