Original URL: http://www.itwire.com/science-news/energy/37325-nasa-says-chile-earthquake-moved-us
By
William
Atkins
Wednesday, 03 March 2010 23:55
The Nazca (Nasca) tectonic plate caused the
earthquake, which was centered off the coast of Chile, after it made a move to
go beneath the adjacent tectonic plate. The Nazca Plate is a tectonic plate in
the eastern Pacific Ocean basin just off the west coast of South America.
The adjacent tectonic plate is called the South American Plate, which is located
east of the Nazca Plate. Also, next to the Nazca Plate are the Antarctic Plate,
to its south, and the Pacific Plate, to its west.
All of these tectonic plates are constantly moving, which cause earthquakes
(some small, others medium, and still others, much larger) and volcanoes (also
of various sizes).
And, while all of that is happening, the Earth is spinning on its axis (which is
why we see the Sun move across the sky during the day, and the Moon across the
sky at night—our period of one Earth day).
In other words, when we see the "Sun set in the west" we really aren't seeing
the Sun move. Instead, we are observing the Earth moving (rotating on its axis).
However, that spin (rotation) is not perfect. Earth’s spin has a tiny wobble in
it. In fact, the spin line (the Earth’s rotational axis) actually moves in an
area about 2,700 square feet (250 square meters).
This wobble is called the “Chandler
wobble” because U.S. astronomer
Seth Carlo Chandler discovered, in 1891, that the wobble exists.
And, the wobble was changed by the Chilean earthquake ever so slightly--about
three inches (7.6 centimeters).
The wobble has a period of about 433 days, which means the axis line turns the
Earth once around in that number of days. The wobble, and another wobble in the
Earth’s spinning motion, results in a total wobble period of about seven years.
According to the National Geographic News article “Chile
Earthquake Altered Earth Axis, Shortened Day,” “Saturday's Chile
earthquake was so powerful that it likely shifted an Earth axis and shortened
the length of a day, NASA announced Monday.”
U.S. geophysicist Richard Gross, with NASA’s Jet Propulsion Laboratory in
Pasadena, California has been studying the 8.8 earthquake centered in Chile that
occurred on Saturday, February 27, 2010.
Dr. Gross’ study of the Chilean quake in
unison with other scientists using a NASA computer-model, along with some data
from the United States Geological Survey (USGS), estimates that the 8.8
earthquake—which is the fifth most powerful earthquake ever recorded by humans
and one of the biggest ones in about one hundred years—probably shortened the
length of one Earth day by 1.26 millionth of a second.
In other words, the Chilean earthquake sped up the spin (rotation) of the Earth
so that it now rotates about 1.26 millionth of a second faster than it did
before the quake.
This change was caused because the area around the earthquake pulled itself
inward just a tiny bit.
That is, the mass of the Earth around the quake site was pushed into the Earth
just a very small amount, causing the planet to spin a little bit faster.
Dr. Gross makes studies of changes in the Earth’s rotation because NASA needs
such measurements to make sure they track spacecraft as precisely as possible.
Gross states, “It's important for us to know how the earth's rotation
changes. It helps us figure out where a spacecraft is and to navigate it for a
precise pinpoint landing.” [The Wall Street Journal (3.3.2010): “Temblor
Tilts Earth by Inches”]
Learn more about the Chilean earthquake and the effect it had on our Earth day
at the March 3, 2010 NPR article “How
The Chilean Quake Moved An Entire Planet.”
