The earthquake that rocked Alaska on March 27, 1964 needs no special introduction. It is the most powerful earthquake recorded in the Northern Hemisphere. Only two others, the great Chilean earthquake of 1960 and the 2004 quake off Sumatra (which caused that terrible tsunami), have approached or surpassed the Alaskan quake’s strength, which struck in the Prince William Sound area shortly after 5:30pm on Good Friday.
Geologists believe that earthquakes occuring along subduction zones tend to be more powerful than quakes along standard fault lines, because greater stresses build up as the upper plate passes over the lower. The Alaskan quake was of that type and, while I wasn’t alive when it happened, the pictures show tremendous damage.
The land buckled and heaved during the 4-minute quake, permanently rising as much as 30′ (the Kodiak area) in places while dropping 10′ in others, creating new beachlines and opening fissures in the surface. In the photo above, you can see how the beach areas of Middleton Island on the left slid nearly 12′ from its original level on the right.
Of course, the forces we are discussing here were astronomically stronger than any man-made structures. Anchorage was heavily damaged, as were a good number of smaller cities and towns. In fact, significant damage was reported over an area covering more than 50,000 square miles from a quake that was felt over more than half-a-million square miles. Thousands of major aftershocks over the next 18 months served to terrorize an already stunned populace trying to put their lives, homes, and infrastructure back together. But its effects were even more far-reaching.
The rapid shift along the plates triggered tsunamis that were detected throughout the Pacific Ocean and caused widespread damage. While deaths from the quake itself (falling buildings, etc.) were incredibly few (10-15, depending on your source), 120 fatalities were caused by tsunamis. Crescent City, on California’s northern coast, was particularly hard hit, where 14-foot waves were responsible for 11 deaths and millions of dollars of damage.
But the location of the Alaskan earthquake (well off the equator in the upper Northern Hemisphere) also caused the planet to wiggle, which means that the effects of the quake were seen worldwide. Small tsumani waves were detected in Cuba, small boats were reportedly capsized off Louisiana’s coasts, and water oscillations were seen in Africa.
Here in the central United States, we occasionally mention the fabled “big one” that supposedly will someday strike the San Andreas Fault and knock the most heavily-populated parts of California into the Pacific, while simultaneously casting a wary glance in the direction of the New Madrid Fault, knowing we stand on shaky ground ourselves. But I think a good number of us would like to believe that “the big one” has already come and gone, striking the Alaskan coast 46 years ago (as of this writing).
Time will tell if that belief stands up to the motion of the tectonic plates.