George Plafker: "Everything was in chaos."
Art Grantz: "I'd never seen anything that destructive
that close up."
Narrator: In 1964, Alaska was shaken by the largest
U.S. earthquake ever recorded: Magnitude 9.2.
(Title Screen)
Narrator: In 1964, scientists did not understand how or why it occurred.
Narrator: Immediately, three U.S. Geological Survey scientists were sent to figure it out.
There were no faults at the surface to explain it.
Even with months of careful observation and field work the cause of the quake remained
a mystery.
Until one of the scientists, geologist George Plafker, considered the quake in terms of
the newly forming theory of plate tectonics.
His realization changed our understanding of these great earthquakes.
George Plafker: "...the oceanic crust is being pushed underneath
that part of southern Alaska at a very low angle and there was slip on this, on the interface
between the oceanic crust and the overlying continental crust.
"
Narrator: These two crusts are converging at the dramatic
rate of an inch and a half each year.
Periodic slip between the crusts produces great quakes, which Plafker called "megathrust"
earthquakes.
Scientists now recognize the distinctive patterns of uplift and downdrop at the earth's surface
characteristic of these quakes.
George Plafker: "One of the obvious things that everybody
wants to know when you have an earthquake like this is how frequently do they occur?
Could you have one tomorrow or is it thousands of years?"
Narrator: By drilling 50 feet into the earth and taking
core samples, Plafker and his team discovered nine megathrust earthquakes had occurred in
south central Alaska over the past 5,500 years.
The average time span between these quakes is 630 years.
Narrator: The 1964 Great Alaska Earthquake was accompanied
by massive tsunamis.
Within minutes one created a wave 20 stories high in parts of Alaska.
Some travelled across the Pacific wreaking havoc in coastal Oregon, California, and Hawaii.
Narrator: The widespread damage and loss of life from
this earthquake led to a determination to use science to save lives in the future.
Peter Haeussler: "South central Alaska here is the infrastructure
center of the state and it's also by far the largest population center of the state.
And the work that we do involves basically....the fundamental characterizing of the earthquake
hazard and knowing which faults are active, which faults can produce earthquakes, understanding
how often these earthquakes occur.
And then another part is understanding the local tsunami hazard.
Narrator: Legacies from the 1964 Great Alaska Earthquake
include: - The USGS Earthquake Hazards Program.
-- NOAA's round-the-clock Tsunami Warning Centers.
-- The Advanced National Seismic System, resulting in Seismic Hazard Maps and improved building
codes.
Narrator: All together, these programs can help predict
strong ground motions from future earthquakes, and minimize risks.
For one example, scientists learned that Valdez was so unstable and at such risk for earthquakes
that the town was moved.
Narrator: The 1964 Great Alaska Earthquake changed our
understanding of quakes and tsunamis and had a profound and lasting impact on how scientific
knowledge can be used to help.
(END)