Vol. 65. 



THE CALIFOKNIAN EARTHQUAKE OP 1906. 



that the hase from which the triangulation started was unaltered 

 hy the earthquake ; the latter is independent of it, for no conceivably 

 permissible alteration in the length of the base would make any 

 material change in the apparent relative movement of neighbouring 

 stations. I shall therefore deal first with this, and especially with 

 the movement of points near the fault-line. 



At the extreme south, a number of stations lying west of the 

 fault have been displaced south-eastwards by the combined effects 

 of the movements of 1868 and 1906, and it is probable that 

 part of this movement took place in connexion with the 1906 

 disturbance. The conditions in this region are, however, somewhat 

 different from those farther north : for here the fault-line trends 

 eastwards from its general course, and movement dies out as 

 a surface-phenomenon. If, for the present, we exclude these 

 stations from consideration, three facts stand out: (1) that all 

 stations to the east have moved south-eastwards, and all to the west 

 have moved north-westwards ; (2) that the south-easterly shifting 

 was less than the north-westerly ; and (3) that stations near the 

 fault-line have moved farther than those more remote. 



These facts are noticed in Messrs. Hayford & Baldwin's report : 

 according to their figures, the average displacement at 0'9 mile from 

 the fault-line on the eastern side was 51 feet, at 2-6 miles 2-8 feet, 

 and at 4 miles T9 feet ; on the west side the figures are, at 1*2 

 miles 9-7 feet, at 3-6 miles 7'8 feet. As a number of stations were 

 utilized in obtaining these averages, at which the displacement 

 attributed to the 1906 earthquake was deduced by inference, it 

 will be desirable to examine the evidence yielded by those stations 

 at which the 1906 displacements Avere directly determined. These 

 form three natural groups : the first consists of 7 stations near and 

 to the south of San Francisco, the second of 13 stations near Fort 

 Ross, and the third of 9 stations in the Point Arena neighbourhood. 

 Subdividing each of these groups according to direction from the 

 fault and again according to distance, we get the following result 

 for stations at a distance of 5 miles or less from the fault-line : — 



Tabular Statement allowing the average displacements of stations 

 within 5 miles of the fault. 





Under 21 miles. 



21 to 5 miles. 



No. of 

 Stations. 



Mean 

 Distance.] Shift. 



No. of 

 Stations. 



Me* 

 Distance. 



in 

 Shift. 



W. side of fault: 



San Francisco group . 



Fort Ross group 



Point Arena group ... 



E. side of fault : 



San Francisco group . 



Fort Ross group 



Point Arena group ... 



2 



7 

 1 



1 



1 5 



miles 



09 



1-3 

 0-9 



feet 



7-9 

 6-9 

 10-7 



2 

 5 



miles 

 35 



4-1 



feet 

 7-5 



8-5 



11 

 02 



1-3 



4-7 

 5-0 



2 

 T 

 1 



3-7 

 4-3 

 24 



0-7 



1-8 

 2-6 



