The temporal evolution of the source mechanism is retrieved for the October 13, 1963 Kurile Islands earthquake by applying centroid moment tensor inversions to successively different narrow frequency windows between 2 and 12.5 mHz. The lateral heterogeneity effect is corrected using model M84A of Woodhouse and Dziewonski [1984>. To the first approximation the frequency-dependent scalar moment follows an &ohgr;-2 decay law and the origin time shift is frequency independent, which can be simply explained by an isoscele source time function 140s long and a total moment release of 62¿1027 dyne.cm. The expansion of the moment rate functions in terms of spline functions enables to retrieve a smooth temporal change of the moment tensor. This second inversion yields a total moment of 71¿1027 dyne.cm with a peak activity at about 70s after the onset in a total source time of 250s. The mechanism has remained unchanged during the main stage. The occurrence of back-slip to the amount of 6.5% of the total moment is implied for the last 80s. ¿American Geophysical Union 1992