he average speed of plate movement is slow, but sudden movements do occur. Plates can stick to each other, accumulate stress, and then release the stress suddenly. That's what happened, for example, in 2011 along a major subduction zone in the Pacific Ocean off the coast of Japan, creating a Richter 9.0 earthquake, comparable to the largest earthquakes ever recorded. The total plate motion was as much as 15 meters (50 ft), and the resulting earthquake caused devastation directly and also by generating large tidal waves. A Richter 9.0 earthquake releases energy equivalent to about 500 megatons (5.0  108 tons) of TNT. The Hiroshima atomic bomb released the equivalent of 13 kilotons (1.3  103 tons). How many Hiroshima bombs equals a 9.0 earthquake?