From Alaska Earthquake Information Center
The northwestward motion of the Pacific plate at about 5 to 7 cm per year causes the crust of southern Alaska to be compressed and warped, with some areas along the coast being depressed and other areas inland being uplifted. After periods of tens to hundreds of years, this compression is relieved by the sudden southeastward motion of portions of coastal Alaska as they move back over the subducting Pacific plate.
As a result of the 1964 quake, the Latouche Island area moved about 18 meters to the southeast. Also, the patterns of uplift and subsidence which had been slowly developing prior to the earthquake were suddenly reversed, with areas around Montague Island being uplifted 4-9 meters and areas around Portage down-dropped as much as 3 meters. The hinge line (line of no vertical change separating the uplift and subsidence zones) extended from near the epicenter in Prince William Sound to the SE coast of Kodiak Island. This vertical deformation affected and area of approximately 250,000 km2 (100,000 miles2). The end results was the movement of the Pacific plate under the North American plate by about 9 meters on average.
If nothing else just pause and consider the final sentence. They are talking about the Pacific Plate and the North American Plate! Huge pieces of the earths crust (loosely speaking) and this one event subducted the pacific UNDER the north american 29.52 FEET.