1964 Alaska earthquake

Overview

The 1964 Alaska earthquake, also known as the Great Alaskan earthquake and the Good Friday earthquake, occurred on March 27, 1964. It is the most powerful earthquake recorded in North American history, with a moment magnitude of 9.2. The earthquake lasted approximately 4.5 minutes and caused widespread damage across south-central Alaska. The seismic event triggered a series of tsunamis, landslides, and ground failures, leading to significant loss of life and property.

Geology and Seismology

The earthquake occurred along the boundary between the Pacific Plate and the North American Plate, specifically in the region known as the Aleutian Trench. This subduction zone is characterized by the Pacific Plate being forced under the North American Plate, leading to significant tectonic stress accumulation. The 1964 earthquake was a megathrust earthquake, which is typical of subduction zones and involves the sudden release of accumulated stress along a fault line.

The earthquake's epicenter was located at a depth of approximately 25 kilometers, near Prince William Sound. The rupture zone extended over 800 kilometers, with a maximum displacement of about 20 meters. The seismic waves generated by the earthquake were felt as far away as California and Hawaii.

Impact and Damage

The earthquake caused extensive damage across a wide area, including Anchorage, the largest city in Alaska. Buildings, roads, and infrastructure were severely affected. The ground in some areas experienced vertical displacements of up to 11.5 meters. In Anchorage, the Turnagain Heights neighborhood saw significant ground failure, leading to the destruction of many homes.

The earthquake also triggered several tsunamis, which caused additional damage along the coastlines of Alaska, British Columbia, and the U.S. West Coast. The most devastating tsunami waves struck the town of Valdez, where the waterfront was completely destroyed, and Seward, where the harbor and rail yard were obliterated.

Tsunamis

The tsunamis generated by the earthquake were responsible for much of the loss of life. The waves reached heights of up to 67 meters in some locations. The tsunamis were caused by both the vertical displacement of the sea floor and underwater landslides triggered by the earthquake. Coastal communities were particularly vulnerable, and the tsunamis caused significant damage and loss of life in places such as Kodiak, Whittier, and Chenega.

Landslides and Ground Failures

In addition to tsunamis, the earthquake induced numerous landslides and ground failures. These geotechnical phenomena were particularly prevalent in areas with steep terrain and loose, unconsolidated soils. The Turnagain Heights landslide in Anchorage is one of the most well-documented examples, where a large section of the neighborhood slid into the ocean, destroying many homes.

Human Impact

The human toll of the earthquake was significant, with 131 people losing their lives. The majority of fatalities were due to the tsunamis rather than the shaking itself. The earthquake and subsequent tsunamis displaced thousands of residents, leading to a humanitarian crisis. Emergency response efforts were hampered by the extensive damage to infrastructure, including roads, bridges, and communication networks.

Economic Impact

The economic impact of the 1964 Alaska earthquake was profound. The total damage was estimated at approximately $311 million (equivalent to about $2.3 billion in 2021 dollars). The destruction of infrastructure, homes, and businesses had long-term economic repercussions for the affected communities. Reconstruction efforts took several years, and the earthquake prompted significant changes in building codes and disaster preparedness strategies in Alaska and beyond.

Scientific and Engineering Lessons

The 1964 Alaska earthquake provided valuable lessons for the scientific and engineering communities. It highlighted the importance of understanding subduction zone earthquakes and their potential to generate large tsunamis. The event also underscored the need for improved building codes and construction practices to mitigate the effects of such powerful seismic events.

Seismologists and geologists conducted extensive studies of the earthquake and its effects, leading to advancements in the understanding of earthquake mechanics and ground motion. The data collected from the earthquake contributed to the development of modern seismic hazard assessment and risk mitigation strategies.

References

Plafker, George. "Tectonic Deformation Associated with the 1964 Alaska Earthquake." Science, vol. 148, no. 3678, 1965, pp. 1675-1687.
National Research Council. "The Great Alaska Earthquake of 1964: Engineering." National Academy of Sciences, 1973.
Lander, James F., and Patricia A. Lockridge. "United States Tsunamis (including United States possessions) 1690-1988." National Geophysical Data Center, 1989.