Tsunami Refraction Diagrams by Digital Computer

Important wave parameters to be considered for tsunami model studies are wave height, period, and orientation. The first two of these parameters can be determined by marigraphic measurements or by visual observations; however, wavefront, orientation, which is an important variable in the construction and operation of a hydraulic model, has never been accurately observed at the problem site (Crescent City, California). A digital computer program was written to plot wave rays from tsunami sources to obtain tsunami-front orientations in the Crescent City area. The refraction diagrams are checked by comparing the computed and actual arrival times of the initial wave fronts. The actual arrival times were obtained from recording tide stations at Crescent City and Hilo, Hawaii. Initial wave-front orientations near the earthquake epicenter are either assumed or taken from the literature. The computer program has been successfully tested against a closed form solution for the refraction around a selected island shape. The technique also compensates for the distorted picture of the earth's surface as presented on a Mercator projection of that surface.