1921] Laiuson: The Mobility of the Coast Ranges of California 455 



had moved by strain creep up to 190Ga. The fault had also moved 

 from aa' to hV. At the time of the earthquake the small circle at B 

 was severed and the two semicircles were displaced, one to the north- 

 west and one to the northeast. They remained, however, on the line 

 bb\ But the geodetic survey showed that the semicircle on the west 

 side was at c and that on the east side at c'. The fault itself, therefore, 

 just as in the case of the Tomales Bay group, apparently shifted from 



Fig. 9 Fig. 10 



Fig. 9. Fort Eoss group. A small circle located at A in 1891 on the San 

 Andreas fault had moved .78 meters to B by strain creep up to 1906. By slip 

 and rebound in that year one half the circle moved 1.43 meters to C and the 

 other half 2.2 meters to D. 



Fig. 10. Point Arena group. A small circle located at A in 1891 on the San 

 Andreas fault had moved .7 meters to B by strain creep up to 1906. By slip 

 and rebound in that year one half the circle moved 2.43 meters to C and the 

 other half 2.23 meters to D. 



the position bb' to the position cc' ; and cc' is found to be practically 

 parallel to aa' and bb\ On the assumption that this shift is real, the 

 actual sudden change of position at the time of the earthquake for 

 points on the west side of the fault was from B to c, or 1.43 meters in 

 the direction 124° ; while the real movement on the east side was from 

 B to c', or 2.2 meters in the direction 333°. The total relative dis- 

 placement by slip on the fault, thus determined as the mean of six 

 stations on the west side and four on the east side is 3.5 meters. If, 

 instead of taking the mean absolute displacement of the points on each 

 side of the fault, I had used a curve such as is suggested by Hayford 

 and Baldwin^^ to determine the mean absolute displacement at the 



12 Earthquake Eeport, p. 133. U. S. C. and G. S. Ept. 1910, App. 5, p. 184. 



