Free oscillations excited by the Alaskan earthquake

Periods of spheroidal and toroidal modes are determined from strain and pendulum recordings of the Alaskan earthquake of March 28, 1964. Combinations of orthogonal strains provide a means for separation and identification of mode types. Results in general confirm the measurements made after the Chilean earthquake of 1960, with a few minor differences attributed to misidentification in the earlier data. A comparison of the mode excitation of the Alaskan and Chilean earthquakes at a single station yields only the estimate that the temporal and spatial extent of these two sources were comparable even though the force systems may well have been quite different.