S-WAVE FOCAL MECHANISM STUDIES OF THE HINDU KUSH EARTHQUAKE OF JULY 6, 1962

Abstract

The mechanism of energy release at the origin or focus of the Hindu Kush earthquake of July 6, 1962, was studied by comparing recorded and theoretical P (longitudinal) and S (transverse) ground displacements produced at large distances from the focus by a system of forces acting at the origin. S-Wave polarization angles were used to solve a set of S-wave mechanism equations for the orientation of the two focal models considered, a single-couple and a double-dipole force system acting at a point focus. These models may be interpreted tectonically in terms of faulting and stress release, respectively, in the focal region. The double-dipole focal model gave the better fit to the S data and was also consistent with P-wave and surface-wave data for this earthquake. The mechanism type and force orientation of the 1962 Hindu Kush earthquake were shown to characterize 56 previous earthquakes in the same focal region. Hence the focal mechanism of all intermediate focus Hindu Kush earthquakes may be considered to be the double-dipole type with pressure and tension axes dipping at about 45°, roughly perpendicular to the trend of the Hindu Kush mountain system, and with the intermediate stress axis lying horizontally along the trend.