1921] Laivson: The Mohility of the Coast Ranges of Calif ornia 453 



be somewhat larger. The actual maximum relative displacement at 

 the fault trace was 6.4 meters, on the Inverness road at the head of 

 Tomales Bay. 



In the foregoing discussion it has been stated that the direction of 

 transverse shift which brought the fault from the position &?>' to cc' 

 in figure 8 is indeterminate, and that, therefore, the distribution of 

 the total relative slip on the two sides of the fault is also indeterminate. 

 There are, however, some considerations which bear upon this question. 

 It seems probable from the remoteness of the fault from the locus of 

 no strain that the elastic fling at the time of the slip was approximately 

 the same on the two sides of the fault. If this be admitted tentatively 

 for the purpose of enquiring into its consequences then since the total 

 slip is known from the geodetic measurements, we have an independent 

 means of ascertaining the position on the fault of the small circle B 

 in figure 8 the moment before the slip occurred. It must have be(m 

 midway between the two semicircles c and c' . If we consider the slip 

 on the fault and the transverse shift separately and suppose the latter 

 to have followed the former, then since hh' is the total relative slip, 

 by the assumed principle of equal fling Blj should equal Bh' . As a 

 matter of fact they are equal by construction based on the data. But 

 if this be so then the only possible direction of transverse shift is 

 normal to the fault trace. I do not, however, lay stress upon this 

 assumed principle of equal fling since I know of no means of estab- 

 lishing its verity. Another consequence of the equality of fling, if it 

 could be relied upon, is that the rate of creep in the azimuth of the 

 fault may be found. Thus if be a small circle on the fault located, 

 let lis say, by survey I, and A the position of the semicircle on the 

 west side and B that of the one on the east side after the slip, then 

 AB 



AB is the total slip and— 2" is the elastic fling. The total creep in the 

 AB 



azimuth of the fault is — ^ OB ; and this divided by the time gives 



us the rate. 



If, on the other hand, the apparent transverse shift be not real, 

 but is to be explained as due to an erroneous assumption of the 

 immobility of the Mocho-Diablo base, much of the foregoing discussion 

 deals with an imaginary complication. It is perhaps worth noting in 

 connection with this luicertainty that, on the assumption that the 

 apparent shift is real and that the elastic fling is equal on the two 



AB 



sides of the fault, then the creep derived from the formula —r OB 



