What caused the 1960 Chile earthquake tsunami?

The 1960 Chile earthquake tsunami was caused by a massive seafloor displacement resulting from the Chile earthquake of 1960, the largest earthquake recorded in the 20th century.12

At the boundary of the Nazca Plate and the South American Plate, years of intense compressional force had built up significant stress. On May 22, 1960, this stress was released when rocks fractured along a 560–620 mile (900–1,000 km) stretch of the plate boundary. This sudden movement forced the leading edge of the South American Plate upward, which in turn thrust the overlying water column upward as well. This displacement created a series of powerful waves that propagated outward in all directions across the Pacific Ocean, causing widespread destruction and loss of life both in Chile and in distant coastal regions.12