The arrangement is mensual. Where the number of earthquakes in any month is above the average, the number is printed in large type; where below the average, in small type.
Earthquakes of the Nineteenth Century, chiefly from Perrey.
Key:
| Jan | January |
| Feb | February |
| Mar | March |
| Apr | April |
| May | May |
| Jun | June |
| Jul | July |
| Aug | August |
| Sep | September |
| Oct | October |
| Nov | November |
| Dec | December |
| Ave | Average per month |
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Ave | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Scandinavia and Iceland | 17 | 11 | 11 | 7 | 7 | 6 | 8 | 8 | 10 | 10 | 11 | 6 | 9·3 |
| British Isles and Northern Isles | 9 | 9 | 10 | 7 | 8 | 6 | 5 | 11 | 12 | 8 | 11 | 12 | 9·0 |
| France, Belgium, Holland | 27 | 17 | 21 | 13 | 13 | 8 | 15 | 17 | 15 | 17 | 21 | 25 | 17·0 |
| Basin of the Rhone | 12 | 12 | 8 | 3 | 3 | 2 | 2 | 4 | 6 | 6 | 8 | 14 | 6·6 |
| Basin of the Rhine and Switzerland | 15 | 17 | 13 | 12 | 11 | 6 | 12 | 11 | 10 | 17 | 24 | 25 | 14·0 |
| Basin of the Danube | 14 | 15 | 9 | 8 | 12 | 8 | 16 | 11 | 11 | 16 | 10 | 12 | 11·8 |
| Spanish Peninsula | 10 | 5 | 6 | 7 | 4 | 6 | 10 | 5 | 9 | 11 | 7 | 5 | 7·0 |
| Italian Peninsula, Sicily, Sardinia, and Malta | 44 | 44 | 48 | 43 | 40 | 34 | 41 | 46 | 27 | 45 | 26 | 39 | 39·0 |
| Turco-Hellenic Territory, Syria, Ægean Islands, and Levant | 22 | 20 | 10 | 10 | 16 | 15 | 14 | 22 | 14 | 17 | 12 | 14 | 16·0 |
| Northern Zone of Asia | 4 | 6 | 6 | 4 | 4 | 3 | 5 | 7 | 6 | 3 | 4 | 5 | 4·7 |
| 1876–1881, Japan (Tokio area) | 39 | 41 | 41 | 30 | 33 | 30 | 27 | 21 | 10 | 28 | 34 | 43 | 31·4 |
| Japan (large earthquakes) | — | 5 | 3 | 3 | 1 | — | 5 | 4 | — | — | 1 | 5 | 2·0 |
| Algeria and North’rn Africa | 5 | 2 | 6 | 7 | 3 | 2 | 2 | 5 | 1 | 4 | 8 | 1 | 3·8 |
| United States and Canada | 4 | 4 | 3 | 3 | 3 | — | 4 | 6 | 3 | 2 | 7 | 5 | 3·8 |
| Java, Sumatra, &c., 1873–4–5–7 and 9 | 35 | 30 | 38 | 33 | 22 | 36 | 27 | 40 | 24 | 35 | 30 | 26 | 31·0 |
| Mexico and Central America | 3 | 2 | 2 | 2 | 6 | 2 | 2 | 1 | 1 | 3 | 2 | 3 | 2·5 |
| Antilles | 9 | 8 | 19 | 12 | 12 | 10 | 9 | 16 | 12 | 10 | 13 | 12 | 11·8 |
| Cuba | 4 | 3 | 2 | 3 | 3 | 4 | 5 | 2 | 6 | 5 | 6 | 4 | 4·0 |
| Chili and La Plata | 14 | 10 | 14 | 8 | 19 | 11 | 16 | 15 | 16 | 9 | 27 | 8 | 13·9 |
| Peru, Columbia, Basins of Amazons, xvi–xix | 92 | 83 | 92 | 27 | 106 | 79 | 94 | 93 | 97 | 77 | 72 | 90 | 87·0 |
| New Zealand, 1869–79 | 31 | 27 | 37 | 23 | 22 | 31 | 27 | 36 | 37 | 21 | 27 | 23 | 28·5 |
| Jan. 1850, Dec. 1857 | |||||||||||||
| Northern Hemisphere | 153 | 162 | 143 | 161 | 126 | 124 | 141 | 156 | 154 | 171 | 151 | 168 | 150·0 |
| Southern Hemisphere | 72 | 43 | 61 | 66 | 46 | 42 | 53 | 39 | 54 | 55 | 57 | 46 | 53·0 |
| 1821–1830 | |||||||||||||
| Northern Hemisphere | 31 | 36 | 31 | 29 | 33 | 33 | 20 | 31 | 24 | 41 | 26 | 34 | 30·0 |
| Southern Hemisphere | 2 | — | 1 | 1 | 3 | 1 | 3 | 2 | 3 | 2 | 1 | 1 | 1·6 |
A glance at this table shows that for most countries in the northern hemisphere the rule that there are generally more earthquakes during the winter months—that is, from October to March—holds good. For countries which lie comparatively near to the Equator, and also for those countries in the southern hemisphere, the rule is not so clear. When examining this table it must be remembered that it does not enable us to judge of the relative frequency of earthquakes in different countries, inasmuch as the periods over which the records were taken are different in different cases.
To the above table might be added the records of P. Merian, who examined the earthquakes felt in Basle up to 1831. As a result he found that during the winter months eighty shocks had been felt, whilst during the summer only forty. Taking the records for the two hemispheres from 1850–1857, compiled by Kluge,[103] in the northern hemisphere we have in the months between October and March 948 shocks against 862 in the remainder of the year. In the same months in the southern hemisphere we have for the corresponding periods the numbers 337 and 300, and thus both hemispheres would appear to follow the same rule. If, however, we examine the table we see that the two seasons are not so pronounced for the southern hemisphere as they are for the northern, and that there may be two or three periods of maximum disturbance as has been previously indicated.
Earthquakes and the planets and meteors.—Just as the moon and the sun may exert an attractive influence upon the earth and cause earthquakes to predominate at certain seasons rather than at others, several investigators of seismic phenomena have thought that the planets might act in a similar manner.
M. J. Delauney, from a study of Perrey’s tables of earthquakes from 1750–1842, found two groups of maxima each with a period of about twelve years, one commencing in 1759 and the other in 1756. Two other groups with twenty-eight year periods respectively commence in 1756 and 1773. These groups coincide with the times when Jupiter and Saturn reach the mean longitudes of 265° and 135°. From this Delauney concludes that earthquakes have a maximum when the planets are in the mean longitudes just mentioned.
The increased number of earthquakes, especially in November, are attributed to the passage of the earth through swarms of meteors, and in like manner supposes the influence of Jupiter and Saturn to be due to their passing through meteor streams situated in mean longitudes 135° and 265°.