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456 Universitij of California Publications in Geology [Vol. 12 



fault, the total relative displacement would have been larger, since the 

 amount of rebound by slip is a function of proximity to the fault. 

 The relative displacement measured at the fault by this method is 

 5 meters, which checks well with 15 feet measured on offset fences, 

 etc. The component of the apparent shift normal to the San Andreas 

 fault is .44 meters, as compared with .57 meters for Chaparral when 

 this station is considered alone. The distribution of the relative dis- 

 placement on the two sides of the fault is, as before, indeterminate 

 under the assumption of real shift, unless we invoke the hypothesis 

 of equal elastic fling. If the elastic fling were the same on the two 

 sides of the fault at the time of the slip of 1906, then the direction of 

 the shift is 10° and its amount is .57 meters. 



Point Arena Group. — The Point Arena group of stations comprises 

 four on the ea.st side of the fault and six on the west. The data 

 necessary for their discussion may be tabulated as follows : 



Station 



Kilometers 

 from fault 

 trace 



Displacement 

 1891-1906 

 in meters 



Direction of 

 displacement 

 1891-1906 



Lane 



.2 E 



1.51 



340° 



Spur 



.0 E 



1.52 



324° 



Clark 



3.8 E 



.83 



329° 



Dunn 



3.9 E 



.79 



329° 



Arena 



7.6 W 



2.54 



161° 



Sinclair 



6.7 W 



2.57 



161° 



High Bluff 



6.8 W 



2.78 



159° 



Point Arena Lighthouse 



6.4 W 



2.45 



161° 



Arena Catholic Church 



5.7 W 



2.67 



163° 



Shoemake 



1.5 W 



3.27 



164° 



The directions of displacement on the west side are very consistent 

 and average 161°. On the east side they are fairly consistent and 

 average 330°. In considering this group I assumed that the rate of 

 creep was the same as at Chaparral, and that the direction of creep 

 was north. The direction of creep is somewhat more north for 

 Chaparral than for Tamalpais ; and if the direction changes the same 

 amount between Chaparral and Arena it would be about north at the 

 latter locality. I then plotted the record of each station in the manner 

 that I have illustrated in the cases of Tamalpais and Chaparral. In 

 this way I found the amount of displacement for each station from 

 the position which it occupied, not in 1891, but in 1906a. The values 

 for such displacements were then plotted in proper proportionate 

 distances from the fault line and a smooth curve, practically a straight 

 line, was drawn through the points as the locus of their positions. 



