1964 Quake: The Great Alaska Earthquake

12 minutes

(male #1) Everything was chaotic.

(male #2) I had never seen anything that destructive.

(female narrator) In 1964 Alaska was shaken by the largest U.S. earthquake ever recorded-- magnitude 9.2.

Shaking went on for over four minutes. One hundred forty-three people died. Total property loss in 2013 dollars is estimated at 2.3 billion. There were gaping fractures, massive landslides, and the destruction of water mains, gas, sewer, telephone, and electrical systems. The epicenter was in Prince William Sound, seventy-four miles southeast of Anchorage, yet effects were observed as far away as Texas and Louisiana. What the 1964 Great Alaska Earthquake taught scientists was as profound and far reaching. Initially, no one understood how or why the earthquake occurred. Immediately, three U.S. Geological Survey scientists were sent to figure it out. The main airport, The Anchorage International, was closed down because the control tower had collapsed and killed the operator. Then we went out separately, mostly separately, so we could cover three times as much ground.

(narrator) The scientists studied the effects from the air on land, and along shorelines. They were astonished to find surface disruption over an area larger than California-- 185,000 square miles. Some areas dropped down as much as eight feet. Others rose up as much as 38 feet. Barnacles, once two feet below the ocean surface, were suddenly several feet above. Mapping this uplift and down-drop became crucial for understanding what happened. With no surface faults visible to explain it, with months of careful observation and field work, the cause of the quake remained a mystery. Right at this time, this idea of plate tectonics, that the surface of the earth is broken up into different plates that move around with respect to each other. It occurred right when this idea was being put forth.

(narrator) One of the scientists, geologist George Plafker, considered the quake in terms of this newly-forming theory of plate tectonics. The theory had new crust forming at mid-ocean ridges, but didn't explain where this crust went.

(Plafker) The most likely one that came to mind is that the oceanic crust is being pushed underneath that part of Alaska at a low angle, and there was slip on the interface between the oceanic crust and the overlying continental crust.

(narrator) These two crusts are converging at the annual rate of 1 1/2 inches. Periodic slip between the crusts produces great quakes, which Plafker called megathrust earthquakes. His realization changed our understanding of these great earthquakes. Megathrust quakes are the largest known on planet earth. They occur in areas of colliding and descending crusts, known today as subduction zones. The uplift and down-drop of large areas from these quakes is caused by the crust being compressed over years of converging plates. It releases like a spring, which is the earthquake. Seaward areas are uplifted, while landward areas drop down. George Plafker identified this pattern common to megathrust quakes in subduction zones.

(Haeussler) The 1964 earthquake was the first megathrust subduction zone earthquake properly interpreted as such. As a result of that, essentially every other large, subduction zone earthquake around the world falls in the shadow of what we learned from the 1964 earthquake.

(narrator) Next the question became, how often do these quakes happen? One thing everybody wants to know, when you have an earthquake like this, is how frequently they occur. Could it be tomorrow or thousands of years?

(narrator) Plafker and his team drilled down 50 feet and collected core samples to find out. They used carbon dating to identify when past megathrust earthquakes occurred in Southcentral Alaska. It's just an example of what has happened in the past. The analogue for that is what happened in the 1964 earthquake, namely abrupt uplift of a broad area of mud flats that are intertidal, and then sudden appearance of freshwater plants growing on that surface. In the cores, where the remains of land plants overlie ocean sediments, this marks a moment of sudden change-- a past megathrust quake. Dating the plant remains provides an age for that quake. The team discovered nine megathrust earthquakes have occured in Southcentral Alaska over the past 5,500 years. The average time span between these quakes was 630 years. Another devastating effect of the 1964 Alaska earthquake was a series of deadly tsunamis. The largest, triggered by the shifting of plates when the quake began, traveled across the Pacific, wreaking havoc in coastal Oregon, California, Hawaii, and beyond. Locally, a number of extremely dangerous tsunamis occured in Southcentral Alaska fjords, like Whittier and Valdez. Most deaths resulting from the 1964 quake came from these local tsunamis in fjords. The scientists recognized that these were produced by underwater landslides that occurred as the quake began. In the 1964 earthquake, of the people who died, most people were killed by tsunamis. There are two ways you can make tsunamis. The way tsunamis were made here in Whittier was by underwater landslides. There's material at the edges of the fjords. It's shaken in the earthquake and slides downward in the fjord's deep part. That generates tsunami waves which hit the shoreline. Notably, those tsunamis hit the shoreline very soon after the beginning of shaking. Here in Whittier, the first tsunami wave was well-observed in the middle of the fjord. Within three minutes, there were three waves that covered a large part of Whittier. It killed about 12 people. There was a lumber mill located about where that hotel is. There were 13 deaths in Whittier, and 12 of them were over there.

