DIRECTIONS OF VIBRATORY MOVEMENT, 367 
DIRECTIONS IN THE TOMALES-BOLINAS DISTRICT. 
By G. K. GiuBert. 
The greater number of my notes as to direction of motion pertain to the shifting 
of houses which left their foundations. Most of the houses in this district which were 
thus shifted stood on light, vertical, wooden piers or props, and fell from their props 
in shifting. The direction of falling was so frequently downhill as to show that the 
slope of the ground was an important factor, and this fact leads me to give little weight 
to data of this character. There were, however, a few houses which, resting upon flat, 
unyielding foundations, were shifted horizontally upon these, and their evidence is of 
ereater value. I think also that some weight should be given to the dominant direction 
in which houses of a group were thrown from their supports. 
Other data as to direction are found in the falling of men and animals, and these 
seem to me of value wherever a dominant direction affected a group of individuals. 
The direction of fall of a single individual might readily be conditioned by muscular 
reactions, and thus give little evidence as to the direction of the strongest tremor. 
I am led to question evidence from the shifting of furniture and the throwing down 
of objects on shelves, because in every instance the direction of vibration of a building 
appeared to be controlled partly by its structure. In view of these considerations, 
I regard the greater number of my observations on direction as of little significance, 
and do not report them. 
The clearest data as to direction are at Inverness. While there was much variety 
in the direction of motion of houses at that locality, it was quite clear that the dominant 
direction was westward. This also was the direction toward which 4 out of 5 water- 
tanks were shifted, and it was the direction toward which the mud on the bottom of 
Tomales Bay was moved. The locality is within less than 1 mile of the fault-trace and 
is on the southwest. side. 
At Point Reyes Station, situated 0.25 mile northeast of the fault-trace, the dominant 
direction of shifting was southward, and an exceptionally definite record was made by 
the school-house, which rested on a firm, flat foundation and was slid toward the south. 
At Olema, 2 miles southeast of Point Reyes Station and similarly related to the fault- 
trace, the dominant direction of motion was southwest, or toward the fault, the best 
single instance being that of a pool of water which spilt in that direction. 
At Dipsea Inn, 0.66 mile northeast of the fault, a pier running northeast from the 
spit was wracked toward its outer end. A line of telephone poles crossing the lagoon 
from the end of the pier was slanted in the same northeast direction. In the Inn objects 
were thrown southwest, and of three cottages injured two were shifted or wracked to the 
southwest. On the mainland nearby a part of Mr. Morse’s pier was wracked to the south- 
west. Collectively these facts indicate a dominant vibration to and from a northeast 
direction. 
At Willow Camp, close to the east angle of Bolinas Lagoon and about a mile northeast 
of the fault, several houses moved short distances toward the southeast. 
These various directions are platted in fig. 65. 
DIRECTIONS INDICATED BY MONUMENTS IN CEMETERIES. 
Prof. F. Omori attempted to determine the directions of the earth’s vibrations by a 
statistical study of the thrown monuments in the cemeteries south of San Francisco. 
The results of his investigations are shown graphically in fig. 66, in which it appears 
that the greater number of monuments were thrown in the quadrant between north- 
east and southeast. The mean direction of overthrow is N. 76° E., which is regarded 
