HR: 1340h
AN: G33A-0025 [Abstracts]
TI: Information on the Earth's Deep Interior Conveyed by the 2004 Sumatra-Andaman Earthquake Using
Superconducting Gravimeter Data
AU: * Rosat, S
EM: rosat@miz.nao.ac.jp
AF: National Astrogeodynamics Observatory, 2-12 Hoshigaoka
Iwate, Mizusawa, 023-0861
Japan
AU: Watada, S
EM: shingo@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, Univ. of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032
Japan
AU: Sato, T
EM: tsato@miz.nao.ac.jp
AF: National Astrogeodynamics Observatory, 2-12 Hoshigaoka
Iwate, Mizusawa, 023-0861
Japan
AU: Tamura, Y
EM: tamura@miz.nao.ac.jp
AF: National Astrogeodynamics Observatory, 2-12 Hoshigaoka
Iwate, Mizusawa, 023-0861
Japan
AB:
The recent Sumatra-Andaman earthquake of magnitude Mw > 9 on 2004 December 26th has strongly excited the low-frequency
seismic modes and, in particular, the degree one 2S1 mode is observed for the first time without any stacking. This mode
corresponds to the first overtone of the sub-seismic mode 1S1, the so-called Slichter triplet (Slichter, Proc. Nat. Acad.
Sci., 1961). On the one hand, theoretical computations suggest that the Slichter modes could not have been excited with
sufficient amplitude to be detected by superconducting gravimeters (SGs) on the Earth's surface. The maximum surface gravity
effect of 1S1 after Sumatra event is 0.3 nGal, that is to say 0.3 10-12 g, where g is the mean absolute gravity value on
the Earth's surface, corresponding to a free air displacement of 10-3 mm (1 nm). On the other hand, the core-sensitive
mode 3S2 and the fundamental radial mode 0S0 were strongly excited, meaning that the earthquake radiated much energy toward
the core. 0S0 is a radial fundamental spheroidal mode called "breathing mode" of the Earth and corresponds to changes in the
Earth's circumference. The high stability of SG records has enabled us to follow the time decay of 0S0 amplitude till the
second Sumatra event on March 28th 2005 and to estimate 0S0 quality factor at a value of 5513 +- 8 from the weighted mean of
12 SG record estimates. Amplitude measurements of 0S0 at most SG sites in the world reveal a latitude dependency that we try
to explain by theory. The amplitude deviation of 0S0 reaches +- 2% while the calibration errors of SGs are usually less than
0.2%.
DE: 1217 Time variable gravity (7223, 7230)
DE: 7255 Surface waves and free oscillations
DE: 7260 Theory
SC: Geodesy [G]
MN: Fall Meeting 2005