=The measure of displacement.=—To afford some measure of the displacements which have been observed upon earthquake faults, it may be stated that the maximum vertical throw measured upon the fault in the Neo valley of Japan (1891) was 18 feet, in the Chedrang valley of Assam (1897) 35 feet, and of the Alaskan coast (1899) 47 feet. Large sections of land were bodily uplifted in these cases within the space of a few seconds, or at most a few minutes, by the amounts given. The largest recorded lateral displacement measured upon an earthquake fault is about 21 feet upon the California rift after the earthquake of 1906; though an amount only slightly less than this is indicated in the shifting of roads and arroyas dating from the earthquake of 1872 in the Owens valley, California. Fault lines once established are planes of special weakness and become later the seat of repeated movements of the same kind. ┌──────────────────────────────────────────────────────────────────────┐ │ PLATE 3. │ │ │ │ [Illustration: _A._ An earthquake fault opened in Formosa in 1906, │ │ with vertical and lateral displacements combined (after Omori).] │ │ │ │ [Illustration: _B._ Earthquake faults opened in Alaska in 1889, on │ │ which vertical slices of the earth’s shell have undergone individual │ │ adjustments (after Tarr and Martin).] │ └──────────────────────────────────────────────────────────────────────┘ [Illustration: FIG. 60.—Diagram to show how small faults in the rock basement may be masked at the surface through adjustments within the loose rock mantle.] The greater number of earthquake faults are found in the loose rock cover which so generally mantles the firmer rock basement, and it is almost certain that the throws within the solid rock are considerably larger than those which are here measured at the surface, owing to the adjustments which so readily take place in the looser materials. Those lighter shocks of earthquake which are accompanied by no visible displacements at the surface do, however, in some instances affect in a measure the flow of water upon the surface, and thus indicate that small changes of surface level have occurred without breaks sufficiently sharp to be perceived (Fig. 60). Intermediate between the steep escarpment and the masked displacement just described is the so-called “mole-hill” effect,—a rounded and variously cracked slope or ridge above the position of a buried fault (Fig. 61). [Illustration: FIG. 61.—Diagram to show the appearance of a “mole hill” above a buried earthquake fault (after Kotô).]