THE EARTH MOVEMENT ON THE FAULT OF APRIL 18, 1906. 117 
Santa Ana. Some pointings were also taken on Gavilan, Point Pinos Light-house, and 
other stations in this vicinity, but not from a sufficient number of stations to furnish 
checked determinations independent of earlier determinations made before 1868. 
Secondary triangulation near Point Arena, forming the western extremity of the trans- 
continental triangulation, was done in the interval 1870-1892, the scheme being sub- 
stantially the same as that shown on map No. 25, except that all stations were occupied. 
The triangulation fixing the initial stations, Fisher and Cold Spring, has been published.' 
Tertiary triangulation in the vicinity of Fort Ross was done in 1875-1876, following a 
scheme similar to that shown on map No. 25, and starting from the line Bodega Head- 
Ross Mountain, as determined before 1868. 
Tertiary triangulation was done during various years from 1851-1899, extending from 
the vicinity of the Pulgas Base northward, spanning San Francisco Bay, to the Golden 
Gate, and thence southward to the vicinity of Colma, including stations shown on sketch 
No. 4 on map No. 25. The greater portion of this triangulation was done before 1868, 
but it is impracticable to separate the computations into two parts dealing with triangu- 
lation before and triangulation after 1868, respectively. 
PERMANENT DISPLACEMENTS PRODUCED BY THE EARTHQUAKES OF 1868 AND 1906. 
The following tables, Nos. 1, 2, and 3, show the permanent displacements of various 
points as caused by the earthquakes of 1868 and 1906. ‘These permanent displacements 
were determined by comparisons of the positions of identical points upon the earth’s 
surface as determined by triangulation done before and after the earthquakes in question. 
While for the sake of brevity in statement these movements are referred to the earth- 
quakes of 1868 and 1906, the evidence furnished by the triangulation simply indicates 
the fact that the displacements in question took place sometime during the two blank 
intervals within which there was no triangulation done fixing the points in question; 
namely, the interval 1866-1874, including the 1868 earthquake, and the interval 1892 to 
July, 1906, including the 1906 earthquake. Neither does the triangulation furnish any 
evidence indicating whether the displacements took place gradually, extending over 
many months and possibly years, or whether they took place suddenly. The evidence 
connecting the displacements of 1906 with the particular earthquake and indicating that 
they were sudden comes from other sources and will be commented upon later in this 
report. 
The permanent displacements indicated in tables 1, 2, and 3, must be carefully dis- 
tinguished from the vibrations of a more or less elastic character which take place during 
earthquakes. These vibrations die down in a few seconds, minutes, or hours. While 
they are in progress, a given point on the earth’s surface is in continuous motion along a 
more or less complicated path which turns upon itself and leaves the point, at the end of 
the vibration, near the initial position. The displacements indicated in tables 1, 2, and 
3, on the other hand, remain for years, possibly for centuries. They are of a permanent 
character. The displaced point remains in the new position until another displacement 
occurs in some later earthquake, or possibly by slow relief of strain accompanied by a 
creeping motion which causes a new permanent displacement. In tables 1, 2, and 3, the 
first column gives the name of the station by which it may also be identified on map 24 
or on map 25, or both. The second column gives its latitude at the time indicated in the 
heading. The third column gives the seconds, only, of the new latitude at the later time 
indicated in the heading. The fourth and fifth columns have the same significance with 
reference to the longitude that the second and third have with reference to the latitude 
of each point. The sixth column gives the north and south component of the displace- 

‘See The Transcontinental Triangulation, Special Publication No. 4, pp. 597-610. 
