THE EARTH MOVEMENT ON THE FAULT OF APRIL 18, 1906. 131 
would be produced at Loma Prieta. Taking the uncertainty in regard to the estimated 
stability of Santa Ana into account as well as the possible errors in the triangulation, 
the following estimates of the uncertainties of the apparent displacements were made. 
The displacements of Loma Prieta in 1906 and 1868 (see tables 1 and 2) are both 
certain. 
The displacements of Black Mountain, Santa Cruz Azimuth Station, Gavilan, Point 
Pinos Light-house, and Point Pinos Latitude Station, as shown in table 3, are also certain. 
These are all combined displacements of 1868 and 1906. These stations were not deter- 
mined between 1868 and 1906, hence it is not possible to determine directly from the obser- 
vations the separate displacements. If it be assumed that the displacements in 1868 of 
the last four of these points were the same as that observed for Loma Prieta (see table 2), 
then the inferred displacements for each of these points in 1906 is as shown at the end 
of table 1. These inferred displacements for these points are, however, very doubtful as 
they depend upon a determination of the displacement of 1868 at a single point, Loma 
Prieta, which is 24 kilometers (15 miles) from Santa Cruz Azimuth Station and more 
than 48 kilometers (80 miles) from each of the other stations. It should be noted also 
that the displacement of Loma Prieta in 1868, which is certain, is very different from 
that of the other four points, Mount Tamalpais, Farallon Light-house, Chaparral, and 
Ross Mountain, for which the displacements of 1868 have been determined directly by 
observations. It is a displacement to the southward instead of to the northwestward 
and is much larger than for the other three points. 
The determination of the displacement of Mount Toro as shown in table 1 is some- 
what uncertain. There is still more uncertainty in regard to the apparent gap late 
ment at Santa Cruz Light-house. 
The very small apparent displacement, 0.12 meter (0.4 foot), of the Lick Observatory 
small dome in 1906 is probably due to errors of observation. 
The two points in this group to the eastward of the fault show apparent displacements 
in 1906 in accordance with the laws deduced from other groups: Lick Observatory, far 
from the fault, 36 kilometers (22 miles), having an apparent displacement 80 small as to 
be uncertain; and Loma Prieta, within 4.8 kilometers (8.0 miles) of the fault, having an 
apparent displacement of 0.97 meter (3.2 feet) in a southerly direction and within 9° 
of being parallel to the fault which here has an azimuth of about 312° (48° E. of 8.). 
Mount Toro is the only station to the westward of the fault in this group for which 
a determination of the displacement of 1906 is not very doubtful. The displacement in 
1906 of 0.95 meter (3.1 feet) at Mount Toro is in a northerly direction with a slight ineli- 
nation to the westward in fair agreement with the deduced laws. Mount Toro is beyond 
the end of the portion of the great fault of 1906 which has been traced on the surface. 
The apparent displacement of Santa Cruz Light-house in 1906, of which the de- 
termination is doubtful, is closely parallel to the fault anil in a northerly direction, 
corresponding to other points to the westward of the fault. 
The inferred displacements of 1906 for four points shown at the end of table 1 are all 
very doubtful, and little significance should be attached to them or to the fact that they 
are somewhat contradictory to each other and all have a southerly tendency, whereas all 
other points to the westward of the fault of 1906 moved in a northerly direction. As a 
check on this conclusion, it should be noted that the inferred displacement for 1906 for 
Santa Cruz Azimuth Station differs by 72° in direction and 1.26 meters (4.1 feet) in 
amount from the observed displacement of 1906 for Santa Cruz Light-house, a point only 
3.9 kilometers (2.4 miles) away. The observed displacement for Santa Cruz Light-house 
is much less uncertain than the inferred displacement for Santa Cruz Azimuth Station 
and hence the contradiction throws additional doubt on the latter and the other three 
points for which the inference is made in like manner. 
