In 1964, George Plafker researched the Good Friday earthquake in Alaska. He concluded that the cause of the earthquake was a megathrust reaction in the Aleutian Trench, a result of the Alaskan continental crust overlapping the Pacific oceanic crust. This meant that the Pacific crust was being forced downward, or "subducted", beneath the Alaskan crust. The concept of subduction would play a role in the development of the plate tectonics theory.