The deep earth isn't all that well studied, so while we know a fair amount about plate tectonics, there could be hidden factors influencing that action in ways we can't anticipate from recorded history. Who's to say there aren't 1000 or 10k year cycles of earthquakes? Something novel could happen too, but our records don't let us set probabilities for 10k year natural disasters the way we can with 100 year tropical storms, floods, or earthquakes.