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January 10, 2005
NASA DETAILS EARTHQUAKE EFFECTS ON THE EARTH
Dr. Benjamin Fong Chao, of NASA’s Goddard Space Flight Center, Greenbelt, Md. and Dr. Richard Gross of NASA’s Jet Propulsion
Laboratory, Pasadena, Calif. 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.
Chao and Gross 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 145o East Latitude. 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 (LOD) 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 LOD 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 the 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
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Contacts:
Gretchen Cook-Anderson/ Dolores Beasley
Headquarters, Washington
Phone: 202/358-0836/1753
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Tsunami Strikes Sri Lanka
On December 26, 2004, tsunamis swept across the Indian ocean, spawned by a magnitude 9.0 earthquake off the coast of Sumatra. Aside from Indonesia,
the island nation of Sri Lanka likely suffered the most casualties, with the death toll reported at 21,715 on December 29th.
DigitalGlobe’s Quickbird satellite captured an image of the devastation around Kalutara, Sri Lanka (top), on December 26, 2004, at 10:20 a.m.
local time—about an hour after the first in the series of waves hit. A Quickbird image taken on January 1, 2004 (lower), shows the normal ocean
conditions. Water is flowing out of the inundated area and back into the sea, creating turbulence offshore. Some near-shore streets and yards are
covered with muddy water. It is possible that the image was acquired in a “trough” between wave crests. Imagery of nearby beaches shows
that the edge of the ocean had receded about 150 meters from the shoreline. Credit: Images Copyright DigitalGlobe
Tsunami Destroys Lhoknga, Indonesia
The Indonesian province of Aceh was hit hardest by the earthquake and tsunamis of December 26, 2004. Aceh is located on the northern tip of the
island of Sumatra. The largest waves struck the northwestern coast of Sumatra. The town of Lhoknga, on the west coast of Sumatra near the capital of
Aceh, Banda Aceh, was completely destroyed by the tsunami, with the exception of the mosque (white circular feature) in the city’s center.
Credit: Ikonos images copyright Centre for Remote Imaging, Sensing and Processing, National University of Singapore and Space Imaging.
Tsunami Damage in Northern Sumatra
This pair of images from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite shows the Aceh province of
northern Sumatra, Indonesia, on December 17, 2004, before the quake (bottom), and on December 29, 2004 (top), three days after the catastrophe. On
December 17, the green vegetation along the west coast appears to reach all the way to the sea, with an occasional stretch of sand (white). After the
earthquake and tsunamis, the entire western coast is lined with a purplish-brown border. The brownish border could be deposited sand, or perhaps
exposed soil that was stripped bare of vegetation when the large waves rushed ashore and then raced away. Another possibility is that parts of the
coastline may have sunk as the sea floor near the plate boundary rose. In places the brown strip reaches inland to a distance of about 2 miles.
Credit: NASA MODIS Rapid Response team
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