Page:Popular Science Monthly Volume 70.djvu/389



ITHIN nine months three regions in the western hemisphere, geologically closely akin but geographically distant one from the other, have been visited by earthquakes, causing an appalling loss of life and property. In all cases the disasters have been preceded by minor earth-shakings for years, and the areas were known to be in zones of earth-unrest. No warning, however, unless the tremors that occur at irregular intervals every month or two could be counted as such, has characterized these last disturbances. But these tremors must be regarded as the climax of a long-continued yielding to strain which has resulted in a series of minor breakings. This faulting culminated in a great fracturing of the earth's crust and a consequent destructive earth-shaking. The kindred conditions of these different areas appear to be, first, a considerable amount of differential relief only obtained where mountains are associated with marine depths; and, in the second place, where newer and less compacted sediments occur upon these slopes.

For several months previous to the afternoon of January 14, 1907, there had been no noticeable increase in the number or intensity of the customary slight shocks that occur in the Island of Jamaica every month or two. In Weather Report IV. of Jamaica, Mr. Maxwell Hall