PERMANENT DISPLACEMENTS OF THE GROUNDS. 
THE RESULTS OF THE SURVEYS. 
Accurate surveys of a part of the region traversed by the fault-line of 1906 were made 
by the U. 8S. Coast and Geodetic Survey at various times. These have been grouped 
for the sake of discussion into three periods, namely: I, 1851-1865; II, 1874-1892; 
IIf, 1906-1907. These surveys, as discust by Messrs. Hayford and Baldwin (vol. 1, 
pp. 114-145), show that in the intervals between the surveys certain definite displace- 
ments of the land took place. They bring out especially well the displacements which 
took place in the region north of San Francisco and the Farallon Islands during the 
time between the II and III surveys, an interval which included the earthquake of 
1906. The field observations and the surveys were complementary; the former deter- 
mined the relative displacements at the fault-line, and the latter the displacements at a 









ee 5. 

distance from it. The results of Messrs. Hayford and Baldwin may be exprest by fig. 5; 
they show that the displacements reached a maximum at the fault and were smaller 
as the distance from the fault was greater, in such a way, that a line which, at the time 
of the II survey, was straight, as A’O’C’, had, at the time of the III survey, been broken 
at the fault and curved into the form A”B’, D’C’. And, altho at a few points there is 
an indication of a compression or an extension at right angles to the fault, generally the 
movement was parallel with it. The figure is drawn to scale from the summary on 
page 133 (vol. 1) and shows how the displacements diminish with the distance from the 
fault. The scale of displacements is 1,000 times that of distances; the curvature of the 
lines is so very small that it would be imperceptible if the two scales were the same. 
The known length of the fault is about 435 km. (270 miles) and it is quite possible 
that it may be somewhat longer below the surface. Whatever may be its length, the 
fault terminates at some points beyond which no slip took place; the eastern side of 
the fault moved towards the southern region of rest and away from the northern region 
of rest; and the western side of the fault did just the opposite; there must have resulted 
near the northern end of the fault a compression of the land on the western side and an 
extension on the eastern; and near the southern end the extension must have been on 
16 
