THE EARTH MOVEMENT ON THE FAULT OF APRIL 18, 1906. 147 
From the figure it will be seen that there existed in each fault what may be called the 
central point, where the disturbance of the ground is greatest and about which the shear 
and depression along the line of dislocation is more or less symmetrical. In the case 
of the Mino-Owari earthquake the central point was in the vicinity of the village of 
Midori in the Néo-Valley, where a very remarkable depression of the ground took 
place. The corresponding point on the Formosa fault was between the villages of 
Bish6 and Kaigenkso. In the California earthquake the northern half of the fault was 
in part under the ocean, but the central point was probably in the vicinity of the 
Tomales Bay, the greatest amount of disturbance having occurred there. 
The greatest vertical dislocation of 18 feet occurred in the Mino-Owari earthquake, 
while the greatest horizontal shear occurred in the California earthquake. In the lat- 
ter the vertical displacement was only 1 or 2 feet, while in the former there was also a large 
horizontal shear of about 18 feet. In the Formosa earthquake, whose magnitude was 
much smaller than the other two, the vertical and horizontal displacements of the ground 
were each of a moderate scale, the maximum amounts being 6 and 8 feet respectively. 
The maximum (vibratory) motion in the Mino-Owari earthquake showed a tendency of 
being directed from the central point toward each end; while, in each of the two other 
earthquakes, the same motion was, as far as can be ascertained, directed from one end 
toward the center. Again, the direction of the maximum (vibratory) motion was, in 
the Formosa earthquake, the same as that of the shear of the depressed ground. In the 
two other earthquakes, however, the reverse was the case. These differences are probably 
due to the variation in the manner of the action of the force along the fault-plane which 
finally produced the dislocations. 

REVIEW OF SALIENT FEATURES. 
The differential displacement of the earth’s crust effected by the movement on the 
San Andreas fault on April 18, 1906, may for convenience be resolved into two com- 
ponents, the horizontal and the vertical. Of these the horizontal movement was the 
more important and was susceptible of measurement, giving minimum values for the 
amount of displacement in this direction practically all along the trace of the fault, 
except at the extreme north and extreme south. The vertical movement was small com- 
pared with the horizontal, and was established halen only in the region to the 
north of the Golden Gate. 
Two kinds of evidence of vertical displacement were available. The first of these was 
the formation of scarps along the fault-trace, and the second was the change on portions 
of the coast of the level of the land Rianieely to sea-level. The scarps that appeared as 
features of the fault-trace were in part fresh facets where none had existed before the 
earthquake and in part accentuations or additions to old scarps due to former movements. 
In both cases exact measurements were rendered difficult by the drag of the soil along 
the rupture, and by the complication due to the larger horizontal movement. But 
making all allowances for the masking effect of drag of the soil, it is certain that the height 
of these scarps, or of the additions to old ones, was quite variable, even in the same general 
locality, within a range of a few inches up to about 3 feet. It is suggested that this 
_ variation is referable in considerable measure to the drag and adjustment of materials in 
the zone beneath the soil; so that the true displacement of the firm rocks lies between the 
extremes observed. 
The evidence of vertical displacement, based on the recognition of scarps, indicates a 
slight upward movement of the crustal block on the southwest side of the fault in the 
northern territory. South of the Golden Gate there is no very satisfactory or consistent 
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