Really scary! Here is a computer model of the maximum wave ampliture of the tsunami caused by the massive 8.9 earthquake today in the shores of Japan. This model has been created by the NOAA Center for Tsunami Research.
This National Oceanic and Atmospheric Administration (NOAA) Global bathymetry map image released on March 11, 2011 shows features of the ocean floor depth (or bathymetry) from a NOAA ETOPO-1 dataset. The image shows the entire Western Pacific basin. Notice how abruptly the Japanese islands rise out of the ocean. Other coastal Asian areas have much more gradual slopes. The islands and mountain ranges throughout the ocean, visible in this imagery, also affect the tsunami travel time and speed. In the open ocean, tsunamis can travel at speeds up to 500 mph (800 kph). This momentum is what creates such a destructive force as the wave moves inland. Tsunami waves rolled thousands of miles across the Pacific Ocean after a massive earthquake off Japan and washed ashore in Hawaii early March 11, 2011, but the tourist hotspot appeared to escape major damage. As sirens blared and Hawaiian authorities rapidly evacuated low-lying areas, the Pacific Tsunami Warning Center reported wave changes at Waianae Harbor at around 3:24 a.m.