When a whole lotta shakin' was goin' on

One day after the magnitude 9.2 earthquake on March 27, 1964, a section of an Anchorage street was several feet higher than another section. It is still the most powerful earthquake ever in North America. Credit Associated Press

A ’64 Quake Still Reverberates

By HENRY FOUNTAIN, NYT, APRIL 7, 2014

When a strong earthquake rocked northern Chile on April 1, scientists were quick with an explanation: It had occurred along a fault where stresses had been building as one of the earth’s crustal plates slowly dipped beneath another. A classic low-angle megathrust event, they called it.

Such an explanation may seem straightforward now, but until well into the 20th century, scientists knew relatively little about the mechanism behind these large seismic events. But that all changed when a devastating quake struck south-central Alaska on March 27, 1964, nearly 50 years to the day before the Chilean quake.

Studies of the great Alaskan quake — undertaken largely by a geologist who, when he began, knew little about seismology — revealed the mechanism by linking the observed changes in the landscape to what was then a theory, plate tectonics.

That theory, that the earth’s top layer consists of large tectonic plates that are moving and colliding, helps explain the formation of mountains, volcanoes and other land features, as well as the occurrence of earthquakes. The Chilean quake, which was measured at magnitude 8.2 and killed at least six people, happened where an oceanic plate, the Nazca, slides beneath a continental one, the South American, at a shallow angle.

(More here.)