20 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
at O” and took the position A”B” and C’D”; the slip D’B” equaled the displacement 
AA”; but the points A” and C”, of course, remained unmoved. 
A third experiment was made. A line A’C’ (fig. 9) was drawn after the jelly had 
been distorted, exactly as in the last experiment; the left piece of wood was then moved 
0.5 em. further and the line was distorted into A”C’; when the jelly slipt and resumed 

its unstrained position, the line AZOC’ broke into the two lines A”B’ and C’D’; the slip 
D’B’ was 1.5 cm., equal to the total displacement of the left piece of wood from its original 
position when the jelly was unstrained; and the distances of points on the line A’B’ 
near the fault, measured from the line A’C’, were about twice the distances from A’C’ 
of points on the line C’D’ at equal distances from #’. But at a distance from #t’ the 
displacements on the left were more than twice as great as those on the right; which agrees 
with the relative displacements actually observed (vol. 1, p. 134). With the exception 
of the straightness of the lines the last experiment reproduces exactly the characteristic 
movements which took place at the time of the California earthquake. The letters in 
figs. 7, 8, and 9 correspond to those in figs. 5 and 6. 
THE INTENSITY OF THE ELASTIC STRESSES. 
The forces which caused the rupture at the fault-plane are measured by the distortion 
of the rock there, and if we can determine the angles which the lines A”O and C”O 
(fig. 6) make with AC at O, we can estimate these forces; these angles can be deter- 
mined approximately from the analogous angles at B’ and D’. Let us determine what 
the latter angles are. The lines A”B’ and C”D’ are constructed from Dr. Hayford’s 
summary of the results of the surveys already mentioned and have the same curvature 
as the lines A”B’ and C’D’ in fig. 5; the data (vol. 1, p. 183) may be collected in a 
table as follows: 
TaBLE 3.— Displacements between II and III Surveys. 


AVERAGE DISTANCE FROM DISPLACEMENT BETWEEN II 
No, or Fau.r. AND III Surveys. 
Points. 
East. West. South. North. 
km. km. m. m. 
10 15 . 1.54 fu85 
3 4.2 A 0.86 dee 
1 6.4 sa 0.58 ae 
12 ae 2.0 ridings 2.95 
re Ae 5.8 2.38 
il 37.0 1.78 



