Before 1964 Earthquake: We did not have a unifying theory of how the earth works

"Before the 1964 earthquake, we did not have a unifying theory of how the earth works," said Peter Hauessler, a USGS research geologist. "The 1964 earthquake was the first time people understood that there were places called subduction zones that produce these really enormous earthquakes."
Plate tectonics is now a widely accepted model that explains everything from why earthquakes happen to how mountains grow. The model says that Earth's surface is divided into stiff slabs of crust called plates. The oceanic plates are born and grow at mid-ocean ridges, the long underwater volcanic chains that wind around the Earth like seams on a baseball. Evidence for this growth was first published in 1963 — progressively older magnetic stripes on the seafloor record spreading away from the volcanic ridges.
end partial quote from:

How the 1964 Alaska Earthquake Shook Up Science

Also see: 

How the 1964 Alaska Earthquake Shook Up Science:50... 

if you haven't read that already. March 27th 2014 was the 50th anniversary.