42 SOUTHERN CALIFORNIA GEOLOGY 



SEISMIC CONDITIONS ARE PROBABLY 

 DECLINING 



It is my opinion that earthquake conditions are be- 

 coming less severe in Southern California, and if such 

 things could be quantitatively determined, it would be 

 found that the region is in the declining curve cf 

 a great seismic cycle. Both the surface geology and 

 physiography, as shown in other portions of this re 

 port, show that the time of great movement was prin- 

 cipally in the Pleistocene epoch — the great Ice Age — 

 and we are living in a time of decreasing earth move- 

 ments, whose tendencies are towards the compacting of 

 the strata to geologic stability and temporary quies- 

 cence. 



These movements, although still somewhat in evi- 

 dence, are not going on today at the rate which they did 

 in the past nor are they apt to increase in the future. 



If these hypotheses be true, it also appears to us 

 that the present-day shakes are merely the lighter 

 after-effects of a former time of greater movement 

 during the Glacial Epochs, rather than the virile mani- 

 festation of a new cycle of activity. Therefore it is 

 improbable that the earthquake-snaps in Southern 

 California are going to increase in severity in the im- 

 mediate future or attain the magnitude that they did 

 in the Pliestocene epoch of the past. 



It is probable that some fifty thousand years from 

 now the down curve of the movement towards quies- 

 cence may cease, and then they may begin to increase 

 again. But what may happen to the human race by 

 that time no one knows. 



