Evaluation of tsunami amplitudes for the pacific coast of Canada

Abstract

Maximum tsunami water levels and currents along the British Columbia outer coast have been computed for waves originating from Alaska, Chile, the Aleutian Islands (Shumagin Gap) and Kamchatka. Three computer models have been developed to generate and propagate a tsunami from each of these source regions in the Pacific Ocean to the continental shelf off Canada's west coast, and into 20 separate inlet systems. The model predictions have been verified against water level measurements made at tide gauges after the March 28, 1964, Alaska earthquake. Simulated seabed motions giving rise to the Alaskan and Chilean tsunamis have been based on surveys of vertical displacements made after the great earthquakes of 1964 (Alaska) and 1960 (Chile). Hypothetical bottom motions have been used for the Shumagin Gap and Kamachatka simulations. These simulations represent the largest tsunamigenic events to be expected from these areas. Maximum wave and current amplitudes have been tabulated for each simulated tsunami in 185 key locations along the British Columbia coast. On the north coast of British Columbia, the Alaska tsunami generated the largest amplitudes. In all other regions of the west coast, the largest amplitudes were generated by the Shumagin Gap simulation. Wave amplitudes in excess of 9 m were predicted at several locations along the coast, and current speeds of 3 to 4 m/s were produced. The most vulnerable regions are the outer coast of Vancouver Island, the west coast of Graham Island, and the central coast of the mainland. Some areas, such as the north central coast, are sheltered enough to limit expected maximum water levels to less than 3 m. The computer models developed in this study are sufficiently general to be applicable to other tsunami-affected regions on the globe.