Great Alaska Earthquake

Earthquake

Also known as: The Good Friday Earthquake, Black Friday

Date: March 27, 1964

Place: Alaska

Magnitude: 8.3-8.6, possibly as high as 9.2

Result: 131 dead, $500 million in damage

The 1964 Great Alaska Earthquake was one of the highest in magnitude ever recorded, between 8.3 and 8.6 on the Richter scale. This magnitude has since been revised to 9.2, making it the strongest earthquake ever recorded in North America. It released as much as eighty times the energy of the 1906 earthquake of San Francisco. The quake took place 125 miles below the earth’s surface but near the shore, so that most of the damage was caused by waves heaving up onto the land and sweeping away whatever was in their path.

Reasons for the Earthquake. Normally the Pacific Plate moves in a northwesterly direction at a rate of about 5 to 7 centimeters per year. The continents, the ocean basins, and everything else on the surface of the earth move along on these plates that float on the underlying convecting material. However, where the plates come together, as is the case in southern Alaska, the movement causes the earth’s crust to be compressed and warped, with some areas being depressed and others uplifted.

As far as scientists can understand, in 1964 the Pacific Plate subducted, or slid under, the North American Plate at the head of Prince William Sound, 56 miles (90 kilometers) west of Valdez and 75 miles (120 kilometers) east of Anchorage. It caused the earth under the water in the harbor to split open and crack. A tsunami, or harbor wave, resulted. Water rushed in at great force to fill the open areas and was pushed up by the section of the seafloor that was uplifted. In the Alaska earthquake, 100,000 square miles of earth uplifted or dropped. Areas north and northwest of the epicenter subsided as much as 7.5 feet. Areas south and southeast rose, over wide areas, as much as 6 feet. Locally, the uplift was much greater: 38 feet on Montague Island and more than 50 feet on the seafloor southwest of the island. The Homer Spit and all the coastline of the Kenai Peninsula sank 8 feet. Cook Inlet and Kachemak Bay protected Seward, but the Seward area dropped 3.5 feet. Tsunamis devastated every town and village along the outer coast and the Aleutian Islands. Also, horizontal movements of tens of feet took place in which the landmass moved southeastward relative to the ocean floor, moving more earth farther than any other earthquake ever recorded, both horizontally and vertically. The area of crustal deformation stretched from Cordova to Kodiak Island. Beginning in Prince William Sound, it moved toward Kodiak at 10,000 feet or about 2 miles per second. The shock was felt over a range of 50,000 miles.

The strong ground motion caused many snowslides, rockfalls, and landslides both on land and on the ocean floor. It smashed port and harbor facilities, covered plants and salmon beds with silt, disturbed and killed salmon fry, leveled forests, and caused ocean saltwater to invade many coastal freshwater lakes. In areas where the land sank, spawning beds, trees, and other vegetation were destroyed. In areas where the seafloor rose, marine animals and plants that need water for survival were forced above ground.

It is thought that the duration of the quake was three to four minutes; however, no seismic instruments capable of recording strong ground motion were in Alaska at the time. The quake served as a test of manufactured structures under extreme conditions and as a guide to improvements in location and design.

An earthquake sends out waves known as aftershocks. There were 52 large aftershocks in Alaska, which continued for a year after the quake. The first 11 of these occurred on the day of the quake, and 9 more happened in the next three weeks. The aftershock zone spanned a width of 155 miles (250 kilometers), from 9 miles (15 kilometers) north of Valdez, for 497 miles (800 kilometers) to the southwest end of Kodiak Island, to about 34 miles (55 kilometers) south of the Trinity Islands.

Geography. South central Alaska and the Aleutian Islands compose one of the most active seismic regions in the world. One thousand earthquakes are detected every year in Alaska, thirty-seven of which measure 7.25 or more on the Richter scale. Anchorage itself rests on a shelf of clay, sometimes called “Bootlegger Clay,” named for Bootlegger Cove, once a rendezvous for rumrunners. This clay assumes the consistency of jelly when soaked with water. In 1959 the U.S. Geological Survey cited a number of places along the bluffs of Anchorage where the clay had absorbed water. However, people did not attend to the report, and the geologists were referred to as “catastrophists” because they predicted a catastrophe where seemingly there was none. When the quake hit, many homes and businesses, especially on the west side of city, sank out of sight.

Thanks to the Good Friday holiday, there were very few fishing boats on the water at the time of the quake. However, one boat, the Selief, had been sailing toward the harbor with $3,000 worth of Alaskan king crab in its hold. The captain of the ship heard warnings on the radio, but, unable to avoid the tsunami, he found himself uplifted by the waters and deposited about six blocks inland from the shore. Another boat, a freighter, was docked in the harbor and unloading its cargo in Valdez. When the quake hit, 31 men, women, and children, who were standing by and watching, were swept away and killed by the wave. The boat rose about 30 feet and then dropped, rose again, and dropped. The third time it was able to get free from its mooring and move out to sea. Two men died of falling cargo, and another died of a heart attack.

