HR: 10:45h
AN: U52A-02    [Abstracts]
TI: Excitation of Earth Rotation and Gravitational Field Changes by the December 26, 2004 Sumatran Earthquake
AU: * Gross, R S
EM: Richard.Gross@jpl.nasa.gov
AF: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: Chao, B F
EM: Benjamin.F.Chao@nasa.gov
AF: NASA/Goddard Space Flight Center, Space Geodesy Laboratory, Greenbelt, MD 20771 United States
AB: Besides generating seismic waves, which eventually dissipate, an earthquake also generates a static displacement field everywhere within the Earth. This global displacement field rearranges the Earth's mass, causing the Earth's rotation and gravitational field to change. The size of these changes depends upon the size, focal mechanism, and location of the earthquake. The Sumatran earthquake of December 26, 2004 is the largest earthquake to have occurred since the 1964 Alaskan earthquake. The coseismic effect of the Sumatran earthquake upon the Earth's length-of-day, polar motion, and low-degree harmonic coefficients of the gravitational field are computed. It is found that this earthquake should have caused the length-of-day to decrease by 2.68 μsec, the position of the mean rotation pole to shift 0.821 mas towards 145°E longitude, the Earth's oblateness J₂ to decrease by 0.90×10^-11, and the Earth's pear-shapedness J₃ to decrease by 0.19×10^-11. This predicted change in the length-of-day is probably not detectable by current measurement systems, the change in oblateness is perhaps just detectable, and the change in the mean position of the rotation pole is perhaps detectable if other effects, such as those of the atmosphere, oceans, and continental water storage, can be adequately removed from the observations.
DE: 1234 Regional and global gravity anomalies and Earth structure
DE: 1239 Rotational variations
SC: Union [U]
MN: 2005 Joint Assembly