The 1964 Anchorage, Alaska earthquake and resulting tsunami struck without warning on Good Friday, March 27.

It was a quiet spring day in Anchorage, a holiday. Temperatures were moderate for the season with a moderate amount of snow on the ground. Children had a day off from school and customer traffic in downtown stores was low. Many residents were preparing or enjoying dinner at home. At 5:36 p.m., a major earthquake began to shake the ground, and the land below south central Alaska moved in waves for the next four long minutes.

Parents and children slipped, tripped and fell on shifting floors in a panicked effort to get outside to avoid breaking windows. Two-inch cracks appeared in the ground in many places. Roads wrinkled and divided and Fourth Avenue in downtown Anchorage broke and collapsed 10 feet or more. Government Hill Elementary School twisted, changed, and became unusable in no time. The outer wall of the JC Penney Building crashed into the street. In the residential district of Turnagain, the ground liquefied like quicksand, slipped and swallowed 75 or more houses.

The four-minute earthquake released energy roughly equivalent to 10 million times the force of an atomic bomb. The mass of the land and ocean absorbed most of the force, but man-made structures in the area were unable to absorb the rest of the force without sustaining massive damage. Total property damage was estimated at $ 500 million.

Anchorage was paralyzed as the gas and water lines were abruptly cut off. Residents resorted to melting snow for water while they awaited repairs. Four days later, the students returned to available schools as life in Anchorage began to recover.

Earthquake

The center of the Alaska earthquake was located about 75 miles east of Anchorage and about 55 miles west of Valdez. It began 14 to 16 miles deep in the earth’s crust, a comparatively shallow depth, where the Pacific plate dips below the North American plate. The huge subduction zone is at the northern end of the Ring of Fire, a semicircle of volcanic and seismic activity that defines the edge of the Pacific Ocean.

The earthquake fault, more precisely the thrust fault, which was the cause of the Good Friday earthquake, extended 750 miles from the Aleutian Islands of Alaska to Valdez. The Pacific plate that day moved approximately 25 to 30 feet to the north, dipping below the North American plate. The crushing of the two massive tectonic plates caused the Alaska earthquake and measured 8.4 on the Richter scale. In later years, the Alaska earthquake measurement was updated to 9.2 on the Mw scale, or moment magnitude, as the Richter scale was determined to be inaccurate for measuring very large earthquakes above 8.0. One day after the initial big earthquake, 11 more tremors of 6.0 or more shook an already nervous population. In fact, the aftershocks continued for almost a year.

The earthquake caused the ground to move up 25 feet on several Alaskan islands and nearly 3 feet up in the city of Valdez. In other areas, the ground has shifted down as much as 9 feet, for example in the city of Portage.

The Alaska earthquake on Good Friday was the strongest ever recorded in North America. It was the second strongest ever recorded worldwide, surpassed in strength by the 9.5 Mw earthquake in Chile on May 22, 1960. The recent earthquake on December 26, 2004 off the coast of the Indonesian island of Sumatra measured 9.0 Mw. The deadliest earthquake occurred in Shensi Province, China, in 1556, where more than 830,000 residents died.

The tsunami

tsunami is an adapted Japanese word meaning “harbor wave”, a reference to the fact that the danger and destructive power of the wave only becomes apparent as it approaches shore.

During the 1964 Alaska earthquake, the North American plate snapped upward, displacing a large volume of ocean water and causing a seismic wave, a tsunami, to drift outward. The wave traveled at approximately 450 miles per hour in the depths of the ocean in a long wave of almost imperceptible height.

As the tsunami wave passed over the continental shelf and neared the coast, its length shortened, its speed decreased, and its height increased as the enormous volume and weight of the water prepared to unleash its incredible energy on anything to his step.

At the shallow Valdez Inlet, the wave reached a maximum height of nearly 200 feet. Later, in the old town of Valdez, a 30-foot wall of water struck and demolished all the structures. Twenty-eight Valdez residents died when the tsunami crashed on land. Later, Valdez was rebuilt at a higher elevation and farther from the boardwalk.

In Seward, Alaska, the earthquake caused part of the bay to slide. The landslide triggered a local tsunami that devastated the port and downtown Seward district, both of which were eventually rebuilt. Twelve residents perished in Seward.

The small town of Portage was washed away by its own local tsunami and was never relocated or rebuilt. Another local tsunami hit the small port of Whittier, killing 12 residents.

The destruction

The original tsunami traveled about 8,400 miles. It caused damage in the Hawaiian Islands and along the coasts of Oregon and California. A 20-foot wave hit Crescent City, California, killing 10 residents. The tsunami was responsible for the deaths of 16 people in Oregon and California.

The tsunami killed a total of 122 people in three states. By comparison, the earthquake caused 9 deaths.

More than 40 years have passed since the Alaska earthquake and tsunami. Meanwhile, building materials and building practices have been applied to produce structures more capable of surviving strong earthquakes. Also in the meantime, the population in vulnerable areas of Alaska has increased tremendously.

Smaller earthquakes along the Alaska Subduction Zone and other fault zones occur daily, presumably relieving internal pressures that would otherwise produce another massive earthquake.

However, no one knows for sure when, where or if another massive and destructive earthquake will hit Alaska.