(narrator) Chenega, a small native village in Prince William Sound, lost 23 people, a third of its population. Today scientists use ocean bottom sonar mapping to identify sub-marine landslide deposits from the past. Additional work, like coring and dating these slides, will help refine understanding of the tsunami hazard and how often these quakes occur. At Valdez there may be six to ten of these big, underwater landslide deposits at depth. So we know that these things happen over and over. We're at the margin of a fjord with big mountains. There's glaciers and streams eroding these things. They're putting sediment at the margins of the fjord. We have the megathrust underneath us here at about 12 to 15 miles depth. In these big earthquakes, it shakes like crazy, releases sediments into the deep parts of the fjord, and then generates tsunamis. If you're living or recreating at the edge of a fjord and an earthquake happens, it's really important to travel to high ground right away. Don't wait to hear a tsunami alarm. If you feel strong shaking that feels like an earthquake, you need to head uphill. Don't wait till the earthquake is over.

(narrator) Some of the most stunning destruction from the 1964 quake came from subareal landslides. Extreme shaking led to significant ground failure and liquefaction in Anchorage. Massive landslides struck the downtown area, Government Hill, and in the Turnagain By The Sea subdivision. Through the ground shaking in the '64 earthquake, these blocks sort of slid sideways as a result. Some buildings collapsed into those areas. Sometimes edges of buildings were sticking off or had failed underneath. There were a few people killed as a result of the damaged buildings.

(narrator) The widespread damage and deaths from this earthquake determined the use of science to save lives in the future. Legacies from the 1964 Great Alaska Earthquake include the establishment of the USGS Earthquake Hazards Program, NOAA's round-the-clock tsunami warning centers, new building codes and innovations in retrofitting older, vulnerable structures. As part of the Advanced National Seismic System, the USGS now routinely monitors all earthquakes that occur in the U.S.

[bell ringing]

(Haeussler) Southcentral Alaska is the infrastructure center of the state. It's also the largest population center of the state. The work that we do involves the fundamental characterizing of the earthquake hazard and knowing which faults are active, which faults can produce earthquakes, understanding how often those earthquakes occur. Another part is understanding the local tsunami hazard, getting an idea how often they occur, and doing tsunami modeling to understand where people would be hit by these tsunamis.

(narrator) Altogether, these programs can help predict strong ground motions from future earthquakes and minimize risks. For example, scientists learned that Valdez was so unstable and at such risk for earthquakes that the entire town was moved. In recent years, megathrust quakes in subduction zones accompanied by tsunamis have occurred in Indonesia, Japan, and Chile. The 1964 Great Alaska Earthquake changed our understanding of earthquakes and tsunamis and had a profound and lasting impact on how scientific knowledge can be used to help reduce risks and save lives.

Funding to purchase and make this educational production accessible was provided by the U.S. Department of Education:

PH: 1-800-USA-LEARN (V) or WEB: www.ed.gov.


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America’s largest recorded earthquake happened on March 27, 2014 in Alaska. United States Geological Survey (USGS) sent geologists to study the impact and effects of the earthquake. The information gathered from the aftermath was essential in resolving key mechanisms of the developing theory of plate tectonics.

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