S-Wave studies of earthquakes of the North Pacific, Part I: Kamchatka

Abstract

The polarization of S waves at stations distributed azimuthally about the source is examined for each of twenty-three Kamchatka earthquakes of 1950-1960. In nineteen of these earthquakes the P and S wave data are in agreement with a double couple source as the point model of the focal mechanism. The S waves indicate a uniform mechanism which repeats itself from earthquake to earthquake and from which it may be inferred that the axes of greatest and least stress at the foci tend to lie in a vertical plane normal to the trend of the Kamchatka-Kuriles arc. The axis of least stress usually plunges almost vertically under the continent, but may also plunge less steeply, at angles as low as 45 degrees. At least two earthquakes may be represented by a single couple source.