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 public holiday. Temperatures were seasonally mild with a moderate amount of snow on the ground. The children had the day off from school and customer traffic in the downtown stores was light. Many residents were preparing or enjoying dinner at home. At 5:36 pm, a major earthquake began to shake the ground, and the ground beneath Southcentral Alaska moved in waves for the next four long minutes.
Parents and children slipped, tripped and fell on moving floors in a panicked attempt to get outdoors to escape broken windows. Two-inch cracks appeared in the ground in many places. Roads wrinkled and split and Fourth Avenue in downtown Anchorage split and collapsed 10 feet or more. Government Hill Elementary School was twisted, shifted, and unusable at one point. The exterior wall of the JC Penney building collapsed onto the street. In the residential district of Turnagain, the ground liquefied like quicksand, sliding down and swallowing 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 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 massive damage. Total property damage was estimated at $500 million.
Anchorage was paralyzed when gas and water lines were abruptly cut off. Residents resorted to melting snow for water as they waited for repairs. Four days later, students returned to available schools as life in Anchorage began to pick up.
Earthquake
The center of the Alaska earthquake was located about 75 miles east of Anchorage and about 55 miles west of Valdez. It started 14 to 16 miles deep in the Earth’s crust, a relatively shallow depth, where the Pacific plate dips below the North American plate. The massive subduction zone sits 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, stretched 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 under the North American plate. The grinding of the two massive tectonic plates caused the Alaska earthquake and it measured 8.4 on the Richter scale. In later years, the Alaska earthquake measurement was updated to 9.2 on the Mw, or moment magnitude, scale, as the Richter scale was determined to be inaccurate at measuring very large earthquakes above 8.0. Within a day of the initial big quake, 11 tremors over 6.0 or higher shock an already nervous population. In fact, the aftershocks continued for almost a year.
The earthquake caused ground to move up to 25 feet on several Alaskan islands and almost 3 feet up in the town of Valdez. In other areas, the ground drifted down as much as 9 feet, for example in the city of Portage.
The Good Friday Alaska earthquake was the strongest earthquake 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 December 26, 2004 earthquake 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 perished.
The tsunami
tsunami is an adapted Japanese word meaning “harbor wave”, a reference to the fact that the wave’s danger and destructive power only become apparent as it approaches the shore.
During the 1964 Alaskan earthquake, the North American plate tore up, displacing a large volume of ocean water and causing a seismic wave, a tsunami, to travel outward. The wave traveled at an estimated speed of 450 miles per hour in the deep ocean in a long wave of almost imperceptible height.
As the tsunami wave passed over the continental shelf and approached the coast, its length shortened, its speed decreased, and its height increased as the enormous volume and weight of the water prepared to release its incredible energy at any moment. anything that got in his way.
At the shallow entrance of Valdez, the wave reached a maximum height of almost 200 feet. Up ahead, in the old town of Valdez, a 30-foot wall of water hit and demolished all structures. Twenty-eight Valdez residents died when the tsunami crashed against the shoreline. Valdez was later rebuilt at a higher elevation and further from the coast.
In Seward, Alaska, the earthquake caused part of the bay to slide. The landslide triggered a local tsunami that devastated the Seward harbor and downtown 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 resulted in 9 deaths.
More than 40 years have passed since the Alaska earthquake and tsunami. Meanwhile, building materials and construction practices have been applied to produce structures more capable of surviving strong earthquakes. Also meanwhile, 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 large and destructive earthquake will hit Alaska.