Fig. 53.—Distribution of preliminary Shocks in Space. (Davison.)[ToList]
Thus, the preparation for the great earthquake is shown, first, by the increased frequency of earthquakes originating within its meizoseismal area; and, secondly, by the uniformity in the distribution of epicentres throughout the same region, the marked concentration of effort which characterises the after-shocks being hardly perceptible during the years 1890-91.
Fig. 54.—Distribution of After-shocks in Space (November-December 1891). (Davison).[ToList]
Distribution of After-shocks in Space.—We have seen that the after-shocks were subject to a fluctuating decline in frequency, rapid at first, and more gradual afterwards. It is evident, from Figs. 54-57, that a similar law governs the area within which the after-shocks originated. During the first two months, epicentres occur over nearly the whole of the meizoseismal area, but afterwards they are confined to a smaller district, which slowly, though not continually, decreases in size.
Fig. 55.—Distribution of After-shocks in Space (January-February, 1892). (Davison.)[ToList]