This view of Earth comes from NASA's Moderate Resolution Imaging Spectroradiometer aboard the Terra satellite.
|
|
|
January 10, 2005
NASA scientists using data from the Indonesian earthquake
calculated it affected Earth's rotation, decreased the
length of day, slightly changed the planet's shape, and
shifted the North Pole by centimeters. The earthquake that
created the huge tsunami also changed the Earth's rotation.
Dr. Richard Gross of NASA's Jet Propulsion Laboratory,
Pasadena, Calif., and Dr. Benjamin Fong Chao, of NASA's
Goddard Space Flight Center, Greenbelt, Md., said all
earthquakes have some affect on Earth's rotation. It's just
they are usually barely noticeable.
"Any worldly event that involves the movement of mass
affects the Earth's rotation, from seasonal weather down to
driving a car," Chao said.
Gross and Chao have been routinely calculating earthquakes'
effects in changing the Earth's rotation in both length-of-
day as well as changes in Earth's gravitational field. They
also study changes in polar motion that is shifting the
North Pole. The "mean North pole" was shifted by about 2.5
centimeters (1 inch) in the direction of 145 degrees East
Longitude. This shift east is continuing a long-term seismic
trend identified in previous studies.
They also found the earthquake decreased the length of day
by 2.68 microseconds. Physically this is like a spinning
skater drawing arms closer to the body resulting in a faster
spin. The quake also affected the Earth's shape. They found
Earth's oblateness (flattening on the top and bulging at the
equator) decreased by a small amount. It decreased about one
part in 10 billion, continuing the trend of earthquakes
making Earth less oblate.
To make a comparison about the mass that was shifted as a
result of the earthquake, and how it affected the Earth,
Chao compares it to the great Three-Gorge reservoir of
China. If filled, the gorge would hold 40 cubic kilometers
(10 trillion gallons) of water. That shift of mass would
increase the length of day by only 0.06 microseconds and
make the Earth only very slightly more round in the middle
and flat on the top. It would shift the pole position by
about two centimeters (0.8 inch).
The researchers concluded the Sumatra earthquake caused a
length of day change too small to detect, but it can be
calculated. It also caused an oblateness change barely
detectable, and a pole shift large enough to be possibly
identified. They hope to detect the length of day signal and
pole shift when Earth rotation data from ground based and
space-borne position sensors are reviewed.
The researchers used data from the Harvard University
Centroid Moment Tensor database that catalogs large
earthquakes. The data is calculated in a set of formulas,
and the results are reported and updated on a NASA Web site.
The massive earthquake off the west coast of Indonesia on
December 26, 2004,
registered a magnitude of nine on the new "moment" scale
(modified Richter scale) that indicates the size of
earthquakes. It was the fourth largest earthquake in one
hundred years and largest since the 1964 Prince William
Sound, Alaska earthquake.
The devastating mega thrust earthquake occurred as a result
of the India and Burma plates coming together. It was caused
by the release of stresses that developed as the India plate
slid beneath the overriding Burma plate. The fault
dislocation, or earthquake, consisted of a downward sliding
of one plate relative to the overlying plate. The net effect
was a slightly more compact Earth. The India plate began its
descent into the mantle at the Sunda trench that lies west
of the earthquake's epicenter. For information and images on
the Web, visit:
http://www.nasa.gov/vision/earth/lookingatearth/indonesia_quake.html .
For details on the Sumatra, Indonesia Earthquake, visit the
USGS Internet site:
http://neic.usgs.gov/neis/bulletin/neic_slav_ts.html .
For information about NASA and agency programs Web, visit:
http://www.nasa.gov .
JPL is managed for NASA by the California Institute of
Technology in Pasadena.
Alan Buis (818) 354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
Gretchen Cook-Anderson/Dolores Beasley (202) 358-0836/1753
NASA Headquarters, Washington, D.C.
2005-009
Facebook
Twitter
You Tube
Flickr
iTunes
UStream
Blog
