The number of earthquakes originating within the area of the British Islands during the three years 1901–1903 is 37, of which 9 occurred in England, 20 in Scotland, and 8 in Wales. In the 15 years 1889–1903 the total number recorded is 152, 39 in England, 90 in Scotland, and 23 in Wales. So far as I know, not a single undoubted earthquake lias originated in Ireland during this period; but four earthquakes (the Pembroke earthquakes of 1892 and 1893, the Hereford earthquake of 1896, and the Carnarvon earthquake of 1903) were felt in many of the eastern counties.
If the coefficient of dilatation ( e ) and the conductivity ( k ) are constant at every point within the earth, and if the temperature (V) was initially the same throughout, the depth of the surface of zero strain after 100 million years is 2.17 miles, the total volume of the crust folded and crushed above that surface is about 184,500 cubic miles, and the mean thickness of the crushed rock spread over the whole surface of the earth is 4.95 ft. (taking e = 0.0000057, k = 400, V = 7000° F .). The smallness of these figures has been claimed by some geologists as a new and strong argument against the contraction theory of mountain evolution.
In his recent work on “Controverted Questions of Geology” (p. 159), Professor Prestwich remarks that the intense cold of the Glacial period may still be perceptible in the underground temperature gradient; that “to a certain depth the rate of cooling is now abnormally slow, owing to the excessive refrigeration the crust then underwent.” The suggestion is a valuable one, and I propose to test it in the present paper by estimating roughly the change which the temperature gradient may have experienced since the close of the Glacial period.
SINCE the great earthquake of 1923 the Empire of Japan has been visited by two destructive earthquakes?the Tajima earthquake of 23 May 1925, in which 325 persons lost their lives, and the much stronger Tango earthquake of 7 March 1927. Both occurred near the Japan Sea coast of the main island, to the north of Kyoto and Osaka. The epicentre of the Tajima earthquake lay in lat. 350 38^.7 N., long. 1340 5o'?5 E.; that of the Tango earthquake about 11 miles to the east in lat. 350 39' N., long. 1350 1' E. The district is one that is almost immune from earthquakes. Koto, in his admirable study of the earthquake, gives a list of about a dozen shocks felt in the province during the Christian era. Three of these, in 675, 701, and 1694, may perhaps vie with the recent earthquake in strength. According to the latest estimate (Imamura) 3017 persons were killed, the great majority in the four central counties of Yosa, Naka, Takano, and Kumano ; 10,633 houses collapsed and 9821 half collapsed, 4961 were burned and 115 half burned. Of the total population in the four counties, z per cent, lost their lives, and of the houses existing before the earthquake 41 per cent, collapsed and i8| per cent, were burned. In Mineyama, the principal town of the district, about 80 per cent, of the houses were destroyed by the shock and most of the rest were burned. The villages of Go and Yamada lost 90 per cent, of their houses. In no place does the loss of life approach the proportions so prevalent in some Italian earthquakes, the highest percentages reached being 24*5 at Mineyama and 27*9 in the village of Yosiwara.
THE sudden movement that causes a great earthquake must alter the conditions of strain in the surrounding crust. The strain may be increased in some regions and decreased in others and the changes may be great enough to precipitate or prevent the occurrence of what Mr. Oldham has called “sympathetic earthquakes”. It thus becomes of some interest to ascertain how far the influence of a great earthquake may extend from its source, and the present brief note is an attempt to examine this point in the case of one well-known and well-studied earthquake, that of Mino-Owari in Japan on 28th October, 1891.
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