SOURCE MECHANISM OF THE TSUNAMI OP MARCH 28, 1964 IN ALASKA

Abstract

The distribution of permanent, vertical crustal dislocations, the times and directions of early water motion in and around the generation area, and the unusual low frequency character of the tsunami record obtained from Wake Island, all suggest that the tsunami associated with the great Alaskan earthquake of March 28, 1964 was produced by a dipolar movement of the earth's crust, centered along a line running from Hinchinbrook Island (Prince William Sound) southwesterly to the Trinity Islands. The positive pole of this disturbance encompassed most of the shallow shelf bordering the Gulf of Alaska, while the negative pole lay mostly under land. Thus, the early effect was the drainage of water from the shelf into the Gulf, thus generating a long solitary wave, which radiated out over the Pacific with very little dispersion. Tilting of Prince William Sound to the northwest produced strong seiching action in the deep, narrow adjacent fjords, thus inundating inhabited places already suffering from earth shock and slumping of the deltas on which they were situated. Preliminary calculations indicate that the initial positive phase of the tsunami contained about 2.3 x 102lergs of energy, as compared with 2.7 x 1022ergs computed for the tsunami of March 9, 1957 in the Andreanof Islands.