Part 18 (1/2)

Seism. Soc. Am., Vol. 2, 1912, pp. 40-91, 124-133.]

[Footnote 132: The only other explanation that seems to have any standing is the psychological hypothesis of Montessus de Ballore as given in Les Tremblements de Terre. He attributes the apparent seasonal variation in earthquakes to the fact that in winter people are within doors, and hence notice movements of the earth much more than in summer when they are out of doors. There is a similar difference between people's habits in high lat.i.tudes and low. Undoubtedly this does have a marked effect upon the degree to which minor earthquake shocks are noticed. Nevertheless, de Ballore's contention, as well as any other psychological explanation, is completely upset by two facts: First, instrumental records show the same seasonal distribution as do records based on direct observation, and instruments certainly are not influenced by the seasons. Second, in some places, notably China, as Drake has shown, the summer rather than the winter is very decidedly the time when earthquakes are most frequent.]

[Footnote 133: A comparison of tropical hurricanes with earthquakes is interesting. Taking all the hurricanes recorded in August, September, and October, from 1880 to 1899, and the corresponding earthquakes in Milne's catalogue, the correlation coefficient between hurricanes and earthquakes is +0.236, with a probable error of 0.082, the month being used as the unit. This is not a large correlation, yet when it is remembered that the hurricanes represent only a small part of the atmospheric disturbances in any given month, it suggests that with fuller data the correlation might be large.]

[Footnote 134: Ellsworth Huntington: The Geographic Work of Dr. M. A.

Veeder; Geog. Rev., Vol. 3, March and April, 1917, Nos. 3 and 4.]

[Footnote 135: Frank Schlesinger: Variations of Lat.i.tude; Their Bearing upon Our Knowledge of the Interior of the Earth; Proc. Am. Phil. Soc., Vol. 54, 1915, pp. 351-358. Also Smithsonian Report for 1916, pp.

248-254.]

[Footnote 136: Harold Jeffreys: Causes Contributory to the Annual Variations of Lat.i.tude; Monthly Notices, Royal Astronomical Soc., Vol.

76, 1916, pp. 499-525.]

[Footnote 137: John Milne: British a.s.sociation Reports for 1903 and 1906.]

[Footnote 138: C. G. Knott: The Physics of Earthquake Phenomena, Oxford, 1908.]

[Footnote 139: A. C. Lawson: The Mobility of the Coast Ranges of California; Univ. of Calif. Pub., Geology, Vol. 12, No. 7, pp. 431-473.]