“The largest quake ever recorded, a 9.5, happened there in 1960.”
Actually, I think the great New Madrid earthquake series in 1811-1812 may have been greater, especially if viewed cumulatively. At least three were extremely powerful. Also, there was an extremely strong earthquake in Assam, I think in the 1950’s, which I seem to recall increased the height of Mt. Everest by 20 feet? The great Lisbon earthquake several centuries ago was no slouch either.
That's my present understanding too.
9.5 is enormously bad. Perhaps they’re going with quakes for which there are actual seismograph readings available. What you said about Everest rings a bell, not sure how long ago that was. The New Madrid quake (the biggest one) rerouted the Mississippi by a few miles, and that takes some doing.