32 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
It seems probable that a very long period will elapse before another important earth- 
quake occurs along that part of the San Andreas rift which broke in 1906; for we have 
seen that the strains causing the slip were probably accumulating for 100 years. There 
have been no serious earthquakes reported along this part of the rift, except at its south- 
ern extremity, since the country has been occupied by white men, altho strong earth- 
quakes have occurred in neighboring regions. It seems probable that more consistent 
results might be obtained regarding the periodicity of earthquakes if only the earth- 
quakes occurring at exactly the same place were considered in the series. The Messina 
earthquake of December 28, 1908, seems to have resulted from a movement on the great 
fault passing thru the Straits of Messina. The last strong movement at the same place 
seems to have occurred in 1783; tho the Calabrian earthquake of 1905 may have been 
caused by a movement on another part of the same fault. 
It is quite possible, however, for strong earthquakes to occur on neighboring faults 
after short intervals. The ruptures of the Haywards fault in 1868 and of the San 
Andreas fault in 1906 are a fair example, tho the interval is rather long. The Iceland 
earthquakes of 1896, already referred to, illustrate this much better. Five strong 
shocks occurred within fifteen days; but they were central, not in the same region, 
but in regions successively more and more to the west. . 
When a rupture occurs, the elastic rebound may carry the sides of the fault beyond 
their positions of no strain, and the friction may temporarily hold them there; or the 
friction may be so great that they do not entirely reach these positions. In either 
case further shocks may be expected before long; but they are apt to be slight, and 
are more likely to constitute after-shocks than independent earthquakes. 
