GENERALIZATIONS CONCERNING EARTHQUAKES 49 



FUTILITY OF ATTEMPTS TO ASCERTAIN LAWS 

 OF PERIODICITY IN CALIFORNLA. 



Such meager data as we possess concerning Cali- 

 fornia seismicity has been closely scanned in hopes of 

 ascertaining some law whereby future earthquakes 

 may be predicted, and several attempts to discover 

 laws of periodicity have been made. But alas, the 

 seismicity has been too slight and the records too in- 

 complete for coming to satisfactory conclusions. 



If data were as abundant and running through the 

 centuries in California as in Japan, Italy, and Pales- 

 tine, or if we had but one rift-zone upon which to blame 

 the individual quakes, prediction might, to a degree, be 

 possible. 



Willis has concluded that there is an interval of 

 about thirty years between the maximum shocks in 

 Northern California, and he has probably had this in 

 mind in his prophecies concerning Southern California, 

 for he fixes the date of the next great release in this 

 part of the State as about three to ten years from now, 

 which would be about 30 years since the San Francisco 

 earthquake of 1906. 



Townley states that the shocks of 1812, 1857, 1872, 

 and 1906, concerning all of which except the latter 

 the data were very incomplete, were the most destruct- 

 ive. The intervals between these are forty-five, fifteen, 

 and thirty-four years. Not much rhythm in that. 

 He also notes that for forty-five years after the earth- 

 quake of 1812 until 1857, there was not another severe 



one. 



Others have deduced an approximately 50-year 

 period from the fact that the greater California 



