Using tsunami waveforms, we estimate the source parameters of the 10 November 1938 Alaskan earthquake. The earthquake ruptured a 300-km-long segment of the Alaskan arc, which corresponds to the aftershock area. The seismic moment is approximately 20¿1020 Nm, or Mw=8.2, and the moment release was concentrated in the eastern end of the aftershock zone. The tsunami and seismic evidence strongly suggest that the 1938 earthquake did not rupture into the Shumagin Islands gap.