The tsunamigenic earthquake of April 1, 1946, in the Fox Islands (Aleutian island arc)

An interpretation of the type, size, and location of the source of the Aleutian earthquake on April 1, 1946, which was characterized by the highest intensity (I = 4), is proposed. The earthquake source is a subvertical reverse fault striking along the island arc and dipping at an angle of 85A degrees toward the deep-sea trench. The reverse fault is located in the lower part of the island slope, within the eastern termination of the Aleutian terrace. The western end of the reverse fault is located in the area of the Krenitsyn Islands (lambda similar to 165A degrees W), where the pattern of isobaths changes, and an abrupt widening of the shelf part of the Fox Islands takes place. Large (M (S) similar to 7) shocks, preceding the 1946 earthquake, occurred here in 1940, 1942, and 1944. Structural inhomogeneities in the island slope in the area of the Sanak Islands (lambda similar to 162A degrees W) determine the eastern edge of the source-reverse fault, whose length within the specified boundaries is about 200 km. The mean magnitude of the earthquake corresponding to such a source is similar to 8.3. According to the regular relation between the rupture length and the mean movement, the vertical displacement of the ocean floor in the source region could attain 5-6 m. A significant vertical displacement of the ocean floor over its large length (similar to 200 km) was responsible for the high tsunamigenic ability of this earthquake. A favorable combination in the source area of the topographic and other conditions necessary for the tsunami formation could additionally contribute to an increase in the intensity of the tsunami. The earthquake of April 1, 1946, in the Fox Islands, as well as the tsunamigenic earthquakes of March 9, 1957, in the Andreanof Islands and February 4, 1965, in the Rat Islands, does not belong to the class of "slow" earthquakes.