Capable of achieving propagation speeds of about 435 miles per hour in deep water, tsunamis can get reflected and refracted due to changes in topography / bathymetry along shorelines. (sciencedaily.com)
Per the second chart below, it appears regional differences account for very minor variations in propagation speeds. (tradeblock.com)
By scattering light, the material slows down the effective propagation speed of the light waves through the medium. (sciencedaily.com)