Effects of the Earthquake. The Alaska earthquake has been called the best-documented and most thoroughly investigated earthquake in history. Within a month, President Lyndon B. Johnson appointed a Federal Reconstruction and Development Commission for Alaska, a commission that thoroughly researched every aspect of the disaster. The committee divided itself into panels, each representing the major disciplines involved in the data gathering: engineering, geography (human ecology), geology, hydrology, oceanography, biology, and seismology. Each of these panels gathered scientific and technical information.

Other prevention measures for the future included the establishment of the Alaska Tsunami Warning Center (ATWC) in 1967, located in Palmer. Strong-motion seismographs and accelerographs were installed in Anchorage shortly after the quake. Risk maps for Anchorage, Homer, Seward, and Valdez, based on extensive geological studies, were prepared by the Scientific and Engineering Task Force of the Reconstruction Commission and were used as a basis for federal aid to reconstruction and as guides to future builders.

The earthquake provided seismologists with a rich field of study, but it also turned the nation’s attention again, and sharply, to the problems of improving the elements of a national natural-disaster policy: zoning and construction codes, prediction and warning systems, rescue and relief organizations, disaster data collection and analysis, and disaster insurance and reconstruction aids.

There were 131 lives lost in the earthquake, a very small number for so great a catastrophe. There are several reasons for this. First, the earthquake happened on a holiday, when the schools were empty and most offices were deserted. Second, it was an off-season for fishing, so there were very few boats in the harbors. Third, there were no fires in residential or business areas, and fourth, there was a low tide at the time, which left some room for water to flow. Most people who died were swept away by tsunamis, 16 of whom were in Oregon and California. The extensive military establishment provided resources that reduced the loss of life, eased some of the immediate suffering, and restored needed services promptly.

The office of Emergency Planning, under the provisions of the Federal Disaster Act, provided additional aid. This included transitional grants to maintain essential public services, an increase in the federal share of highway reconstruction costs, a decrease in the local share of urban renewal projects, debt adjustments on existing federal loans, federal purchase of state bonds, and grants for a state mortgage-forgiveness program. In all, the earthquake generated $330 million of government and private funds for rescue, relief, and reconstruction.

Because Anchorage is the most populated and most developed area in Alaska, most of the financial losses occurred there. A J. C. Penney building was destroyed, and a Four Seasons apartment building, which was under construction and not yet occupied, totally collapsed. Many other buildings were damaged beyond repair. The Denali Theater on Fourth Avenue in Anchorage was showing a late afternoon matinee when the entire building sank 15 feet. All the children in attendance were able to crawl out, once the building stopped shaking. Almost all the schools in Anchorage were demolished.

Railroads twisted, and a diesel locomotive was thrown 100 yards from the track. Oil storage tanks at Valdez, Seward, and Wittier ruptured and burned. Many bridges, ports, and harbor facilities were destroyed. An incredible 75 percent of Alaska’s commerce was ruined—$750 million worth. A landslide at Turnagain Heights destroyed about 130 acres of residential property, including 75 houses. Another landslide at Government Hill caused severe destruction.

A wide area outside the state of Alaska also felt the effects of the quake. Buildings in Seattle, 1,000 miles away, swayed. The tsunami hit Vancouver Island, California, Hawaii, and even Japan. Water levels jumped abruptly as far away as South Africa; shock-induced waves were generated in the Gulf of Mexico. An atmospheric pressure wave was recorded in La Jolla, California. The day became referred to as Black Friday, because of the death and destruction.

Bibliography

Cohen, Stan. 8.6: The Great Alaska Earthquake March 27, 1964. Missoula, Mont.: Pictorial Histories, 1995.

Herb, Angela M. Alaska A to Z: The Most Comprehensive Book of Facts and Figures Ever Compiled About Alaska. Bellevue, Wash.: Vernon, 1993.

Hulley, Clarence C. Alaska: Past and Present. Portland, Oreg.: Binsfords & Mort, 1970.

Lane, Frank. The Violent Earth. Topsfield, Mass.: Salem House, 1986.

Murck, Barbara W., Brian Skinner, and Stephen C. Porter. Dangerous Earth: An Introduction to Geologic Hazards. New York: John Wiley & Sons, 1997.

National Research Council Committee on the Alaska Earthquake. The Great Alaska Earthquake of 1964. Vols. 1 and 2. Washington, D.C.: National Academy of Sciences, 1969-1970.

Paananen, Eloise. Earthquake! The Story of Alaska’s Good Friday Disaster. New York: John Day, 1966.

Ward, Kaari, ed. Great Disasters: Dramatic True Stories of Nature’s Awesome Powers. Pleasantville, N.Y.: Reader’s Digest Association, 1989.