THE 



QUARTERLY JOURNAL 



OF 



THE GEOLOGICAL SOCIETY OF LONDON. 



Vol. LXXVII 



FOR 1921. 



1. A Seasonal Yaeiatiois" in tlie Frequency of Earthquakes. 

 (Second Communication.) B}^ Richard Dixox Oldham, 

 F.E.S., F.G.S. (Read November 17th, 1920.) 



In an earlier communication to this Society ^ it was shown that 

 there is a slight excess of frequency of earthquakes, above the 

 general average, during the day in summer and during the night 

 in winter. It was also pointed out that this might possibly be a 

 result of the unequal range of variation of the gravitational stresses 

 ;set up by the sun, and, if so, might be expressed in the form that 

 there was an excess of frequency of earthquakes during that half 

 • of the da}^ which contained the ujjper meridian passage when the 

 declination of the stress-producing body and the latitude of the 

 place were of the same name, and during the half which contained 

 the lower meridian passage when they were different. If this were 

 the true statement of the variation, a similar effect ought to be 

 noticeable, and of greater amplitude, when the record was tabulated 

 by lunar time and declination. Such Avas actually found to be the 

 ■case in the only record already tabulated in a form permitting 

 the application of the test, but the number of shocks contained 

 in this record was not large enough to give more than yqyy small 

 weio'ht to the numerical values obtained from it. 



Since then I have been able, with the assistance of the Govern- 

 ment grant of the Ro^^al Society, to prepare a fresh tabulation of 

 the records of Italian earthquakes b}^ lunar, as well as by solar, hour- 

 angle and declination. The period chosen Avas the 19-3^ear lunar 

 cycle covering the years 1896 to 1911^, this being the period for 



1 Q. J. G. S. vol. Ixxiv (1918-19) pp. 99-104. 

 -Q. J. G. S. No. 305. B 



