150 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
ments are separated. These stations are found to have moved in a nearly north direction 
an average amount of 1.56 meters in the interval between “before 1868” (1856-1860) 
and “after 1868’ (1874-1891). Since the values upon which this average is based were 
arrived at in part by methods of interpolation, there is no great variation from the average 
at any of the ten stations. The interval within which this northerly movement took place 
is rather indeterminate, but may be placed doubtfully at 32 years. 
Under the hypothesis here presented this movement continued at a probably uniform 
rate for the next 16 years up to the time of the earthquake of 1906. This would give usa 
total northerly movement for the interval from 1856-1860 to 1906 of 2.34 meters. Now 
the northerly component of the combined earlier and 1906 movements, shown in table 3 
of Hayford and Baldwin’s paper, is on an average 4.95 meters for the five stations west 
of the feult-line. This includes thé sudden movement of 1906 plus the slow creep of 
2.34 meters above deduced. The value for the northerly component of the sudden move- 
ment of those points in 1906 is thus 4.95 —2.34, or 2.61 meters. Similarly the southerly 
component of the combined movements for the five stations to the east of the fault is 
found to be on the average 0.09 meters. The southerly component of the sudden move- 
ment of 1906 was therefore 0.09+ 2.34, or 2.43 meters. The absolute movement on the 
two sides of the fault on April 18, 1906, was thus nearly the same in amount. 
The reference of the earlier movement to a slow creep thus appears to harmonize with 
and therefore tends to confirm the a priori assumption that the absolute movement of 
1906 should have been the same on both sides of the fault. Were data available as to 
the time at which other groups of stations were determined in position, it is probable that 
a similar result would be reached. We may consider, therefore, that the earlier move- 
ment is better explained on the hypothesis of slow creep, continuing up to April 18, 1906, 
than on the assumption that it occurred at or about the time of the earthquake of 1868. 
This conclusion applies to the region north of San Francisco Bay. To the south of the 
Bay the data available are inadequate for a satisfactory separation of the two movements, 
except in the case of Loma Prieta, and here the earlier movement appears to have been 
southerly. 
Another result of the geodetic resurvey which points to a slow creep of the region 
under strain precedent to April 18, 1906, is the distribution of the displacement on 
that date. The measurements of the absolute displacement on the two sides of the fault 
show that it was notably greater near the fault than at points remote from it. Thus 
if we imagine a series of points in a straight line transverse to the fault before the 
earthquake that line was so deformed that the segment to the west of the fault 
curved northerly and the segment to the east curved southerly in approaching 
the fault-trace. This deformation can be most readily explained by supposing that the 
series of points upon the assumed straight line were determined as to position in the 
first instance upon the surface of a portion of the earth under elastic strain, so that when 
relief was effected by rupture, the points tended to assume positions relative to one 
another which they would have had if they had been determined before the advent of the 
strain. 
It may be further pointed out that the conclusion reached by Hayford and Baldwin tothe 
effect that the absolute movement on the west side of the fault was on the average twice as 
great as the movement on the east side is founded on the assumption of the stability of 
the base-line Diablo-Mocho. In view of the unknown extent of the earth movement of 
April 18, 1906, it would seem preferable to make the assumption that the relief from strain 
was approximately distributed equally on the two sides of the fault and from this infer 
the amount of the southeasterly displacement of Diablo and Mocho. The assumption 
that Diablo and Mocho were not affected by the disturbance of April 18, 1906, is based 
on the following considerations: 

