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Satellite altimetry measurements of sea surface heights for the first-time captured the Indian Ocean tsunami generated from the December 2004 great Sumatra earthquake. Analysis of the sea surface height profile suggests that the tsunami source, or the seafloor deformation, of the great earthquake propagated to the north at an extremely slow speed of less than 1 km/sec on average for the entire 1300-km-long segment along the northern Sumatra-Nicobar-Andaman Trench. The extremely slow propagation speed produces a very long duration of tens minutes, longer than earthquake source duration estimated (480-500 sec) from short-period P-wave radiation. The satellite altimetry data requires a total seismic moment of 9.86 × 10 22 Nm (Mw=9.3). This estimate is approximately 2.5 times larger than the value from long-period surface wave analysis but nearly the same as that from the ultra-long-period normal mode study. The maximum amount of slip (∼30 m) is identified in an offshore region closest to the northern most part of Sumatra where the largest tsunami run-up heights were observed.

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Sea surface height data from the TOPEX/POSEIDON altimetry satisfy continuous (or periodic) data acquisition and wide observation in a horizontal space, which makes it possible to investigate the typical/dominant spatial and temporal scales of ocean variabilities. Here we estimate nonseparable horizontal space-time decorrelation scales from the TOPEX/ POSEIDON altimeter data, because each ocean phenomenon/ variability is linked in the space and time coordinates. In the analysis procedure the direction of the anisotropy, e.g., the westward propagation of a planetary disturbance, is not assumed a priori, and the data alone decide the direction. Additionally, the observation error in the data is evaluated in the present analysis. The observation error is also an important value for objective analysis schemes and assimilation procedures to decide "weight of the data." This analysis is for the establishment of an optimum interpolation system, for developing the design of an optimum observation network, and for an assimilation system, Comprehensive Ocean Modeling, Prediction, Analysis and Synthesis System in the Kuroshio region (COMPASS-K) ] at the Meteorological Research Institute. 955