## 1. Introduction

[2] Earthquake tsunamis are difficult to predict because the mechanism of undersea earthquakes is poorly understood and the resulting force that triggers a tsunami is difficult to measure [*Mofjeld et al.*, 1999]. Even several months after the devastating tsunami of the 26 December 2004 Sumatra-Andaman earthquake, the precise tsunami source and generation mechanism are still unknown [*Lay et al.*, 2005; *Ammon et al.*, 2005]. Nevertheless, numerical models play a fundamental role in tsunami research [*Shuto*, 1991; *Johnson*, 1999]. Most tsunami models are based on two-dimensional shallow water equations [*Satake*, 1995]. To simulate earthquake tsunamis, models are often initialized by an instantaneous perturbation on the sea surface. The surface perturbation is assumed to exactly match the vertical component of the seafloor deformation due to faulting [*Abe*, 1973; *Satake*, 1994]. Specifically, the deformation is estimated from the seismic moment, *M*_{o} = μ*AD*, where μ is the fault rigidity, *A* is the fault area, and *D* is the average displacement across the fault. The initially estimated seismic moment for the December earthquake is 4.0 × 10^{22} Nm (M_{w} = 9.0) and gives the displacement 5 meters, while the upgraded moment 8.2 × 10^{22} Nm (M_{w} = 9.2) gives the displacement 10 meters, both using the estimated fault area 200 × 1300 km^{2} and rigidity 3.0 × 10^{10} N/m^{2} [*Lay et al.*, 2005]. Obviously, there is a great uncertainty in quantifying the vertical component from the total displacement. Although this approach has been widely used in tsunami studies [*Johnson*, 1999], attempts to match observations have been disappointing [*Mofjeld et al.*, 1999]. For instance, the modeled tsunami based on the seismic estimation of the 1992 Nicaraguan earthquake is several times smaller than the actual measurement of tide gauges [*Imamura et al.*, 1993].

[3] This study differs from previous studies in three aspects: First, the seismic waveform inversion [*Ji et al.*, 2002] is used to obtain the three-dimensional seafloor displacements of the earthquake [*Ammon et al.*, 2005]. Second, a three-dimensional ocean-general-circulation-model (OGCM) is employed to couple the waveform inversion and therefore captures the full earthquake forcing at the ocean bottom [*Voit*, 1987; *Kanamori and Kikuchi*, 1993; *Tanioka and Satake*, 1996]. Third, satellite observations in the open ocean will be used to verify the seismic inversion and model simulation. By cross-examining the two independent results and comparing with the satellite observations, we are able to obtain the best possible information on the rupture history of the earthquake, which provides insight into the earthquake-tsunami generation mechanism and allow us to demonstrate the possibility of using the modern seismic data and state-of-the-art modeling technologies for future tsunami prediction.