Abstract
The 2011 Tohoku earthquake tsunami caused widespread and serious damage especially to the coastal areas in the Tohoku region. While a number of hydrographic observation facilities were damaged, there exist movies capturing tsunami propagation and inundation, which are considered to be useful for obtaining hydrographic properties of tsunami behaviors. Many of the studies using moving images, however, have mainly focused on determining velocities of tsunami runup or backrush on lands because of their availability and relatively easy manipulation. In this study, we tried to estimate time series of velocities of the tsunami in Ofunato Bay, using a movie that captured the first tsunami wave attack. Time series of the original images were converted to images of brightness values and then their distortion corrections were made using our field survey data. The maximum uprush and downrush velocities of the first tsunami wave were estimated at approximately 6 m/s.
