The 1896 Sanriku earthquake was one of the most devastating tsunami earthquakes, which generated an anomalously larger tsunami than expected from its seismic waves. Previous studies indicate that the earthquake occurred beneath the accretionary wedge near the trench axis. It was pointed out recently that sediments near a toe of an inner trench slope with a large horizontal movement due to the earthquake might have caused an additional uplift. In this paper, the effect of the additional uplift to tsunami generation of the 1896 Sanriku tsunami earthquake is quantified. We estimate the slip of the earthquake by numerically computing tsunamis and comparing their waveforms with those recorded at three tide gauges. The estimated slip for the model without the additional uplift is 10.4 m, and those with the additional uplift are 5.9--6.7 m. This indicates that the additional uplift of the sediments near the trench has a large effect on the tsunami generation. ¿ 2001 American Geophysical Union