What was the largest earthquake ever recorded by instruments, measured at magnitude 9.5?

The 1960 Valdivia earthquake was the largest earthquake ever recorded by instruments, with a moment magnitude of 9.5.

It struck southern Chile on May 22, 1960, after a rupture along the subduction boundary where the Nazca Plate dives beneath the South American Plate. The immense rupture extended for roughly 1,000 kilometers and generated severe shaking and a Pacific-wide tsunami.

The earthquake caused catastrophic damage in Chile and tsunami impacts were recorded across the Pacific, including in Hawaii, Japan, the Philippines, New Zealand, and the west coast of the United States. Its death toll estimates vary because records from affected areas were incomplete.

Magnitude describes earthquake size, while intensity describes shaking at a particular place. The event is often called the Great Chilean earthquake or the 1960 Chile earthquake. The moment magnitude scale is preferred for very large earthquakes because it represents seismic moment more reliably than the original local magnitude scale.