On Today's Day: The Great 1964 Alaska Earthquake

On today's day in 1964, the largest recorded earthquake in U.S. history occurred in the south-central Prince William Sound region of Alaska. It was of a magnitude 9.2 and occurred at a depth of 25 kilometers (16 mi). It is also the second largest earthquake ever recorded, next to the M9.5 earthquake in Chile in 1960.

About the 1964 Alaska Earthquake

The earthquake lasted approximately 4.5 minutes and was felt over an area of almost 1,300,000 square km (502,000 square miles)¹. It also triggered a swell of devastating tsunamis, landslides, and submarine slumps, which caused massive property damage and loss of life.

For example, the earthquake tilted an area of at least 120,000 square km (46,442 square miles). Landmasses were thrust up locally as high as 25 meters (82 feet) to the east of a line extending northeastward from Kodiak Island through the western part of Prince William Sound. To the west, the land sank as much as 2.5 meters (8 feet)¹.

In addition to the earthquake, the event triggered a major tsunami that caused casualties and damage from the Kodiak Islands to northern California². The earthquake and ensuing tsunami caused 139 deaths and USD$400 million in property loss. The earthquake caused 15 deaths, while the tsunami caused 124 deaths (106 in Alaska, 13 in California, and 5 in Oregon)³.

Scientific Breakthroughs

Furthermore, the quake also led to significant scientific breakthroughs in subduction earthquakes and how to minimize their destruction.

Only then did seismologists and scientists know much about the processes beneath the Earth. However, the Alaskan earthquake led geologists to realize the subduction zones' existence. They defined them as areas where two tectonic plates (huge slabs of rock made of the earth’s crust and upper mantle) meet, and one bends under the other. It was this process that led to this earthquake. It’s estimated that the fault slipped between 9 to 18 meters (30 to 60 feet), which is considered a lot⁴.

Furthermore, soon after the earthquake, a broad earthquake-monitoring system was created to gather data and help seismologists predict future earthquakes and their potential damage. The data helped engineers develop earthquake-resistant structures to limit future casualties and property damage⁴.

Seismicity in Alaska

Alaska has 50 to 100 earthquakes daily and accounts for 11 % of the world’s earthquakes and over half of all earthquakes in the U.S. With more than 20,000 earthquakes reported annually, Alaska is by far the most seismically active state. Its largest earthquakes are caused by the subduction of the Pacific plate beneath Alaska as the Pacific plate moves under the North American plate between 5-7 centimeters per year⁵.

Some photos of the earthquake damage are available from the USGS here.

Picture 1: Damage caused by the 1964 Alaska earthquake.

Sources:

1) Britannica. Alaska Earthquake of 1964. Accessed on 27-Mar-2023. Available at: https://www.britannica.com/event/Alaska-earthquake-of-1964
2) USGS. 2014. The 1964 Great Alaska Earthquake and Tsunami. Accessed on 27-Mar-2023. Available at: https://www.usgs.gov/news/state-news-release/1964-great-alaska-earthquake-and-tsunami
3) National Center for Environmental Information. 1964 Alaska Earthquake Information. Accessed on 27-Mar-2023. Available at: https://www.ngdc.noaa.gov/hazel/view/hazards/earthquake/event-more-info/4311
4) History. 1964 Alaska Earthquake. Accessed on 27-Mar-2023. Available at: https://www.history.com/topics/natural-disasters-and-environment/1964-alaska-earthquake
5) Shakeout. The Great Alaska Shake Out. Accessed on 27-Mar-2023. Available at: https://www.shakeout.org/alaska/whyparticipate/#:~:text=EARTHQUAKE%20HAZARDS&text=Alaska's%20largest%20earthquakes%20are%20caused,that%20great%20earthquakes%20are%20rare.