146 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
NOTE ON THE COMPARISON OF THE FAULTS IN THE THREE EARTHQUAKES OF 
MINO-OWARI, FORMOSA, AND CALIFORNIA. 
By F. Omori. 
The three great earthquakes of Mino-Owari (Central Japan) on October 28, 1891, 
of Kagi (Formosa) on March 17, 1906, and of California on April 18, 1906, were oleh 
accompanied by the formation of remarkable geological faults, whose total lengths were 
about 100, 50, and 430 kilometers respectively. The aistocatign in the California 
earthquake was formed partly along, and partly off, the coast of California, belonging to 
the category of longitudinal faults. 
The dislocation in the Mino-Owari and Kagi earthquakes were, on the other hand, 
formed nearly at right angles to the course of the Main Island (Nippon) and the axis of 
Formosa Island respectively, both belonging to the category of transverse faults. 
SAN FRANC/SCO 
EARTHQUAKE 

3" a 





FORMOSA 
EARTHQUAKE 
MOUNTAINS 
V/s 
MINO- OWAR/ 
EARTHQUAKE 
—<—<——= 
SE. pee 
Fig. 43 a.— Full line is fault (ascertained). Shaded part is depressed region. Dotted line is probable 
continuation of fault. Lightly shaded part represents probable depression. Arrow indicates the 
direction of maximum (vibratory) motion. 
Notwithstanding these differences, there are certain similarities among the three cases. 
Thus, in each of the three earthquakes, the direction of motion at different places in the 
immediate neighborhood of the fault was not perpendicular, but more nearly parallel, 
to the strike of the latter. This seems to indicate that the formation of the faults was 
mainly due, in each case, not to such actions as a simple falling down or sudden creation 
of a cavity underground, but to the existence of shearing stresses in the plane of frac- 
ture possibly of two opposing forces acting either from the center toward both ends of 
the fault-line, or toward the center from both ends. 
The accompanying figure is a diagrammatic illustration of the three faults, the line ab 
indicating, in each case, a straight line (say, road) which suffered a shearing movement in 
such a way that the part b on the depressed side was displaced to the new position b’, 
and generally transformed into a curve. 

