SEASONAL PERIODICITY IX EARTHQUAKES 

 By William A. Spalding. 



Air. Stephen Taber's study of earthquakes in the region 

 of Charleston, South Carolina, during the period 188r)-1913'' 

 is a valuable contribution to the data and theory of seismol- 

 ogy. I am particularly interested in his discussion of peri- 

 odicity in earthcjuake frequency, as that is a phase to which 

 my attention has been directed during the past twenty years. 

 Mr. Taber's curves are deduced from a monthly distribution 

 of the 395 earthquakes under observation, and are analyzed 

 mathematically for annual, semi-annual and quarter-yearly 

 periodicities, using the methods adopted by Dr. Knott. The 

 study is made more interesting by dividing the entire period 

 into two epochs: first, 1886-1897. with its record of 318 

 earthquakes; and second, 1898-1913, with 77 earthquakes. 

 While the investigator concedes that the number of earth- 

 quakes in the latter inter\'al is too small by itself to be of 

 value in determining periodicities, still the fact that the two 

 curves thus separately deduced correspond closely in their 

 characteristics lends additional interest to the study and is 

 mutually confirmatory. This double testimony is again con- 

 firmed by curves based upon earthquake-days during the 

 same intervals, thus eliminating a number of minor shocks 

 and reducing the problem to a simpler basis. ]\Ir. Taber's 

 conclusions are as follows :- 



"There is probably no real semi-annual periodicity in the 

 earthquake activity of this region (Charleston. S. C.) Annual 

 and quarterly periodicities are indicated, though the data are 

 most too meager to determine this matter with certainty. 

 However, the marked similarity of the difi^erent curves 

 strongly supports the hypothesis that there are real annual 

 and quarter-yearly periodicities." 



My purpose in writing this is to institute another sea- 

 sonal comparison, varying slightly from Mr. Taber's', but 



•"Seismic Activity in the .'Atlantic Coastal Plain near Charleston, 

 South Carolina," a paper read in part .before the Le Conte Scientific Society 

 at the University of South Carolina February 6, 1914, and publislied in the 

 Bulletin of the Seismological Society of America, 4, 108, Septe'mber, 1914. 



'Ibid., p. 123. 



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