Cascadia Fault (IMAGE) University of Washington Caption Slow earthquakes happen between the hazardous locked zone and the viscous portion that slips silently. They are found on subduction zones, like Cascadia's, where a heavy ocean plate, in this case the Juan de Fuca Plate, sinks below a lighter continental plate. Credit Univ. of Washington Usage Restrictions With credit License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.