The geological record reveals that "great earthquakes" (those with moment magnitude 8 or higher) occur in the Cascadia subduction zone about every 500 years on average, often accompanied by tsunamis. There is evidence of at least 13 events at intervals from about 300 to 900 years with an average of 570–590 years.[15] Recent findings conclude that the Cascadia subduction zone is more complex and volatile than previously believed.[18] In 2010, geologists predicted a 37% chance of an M8.2+ event within 50 years, and a 10% to 15% chance that the entire Cascadia subduction zone will rupture with an M9+ event within the same time frame.[19][20]