136 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
The amplitudes recorded are very small and are not very regular. The nearest point 
where a determination could be made for the first preliminary tremors was Sitka, and there 
the earth-amplitude was just under 0.6mm. At Ottawa it had already diminished very 
greatly, being about one-hundredth as much for both components. These values are 
somewhat uncertain, as the periods were very near those of the pendulums. Table 17 
shows the amplitudes at a number of stations; in general they lie between 0.002 mm. 
and 0.02 mm. The reason for the absence of a progressive diminution is not at all clear. 
It does not seem to be sufficiently accounted for by differences in the foundation. It is 
possible that the discordance may be largely due to inaccuracy in the constants of the 
instruments, especially the omission of the solid friction, and also, possibly, to the 
application of the formula to parts of the record where the movement has not been 
sufficiently regular for the formula to apply accurately. 
During the second preliminary tremors there is a very large increase in the amplitude, to 
about 10 times that of the first preliminary tremors; we find the same kind of irregularity 
in the amplitudes at successive stations but we do not find the proportion between the 
amplitudes of the first and second preliminary tremors constant; at Leipzig, the amplitude 
of the second preliminary tremors was 10 times that of the first preliminary tremors, 
whereas at Jena it was 20 times as great. This probably indicates a lack of accuracy in 
the determination of earth-amplitudes. 
DURING THE REGULAR WAVES AND THE PRINCIPAL PART. 
In the megaseismic district. —The temporary nature of the vibrations makes it impos- 
sible to get satisfactory measures of the amplitudes, unless a permanent record of some 
kind is made. There are, fortunately, a few such records which enable us to form a rough 
conception of the amount of the movement. 
Professor Omori, guided apparently by the damage done, estimates that, on the filled-up 
grounds of San Francisco, the amplitude of the vibration was 50 mm. (2 inches), and the 
period 1 second. The distance from the fault was about 14 km. 
On the rock at Berkeley Observatory (distant 30 km.) the vertical component of the 
amplitude was 23 mm. (1 inch), and the horizontal component, according to the Ewing 
duplex pendulum, more than 11 mm. 
At Mare Island (distant 40 km.) Professor See estimated the horizontal amplitude in the 
soft made ground at 50 to 75 mm. from the displacement of loose dirt about piles which 
supported buildings (vol. 1, p. 212). 
At a number of stations in the megaseismic district, given in table 18, which were pro- 
vided with simple instruments, the amplitude of the movement was greater than the 
instruments could record, that is, in general, was greater than 10 mm.; and it is prob- 
able that it was several times greater. 
TABLE 18.— Amplitudes in the Megaseismic District. 
DISTANCE FROM 
AULT. 
STATION. CoMPONENT. DIsPLACEMENT. 
Los: Gatos - sear fe peas Horizontal 
San Francisco ... . Horizontal 
San Jose 5 as mea Horizontal 
Ogkiand 2) (se. aaa Horizontal 
Alameda) 2, 2.8. ieee Horizontal 
Vertical 
Horizontal 
North-south 
East-west 
Mare Island .° 2 i Horizontal 
Carson’ City =. i.e Horizontal 
Berkeley . 
Mount Hamilton 






1 Bull. Imperial Earthquake Investigation Commission, vol. 1, p. 19. 
